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UNIVERSITY OF SASSARI
DESERTIFICATION RESEARCH GROUP
THE STRATEGIC USE OF ATRIPLEX AND OPUNTIA
TO COMBAT DESERTIFICATION
Mulas M., Mulas G.
Short and Medium- Term Priority Environmental Action Programme
(SMAP)
February 2004
2
INDEX
Summary .......................................................................................................................... 4
1. Introduction: desertification .................................................................................…... 5
2. Actions and experiences on the use of Atriplex and Opuntia to combat desertification
in the world
2.1. Atriplex
2.1.1. West Asia and North Africa (WANA)................................................................... 8
2.1.2. South America ..................................................................................................... 17
2.2. Opuntia
2.2.1. West Asia and North Africa (WANA) ................................................................ 22
2.2.2. American Continent …......................................................................................... 30
3. Scientific appendix
3.1. The genus Atriplex
I. Spreading and growing area ........................................................................... 34
II. Taxonomy, botany and physiology ...............................….................…....... 34
3.1.1. Management of Atriplex plantations
I. Choice of species ….........................……....................................……........... 37
II. Propagation and planting ............................................................................... 40
III. Irrigation ...................................................................................................... 40
IV. Nutritive value and utilisation as feed for livestock ……………................ 44
3.2. The genus Opuntia
I. Spreading and growing area ........................................................................... 49
II. Taxonomy and botany of Opuntia ficus-indica .........………………........... 49
III. Economic and ecological role of Opuntiae ...……....................................... 51
IV. Propagation ……………....................……………...................................... 53
3
3.2.1. Ecophysiology of the genus Opuntia
I. Structural adaptation to arid environments ..................................................... 56
II. Drought resistance mechanisms .……........................................................... 57
3.2.2. Growing management of the genus Opuntia
I. Choice of species and cultivars ….................................................................. 61
II. Planting ......................................................................................................... 61
III. Soil fertilisation ............................................................................................ 64
IV. Nutritive value and utilisation as feed for livestock ………………...……. 64
V. Resource management ........…............……………………………….......... 71
VI. The use of Opuntia as a water source for cattle........................................... 75
Conclusions ................................................................................................................... 76
Bibliography .................................................................................................................. 80
4
SUMMARY
The desertification of wide areas of the world has been increasing continuously.
Therefore, a strategy to combat this process is now a need, in order to preserve the
natural fertility of endangered environments and to restore the degraded ones whenever
that is technically possible.
The large-scale use of fodder shrubs of the genera Opuntia and Atriplex to
combat desertification is presented in this review.
Information on Opuntia ficus-indica, Atriplex nummularia, A. halimus and A.
canescens, which are the most used species of these genera in North Africa, Middle
East and American continent, is given. A technical and scientific evaluation of their use
is briefly presented, while further information on their biology, propagation and field
management is reported in the scientific appendix.
The review covers the possibility of grazing areas planted with these species, the
need of a rest period after grazing to allow vegetation regrowth, and the use of pruning
practices to periodically regenerate their canopy. The nutritional value of the studied
species and the possibility of using them together or in association with other available
fodder resources in livestock feeding, in order to optimise their use, are also discussed.
Key words: desertification, agroforestry, fodder shrubs, Atriplex, Opuntia.
5
1. Introduction: desertification
Since the early seventies, desertification has been one of the most important
concerns for environmental policy at an international level.
In 1992, during the Rio de Janeiro World Summit on Environment, the
desertification process was defined as "... land degradation in subtropical arid, semi-
arid, and dry areas resulting from various factors including human activities and
climatic variations ...". The use of the word "desertification" was due to the fact that
lands affected by soil degradation, as a consequence of a loss of their productivity, show
desert-like characteristics.
Desertification changes dramatically the characteristics of a certain environment,
and has serious social implications that affect the economy of entire countries. In fact,
this problem is more serious when the affected lands are occupied by people that live
essentially by agriculture and sheep farming.
Africa is the most seriously affected continent by desertification. In fact, this
process affects more than one billion hectares there.
In 1973, the Sahelian countries of Africa founded a centre for desertification
control by means of the following actions: "... activity oriented to sustainable land
development in arid, semi-arid, and dry areas by reduction and/or prevention of
desertification, as well as by partial restoration of affected lands and recuperation of
desert areas ...".
Moreover, in 1977 the conference of the United Nations on desertification
founded the United Nations Environment Programme (UNEP) and started an action for
desertification control. In June 1994, countries seriously affected by aridity and
desertification, located mainly in Africa, subscribed the Convention of the United
Nations on desertification control.
In 1985, Mali adopted a National Program for Desertification Control divided in
eight subprograms and forty-eight projects. In 1991, the monitoring group of the
Program listed 236 projects on desertification control and natural resources
management with specific activities in the following fields:
6
- water resources management;
- improvement of agriculture productivity;
- erosion control (banks and dunes reinforcement);
- agroforestry promotion by nursery implementation, reforestation and windbreak
planting;
- pisciculture development;
- planning and management of crop and forestry;
- beekeeping;
- promotion of cattle feeding (fodder production, range land management);
- hydrological management in the neighbourhood of urban centres;
- use of energy sources that can be found in the country;
- "new technology" application: use of solar energy in water heating and domestic
lighting;
- subsidiary activities: literacy campaign, health care, communication.
Many of the above listed activities were successful, while others were not.
Forestry management is certainly one of the main activities to combat
desertification (Berthe, 1997). Plant cover is important for soil protection because it
helps to control erosion and to regulate the level of the water-bearing stratum.
Vegetation is also a potential fodder and fuel wood resource. However, forest plantation
in lands affected by desertification is not easy, because of the slow plant growth and
irregular rainfall typical of arid areas.
In harsh ecological scenarios, characterised by stony soils without organic
matter, rainfall under 300 mm, and very high salt concentration, the use of tolerant plant
species is fundamental.
In the seventies, forest plantations were implemented in Niger and Mali using
some drought resistant and fast growing species such as Eucaliptus spp., Tamarix spp.,
Ficus spp., Acacia spp., Euphorbia balsamiphera, Prosopis juliflora. However, these
and other similar efforts were not always successful, as a consequence of the specific
ecological requirements of the used species and the often not respected need to avoid
grazing for a certain period in reforestation areas.
The gradual and slow implementation of fodder trees and shrubs have created
new perspectives in desertification combat (Le Houérou, 2000). Small trials of
7
desertification control started in the first half of the XX century. Later on, in the
seventies, large trials were implemented in many arid areas of the world such as those
found in the Mediterranean basin, South Africa, Australia, Chile, Brazil, and USA.
In the Mediterranean region, about a million hectares are currently planted with
fodder trees and shrubs, with a continuous increase in species diversification and
growing areas. At the same time, the use of herbaceous species have decreased in that
environment.
The advantages of using tree and shrub species in reforestation are related to
their high resistance to aridity and their ability to produce biomass in extreme
environmental conditions, thus being a fodder reserve for the livestock. These
plantations can favour the permanence of nomad people in areas where the underground
water resources can be used more efficiently by the roots of trees and shrubs than by
those of herbaceous species. Furthermore, the presence of a permanent root and canopy
biomass may be useful to control erosion and to modify the microclimate of the area
(e.g. by shading, organic litter production, etc.).
In extensive systems, trees and shrubs can be associated with cereal crops, thus
restoring the ecological situation and providing some useful by-products, like fuel wood
and game.
The main problems affecting these plantations are linked to the high costs of
implementation and protection against uncontrolled grazing. In fact, tree and shrub
plantations have a long development period, need seeds or cuttings of good quality for
their propagation, require good field practices (e.g. irrigation at planting time and in the
following months) and need specific techniques of utilisation. For these reasons,
projects to increase the use of tree and shrub species in arid environments should be
integrated with others regarding complex capacity building actions.
8
2. Actions and experiences on the use of Atriplex and Opuntia to combat
desertification in the world
2.1. Atriplex
2.1.1. West Asia and North Africa (WANA)
The West Asia and North Africa (WANA) region, which extends from Morocco
to Afghanistan and from Turkey to the Arabic peninsula, is the largest continuous arid
area of the world.
The WANA region has limited natural resources and few soils suitable for
agriculture. Rains are scarce and irregular, and only limited areas are classified as
humid or sub-humid. The plant growing season lasts not more than 180 days (El-
Beltagy, 1999). There are only few permanent rivers and most lands are hilly with
superficial and poor soils. Most lands are arid deserts which cross the WANA region
from West to East, from Sahara in Africa to the Thar desert in South Pakistan, until
Karakum along the North Eastern Iran border. Only two strips of land, along the North
and South borders of the desert zone, are suitable for agriculture and represent about
14% of the total desert area. Sustainable agriculture follows only extensive models
there. In spite of its critical arid conditions, the region is an important centre of
biodiversity.
WANA shows an extremely high population growth rate. In the early sixties, the
WANA population was of 200 millions inhabitants. In 1990, it was of 470 millions and
the prediction for 2020 is of 930 millions. In order to cope with this demographic
explosion, food production has increased by exploiting dramatically the natural
resources (soil, water, and natural vegetation).
With the aim of improving agricultural yields by means of irrigation, superficial
and underground water have been exploited in many areas of WANA. In the last 30
years, many countries have made large-scale works to keep and use water of the few
perennial rivers present in the area. Since 1991, about 35% of the cultivated lands have
9
been irrigated. This water exploitation has caused a reduction in water resources in the
underground layers, an increase in water salinity, and a loss of soil fertility.
In the areas with higher rainfall (400 mm/year), soils are more exploited and tree
cultivation is more widely distributed. However, these areas of higher fertility and
potential use present a higher desertification risk too. Moreover, the seasonal climatic
variability causes two fodder deficit periods during the year: one in the winter season
(from two to four months) and one in summer (from five to six months). As a
consequence, breeders have difficulties in managing livestock feeding and have to
supplement cattle diet with a large amount of concentrate in these periods.
Some species of the genus Atriplex are indigenous of the WANA region and
others have been introduced, to verify their potential as a fodder resource (Le Houérou,
2000). Some of the spontaneous species are Atriplex halimus subsp. halimus and subsp.
schweinfurthii, A. leucoclada, and A. mollis; while the most important introduced ones
are A. nummularia, A. canescens. A. lentiformis, and A. semibaccata (Le Houérou,
1992a).
Until now, the best combination has been to associate typical cereal crops, like
barley, with forage shrubs. The latter can provide environmental benefits and restore
soil fertility, as a consequence of their drought resistance, organic matter supply, and
deep root development. Another advantage of this system is that cattle can successively
graze barley stubbles and Atriplex shrubs during summer and autumn.
Among the available forage shrubs, some species of the genus Atriplex,
particularly A. halimus and A. nummularia, have given the best results (Arif et al.,
1994). For instance, the association of barley with forage shrubs of the genus Atriplex
(strip crop or alley crop) has increased crop yield by 25% (Brandle, 1987).
Atriplex halimus L. originated from North Africa. It is well adapted to saline-
clay soils under less than 150 mm/year of rainfall (Le Houérou, 1980a). In absence of
grazing, this species can grow up to 4 m in height (Négre, 1961). A. halimus is one of
the most palatable Atriplex species for cattle in the dry lands of the WANA region
(Tiedeman and Chouki, 1989).
Atriplex nummularia Lindl. is a perennial upright shrub, originated from the arid
and semi-arid areas of Australia. It grows where rainfall is at least 180 mm/year
10
(Thornburg, 1982). Its root system may develop over 3 m in depth and up to 10 m in
width (Jones, 1970).
In Saudi Arabia, have showed that, among various Atriplex species, A.
nummularia produced the highest biomass yield and had a high crude protein content
(16%) (Hyder, 1981).
In Egypt, crude protein levels of 12.7%, 9.1%, and 11.8%, respectively, for fresh
biomass, hay, and silage of A. nummularia were found. Moreover, A. nummularia had
positive effects on the growth rate of wool and body weight of sheep fed under
controlled conditions (Abou El Nasr et al., 1996).
The use of A. nummularia as a forage in unfavourable environments, such as the
WANA lands, gave good results (Figs. 1 and 2). This resistant and vigorous species
shows strong resprouting after cutting or grazing (Fig. 3).
Recently, thousands of hectares of the WANA area have been planted with
forage shrubs and have been subjected to combined techniques of water harvesting
(Boulanouar et al., 2000; Nefzaoui et al., 2000a; Redjel and Buokheloua, 2000). Dry
biomass production varies depending on the species and plant density. For instance, in
Morocco, a three-year-old plantation of A. nummularia at a density of 1,000 plants/ha
showed a yield of 1,250 kg of dry matter/ha, which corresponds to a surplus of 625
forage units and 200 kg of crude protein/ha with respect to the yield of the associated
herbaceous crop (El Mourid et al., 2001).
Atriplex shrub can be used as a forage reserve during summer and autumn, due
to its high content of protein and minerals (Tab. 1). Therefore, this species supplies the
critical lack of forage resources before the spring growth of herbaceous species, in arid
regions (Kessler, 1990). Indeed, this nutrient supply allows cattle to resist prolonged
periods of scarce feed caused by drought (Le Houérou, 1980b).
Other species of the genus Atriplex are widespread in the WANA region, such as
A. leucoclada, a biennial species originated from the Middle East and easily propagated
in Syria (Sankary, 1986) and Libya (Le Houérou and El Barghati, 1982), A. glauca,
found in clayey soils (Le Houérou, 1969), and A. mollis, with upright shape and found
in sandy soils (Le Houérou, 2000).
11
Figure 1. Young plantation of Atriplex in Morocco.
12
Figure 2. Three-year-old plantation of Atriplex in Morocco.
Figure 3. The effects of direct grazing in a five-year-old plantation of Atriplex in
Morocco.
13
Table 1. Chemical composition (as % of dry matter) of three diets containing Atriplex
(adapted from Abou El Nasr et al., 1996).
FS SH SS Dry matter Crude protein Crude fibre Crude lipid Ashes Neutral detergent fibre Detergent fibre Hemicelluloses Cellulose
38.6 12.7 28.7 3.4 24.9 59.4 36.8 22.6 27.5
87.2 9.1 29.3 2.2 26.5 63.8 39.2 24.6 28.3
33.1 11.8 20.4 4.0 22.5 60.1 38.4 21.7 29.9
FS: fresh Atriplex; SH: Atriplex hay; SS: Atriplex silage.
Figure 4. Sheep eating Atriplex nummularia.
14
Among the species of Atriplex introduced in different times in the WANA
region, there are the following: A. amnicola (A. rhagodioides), A. undulata, A. lampa,
A. lentiformis, A. breweri, A. barclayana, A. canescens, A. isatidea, A. paludosa, A.
cinerea, A. polycarpa, A. repanda, A. nummularia (cv. Grootfontein from South
Africa), A. inflata, and A. halimoides.
In spite of its low productivity, A. canescens is another species of interest,
because of its high chilling resistance (Forti, 1986). This species originated from North
America and has some cultivars ('Wytana', 'Rincon', 'Marana' and 'Santa Rita') adapted
to different ecological conditions.
Other promising species in the WANA environments are the following: A.
amnicola, palatable, but sensitive to chilling and overgrazing; A. undulata, productive,
palatable and chilling tolerant; A. lentiformis, tolerant to salinity by sodium carbonate
and showing good self-sowing ability; A. semibaccata, biennial species that spreads
very fast but disappears quickly afterwards.
Throughout Syria, experiences were performed mainly with the species Atriplex
leucoclada, A. canescens, A. nummularia, and A. polycarpa. The best results were
recorded with the most chilling resistant species, such as A. canescens (El Fikiki et al.,
2000; Murad, 2000; Rae et al., 2000).
In Jordan, the most used species were Atriplex halimus and A. nummularia,
included in many projects developed by national and international institutions
(Mohamed, 2000; Nesheiwat, 2000; Tadros, 2000).
Many studies on Atriplex have been carried out in large areas (over 40,000 ha) of
Morocco. Atriplex nummularia has covered more than 60% of the planting areas in
trials to combat desertification and increase natural forage resources (Boulanouar et al.,
2000; Fagouri et al., 2000; Tazi et al., 2000a; 2000b). In addition to the well-known A.
nummularia, the species A. vesicaria, A. semibaccata, A. paludosa, and A. halimus have
also been largely studied. Following these experiments, many questions have been
raised regarding their planting costs, which are too high for animal breeders.
In an area of 2,000 ha of Saudi Arabia, tests have been performed with Atriplex
leucoclada (autochthonous), A. canescens, A. lentiformis, A. halimus, and A.
nummularia (Mirreh et al., 2000).
15
In the most arid environments of Pakistan, the chilling tolerant Atriplex
canescens and A. lentiformis are the most widespread species. In addition to both
species, A. nummularia is common in the least cold areas of those environments. In that
country, many projects to combat desertification and to improve the rangelands have
been promoted by public institutions and Non-Governmental Organisations (Mirza,
2000; Nawaz, 2000).
In Iran, more than 20 species of Atriplex grow spontaneously. Most of them are
herbaceous (Koocheki, 2000), while only Atriplex griffthi, A. leucoclada, and A.
verrucifera are shrubs. In spite of that, a large extension of fodder shrub plantations is
found in that country. Plantations are composed by exogenous Atriplex species, such as
A. lentiformis, A. halimus, A. nummularia, and, especially, A. canescens (Rashed,
2000). The latter species is the best adapted to the environmental conditions of Iran,
because of its cold tolerance (Nejad and Koocheki, 2000).
In Turkey, Atriplex nitens and A. laevis are two important autochthonous
shrubby species (Tahtacioglou, 2000).
In Algeria, the use of Atriplex species was initially promoted by public
institutions. Afterwards, it was included in development projects having a participatory
approach (Redjel and Boukheloua, 2000).
Many species of Atriplex, especially A. halimus and A. nummularia, have been
used in public and non-governmental projects in Tunisia (Nefzaoui et al., 2000a).
When Atriplex shrubs are associated with other crops (alley crop), such as
barley, oats or Lucerne, they play an important role in wind breaking, soil protection
and creation of a favourable microclimate to other forage species, which then increase
their growth and yield (El Mzouri et al., 2000).
Feed integration with forage shrubs and cactus pear cladodes provide good
results. In fact, Atriplex has a good protein and a low energy content, while Opuntia
cladodes have good energy and water contents.
Straw can be integrated with Atriplex and Opuntia cladodes. It is known that the
latter increase straw swallowing. In addition, due to their good protein content, the
combination of the two species can replace Soya in livestock feed, thus allowing to
lower the feeding costs (Nefzaoui, 2000).
16
Finally, the use of Atriplex and Opuntia cladodes as forage sources allows to
cover the feed needs of livestock in critical periods and to alleviate the pressure on
rangelands. As a consequence, overgrazing and desertification can be avoided in the
WANA region (Fig. 4).
17
2.1.2. South America
In the IV Region of Chile (Coquimbo), sheep and goat keeping is the only
agricultural activity performed in large areas. In these lands, tree and shrub cover has
been partially removed and the desertification process has already started.
When left undisturbed, the landscape of Coquimbo is dominated by a shrubby
maquis, named "matorral", associated with cactus species (Cactaceae and
Bromeliaceae), that spreads at different densities depending on land exposition.
In that arid environment, the high pressure of agriculture and cattle keeping have
determined disastrous consequences, especially under precarious social and economic
conditions. Similarly, cultivation of unsuitable lands, overgrazing and overexploitation
of woody species have caused the degradation of large areas, characterised by strong
soil erosion, landscape alteration, and extremely poor people (Caldentey and Pizarro,
1980).
In spite of the above listed problems, livestock keeping remains the main
economic activity in the region. This non sustainable system is characterised by
irregular amount and frequency of rainfall, and lack of plant cover during many months,
because the main forage sources are annual herbaceous species.
To cope with this difficult situation, since 1960, institutions such as the
Corporacion de Fomento de la Producion (CORFO), the University of Chile, the
Servicio Agricola y Ganadero (SAG), and the Instituto Nacional de Investigaciones
Agropecuarias (INIA) have been working together. The main objective has been to find
species able to increase forage availability in arid areas affected by desertification.
Interesting results have been obtained using local and exogenous shrub species,
especially Atriplex nummularia, A. repanda, A. semibaccata, Kochia brevifolia, Acacia
saligna, and Galenia secunda.
Since the seventies, the CORFO has planted forage shrubs extensively.
Nowadays, more than 48,000 hectares of Coquimbo, are planted with forage shrubs.
Atriplex nummularia has been the most used species (more than 90% of the area), being
followed by A. repanda (Lailhacar, 2000). Positive characteristics of A. nummularia
18
are: good forage yields, strong resistance to extreme drought, resistance to grazing with
fast resprouting, resistance to disease, and easy propagation. Moreover, its fuel wood
has a good energy content.
In the arid IV Region of Chile, A. nummularia is currently the most important
species in projects on reforestation and desertification control. The geographic location
and some climatic parameters of the districts of the Coquimbo region are reported in
Tables 2 and 3, respectively (Caldentey, 1987; Soto, 1996). In these environmental
conditions, forage shrub plantations can provide a supplement to cattle feed, which is
based mainly on pasture, when forage availability from herbaceous cover is low, due to
drought.
Spontaneous annual herbaceous species are negatively affected by grazing in
two periods: in the beginning of growth, when their availability is still very low; and at
the end of the growing cycle, during flowering and fruit set, when natural sowing is
necessary to guarantee the survival of the vegetal cover (Soto, 1996). The presence of
forage shrub plantations allows a rest period of natural rangelands and assures feed for
livestock maintenance.
Therefore, the role of forage shrubs is not to increase milk, meat or wool
production during the good season, like the herbaceous forages, but to provide green
forage, rich in protein, during the dry season, in order to reduce animal weight loss.
Many studies have been carried out on Atriplex repanda, with the aim of
improving its seed germination rate, which is very low (Lailhacar, 2000). Contrary to
the interesting results obtained using A. semibaccata, direct sowing of A. repanda has
not been successful. The agamic propagation of A. repanda has also been investigated
(Peña, 1979).
In some areas of Southern Coquimbo, with rainfall ranging from 100 to 220
mm/year, yields of A. nummularia plantations have varied from 50 to 900 kg of dry
matter/ha per year, depending on age, field management and plant density. In areas with
143 mm/year of rainfall, average yields of 1,806 g/plant have been observed (Soto,
1996).
Planting density directly affects yield. As A. nummularia planting densities
increase from 625 to 10,000 plants/ha, yields increase. However, leaf production
decreases at planting densities over 2,500 plants/ha (Soto, 1996).
19
Table 2. Districts of the IV Region of Chile (Coquimbo) having Atriplex nummularia
plantation experiments (adapted from Soto, 1996).
Sector Agroclimatic district
North - Coast (NC) North – Inland (NI) South – Coast (SC) South – Inland (SC)
II: La Serena – Talinay XVII: Ovalle III: Amolanas – Los Vilos XIII: Illapel
Table 3. Mean annual climatic parameters of the districts of the IV Region of Chile
(Coquimbo) (adapted from Caldentey, 1987).
Year value per district Variable
Unity of measure NC NI SC SI
MT SR SH DD RH R
PET WD HI
°C
lux/day
hours degree-days
% mm mm mm ---
13.8 343 3091 1401 85
113.0 821.8 708.8 0.14
15.2 432 4848 1904 61
143.9 1443.7 1299.8 0.10
14.1 362 4051 1472 82
201.1 912.7 725.5 0.22
15.0 394 4418 1865 68
243.7 1202.5 980.7 0.20
Frost-free period Maximum temperature of the hottest month Minimum temperature of the coldest month Chilling Temperature sum (September-February) Radiation sum (September-February)
days °C
°C
hours degree-days
kcal/m2
365 19.9
8.4
104 875
81
320 28
5.5
455 1307
101
345 24.1
7.0
232 926
86
320 27.2
4.6
780 1274
93
MT = mean temperature; SR = solar radiation; SH = shining; DD = degree days; RH = relative humidity; R = average year rainfall; PET = potential evapotraspiration; WD = water deficit; HI = humidity index. NC = North Coast; NI = North Inland; SC = South Coast; SI = South Inland.
20
In the Coquimbo region, under average climatic conditions, yields of A.
nummularia can reach 1,000-1,500 kg of dry matter/ha per year, using 1,600 plants/ha.
In order to obtain these yields, it is necessary to avoid overgrazing and to use forage
shrubs from summer (November-January) until the start of winter rains, to allow a
successive vegetation resprouting. The period of shoot growth during the rest period of
A. nummularia varies from 4 to 7 months. In a 42-month-old plantation of A. repanda,
yields varied from 1,000 to 5,000 kg of dry matter/ha per year, as planting densities
increased from 700 to 18,500 plants/ha (Soto, 1996).
Many trials have been conducted on the nutritive value of different species of
Atriplex (Silva and Pereira, 1976). In particular, the amino acid composition of Atriplex
is in general well balanced, except for its low methionine content (Padilla, 1986).
Atriplex repanda, A. undulata, and A. clivicola shrubs are palatable to livestock
(Lailhacar, 2000) and can markedly increase the productivity of lands previously
formed by wild herbaceous species only (Concha, 1975; Olivares and Gastò, 1981).
The first grazing of Atriplex is recommended not before 18 months from
plantation. It is advisable to prune the plants every 4-5 years, by cutting-down woody
branches at 25 cm above the soil level, in order to regenerate the canopy and to avoid an
excessive growth in height, especially in the case of A. nummularia. Plant growth in
height increases the proportion of woody tissues, causing a decrease in leaf production
and leading to plant senescence (Rivera, 1996). Appropriate management of forage
shrubs requires a rest period from grazing and pruning at 25-50 cm above the soil, when
senescence starts and leaves tend to grow at the higher parts of the plants (Pagliaricci et
al., 1984; Olivares et al., 1986; 1989). The responses of A. nummularia to these
management practices are a lot better than those of A. repanda (Garcia, 1993; Soto,
1995).
A further recommendation on the use of Atriplex nummularia is to associate this
forage with Opuntia ficus-indica cladodes. The inclusion of young cladodes of cactus
pear in the diet, increases milk production of goats. (Azocar and Rojo, 1992). This
strong effect could be attributed mainly to the high water content of Opuntia cladodes
that counterbalances the high salt content of Atriplex leaves.
Pruned woody branches are an important energy resource. For instance, the
energy content of A. nummularia wood is of about 4,538.3 kcal/kg (Garcia, 1993).
21
Yields of fuel wood obtained from Atriplex plants can also be considerable (Rivera,
1996).
Since the use of A. nummularia in the IV Region of Chile has given encouraging
results, more plantations of this species have been programmed in that area (Soto,
1996).
22
2.2. Opuntia
2.2.1. West Asia and North Africa (WANA)
The West Asia and North Africa (WANA) region is a continuous and
homogenous area limited by the Mediterranean basin, North Africa, West Asia,
Afghanistan, and Pakistan.
The social and economic situation of this region is very difficult and complex.
The WANA region is affected by serious problems such as high population growth rate,
limited availability of natural resources (i.e. land and water), low and irregular rainfall,
increased urbanisation, increased food demand by people, and increased number of
livestock unity. Fertile lands are not sufficient to supply the increased demand for food.
As a consequence, overgrazing, soil erosion and desertification occur.
In the arid and semi-arid areas of the WANA region, where average annual
winter rainfall is of 200-350 mm, the main economic activity consists of meat, milk,
leather and wool production by small ruminants (sheep and goats). In this region, except
for Iraq, in the last 20 years, the total population of sheep and goats has increased from
62 millions to over 80 millions of heads (about 25% increase) (El Mourid et al., 2001).
The increased number of livestock heads and the new feeding techniques based
on concentrates have eliminated nomadism among breeders. The consequent
overgrazing, vegetation cover removal by soil ploughing and deforestation favour soil
erosion and degradation. These impoverished soils do not produce sufficient amounts of
forage to livestock (Nefazaoui and Ben Salem, 1998). In fact, in many countries, the
contribution of natural rangelands to livestock feeding has decreased from 70% in 1950
to 10-25% in 2001 (El Mourid et al., 2001).
Inadequate policies regarding soil use and the absence of regulations to protect
arable soils have aggravated the situation. Moreover, in many countries of the WANA
region, traditional institutions, which controlled the use of rangelands in the past, have
been replaced by modern systems that allow free access to grazing lands, without limits
of land extension or head number.
23
Recently, in many countries of WANA, the area cultivated with barley crop,
currently the most important livestock feed, has increased sharply. In fact, barley has
become the most important livestock feed. However, this increase has been associated
with the cultivation of marginal lands, not used previously, and the introduction of
monocultivation.
In order to cope with the degradation and overexploitation of arable lands,
various actions to improve yields, especially of forage, have been proposed in the last
years. These programmes have been based mainly on the integration of well-established
field management techniques with modern and more rational technologies, which
include the introduction of new crops and new livestock breeding techniques (Tab. 4)
(Nefzaoui and Ben Salem, 2002).
Starting from 1996, various institutions, such as IFAD, AFEDS, and IDRC, with
the technical assistance of ICARDA and IFPRI, have implemented a project named
"The Development of Integrated Crop/Livestock in the Low Rainfall Areas of West
Asia and North Africa". The following eight countries have been involved in the
project: Algeria, Libya, Morocco, and Tunisia, in the Maghreb, and Iraq, Jordan,
Lebanon, and Syria, in the Mashreq. The realisation of this Maghreb/Mashreq project
have demonstrated the strong desire of these countries to overcome this critical situation
(El Mourid et al., 2001).
Two strategies taken into consideration in the Maghreb/Mashreq project have
been the use of cactus plants and the plantation of forage shrubs. Both strategies have
been effective against desertification and have provided an alternative source of forage
to livestock, which has been increasingly bred in the WANA region.
Plants of the genus Opuntia can grow in the harsh environmental conditions of
arid lands, especially if their field management is associated with dry farming
techniques. These crops are an important alternative feed source for livestock,
especially in critical periods of feed scarcity. Moreover, cactus plants protect natural
resources by controlling soil erosion, especially when planted in hillsides (Figs. 5 and
6).
In the large predesertic areas of Tunisia and Algeria, the desertification process
has been stopped and the natural vegetation cover has recovered, by means of an
integrated approach.
24
Table 4. A common calendar of small ruminant feeding in the WANA region (adapted
from Nefzaoui and Ben Salem, 2002).
Period Physiological
stage Zone Type of feed Integration
May-July Mating-starting
pregnancy Arable lands Cereal stubbles
Bran, barley, Opuntia
August-September
Pregnancy Arable lands Cereal stubbles,
straw Bran, barley,
Opuntia, shrubs
October-January
End pregnancy-starting lactation
Rangelands, arable lands
Fallow land, hay, natural
grazing
Barley, wheat bran, olive industry by
products
February-April
Weaning-fattening
Rangelands, arable lands
Natural grazing, fallow land,
growing barley, straw
Shoots and leaves of olive, barley,
bran
25
Figure 5. One-year-old plantation of Opuntia ficus-indica.
26
Figure 6. Opuntia ficus-indica some years after planting.
27
Opuntia cultivation has been combined with the application of water storage
techniques and soil surface modification in waves (Griffiths, 1933; Le Houérou, 2000).
Soil waves roughly follow the contours and contain, in their internal sides, two rows of
Opuntia plants (Nefzaoui and Ben Salem, 2000).
Species of the genus Opuntia are characterised by a deep and wide root system,
which is able to stabilise soil surfaces in hilly areas. In order to better protect the area
from wind erosion and sand dunes movement, Opuntia planting is often accompanied
by soil surface cover with palm leaves (IFAD, 2000a; 2000b).
Currently, the total area cultivated with Opuntia in the WANA region is of about
900,000 ha (Nefzaoui and Ben Salem, 1998).
Since ancient times, Opuntia plants have been commonly used as a forage in
Maghreb countries (Tunisia, Algeria, Morocco and Lybia) (Monjauze and Le Houerou,
1965; Boulanouar et al., 2000; Nefzaoui et al., 2000a; Redjel and Boukheloua, 2000),
but not in Mashreq countries. However, exchange of information and experiences
between these two regions has lead to the start of Opuntia cultivation in Jordan and
Syria in 1999 (El Mourid et al., 2001).
In Libya, the use of Opuntia has increased markedly and its crop surface is
currently very large (El Mourid et al., 2001).
The genus Opuntia has also been successfully introduced in the most arid zones
of Pakistan (Mirza, 2000). Initially, Opuntia was planted mainly in communal lands of
that country, but recently this cultivation has sharply increased in private animal farms
also, where it is frequently associated with other forage plants. Opuntia species are well
adapted to arid environments, where they can produce high quantities of green biomass
(Fig. 7).
In areas having rainfall from 150 to 400 mm/year, without fertilisation, Opuntia
ficus-indica var. inermis can produce from 20 to 100 t of cladodes/ha per year,
respectively (Monjauze and Le Houerou, 1965).
The nutritive value of Opuntia cladodes varies considerably among species and
cultivars. It is also influenced by cladode age, by seasonal temperature and rainfall
conditions, and by various agronomic factors, such as soil type and growing conditions.
Cladodes of Opuntia have a high content of water (90%), ash (20% of dry matter),
calcium (1.4% of dry matter), soluble carbohydrates, and vitamin A. On the other hand,
28
they have a low content of crude protein (4% of dry matter), crude fibre (10% of dry
matter), and phosphorous (0.2% of dry matter) (Nefzaoui et al., 1995).
In many trials, the use of nitrogen and phosphorus fertilisers has increased the
crude protein content of Opuntia cladodes from 4.5% to 10.5% of dry matter (Gonzales,
1989). However, fertilisation is usually not feasible, because of the low rainfall and
scarce economic resources typical of the arid lands of the WANA region.
Nutritive value of cladodes varies with cladode age. Crude protein content
decreased (from 5 to 3% of dry matter), while fibre content increased (from 9 to 20% of
dry matter) when cladodes grew from 1 to 5 years old (Nefzaoui and Ben Salem, 2000).
In general, Opuntia forage has high palatability. Sheep fed Opuntia cladodes
could swallow up to 9 kg/day of this forage (Monjauze and Le Houerou, 1965).
Moreover, the use of Opuntia forage caused an increase in straw intake by sheep. This
is an important positive effect, considering that straw is the main forage source for
livestock in the arid lands of WANA (Ben Salem et al., 1996).
The increase of straw intake could be attributed to a better rumen fermentation
induced by Opuntia ingestion. Opuntia cladodes ingestion increased by 2.5 times the
ingestion of the easily fermentable fibre by livestock. Moreover, sheep fed straw and
more than 500 g of Opuntia cladodes per day did not show digestion problems (Tab. 5)
(Nefzaoui and Ben Salem, 1998).
Opuntia could help solving the problem of water provision to livestock in the
arid lands of WANA. In these areas, water is a valuable good and its absence during
summer or drought can seriously compromise livestock survival. In addition, livestock
spend a lot of energy in the search for water and the degradation of areas nearby water
areas is a serious problem due to continuous trampling. In this context, the high water
content of Opuntia tissues is a good water source for livestock. Sheep fed a diet
containing about 300 g of Opuntia dry matter can basically eliminate direct water
consumption (Nefzaoui and Ben Salem, 1998).
29
Figure 7. Opuntia ficus-indica some years after planting.
Table 5. Intake level of straw and of Opuntia fresh cladodes by sheep (adapted from
Nefzaoui and Ben Salem, 1998).
Level of spineless cactus intake (g of dry matter/day) 0 150 300 450 600 Straw intake (g/day) 550 547 523 643 716
30
2.2.2. American Continent
The family Cactaceae has about 130 genus and 1,500 species. Three hundred of
them belong to the genus Opuntia Mill. These species live in arid or semi-arid zones
and are characterised by the CAM-type photosynthetic metabolism (Crassulacean Acid
Metabolism) and a high water-use efficiency.
Many species of the genus Opuntia, widespread in Latin America, produce
commodities that are consumed fresh by man, as edible fruits and shoots (Pimienta
Barrios, 1994). These plants can also be used as forage. The use of Cactaceae in human
and livestock feeding is an ancient practice. Cactaceae spread out as forage in many
parts of the world, especially in Mexico, Brazil, Italy, Tunisia, South Africa,
Madagascar and Southern USA (Monjauze and Le Houérou, 1965).
Currently, Opuntia ficus-indica (L.) Mill. is the most commercially important
species in Argentina, Chile, Mexico, and Brazil. It is also cultivated in other countries,
such as Italy, Greece, Algeria, and South West of USA (Russel and Felker, 1987).
Opuntia is mainly propagated agamically by shoots, fruits and one-year-old or
older cladodes. When propagating Opuntia by seeds, the following problems occur:
genetic segregation of characters, a long juvenile period and slow plant growth. In
agamically propagated plants, fruit production starts from the second or third year after
planting and reaches the maximum yield at the seventh year. Normally, a planting
density of 2,000 plants/ha can assure yields of 30 t of good fruit/ha after four years from
planting (Yasseen et al., 1996). Yields are lower in Mexico, as a consequence of high
soil pH (Barbera, 1987a).
Opuntia plantations are frequently located in the arid sides of hills, in order to
avoid plant decay by pathogens, when rainfall is abundant or when the soil is heavy and
clayey. The most used planting distances range from 5 to 6 m along the row and from 5
to 14 m between rows (Yassen et al., 1996).
Some Opuntia species produce inedible fruits, called xoconoxteles, while other
species produce sweet and edible fruits commonly named tuna (Tab. 6) (Pimienta-
Barrios, 1990).
31
Table 6. Chemical composition of Opuntia ficus-indica fruit (adapted from Pimienta-
Barrios, 1990).
Chemical parameter Quantity
Water 85-90% Total soluble solids 12-17% Total sugars 10-17% Reducing sugars 4-14% Proteins 1.4-1.6% pH 5.3-7.1 Fats 0.5% Fibre 2.4g/100g Titratable acidity (citric acid) 0.01-0.12% Ascorbic acid (vitamin C) 4.6-41 mg/100g Viscosity (30°) 1.37 cps Triptophan 8.0 mg/100 g protein Calcium 49 ppm Magnesium 13-15 mg/100 g Phosphorus 38 ppm Iron 2.6 ppm Vitamin A 0.002 ppm Thiamine 0.0002 ppm Riboflavin 0.02 ppm Niacin 0.20 ppm Nicotinic acid 0.40-0.60 mg/100 g
32
Opuntia fruit have been traditionally used by Mexicans and Indians of New
Mexico, Arizona, California and Utah (Bailey, 1976). Opuntia fruit can be consumed
fresh or boiled in water, or can be dried for storage and winter consumption.
Many by-products can be obtained from the fruit pulp of Opuntia. For example,
in Mexico, the following by-products are traditionally obtained: "queso de tuna"
(mustard), "colonche" (fermented juice), "melococha" (marmalade), "miel de tuna"
(syrup), and "tunas passas" (dried fruits) (Pimenta-Barrios, 1990; Barbera, 1991a;
1991b).
Young cladodes (nopalitos) of 10-15 cm of length are also edible, as vegetable
or as an ingredient of some food products.
In the tropical and subtropical areas of Latin America, where annual rainfall is
often under 200 mm and concentrated in short periods, and mean temperature is high,
forage production cannot be assured by common forage crops, such as sorghum and
other drought resistant annual grasses. In this large area, the main feed source to
livestock is the spontaneous vegetation cover, which grows in periods of greater water
availability. For this reason, livestock are under-fed and their production is poor during
most part of the year. Moreover, in these environments, the use of large amounts of
concentrates is not feasible because of the very high costs involved (Crosta and
Vecchio, 1979).
Many Opuntia species are an important alternative forage source, particularly
during dry periods when other fodder species are scarce.
Cut-off branches and fruit of many autochthonous species of Opuntia are used to
feed cattle raised in South-Eastern USA and in Mexico. Opuntia lindheimeri is
commonly used as forage for the livestock in critical periods, in Texas and Mexico.
During the dry season, when the grass had already been grazed and senescence has
begun, cactus plants remain green and juicy (Russel and Felker, 1987).
In order to allow cladode consumption by the livestock, spines can be easily
burned by flames applied directly on the plant surface or can be taken off by other
methods, such as immersion in water, vapour application or washing in soda. Prickly
species have a higher nutritive value than spineless ones (Yassen et al., 1996).
33
In North-Eastern Brazil, farmers prefer to let the livestock graze directly cactus
plants. However, grazing damages the plants and shortens their life, thus being less
convenient than controlled distribution of cladodes portions in the barn (Santana, 1992).
Even though the nutritive value of Opuntia is not very high, especially for its
low percentage of crude protein, its cultivation is absolutely necessary in arid and semi-
arid environments. In fact, in some periods of the year, cactus is the only available
forage source for livestock.
Cactus forage is rich in digestible carbohydrates, lipids and vitamins. Moreover,
it is a juicy fodder and is the main water source for livestock, which can thus survive a
long time without drinking water directly (Monjauze and Le Houérou, 1965; Russel and
Felker, 1987). However, due to its excessive water content, livestock feeding mainly
cactus can suffer from frequent diarrhoea episodes, which reduce cactus digestibility
and nutritive value. This diet also causes animal weight loss, probably due to its
inappropriate protein/energy balance (Santana, 1992).
In order to avoid the problems discussed above, it is recommended to integrate
the cactus diet of the livestock with concentrates or silage having a high protein content,
in order to balance its protein/energy ratio.
34
3. Scientific appendix
3.1. The genus Atriplex
I. Spreading and growing area
Atriplex is the largest and most diversified genus of the family Chenopodiaceae.
This genus contains about 200 species spread mainly in temperate and sub-tropical
areas. Only few Atriplex species grow in the polar region. In general, plants of the genus
Atriplex grow in saline or alkaline soils, and in arid, desert or semidesert environments
(Rosas, 1989; Par-Smith, 1982). The genus is largely widespread in Australia, where a
high diversity of species and sub-species is found.
Perennial herbs are the main components of the family Chenopodiaceae, while
shrubs and trees are less common. Species of this family are halophytes or salt tolerant.
They can survive in soils containing high percentages of inorganic salts. Frequently,
these plants dominate the vegetation cover of salt marshes. Because of the high
frequency of saline soils in dry lands, many species of Chenopodiaceae have developed
xerophytic adaptations.
Chenopodiaceae plants are largely distributed in temperate and subtropical
saline habitats, particularly in the coastal areas of the Mediterranean Sea, Caspian Sea
and Red Sea, in the arid steppes of Central and East Asia, in the margins of the Sahara
desert, in the alkaline prairies of USA, in the Karoo of Southern Africa, in Australia,
and in the pampas of Argentina. They also grow as weeds in the saline soils of urban
areas, especially where water pollution and soil alteration have caused salinity
problems.
II. Taxonomy, botany and physiology
Plants of the family Chenopodiaceae are characterised by deep and well-
developed roots, able to absorb large amounts of underground water.
35
Leaves are alternate, small, with a surface of a powdery aspect covered with
trichomes, lobate, sometimes prickly, and shaped to reduce water loss by transpiration.
Some genus have fleshy stems, with short internodes and no leaves, thus having a
general cactus-like aspect. Flowers are not showy, small, hermaphrodite or unisexual,
and grouped in spike or cyme inflorescences. Pollination is made by wind. Petals and
sepals are very similar and usually formed by five, three or two greenish or brown
lobes. The number of anthers is normally equal to or slightly lower than that of the
calyx segments. Anthers are arranged above the ovary or over a disk. The one-celled
ovary has three carpels and is connected to two stigmas. It produces only one ovule that
matures as an achene (Rosas, 1989).
The family Chenopodiaceae contains more than one hundred genera, which are
divided in the following two tribes, on the basis of the embryo shape:
- Spirolobae, having the embryo twisted like a spiral and the endosperm divided in two
parts by the embryo;
- Cyclobae, showing the embryo shaped like a horseshoe or a semicircle that includes
the endosperm completely or partially.
The genus Atriplex belongs to the latter tribe (Rosas, 1989).
The flower of Atriplex is wrapped by two bracts that allow to distinguish the
different species on the basis of their shape and the presence or absence of welding
between them.
Species of the genus Atriplex are characterised by high tolerance to drought and
salinity. Moreover, they can provide a high quantity of leaf biomass during
unfavourable periods of the year, being used as a forage rich in protein and carotene.
Plants of the genus Atriplex are able to fix CO2 following the C4 biosynthetic
way. These plants are characterised by high productivity, drought resistance and high
efficiency in solar radiation use. They also require good amounts of sodium, an essential
element of metabolism.
Most species of the genus Atriplex are dioecious; however, there are also some
monoecious shrubs. When the staminate flowers of Atriplex deserticola mature, the
plant has a characteristic yellow colour. The pistillate flowers mature only afterwards
(Rosas, 1989).
36
Plant habitus of Atriplex is highly variable. There are annual herbaceous species
as well as woody shrubs that may reach 3 m of height are present.
Leaves are alternate, stalked or sessile, showing paper consistence. Species of
Atriplex adapted to desert environments show thick and almost cartilaginous leaves,
covered by dense trichomes and by salt crystals that cover completely the leaf blade.
Internodes are frequently elongated, even if in some cases they are very short,
determining a dwarf habitus.
Leaf shape is quite variable: triangular and large, up to 6 cm of length; ovate
with acute apex; ovate with obtuse apex; elliptical and of herbaceous consistence; or
shape adapted to high mountain environments.
Leaf of Atriplex show Kranz anatomy, characterised by an orderly arrangement
of mesophyll cells around a layer of bundle-sheath cells, forming concentric centers
around the vascular bundle (wreathlike arrangement). Kranz anatomy is associated with
the four-carbon (C4) photosynthetic pathway, which is a metabolism of high
photosynthetic efficiency (Raven et al., 1992). In the C4 metabolism, carbon dioxide is
linked to phosphoenolpyruvate to generate oxaloacetate, a compound of four carbon
atoms that originated the name of this metabolic cycle. This reaction occurs in the
mesophyll tissue, where the oxalate is then reduced to malate. Subsequently, malate
reaches the bundle-sheath cells surrounding the vascular bundles of the leaf, where it is
decarboxylated to yield carbon dioxide and pyruvate. The free carbon dioxide then
enters the Calvin cycle, while the pyruvate returns to the mesophyll cells, where it
reacts with adenosine triphosphate (ATP) to form more molecules of
phosphoenolpyruvate, to restart a new cycle. Hence, the anatomy of the leaves of C4
plants imparts a spatial separation between the C4 pathway and the Calvin cycle (Taiz
and Zeiger, 1991).
Flowers are monoecious, solitary or in clusters in the axils or terminals.
Staminate flowers have a 3-5-parted calyx and no bracts. Pistillate flowers are hard or
cartilaginous, and protected by two separated or joined (at least in the base) bracts.
Calyx of pistillate flowers is usually absent. The fruit is enclosed by the bracts and the
pericarp is membranous. The seed is usually free, erect, rarely horizontal, the perisperm
is powdery, and the primary root may be basal, lateral or apical (Rosas, 1989).
37
3.1.1. Management of Atriplex plantations
I. Choice of species
The choice of the best species to cultivate is fundamental and determined by
many factors, such as temperature and rainfall, soil type, water availability for
irrigation, and crop purpose. In addition, yields can vary considerably among species.
Many Atriplex species are native to Australia, where many studies focused on
soil salinity combat (Malcom, 2000). Such trials were very useful for a better
characterisation of these genetic resources, and for the optimisation of Atriplex
plantation management (Malcom et al., 1988).
Among the most used Atriplex species in North Africa, A. nummularia and A.
halimus are particularly important. Both species have been studied deeply in the semi-
arid environments of Southern Europe (Papanastasis, 2000). For instance, in the South
of Spain, A. halimus produced yields of edible biomass of 450-500 g/plant per year, in
spite of its low nutritive value, due to its high content of non-proteic nitrogen (Correal
et al., 1990a). Atriplex halimus responded better to direct grazing than A. nummularia
(Aouissat et al., 1993).
In Southern Africa, several shrub species were compared in trials on
desertification combat. The best results were obtained using Atriplex nummularia and A.
halimus, followed by A. undulata and A. breweri (Van Heerden et al., 2000a; 2000b).
A. nummularia
This is the most widely distributed species of the genus Atriplex.
The species originated from Australia and is divided in three subspecies (Par-
Smith, 1982):
- subsp. nummularia;
- subsp. omissa Par-Smith;
- subsp. spathulata Par-Smith;
38
All subspecies are octoploids (2n = 72). The subspecies nummularia is the most
common one and is originated from Southern Australia, New South Wales, Victoria and
Queensland. The subspecies omissa is the rarest, while the subsp. spathulata is
relatively rare in Western Australia. Plantations of A. nummularia have become more
widespread in South Africa and in Northern Africa in the last 75 and 40 years,
respectively (Franclet and Le Houérou, 1971; Le Houérou, 1994).
Some details on the characteristics of A. nummularia are reported bellow:
- dioecious species showing shrubby habitus, which can reach 1.30 m of height;
- good yield potential: when irrigated and with a salinity of 15-20 mS/cm of EC, yields
can be higher than 30 t of dry matter/ha per year (Le Houérou, 1994);
- high water-use efficiency: about 15-20 kg of dry matter/ha per year per mm of rain (Le
Houérou, 1992a; 1994);
- relatively high drought tolerance: it can grow in environments characterised by less
than 200 mm/year of rainfall;
- good salinity tolerance;
- good flooding resistance during long periods: in Northern Africa, plants survived after
three months of flooding;
- fast and abundant resprouting after grazing, related also to species ability to produce
epicormic buds (both dolicoblasts and brachyblasts, depending on the season);
- well-developed roots, up to 10 m in depth, able to use a superficial aquifer;
- poor resistance to overgrazing, which is the main limit to use the species.
After complete leaf removal, the plant needs a rest period of about 8-10 months
to recover. On the other hand, if the plant is never grazed, its lifespan will be not longer
than 12-15 years. Every 5 years, a renovation pruning at 20-40 cm above the soil is
recommended (El Mzouri et al., 2000).
Many studies have determined the yield potential of A. nummularia, taking into
consideration the variability of the used germplasm (Acherkouk, 2000) and the
application of alley-crop management (El Mzouri et al., 2000).
39
Atriplex halimus
This is the second most diffused species of Atriplex. More than 80,000 hectares
are cultivated with A. halimus throughout Syria, Jordan, Egypt, Saudi Arabia, Libya and
Tunisia.
This species has two subspecies: subsp. halimus and subsp. schweinfurhii. The
distribution of the subspecies halimus goes from semi-arid to humid regions. It is very
common on the coasts of the Mediterranean basin. It spreads from Morocco to the
English Channel, reaching the extreme Northern regions of the North Sea. The
subspecies halimus has a typical upright habitus and very short (20-cm long) and leaf-
covered fruit-bearing branches. On the opposite, the subspecies schweinfurhii has a
shrubby habitus with entangled branches. Its fruit-bearing branches are 50-cm long and
have no leaves. Even though the subspecies schweinfurhii is widespread in arid and
desert areas, it grows only in the soil depressions where ground water is present.
Both subspecies show high variability for characteristics such as the ratio
between leaves and woody parts, palatability and plant habitus. Unfortunately, the
grazing pressure has determined a reduction of variability within the population of each
subspecies. Fortunately, some favourable crosses assure the survival of highly palatable
plants within each new generation.
The Atriplex halimus subsp. schweinfurhii tolerates salinity levels which are
close to sea salinity level that is EC 55 mS/cm (Zid, 1970). The best yields, of about 15-
20 t/ha/year, can be obtained with salt concentrations under 300 mM/L of NaCl-
equivalents. Some populations able to survive to salinity levels above that of sea water
(until EC 60 mS/cm) have been studied (Franclet and Le Houérou 1971; Malcom and
Pol, 1986; Le Houérou, 1986; 1993). Anyway, Atriplex halimus is also able to grow and
produce normally in non-saline soils.
The nutritive value and the utilisation of this species have also been largely
studied in the arid environments of Southern Europe (Delgado and Muñoz, 2000;
Muñoz et al., 2000), as well as in those of Southern Tunisia (Khorchani et al., 2000)
and Middle East (Hamadeh et al., 2000).
This species is also very important for its ability to produce wood biomass under
very difficult environmental conditions, such as those of Southern Morocco
(Benchaabane, 2000).
40
II. Propagation and planting
The main shrubby species of Atriplex can be propagated agamically.
Nevertheless, the most used propagation technique is by seed, which requires seedling
management in nurseries (Figs. 8, 9 and 10). Many trials have been carried out to
improve Atriplex seed germination and manipulation, obtaining some positive results in
laboratory conditions (Lailhacar and Laude, 1975; Von Holdt, 2000). In a specific study
on cross-breeding of Atriplex canescens, hybridisation had a negative effect on the
percentage of germination. Therefore, mass selection in unselected and genetically
variable populations could be more effective than hybridisation for improving
germination and survival performance of native A. canescens (Soliman and Barrow,
2000).
Planting density affects mean yield per plant, which tends to decrease as
densities increase from 2,500 to 10,000 plants/ha (Van Heerden et al., 2000b).
III. Irrigation
The genus Atriplex can grow and reproduce under rainfall conditions ranging
between 100 and 400 mm/year, with yields varying from 1,000 to 3,000 kg of dry
matter/ha per year (Sankary, 1986).
Atriplex has a high water-use efficiency. In fact, A. nummularia, A. halimus, and
A. canescens produce 10-20 kg of dry matter/ha per year per mm of rain (Forti, 1971;
Correal et al., 1990b). In spite of the high water-use efficiency of Atriplex plants (Silva
and Lailhacar, 2000a; 2000b; 2000c), when they are planted in regions with an average
rainfall of 200-300 mm/year, it is convenient to irrigate the crop with at least 200-250
mm of water/year (Le Houérou, 1992a).
In Western Australia, plantations of Atriplex irrigated with 500 mm/year yielded
more than 5 t of dry matter/ha per year (Malcom and Pol, 1986).
In Saudi Arabia, six species of Atriplex irrigated with 420 mm/year of water
provided by a centre-pivot were compared. In the first year, average yield was 3,290
kg/ha, while in the fourth year it was 6,579 kg/ha.
41
Figure 8. Abundant seed production by Atriplex nummularia.
42
Figure 9. Seedlings of Atriplex nummularia.
43
Figure 10. Seedlings of Atriplex nummularia in pots ready for the transplant.
44
Water-use efficiency, as the ratio between the biomass produced by the plant
canopy and the supplied water, was 7.8 and 15.7 kg of dry matter/ha per year per mm of
water, respectively, in the first and fourth year (Mirreh et al., 2000).
At irrigation levels ranging from 100 to 400 mm of water/ha per year, some
Atriplex species, such as A. nummularia, A. halimus subsp. halimus, A. halimus subsp.
schweinfurthii and A. canescens subsp. liners, showed water-use efficiency values of 5-
10 kg of dry matter/ha per year per mm of water and yields of 2,000-4,000 kg dry
matter/ha per year. Therefore, these forage shrubs showed a water-use efficiency high
enough to produce a quantity of dry matter twice that of wheat and barley, and 4-5 times
higher than that of Lucerne (Le Houérou, 1992a).
IV. Nutritive value and utilisation as feed for livestock
The genus Atriplex grows preferably in arid and semi-arid regions of the world.
Large plantations are located in Northern Africa and Iran, while smaller ones are
present in Israel, Jordan, Syria, South Africa, Mexico, Australia, and USA. Atriplex
nummularia is the most used species in Northern Africa, while A. canescens, which is
more cold resistant, is the most common one in Iran. In addition to the above mentioned
species, A. halimus, A. lentiformis, A. glauca and A. leucoclada have also been
introduced for their potential forage use.
High adaptation to saline soils and high water-use efficiency, mainly linked to
the C4 metabolism, are important qualities of Atriplex shrubs. In fact, they have been
introduced in many harsh environments to supply feed to livestock in periods of scarcity
and to improve the protein content of their diet. The increase of forage production in
highly grazed areas is the main strategy to reduce soil erosion risks linked to
overgrazing and degradation.
Species of the genus Atriplex also have a high ability to absorb nitrogen from the
soil and can benefit from the action of nitrogen-fixing microorganisms (Ismaili et al.,
2000).
The main components of the forage (i.e. leaves) of six-year-old plants of some
Atriplex species are reported in Table 7. Of the five studied species, A. canescens has
the lowest values of digestible protein and total digestible nitrogen. As a consequence,
45
the values of digestible and metabolisable energy are also low. Differently, A.
lentiformis and A. nummularia have a higher nutritional value (Mirreh et al., 2000).
Lucerne hay and Atriplex leaves showed the highest values of protein, Acacia
forage was intermediate and wheat straw had the lowest values. Moreover, the hay of
lucerne and Atriplex forage seemed to be the most effective nitrogen sources for rumen
microorganisms (Silva and Pereira, 1976).
Many studies have shown the high nutritional value of A. nummularia forage (i.e.
leaves), characterised by a protein content similar to that of the lucerne hay (Tab. 8)
(Chiriyaa and Boulanouar, 2000).
Because of its low energy content, animals fed exclusively Atriplex showed a
progressive decrease in body weight. For this reason, Atriplex nummularia forage
should be employed as a protein integrator of diets based on the use of straw and rough
forages.
Many studies have reported that in Atriplex species the portion of digestible
nitrogen is of 65%, but only 55% of that is retained and available (Yaron et al., 1985;
Benjamin et al., 1986). Le Houérou (1991) affirmed that at least 45% of the digestible
nitrogen eliminated is non-proteic nitrogen. About 50% of that is represented by
glycinbethaines, which can be degraded by rumen microorganisms only when the
available energy is sufficient for their development, and when livestock are accustomed
to a diet rich in salts.
Small ruminants exclusively fed Atriplex spp. forage had a negative nitrogen
balance. The main reason for that are the lack of available carbohydrates in the diet and
the fast hydrolysis of crude protein in the rumen. These two events lead to the
accumulation of ammonia in the rumen that cannot be used by livestock (Hassan et al.,
1979; Kandil and El Shaer, 1988). When the diet is not composed exclusively by
Atriplex and is integrated with forages having more carbohydrates and energy, the
quantity of retained and available nitrogen increases significantly.
Many studies have showed the positive effects of using straw to integrate diets
based mainly on Atriplex nummularia (Correal and Sotomayor, 2000) and A. halimus
(Sotomayor and Correal, 2000).
46
Table 7. Composition of the forage (i.e. leaves) of six-year-old plants of five Atriplex species (adapted from Mirreh et al., 2000).
Species
Crude protein (% dry matter)
Digestible protein (% dry matter)
Digestible nitrogen (% of N)
Digestible energy
(Mcal kg-1)
Metabolizable energy
(Mcal kg -1)
A. lentiformis 23.4 17.1 53.4 2.35 1.92
A. canescens 11.1 6.3 47.1 2.07 1.70
A. halimus 20.5 14.5 49.7 2.19 1.79
A. leucoclada 16.7 11.1 49.9 2.20 1.80
A. nummularia 18.2 12.5 52.9 2.33 1.91
Table 8. Chemical composition and in vitro digestibility of A. nummularia and other forages (adapted from Chiriyaa and Boulanouar, 2000).
Wheat straw Lucerne hay Atriplex
nummularia leaves
Acacia cyanophylla
leaves
Crude protein (g/kg) 52 136 137 109
Ash (g/kg) 85 106 308 129
Neutral detergent fibre (g/kg) 703 466 348 342
Acid detergent fibre (g/kg) 421 307 152 209
Acid detergent lignin (g/kg) 69 92 80 132
IVDMD (g/kg)a 447 586 622 488
Tannins (g/kg) - 0.13 0.07 11.20
Total nitrogen (% dry matter) 0.83 2.18 2.19 1.74
ADIN (% N)b 9.99 3.52 7.30 11.54 a IVDMD = in vitro dry matter disappearance b ADIN = acid detergent insoluble nitrogen
47
The salt content of the edible parts of Atriplex plants, such as leaves and young
shoots, is high. For this reason, sheep fed Atriplex need to drink frequently and the
amount of ingested water may reach 11 L/head/per day (Le Houérou, 1991; Mirreh et
al., 2000). This behaviour is more evident when A. halimus is one of the components of
the diet. The large amount of ingested water is caused by the need to get rid of the salt,
previously accumulated, by the urine. For every gram of ingested sodium chloride, there
is a need of approximately 70-74 ml of water (Wilson et al., 1969; Hassan et al., 1979).
Normally, the intake of a given forage can be determined by the following two
methods: I) by free grazing, associated with a continuous visual observation of the
forage quantity present before and after livestock ranging, and the determination of the
quantity of forage consumed, or by measurements of livestock weight, or by the
introduction of a esophageal cannula; II) permanent stabling and evaluation of the
amount of ingested forage by measuring either the amount of consumed forage directly
or the ingestion time.
The meaning of the word palatability has not been well defined yet. The Sub-
committee of the Range Research Methods defined palatability as “quality that
determines the preference for a particular forage species by livestock having the
possibility to choose among many alternatives” (Marten, 1970).
When using Atriplex in projects on desertification combat and improvement of
forage production, it is important to take into consideration the acceptability of a new
feed by the livestock. Therefore, the determination and possible improvement of the
palatability of new forages is fundamental.
In 1970 in the Research Station of Bou R’bia INRAT at Sarson, in Tunisia, a
highly palatable clone of A. halimus (INRF 70100) was tested (El Hamrouni and
Sarson, 1975). However, in general, Atriplex nummularia forage shows a higher
palatability than A. halimus does.
48
Table 9. Intake of three different forages of Atriplex by sheep (adapted from Abou El Nasr et al., 1996).
Fresh Hay Silage
Number of animals 4 4 4
Initial weight (kg) 39.3 40.2 38.6
Final weight (kg) 39.6 35.3 42.7
Weight variation (g/day) 6.66 -109 91.1
Intake
g dry matter/kg weight0.75 64.3 53.7 70.4
g crude protein /kg weight0.75 8.17 4.89 8.31
g digestible fibre/kg weight0.75 38.2
34.3 42.3
Table 10. Periodical increase of live weight and average daily weight variation of lambs fed wheat straw in association with a nitrogen supplement (i.e. lucerne hay, Atriplex nummularia leaves and Acacia cyanophilla leaves) (adapted from Chiriyaa and Boulanouar, 2000).
Period Diets
Wheat straw
only
Wheat
straw +
Lucerne hay
Wheat
straw +
Atriplex
leaves
Wheat
straw +
Acacia
leaves
Periodic variation of weight (kg)
0-7 weeks -4.65 -1.81 -1.75 -3.23
7-14 weeks -0.65 0.27 2.00 -1.82
0-14 weeks -5.29 -1.54 0.25 -5.04
Average daily weight variation (g)
0-7 weeks -132.7 -51.8 -50.0 -92.3
7-14 weeks -18.5 7.7 57.1 -51.8
0-14 weeks -75.6 -22.0 3.6 -72.0
Total weight variation (%) -15.9 -4.6 0.8 -15.6
49
3.2. The Opuntia genus
I. Spreading and growing area
The genus Opuntia originated from the tropical regions of North America,
particularly from Mexico. In that country, fossil seeds of the seventh millennium b.C.
were found, indicating the use of this species as food in prehistoric times (Barbera and
Inglese, 1993). In pre-Columbian times, the prickly pear (Opuntia ficus-indica) and
other Cactaceae had a fundamental role for the survival of the population living in the
area comprised between Southern USA and Mexico (Pimienta-Barrios, 1990).
In the first half of the XVI century, Opuntia ficus-indica, similarly to other
vegetal and animal species, was introduced into Europe by Spanish colonisers (Prescott,
1843). Later on, the species spread out in all continents, especially in areas with warm
and dry climate. Currently, spontaneous and cultivated genotypes of this species are
present in many countries. For example, in Australia and South Africa, Opuntia ficus-
indica is generally considered a weed, because of its easy propagation and of the
damages it causes to sheep wool. On the contrary, in Brazil, Tunisia and Italy, the
species is an important forage or fruit crop.
For centuries, the prickly pear has been part of the landscape of the coastal
regions of the Mediterranean, thus confirming its ability to adapt to different climatic
conditions.
II. Taxonomy and botany of Opuntia ficus-indica
The first morphological classification of Opuntia species was made by people
indigenous to Mexico, who attributed different names, with a common etymological
origin, to the different taxa of Opuntiae (Pimienta-Barrios, 1990). Later on, many
authors contributed to the classification of the genus Opuntia. According to the most
used classification, which was made by Britton and Rose (1963), the genus Opuntia is
comprised in the family Cactaceae, order Caryophyllales, sub-class Caryophyllidae.
50
The family Cactaceae contains succulent caulinary species divided in the following
tribes: Pereskieae, Opuntieae and Cereae.
The genus Opuntia belongs to the tribe Opuntieae and is subdivided in the
following four subgenus: Platyopuntia, Cylindropuntia, Tephrocactus and
Brasiliopuntia. The subgenus Platyopuntia contains from 150 to 300 described species,
including the series of Ficus-indicae, which contains Opuntia ficus-indica Mill.
Among Cactaceae, Opuntia ficus-indica is the most agronomically important
species for the production of edible fruits and cladodes, which can be used as a forage
or as a vegetable (Scheinvar, 1995).
The domestication of O. ficus-indica started about 8.000 years ago (Bravo, 1991;
Pimienta-Barrios and Muñoz-Urias, 1995). Prickly and spineless types are known. The
spineless type (O. ficus-indica f. ficus-indica) originated from the wild or prickly type
(Opuntia megacantha Salm-Dick). Many other species names, such as Strepthacanthae
and Ficus-indicae (Britton and Rose, 1919), correspond to morphological variations of
O. megacantha. Many authors consider O. megacantha as a synonymous of O. ficus-
indica (spineless type) (Benson, 1982; Gibson and Nobel, 1986), because some
branches of spineless plants under stress may produce prickly shoots (Griffith, 1914; Le
Houérou, 1996). Moreover, seedlings of spineless species show high morphological
variability with the recurrence of prickly types.
In the family Cactaceae, the basic chromosome number is equal to 11, while the
somatic chromosome number is almost always 22. Many sources consider prickly and
spineless types of O. ficus-indica as octoploids (2n = 88) (Spencer, 1955). Other
authors, instead, describe this species as a diploid (2n = 22) (Weedin and Powell, 1978),
even if this latter evaluation is probably due to an identification mistake.
The prickly pear is a woody perennial species with plants variable in height from
1 to 5 m. Its main morphological characteristics are the following: branches are
transformed in elliptical or ovoid, flat organs, named cladodes. Leaves are rudimentary,
conic, and ephemeral. Over the cladode surface, there are some areolas, which
differentiate at the leaf axillae and show spines of variable size.
Flowers are hermaphrodites with yellow or orange corolla. Fruit is a berry that is
white, yellow or red, at ripening, and has numerous seeds. Roots are usually superficial,
thus facilitating the absorption of little rainfall. At the same time, the root system is
51
strong and able to explore unfavourable soils. The ability to colonise soils of low
fertility is increased by the ability to host nitrogen-fixing symbiotic microorganisms in
the roots.
III. Economic and ecological role of Opuntiae
The importance of cactus pear is linked to the numerous economically relevant
uses of the species, as extensive crops and as spontaneous populations (Barbera, 1987b;
Barbera et al., 1988; Pimienta Barrios, 1994). The species requires few cultural
practices such as superficial tilling, little pruning and irrigation, and very few treatments
against pests. As a consequence, the energy costs of this crop are very low (Baldini et
al., 1982; Barbera, 1991a; 1995).
The main use of cactus pear is undoubtedly for the consumption of fresh fruit,
which is marketed in many countries. For this reason, some efforts have been made to
improve the organoleptic characteristics of the fruit, to eliminate its irritant glochyds, to
decrease its seed number, and to optimise postharvest cold storage.
Many by-products can be obtained from the fruit pulp. An edible oil extracted
from the seeds has the following main characteristics: high unsaturation level, high
percentage of linoleic acid, and low content of linolenic acid. For those and other
chemical and physical characteristics, the cactus pear oil belongs to the same group of
soya bean, maize, and sunflower oils (Sepúlveda and Sáenz, 1988).
Indigenous populations of Mexico used to eat the fruit and young cladodes of
10-15 cm of length as vegetables. Currently, those cladodes (nopales) are commonly
used in many Mexican dishes (Hoffmann, 1995).
For a long time, cactus pear has also been used as feed for sheep, goats, cattle,
and pigs (Monjauze and Le Houérou, 1965). Many experiments on the use of cactus
pear in livestock feeding, have been carried out in arid and semi-arid areas of Mexico
(Ponce, 1995), Brazil, Chile and South Africa. Its cladodes are rich of water and can
satisfy the drinking needs of livestock in some periods of the year (Crosta and Vecchio,
1979). A diet based exclusively on Opuntia cladodes has a low nutritive value because
it is rich in digestible carbohydrates, lipids and vitamins, but is low in protein content
52
(Santana, 1992). Therefore, cladodes cut into small pieces should be supplemented with
other forages (hay, pasture) and concentrates (Monjauze and Le Houérou, 1965).
The species is also used as wind break and as enclosure of plots of land, as found
in Sardinia where it is part of the natural landscape.
In the past, the Spanish colonisers were attracted by the presence of a cochineal
scale insect (Dactilopius coccus) on cactus pear plants in Mexico. After drying and
grinding the insect body, a powder could be extracted and used as a tissue colouring
agent, as a water soluble colouring agent for the food and pharmaceutical industry, and
as a lacquer to make paints. The powder could also be used for the extraction of
carminic acid (10% of the raw material) which is used as a staining agent in histology
and microbiology (Barbera, 1991b).
Young cladodes are ingredients of some traditional foods and of some herbal
formulations. Because of their high content of fibre and mucilage, young cladodes have
a hypoglycaemic effect related to glucose absorption and a consequent non stimulation
of insulin production. Similarly, due to the adsorption of bilious salts and a further use
of the haematic cholesterol, young cladodes also have a hypocholesterolhaemic effect
(Mulas, 1992). Moreover, it seems that cactus pear cladodes have antipyretic,
antinflammatory, analgesic, and antispasmodic effects, while its dry flowers can be used
to prepare diuretic infusions (Barbera, 1991b; Mulas, 1992).
Species of the genus Opuntia show morphological, physiological and
biochemical characteristics that allow them to grow in harsh environments,
characterised by low rainfall and poor soil fertility (Martinez and Villa, 1995).
Cactus pear grows in sandy or intermediate textured, superficial soils having low
organic matter content (Barbera et al., 1993). The adaptability of the species is so high
that it can colonise the sterile soils around the Etna Vulcan (Sicily, Italy), thus creating
soil conditions favourable to other more profitable crop (Bonifacio, 1961; Barbera et al.,
1993). A similar soil improvement was also observed in subtropical regions, where the
roots and cladodes of cactus pear were transformed in organic matter, leading to higher
availability of nutrients, increase in microorganisms, and improvement of water budget
and soil structure (Monjauze and Le Houèrou, 1965). Opuntiae can also partially shade
the soil, with a subsequent decrease of temperature, light intensity, speed of organic
matter degradation, transpiration, and evaporation.
53
In very sandy soils, cactus pear limits sand removal, thus reducing wind erosion,
because of its widely distributed and superficial roots (Crosta and Vecchio, 1979).
The ability to live in symbiosis with nitrogen-fixing bacteria is another positive
ecological characteristic of the species that has also been studied (Llovera et al., 1995).
IV. Propagation
Opuntia ficus-indica can be propagated agamically or by seed. Agamic
propagation is made by cutting. A cactus pear cutting is usually formed by a two-year-
old cladode bearing two or three one-year cladodes (Barbera, 1991a). This propagation
technique has many advantages. It is easy, fast and inexpensive, and allows to obtain
uniform plants. In addition, the young plants are genetically identical to the mother
plant, allowing to maintain favourable characters (Pimienta Barrios, 1990).
In wild populations of cactus pear, agamic propagation is common, as a
consequence of cladode abscission by natural causes or by animal action.
Whenever cladodes are not available for propagation, in vitro micropropagation
techniques can be used. Explants (i.e. axillary buds) should be treated with
benziladenine. By using one cladode for explant extraction, up to 25,000 plants can be
produced (Escobar et al., 1986).
Root resprouts or mature flowers can also be used for propagation. In fact,
receptacle axillary buds of mature flowers have the ability to generate new roots and
shoots (Pimienta Barrios 1990).
Grafting of cactus pear is rarely performed and has the only aim of obtaining
ornamental plants (Portolano, 1970).
Seed propagation of Opuntia ficus-indica is less practised than that of other tree
species. The seed is covered by a head coated with a hard layer, that is a false aril
originated from the funiculus that surrounds the ovule and lignifies when the seed is
mature. Around the hilum, the funiculus and the raphe give origin to the strophiole,
which is a tissue formed by not-lignified cells (Gallo and Quagliotti, 1989). The
endosperm is absent, the cotyledons are leafy and fleshy, while the hypocotyl is not
succulent.
54
Seed germination is gradual and lasts from a minimum of 4-5 days to a
maximum of 4-5 months. The germination process requires the presence of light and an
optimal temperature of 25-30 °C (Gallo and Quagliotti, 1989).
Propagation by seed has many disadvantages: germination is slow and preceded
by a dormancy period; seedlings are genetically and phenotypically non uniform; plants
show a very long juvenile period (Escobar et al., 1986; Pimienta Barrios, 1990).
Dormancy during the germination phase seems to be caused by the funiculus cover that
slows down seed imbibition. An increase in germination rate and percentage may be
obtained by mechanical or chemical scarification. However, in one trial, the first
method acted efficiently on the funiculus cover, while chemical scarification with a HCl
solution at 20% for 24 hours induced a low germination rate (Beltran and Rogelio,
1981).
Seed propagation shows polyembriony, i.e. the development of many embryos.
One of these is of zygotic origin and derives from the fecundation of the embryonic sac,
while the others are apomitic, and derive from cells of the same embryo sac or from the
nucellar tissue (Pimienta-Barrios, 1990).
Many studies on the agamic propagation of Opuntia ficus-indica by young
shoots were carried out in Central-Western Sardinia (Mulas et al., 1992a; 1992b). In a
two-year-long trial, cuttings planted in autumn, winter or spring were compared (Mulas
et al., 1992b). The optimal conditions for rooting were evaluated by the following
parameters: number of unviable cuttings, weight variation of cuttings, root weight per
cutting, and number of shoots and fruit per rooted cutting. Meteorological data observed
during the experimental period were also recorded. Time of planting influenced all
studied parameters. Cuttings planted in autumn had the lowest number of unviable
cuttings and the highest number and weight of roots per cutting, while winter planting
showed the worst results regarding both parameters. The highest numbers of shoots and
fruit per cutting were observed at spring and winter plantings, respectively.
Meteorological conditions were also important, especially rainfall that influenced
positively the hydration of the cuttings. Consequently, a higher number of roots per
cutting was observed after the autumn plantation.
Therefore, under the temperature and rainfall conditions of Mediterranean
environments, autumn is the most favourable time for cactus pear planting.
55
Portions of cladodes can be used as cuttings, in order to save propagation
material. In fact, cuttings of different sizes and bearing a different number of buds can
be planted.
Different kinds of cuttings, bearing from 1 to 3 buds, having variable sizes (up to
a maximum of 1/4 of the whole cladode) were compared in autumn and spring plantings
(Barbera et al., 1993). The percentage of survival, time of root growth, and number and
size of the new shoots were evaluated. When the aim is to reduce the time of nursery
growth, it is better to choose cuttings of 1/4 of the whole cladode size and the spring
planting. On the other hand, smaller cuttings showed a good survival rate and
maximised productivity in terms of plant number. However, this method requires more
time to obtain plants ready to transplant.
An extensive review on seed and cutting propagation of cactus pear has been
already presented (Mondragòn and Pimienta-Barrios, 1995). Information on the
propagation by tissue culture of this crop is also largely available (Villalobos, 1995).
56
3.2.1. Ecophysiology of the genus Opuntia
I. Structural adaptations to arid environments
Species of the genus Opuntia are perennial dicotyledonous provided of cladodes
that are modified trunks. Because of their ephemeral nature and early fall, these plants
have no leaves. Cladodes are covered by a thick epidermis covered with cuticle waxes
that reduce water loss by transpiration. Stomata are deeply placed at the cladode surface
and can remain closed during most part of the day, under high temperature and light
conditions.
Cactus pear is characterised by superficial and succulent roots that spread out
horizontally. In very arid environments, the main roots give origin to secondary
succulent roots that develop in depth, where higher humidity can be found (Nefzaoui
and Ben Salem, 2002). The most active roots are in the superficial soil layers, up to 30-
cm in depth, and in an 8-m range of lateral growth (Sudzuki Hills, 1995). Because of
The particular xeromorphic characteristics of the Cactaceae root apparatus allow their
survival in very arid environments. In fact, their thin hairy roots can be covered by a
small waterproof layer or be quickly eliminated, in order to avoid water loss, under
elevated stress conditions.
The main drought tolerance mechanisms of the family Cactaceae are the
following (Sudzuki Hills, 1995):
- reduction of root surface and water permeability;
- fast absorption of small water amounts fallen as ephemeral rains, due to a fast
development of roots that disappear when the soil dries up;
- creation of a more negative water potential. The latter is considered a drought-
resistance mechanism.
Cactaceae plants are able to link the absorbed water to a hydrophilous matrix
(mucilage) that loses water by transpiration very slowly. This hydrophilous matrix is
stored in the succulent mesophyll cells of the cladodes (De Kock, 1983).
The wall of the epidermal cells is impregnated with a thick waxy layer. This
cuticle layer has many functions such as to prevent transpiration, to reflect part of the
57
solar radiation and to avoid microorganism penetration into the dermal tissue, since they
cannot decompose the cuticle compounds (Gibson and Nobel, 1986). Cladodes can lose
more than 60% of their water content before their cells collapse (De Kock, 1983). Even
if the exact function of the mucigel forming the cell parenchyma is not well understood,
it is known that it contributes to the resistance against transpiration loss, thus helping to
save water (Gibson and Nobel, 1986).
Prickles and glochyds have various functions. For instance, prickles protect the
plant against animals and help to reduce water loss (Levitt, 1980). However, their main
function is to favour water condensation near the cladode surface (Buxbaum, 1950).
Moreover, prickles contribute to decrease the daily temperature of plant tissues and to
reduce light interception by the cladodes (Nobel and Hartsock, 1983).
Species of the genus Opuntia have extraordinary characteristics that allow them
to store a large amount of water in succulent organs. Their superficial and widespread
roots are able to absorb soil water even when humidity is too low for the survival of
most plants. Therefore, rainfall of short duration and little amount (few millimetres) can
be efficiently used by Opuntia plants.
II. Drought resistance mechanisms
Opuntia ficus-indica is a typical species of arid and desert environments, even if
it also grows in temperate zones. The species shows many morphological and
physiological adaptations to its natural environments. For instance, because of the
absence of permanent leaves, the photosynthetic process occurs in the green cladodes
(Benson, 1963; Pimienta-Barrios, 1990). Those cladodes have an aquiferous
parenchyma, which can store water efficiently. Water loss by cuticular transpiration is
efficiently reduced by some thick epicuticular and intracuticular waxy layers. Stoma
morphology favours the reduction in water loss by transpiration and the photosynthetic
process. In fact, Opuntia ficus-indica shows the Crassulacean Acid Metabolism (CAM)
that is an adaptation in which stomata open at night, for gas exchange, and close during
the day; thus reducing water loss by transpiration.
CAM plants have a metabolism adapted to save water during drought and to
maintain net photosynthesis positive at the same time, thus maximising their water-use
58
efficiency. Because of the high CO2 concentrations in the tissues of these plants,
photorespiration and photoinibition are negligible, and a slow but efficient metabolism
is favoured.
The main characteristics of the CAM mechanism are the following: 1) stomata
are closed during the day and open at night; 2) night carboxylation, consisting of starch
breakdown and malic acid production and accumulation in the vacuoles, thus
determining a pH decrease at night; 3) decarboxylation of malate and CO2 fixation by
Rubisco, during the day (closed stoma), with synthesis of starch and other glucans.
In CAM plants, the formation of C4 acids is temporally separated from
decarboxylation and refixation. At night the CO2 absorbed by the open stomata is fixed
as malic acid. The accumulation of high quantities of malic acid (C4 acid) causes an
increase in cell acidity that reaches a maximum before dawn. With the onset of day, the
stomata close, and the malic acid of the vacuoles is decaboxylated by the NADP malic
enzyme. The internally released CO2 cannot escape from the tissue and reaches a
concentration that inhibits photorespiration. Subsequently, CO2 enters the normal C3
cycle that leads to starch synthesis (Pimienta-Barrios, 1990).
Species of the genus Opuntia are obliged CAM, showing the same
photosynthetic metabolism, even when plants are irrigated (Osmond, 1978).
Under severe water deficits, the CAM mechanism is modified. In those
conditions, since stomata are closed day and night, not allowing the night CO2
assimilation, the CO2 released in respiration is used. In this way, at least some
photosynthetic activity can be performed during the day (Ting, 1983). In two-week-old
cladodes and in flower buds, stomata opening was observed during the day, but in that
case photosynthesis followed the normal Calvin cycle (Acevedo et al., 1983).
Young cladodes have a C3 photosynthetic metabolism. During the day, their
open stomata absorb water from the older cladodes, producing a strong water loss by the
plant (Nobel et al., 1994; Wang et al., 1997). For this reason, during prolonged drought,
the plant does not produce new cladodes, using a physiological mechanism against
water stress and loss.
Mycorrhizal symbiosis helps the optimisation of water absorption by the roots
and water storage in reserve tissues (Pimenta-Barrios et al., 2002). Even though only
few studies have focused on this aspect, it seems that symbiosis with mycorrhizal
59
microorganisms improves the performance of the host plant, due to its greater ability to
absorb water. Considering that water deficit is the main factor limiting productivity,
mycorrhizae can be important in those conditions (Allen, 1991; Titus and Del Moral,
1998). In addition, a reduced root system, as a consequence of high water stress, allows
the plant to save energy. Therefore, mycorrhizal symbiosis is probably less expensive
for the plant than the presence of a large root system.
The CAM mechanism is more efficient in climatic conditions of hot days and
cold nights. For this reason, cactus pear plantations grow better in those environments
(Nobel and Hartsock, 1984).
In addition to their elevated drought resistance to water deficit, species of the
genus Opuntia are highly tolerant to extreme temperatures. Differently from most
plants, whose leaf temperatures are similar to that of the surrounding environment, the
Opuntiae photosynthetic organs may reach temperatures 15 °C above the environmental
ones (Gates et al., 1968). For instance, the phosphatase and aldolase enzymes of
Nopalea dejecta plants showed their maximum rate at 60 °C (Sanwal and Krishnan,
1961). Consequently, the enzymatic systems of Opuntiae can operate normally under
the high desert temperatures.
CAM plants generally show an optimal level of CO2 assimilation when night
temperatures are around 10-15 °C.
The effects of different growth temperatures on the net CO2 assimilation rate by
Opuntia were studied (Nobel and Hartsock, 1984). The best results were obtained with
the combination of 25 °C during the day and 15 °C at night. A 67% reduction of the
assimilation rate was recorded with temperatures of 10 °C during the day and 0 °C at
night. Under higher day and night temperatures (35°C and 25 °C, respectively),
assimilation rate of CO2 was reduced by 35%. Finally, with temperatures of 45 °C
during the day and 35 °C at night, net CO2 assimilation rate was absent.
The reduction of photosynthesis with high day and night temperatures is due to
stomatal closure during the night (under very high temperatures) and higher respiration
rate. In fact, in those conditions, most CO2 is linked to the organic acids produced
during the respiration process.
The ecological and agronomic success of Cactaceae plants, like Opuntiae,
depends on their different adaptation mechanisms, such as the ability to store water in
60
the acquipherous parenchyma of cladodes and to assimilate CO2 at night (Nobel, 1988;
1995).
Opuntiae plants are able to tolerate long water deficit periods, by keeping
photosynthetic tissue turgid and photosynthetic active (Nilsen et al., 1990; Nobel,
1995). In fact, thanks to the photosynthetic ability of O. ficus-indica cladodes, this
species can produce organic carbon up to three months, when soil water capacity is
under 5%. In this way, plants are able to store energy that will sustain their growth until
the next period of water availability.
61
3.2.2. Growing management of the genus Opuntia
I. Choice of species and cultivars
When the Opuntia plantation is specialised on fresh fruit production, cultivar
choice is particularly important. In this case, it is fundamental to know the market
demand and the kind of fruit preferred by consumers, thus having a better saleability.
When the plantation is used as forage, both fruit production and cultivar choice
are of secondary importance. Because Opuntia is largely distributed in arid and semi
arid zones for centuries, usually adapted local biotypes are cultivated. Nevertheless, in
order to avoid the need of removing prickles before livestock utilisation, it is
recommended to choose spineless cultivars, whenever management of the plantation is
possible (Fig. 11).
The following factors should be taking into consideration when choosing the
cultivar:
- high yield and good quality;
- climate and soil adaptability;
- low cultural requirements;
- resistance to pests and diseases.
II. Planting
When protection against soil erosion and degradation is the main objective of
Opuntia plantations, the most used planting methods are the following:
- making holes without a prefixed order, planting cuttings in the areas less subjected to
erosion, especially in depressions where rainwater and its muddiness can be gathered.
- along rows or strips, following the contours at variable distances depending on surface
slope; cuttings are planted in 30-cm deep furrows ridges; single rows or strips of two or
three rows will be spaced from 6 to 8 m.
62
Figure 11. Prickly (above) and spineless (below) cultivars of Opuntia ficus-indica.
63
Even if cactus pear propagation by seed is possible, propagation by cuttings is
preferred because of faster plant growth. In strip plantings, cladodes should be planted
perpendicularly to the furrows direction, in order to allow the branches to develop freely
towards the outside. Generally, rooting of cuttings is very high, between 80 and 95%,
particularly if two cladodes are used to obtain each plant. Unviable cuttings are
generally due to rot and pest attacks.
The preparation of cladodes for planting requires a clean cut made at the point of
their attachment to the well developed plant. Air exposure of detached cladodes for
some weeks will then allow the wounded surface to heal. After that, cladodes can be
buried obliquely, leaving half or three quarters of their length under the soil, in order to
offer less resistance to the wind.
Cuttings should be represented by two or three-year-old cladodes and it is even
better to use branches bearing three or more cladodes. The best planting time should be
distant from the rainy season, in order to avoid the risk of cladode rot. Because of the
high palatability of young cladodes, it is necessary to avoid plant grazing and the
consequent plant destruction during the first years (Inglese, 1995).
If the plantation purpose is forage production, higher planting densities should
be used. A high competition among plants reduces their reproductive activity,
increasing their juvenile period and, consequently, the period of new cladode formation,
which is the main objective of forage production. In this case, the main goal is to
maximise biomass yield and considerably reduce the amount of land available for each
plant.
The main limit of high-density systems is the shading among plants observed
during their different growth stages. In fact, poor irradiation makes cladodes thinner and
plant architecture less adapted to intercept the photosynthetically active solar radiation.
In Mexico, a typical Opuntia plantation for forage production has compact rows
not taller than 1.50 m, a density of about 40,000 plants/ha and planting distances of 80
cm in the row x 40 cm between the rows. A similar planting system is used in Brazil,
where the planting density is the same, but distances are 100 cm x 25 cm. These
systems are more intensive than the most diffused one, in which planting distances are
200 cm x 100 cm. After two years from planting, yields of 246 tons/ha can be obtained
in the Mexican and Brazilian systems mentioned above, while only 100 tons/ha can be
64
produced in the lower density system. Therefore, the more intensive Opuntia plantations
of Brazil are certainly more efficient than the traditional less-intensive ones.
III. Soil fertilisation
Opuntia usually produces low yields, because it grows under very limiting
environmental conditions. Wild cactus pear plants spread on poor soils, with low
organic matter level, and in regions characterised by a short growing season. Those
factors do not allow the species to express its potentialities.
In many countries, several fertilisation trials showed that fruit and cladode yields
can increase sharply by fertilisation. For instance, high nitrogen applications, until 160
kg/ha, caused an increase in the number of new cladodes of O. engelmannii.
In addition to increases in yield, fertilisation also increased the protein content of
Opuntia forage (Gonzales, 1989). In fact, O. lindheimeri plantations fertilised with 67,
124 and 135 kg of nitrogen/ha showed increases of forage protein content of 3.1, 4.2
and 4.4 percentage points, respectively.
IV. Nutritive value and utilisation as feed for livestock
Opuntia plants have several characteristics that are advantageous for forage use:
wide spreading, fast growth, low-cost cultivation, high palatability, and resistance to
long drought periods (Shoop et al., 1977). For these reasons, cactus pear has become an
important supplement in livestock feeding, especially during the dry season and/or
when other forages are scarcely available. Both cladodes and fruits may be used as fresh
forage or stored as silage (Castra et al., 1977).
Contrary to what is commonly believed, the use of cactus pear as forage is a
relatively old practice. The first information on this use, which dates back to before the
Civil War (1861-1865), indicates Texas as a major area of its utilisation (Griffith,
1905). Later on, cladodes were transported from Texas to other regions of the USA,
such as Brownsville, Indianola, San Antonio, and Eagle Pass.
For a long time, large areas of Opuntia have been cultivated in Algeria,
Morocco, Mexico, and especially in Brazil and Tunisia, where cactus is used as a forage
65
reserve for periods of prolonged drought. In many arid or semi-arid areas (e.g. Tunisia,
Mexico, South of Texas and South Africa), breeders largely use Opuntia as an
emergency forage, by direct grazing of wild or cultivated populations, in order to cope
with dry periods and to limit grazing pressure over the natural vegetation cover (Le
Houèrou, 1992b; Nefzaoui et al., 2000a).
In different regions of the world, both cultivated and wild populations of
Opuntia have become important as forage plants. Currently, Opuntia plants are
cultivated in Africa, Argentina, Bolivia, Brazil, Chile, Columbia, Palestine, Italy,
Mexico, Peru, Spain, and USA (Curtis, 1979; Le Houèrou, 1979; Brutsh, 1984; Russel
and Felker, 1987; Andrade, 1990; Barbera et al., 1992; Flores Valdez and Aguirre
Rivera, 1992; Felker, 1995).
Opuntia, as most feeds, is an incomplete and not well-balanced feed, it is a
valuable source of energy and water. Cladodes have a low content of crude protein,
fibre, phosphorous and sodium (Le Houérou, 1992b; Nefzaoui, 2000). In general,
Opuntia cladodes have a water content of about 90% (on a fresh weight basis) and an
ash content of about 20% of dry matter. Their crude protein content is often under 5%,
but in some cases it can reach values as high as 10% of dry matter. Their fibre content is
about 10% of dry matter (Tab. 11). However, if Opuntia cladodes are associated with
other forages able to compensate for these deficiencies, it is possible to obtain well-
balanced diets.
Nitrogen-free extract, including soluble and polymeric sugars, is about 60% of
dry matter. Due to the low phosphorous (0.03%) and sodium (0.01%) content of
cladodes, the diet should be integrated with other forages rich in those elements.
Fertilisation with nitrogen and phosphorous may increase the crude protein
content of Opuntia cladodes from 4.5 to 10% of dry weight (Gonzales, 1989). Some
Opuntia clones coming from Brazil showed a crude protein content above 11% of dry
matter (Gregory and Felker, 1992). The possibility of cross-breeding and selecting
cultivars with higher protein content may be an useful tool in countries where crop
fertilisation is expensive. However, cladode protein deficiency may also be restored by
integrating livestock diet with other forages (Ben Salem et al., 2002).
66
Table 11. Average chemical composition of Opuntia cladodes used as forage (adapted
from Nefzaoui and Ben Salem, 2002).
Species Water (% fw)
Ash Crude protein
Crude fibre
Nitrogen free extract
Ca Mg P K Na
(% of dry weight)
O. engelmannii
&
O. lindermerii
85 2.9 8.7 7.85 8.3 1.6 0.04 3.0
O. ficus-indica
(mean data from
many countries)
89 17 4.8 10.9 65
O. ficus-indica
California
90
10.4
64
6.3
1.4
0.033
1.2
0.033
Chile
89
8.9
3.9
1.3
0.012
2.0
0.003
Tunisia
87 27 3.8 8.6 58 8.7 - 0.04 1.1 0.05
67
Livestock intake of cladodes can be high. For example, Jersey cattle fed Opuntia
forage, integrated with 1 kg/day of concentrate, ingested 51 kg/day of fresh cladodes
(Woodward et al., 1951). Cattle fed exclusively fresh cladodes showed intake levels as
high as 60 kg/day (Metral, 1965).
In other studies, in cattle fed Opuntia cladodes only, intake was equal to 77
kg/day (Viana, 1965), while in sheep it varied from 2.5 to 9 kg/day (Monjauze and Le
Houérou, 1965).
In one study, sheep showed higher intake of Opuntia ficus-indica forage (11
kg/day) than that of O. robusta (6.5 kg/day) (Flores Valdez and Aguirre Rivera, 1992).
Opuntia intake increases as the water content of its cladodes increases, probably
because the animal needs to increase intake, in order to maintain constant its energy
intake. A higher water content could also be associated with a higher palatability of
cladodes.
In sheep, cladodes can have laxative effects, due to their fast passage in the
rumen. These effects are more evident when the amount of cladodes in the diet is over
60% of the total. However, these negative effects can be avoided supplementing the diet
with straw or hay, which increase fibre concentration and slow down passage rate.
Sheep fed straw can ingest more than 600 g/day (on a dry matter basis) of
cladodes, without having any digestive problems (Nefzaoui et al., 1993).
Mixing cereal brans, which is a low quality feed, with molasses increases diet
intake (Preston and Leng, 1987). Probably the same effect could be obtained using
cladodes, since their high carbohydrate content could have a role similar to that of
molasses. The gross energy content of cladodes ranges from 3,500 to 4,000 kcal/kg of
dry weight, but only a half of this energy, mainly provided by carbohydrates, is used by
livestock (De Kock, 1983; Ben Thlija, 1987).
In North Africa, a region characterised by arid or semi-arid climate, generally
cereal residues and natural grazing are not sufficient to satisfy the feeding requirements
of small ruminants for meat production. Feed integration with cladodes may be a valid
and economically sustainable alternative. In fact, when cladodes are added to the diet,
sheep body weight can increase up to 145 g/day (Tien et al., 1993). Goats fed Lucerne
hay and cladodes had increases of 436 g/day in milk production compared to animals
not fed cladodes (Azocar and Rojo, 1991). Cladodes, associated with other forages rich
68
in proteins, can replace cereal grains (Ben Salem et al., 1998) or maize silage (Metral,
1965), without negative effects on the daily weight increase of adult and young sheep.
When sheep are fed increasing quantities of Opuntia, total diet intake and the
intake of other associated forages increase (Tab. 12) (Ben Salem et al., 1996).
Cactus pear cladodes have high digestibility. In sheep, their digestibility is
similar to that of the most commonly used forages. The fast rumen passage rate of
cladodes allows the livestock to ingest further feed and does not impede a proper use of
the remaining components of the diet. This fact is of fundamental importance in arid
zones, where the livestock usually get a poor diet, based mainly on straw or cereal
stubbles, not able to assure a proper daily body weight increase.
The combination of O. ficus-indica with cereal straw is a good alternative to
sustain small ruminants in arid and semi-arid regions (Ben Salem et al., 1996). In fact,
the addition of cladodes to the diet can increase its nutritional value and can stimulate
the intake of low palatable forages such as straw in sheep (Ben Salem et al., 1996;
Nefzaoui et al., 1993) (Tab. 12 and 13).
Because of their high content of soluble carbohydrates, which facilitate the use
of non-protein nitrogen by ruminants, cladodes may also be a valuable complement to
straw treated with ammonia or urea (Nefzaoui et al., 1993). Barbarine sheep ingested a
high quantity of Opuntia (ad libitum) cladodes (about 450 g of dry matter/day), if given
at the same time from 300 to 600 g/day of straw treated with ammonia (Tab. 13)
(Nefzaoui et al., 1993). The treatment of straw with urea or ammonia is necessary to
supply the nitrogen deficit of the diet. Another alternative is to add hay of Atriplex
nummularia (about 300 g of dry matter/day) to cladode-based diets. Atriplex is a good
source of protein and, furthermore, the nitrogen supplied facilitates the organic matter
digestion by sheep (Nefzaoui et al., 1996).
In one trial, lambs were fed Opuntia cladodes ad libitum, as an alternative to
more expensive cereal grains, supplemented with one of the following nitrogen sources:
urea (D1), Atriplex halimus (D2), Atriplex nummularia (D3) and soya bean meal (D4).
Diets were isonitrogenous and isoenergetic, had an identical and limited amount of hay,
and included some barley also. Voluntary dry matter intake was 707, 863, 858 and 680
g/day, for D1, D2, D3 and D4, respectively.
69
Table 12. Effects of feed integration with spineless cactus pear (Opuntia ficus-indica f.
inermis) cladodes on intake, total digestibility and water consumption of sheep fed
straw-based diets (adapted from Ben Salem et al., 1996).
Quantity of spineless cactus (g of dry matter/day) 0 150 300 450 600
Dry matter intake (g/day) Straw(a diet component) 550c 574bc 523c 643ab 716a Cactus + straw (total diet) 550e 724d 823c 1093b 1278a Intake of dry matter (g/kg BW0.75 day)
Straw 43.6b 42.2bc 37.7c 44.8b 54.7a Cactus + straw 43.6e 53.3d 59.6c 76.3b 97.6a Total diet apparent digestibility (in decimals)
Dry matter 0.433b 0.466ab 0.491ab 0.514a 0.534a Organic matter 0.453b 0.504ab 0.543a 0.577a 0.587a Crude protein 0.495c 0.550bc 0.537bc 0.585ab 0.643a Crude fibre 0.525 0.508 0.534 0.523 0.468 Neutral detergent fibre 0.504 0.495 0.483 0.523 0.506 Acid detergent fibre 0.524 0.473 0.473 0.522 0.484 Intake of digestible organic matter and crude protein (% of maintenance requirements) Digestible organic matter 93 123 158 193 212 Digestible crude protein 52 52 64 93 111 Water consumption (l/day) 2.42a 1.49b 0.14c 0.11c 0.00c a,b,c,d,e Means in the same row labelled with different letters are statistically different (P<0.05).
70
Table 13. Straw integration with spineless cactus in diets of sheep (adapted from
Nefzaoui et al., 1993).
Straw level 300
g/day
600
g/day
US* ATS* UTS* US* ATS* UTS*
Dry matter intake (g)
Opuntia 445 447 425 432 462 439 Straw 254 242 249 494 466 486 Diet digestibility (%) Organic matter 67.9 64.0 63.3 66.5 69.8 72.6 Crude protein 41.1 48.0 43.3 45.9 61.0 77.1 Crude fibre 37.5 30.5 29.2 46.5 49.2 52.7 Retained nitrogen
-0.2 -0.2 -0.6 0.8 2.8 3.9
*US: untreated straw; ATS: ammonia treated straw; UTS: urea treated straw.
71
Urea and A. halimus supplementation led to low growth rates (55 and 58 g/day,
respectively) compared to A. nummularia or soya bean meal (74 and 70 g/day,
respectively). Therefore, the cactus-based diet was efficiently supplemented with
Atriplex nummularia in sheep (Tab. 14) (Nefzaoui et al., 2000b).
Goats fed natural pasture supplemented with a mixture of cladode portions (100
g of dry matter/day) and Atriplex nummularia (100 g of dry matter/day) showed a daily
body weight increase from 25 to 60 g/day (Nefzaoui et al., 2000a).
Acacia cyanophylla Lindl. (sin. Acacia saligna), a widely spread shrub
introduced in arid environments, is often used as forage in association with Opuntia. In
fact, Acacia is rich in crude protein (about 13% of dry matter). Barbarine sheep fed four
different diets showed a low intake of acacia (250 g of dry matter/day) (Tab. 15)
(Nefzaoui et al., 1996), probably because of the high content of tannins in acacia (4-7%
of dry matter) (Nefzaoiu et al., 1996; Ben Salem et al., 1998).
Since its high tannin content limits acacia intake, an appropriate nitrogen source
should be added to these diets, such as straw treated with urea or ammonia and, more
frequently, Atriplex nummularia. Results obtained in sheep fed diets based on acacia
supplied with Atriplex nummularia and Opuntia cladodes, in order to replace more
expensive cereal grains, are good (Ben Salem et al., 2002).
In conclusion, the use of non-conventional forage species could be economically
advantageous in countries characterised by arid or semi-arid climate.
V. Resource management
Opuntia can be used as an alternative forage in various ways and can assure the
survival of livestock during long periods of drought in arid and semi-arid regions.
Direct grazing is the easiest and cheapest method. However, it is not the most
efficient and sustainable one, because the risk of overgrazing is considerable.
Cultivated Opuntia plants can be used differently, by cutting cladodes in small
pieces or in thin strips and giving them directly to the livestock in cribs or in a place far
from the cultivation (Fig. 12). Cladode portions can be mixed with straw or low quality
Lucerne hay, and silage. Some cactus pear fruit are usually added to the mixture.
However, when they are not available, molasses can replace them.
72
Table 14. Effects of the association of different nitrogen sources with diets based on
cactus pear on lambs (adapted from Nefzaoui et al., 2000b)
Dieta D1 D2 D3 D4
Intake (g of dry matter/day):
Opuntia 241 252 241 228 Atriplex halimus 0 224.2 0 0 Atriplex nummularia 0 0 225.8 0 Soya bean meal 0 0 0 57.6 Barley 308.8 243.6 243.6 243.6 Hay 149.0 142.9 147.5 150.6 Urea 8 0 0 0 Total intake 706.8 862.7 857.9 679.8 Average daily weight gain (g/day)
55 58 74 70
aDiets were: D1 = cactus ad libitum + 170 g hay + 355 g barley + 8g urea; D2 = cactus ad libitum + 170 g hay + 280 g barley + 740g Atriplex halimus; D3 = cactus ad libitum + 170 g hay + 280 g barley + 740g Atriplex nummularia; D4 = cactus ad libitum + 170 g hay + 280 g barley + 65g soya bean meal.
Table 15. Nutritional value of diets based on cactus pear cladodes (Opuntia ficus-
indica) and acacia (Acacia cyanophylla) in sheep (adapted from Nefzaoui et al., 1996).
Dietsa R00 R21 R22 R23 Intake, g dry matter/day Opuntia 0 167 246 267 Acacia 241 373 211 177 Diet digestibility (%) Organic matter 67.7 76.5 73.9 74.6 Crude protein 45.8 49.4 34.8 16.9 Crude fibre 62.8 80.5 77.4 79.9 Retained nitrogen (g/day)
2.77 2.73 0.46 -1.07
Nutritional valueb Energy 147 151 131 116 Nitrogen 75 67 32 10 a In all diets, a limited amount of hay was distributed. bNutritional value is expressed as percentage of sheep maintenance requirements in energy (intake of digestible organic matter) and nitrogen (intake of digestible crude protein).
73
Figure 12. Goat eating Opuntia ficus-indica.
74
Cladodes should be associated with legumes or cereal straw, because of their
low protein content. Often the diet can be completed by small quantities of bone meal,
salt and lime, which provide phosphorous and sodium (De Kock, 1983).
After harvest, cladodes may also be partially dried and stored, to be used
successively in the period of highest aridity, when natural grazing is absent.
The best way to obtain good silage is to cut cladodes in small pieces and to add
oats straw and a small quantity (respecting a ratio of 84:16 with cladodes) of lucerne
hay and molasses (2%).
The management of Opuntia plantations subjected to direct grazing requires a
continuous and careful control. Young plants are particularly sensitive to grazing and
may be destroyed by the livestock. Even adult plants may suffer severe damages if
excessively grazed, with a progressive decrease in resprouting, and a consequent
decrease of total yield. Therefore, the most rational way to use an Opuntia plantation is
to divide the area into small closed plots. Each plot should be intensively used for few
months, with a successive resting period of about three years, to allow plant recovery.
Another important aspect is that more than 50% of the total yield may be discarded by
the animals, because often cladodes are partially eaten and then left. Moreover, an
excessive use may destroy the whole plantation (Monjauze and Le Houérou, 1965; De
Kock, 1980). Nevertheless, direct grazing management system, other than being the
least expensive, allows the livestock to graze the grass growing among the cultivated
shrubs.
An opposite type of management is the complete avoidance of direct grazing, by
cutting and distributing cladodes in cribs to livestock. In this case, the loss of forage is
negligible, and the risk of over-exploitation is very low and limited cases when cladodes
are taken off from very young plants. Cladode distribution in cribs requires intensive
work. However, this is the only rational way of managing plantations when the ability
to manage the rangelands is scarce, as observed in some regions of Northern Africa
(Nefzaoui and Ben Salem, 2002).
When using the prickly varieties, it is necessary to previously take off cladode
prickles by using propane burners. Therefore, in order to facilitate the manipulation of
Opuntia forage, it is better to use plantations of the spineless varieties O. ficus-indica
var. inermis (Shoop et al., 1977).
75
In Texas and Mexico, usually the entire plant is burned before the cladode is
harvested, while in Northern Africa detached cladodes are burned separately, and
subsequently cut in small pieces by hand or with the aid of a special machinery.
VI. The use of Opuntia as a water source for cattle
The lack of water can cause a reduction in feed intake and a consequent decrease
of body weight in livestock. In arid areas, providing livestock with the right amount of
water quantity is very difficult during the drier seasons. In those conditions, livestock
have to spend a lot of energy to reach water sources and soil degradation around these
areas has become a serious problem.
Feeding Opuntia may be a way of at least partially supplying water to livestock,
because the water content of cladodes is around 85% of fresh weight. For instance,
when lambs are fed high amounts of Opuntia, almost no additional water is needed
(Cottier, 1934; Woodward et al., 1951). Sheep fed a high quantity of cladodes during
long periods (from 400 to 500 days) gave up drinking. Sheep fed acacia and barley with
the addition of cladodes showed a water request of only 0.6 L/day.
Therefore, the use of Opuntia as a water source for livestock can be of
fundamental importance in arid environments.
76
CONCLUSIONS
Because of the increasing world population and, particularly, the increasing
demographic pressure in regions under desertification risk, solutions to the consequent
progressive desertification process have been searched for. The need to find an
economic value, even if limited, to the large areas neighbouring the ecologically
degraded lands is another major concern.
The use of tree and shrub species which are able to develop under extreme
aridity and on very poor soils and, at the same time, have a potential forage use could be
a solution to these problems.
Species of the genus Opuntia, particularly O. ficus-indica, and of the genus
Atriplex, such as A. nummularia, A. halimus and A. canescens, have useful
characteristics to combat desertification successfully, and can assure feed production for
livestock and incomes sometimes higher than those of traditional forage systems (Le
Houérou, 2000).
The use of these species has a strategic value that should be combined with
adequate technology, capacity building of users and their involvement in the
management of plantations.
In fact, the ecological and agricultural value of these species depend on the
adoption of some procedures: correct planting, which needs technical and economic
efforts often above the possibility of the local communities; the plantation survival,
since these systems tend to be fragile; the right management of plantations, that are
often considered an exogenous element by users; and the renewal or evolution of
plantations towards a vegetation cover ecologically sustainable, respecting the system
potential.
This approach of agroforestry management of marginal lands is surely more
accepted by local communities than the traditional forestry projects, where the technical
result is often linked to livestock exclusion from the interested areas.
77
Moreover, the use of shrub species represents a clear advantage with respect to
other marginal agricultural systems, such as the systems based on barley monoculture,
which is responsible for the degradation, erosion and salinity problems of many lands
under desertification risk.
In fact, shrubs assure a permanent soil cover, thus maximising antierosion
effects. Their well-developed roots are able to use deep-water reserves or ephemeral
rains, and better contribute to an increase in soil fertility.
In addition, species of the genera Opuntia and Atriplex integrate each other,
since the first are rich in water and fibre, and the second are mainly rich in protein.
Opuntia cladodes water content can be useful to counterbalance the higher water
requests of the livestock fed the salty Atriplex leaves. Both kinds of forages could be
associated with the low-quality feeds generally available in arid regions, such as cereal
straws (Chiriyaa and Boulanouar, 2000).
However, the right management of Opuntia and Atriplex species involves not
only the right combination of forages, in order to balance the livestock diet, but also a
right turning of Atriplex grazing and a controlled biomass yield removal of Opuntia.
Proper plant pruning of Atriplex plants is also fundamental to renew vegetation (Fig.
13).
Technical measures involved in shrub planting are difficult and expensive and,
furthermore, should be associated with information and capacity building activities for
the final users (Fig. 14).
Finally, further research is necessary to study the implementation of forage
shrub plantations in an evolutionary process in which the vegetation cover develops
towards a more stable ecological equilibrium, with the achievement of a higher
biodiversity and a sustainable management.
78
Figure 13. Wood production by a six-year-old Atriplex nummularia shrub.
79
Figure 14. Strip cultivation of Atriplex nummularia with cereals.
80
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