Embed Size (px)
Citation preview
Mekelle University
College of Dryland Agriculture
and Natural Resources
Department of Land Resource Management and Environmental
Protection
Soil Fertility Assessment under Trees, Agricultural Crops and Pasture Land Use
Systems in Rainfed Environments in Central Ethiopia:
Case Study at Tiyo District, Arsi, Ethiopia
By: Dessalegn Lemi
E-mail: [email protected]
A Thesis Submitted in Partial Fulfillment of the Requirements for the Master of Science Degree
in Tropical Land Resource Management
Advisors:
Fassil Kebede (PhD)
Associate professor of soil science
Charles Yamoah (PhD)
Associate professor of soil science
May, 2010
CoDANR
ii
Declaration
This is to certify that this thesis entitled “soil fertility assessment under tree, agricultural crop and
pasture based land use systems in rainfed environments in central Ethiopia: A case study from
Tiyo district, Arsi, Ethiopia” submitted in partial fulfillment of the requirements for the award of
the degree of M.Sc., in Tropical Land Resource Management to College of Dryland Agriculture
and Natural Resources, Mekelle University, through the Department of Land Resource
Management and Environmental Protection, done by Mr. Dessalegn Lemi, Id.No.
FDA/PS0037/00 is an authentic work carried out by him under our guidance. The matter
embodied in this project work has not been submitted earlier for award of any degree or diploma
to the best of our knowledge and belief.
Name of the student Dessalegn Lemi Signature & date ________________
Name of the advisors:
1. Fassil Kebede (Dr.) Signature & date_____________________
2. Charles Yamoah (Dr.) Signature & date_____________________
iii
Table Contents
Abstract ---------------------------------------------------------------------------------------vi
Acknowledgement-------------------------------------------------------------------------- vii
Acronyms----------------------------------------------------------------------------------- viii
List of Tables---------------------------------------------------------------------------------ix
List of Figures---------------------------------------------------------------------------------x
Chapter I. Introduction-----------------------------------------------------------------------1
1.1. Background --------------------------------------------------------------------------------------------- 1
1.2. Statement of the Problem----------------------------------------------------------------------------- 3
1.3. Hypothesis ---------------------------------------------------------------------------------------------- 3
1.4. Objectives----------------------------------------------------------------------------------------------- 4
1.4.1. General Objective -------------------------------------------------------------------------------- 4
1.4.2. Specific Objectives------------------------------------------------------------------------------- 4
Chapter II. Literature Review ---------------------------------------------------------------5
2.1. Land Uses of Tiyo District ----------------------------------------------------------------------- 5
2.2. Soil Properties under Different Land Use---------------------------------------------------------- 5
2.2.1. Soil Physical Properties ------------------------------------------------------------------------- 6
2.2.1.1. Bulk Density --------------------------------------------------------------------------------- 6
2.2.1.2. Soil texture ----------------------------------------------------------------------------------- 7
2.2.2. Soil Chemical Properties ------------------------------------------------------------------------ 7
2.2.2.1. Soil pH---------------------------------------------------------------------------------------- 7
2.2.2.2. Soil Electrical Conductivity (EC)--------------------------------------------------------- 8
2.2.2.3. Soil Organic Carbon ------------------------------------------------------------------------ 8
iv
2.2.2.4. Available Phosphorous --------------------------------------------------------------------11
2.3. Visual Soil Assessment Techniques ---------------------------------------------------------------12
Chapter III. Materials and Methods ------------------------------------------------------ 14
3.1. Description of the Study area -----------------------------------------------------------------------14
3.1.1. Location of the Study Site----------------------------------------------------------------------14
3.1.2. Topography---------------------------------------------------------------------------------------15
3.1.3. Climate--------------------------------------------------------------------------------------------15
3.1.4. Vegetation ----------------------------------------------------------------------------------------15
3.1.5. Geology and Soil --------------------------------------------------------------------------------16
3.1.6. Land Use------------------------------------------------------------------------------------------16
3.2. Methods ------------------------------------------------------------------------------------------------16
3.2.1. Study site selection criteria --------------------------------------------------------------------16
3.2.2. Experimental Design and Layout -------------------------------------------------------------17
3.2.3. Soil Fertility Assessment Using VS Approach in the Field -------------------------------17
3.2.4. Soil sampling and sample preparation--------------------------------------------------------17
3.2.5. Determination of Soil Physico-Chemical Properties ---------------------------------------18
3.2.6. Statistical Analysis ------------------------------------------------------------------------------18
Chapter IV. Results and Discussions----------------------------------------------------- 19
4.1. Effect of Land Use on Soil Properties -------------------------------------------------------------19
4.2. Effect of Land Use on Soil physical properties.--------------------------------------------------19
4.2.1. Bulk Density -------------------------------------------------------------------------------------19
4.2.2. Soil texture ---------------------------------------------------------------------------------------20
4.3. Effect of Land Use Type on Soil Chemicals Properties-----------------------------------------21
4.3.1. Soil pH --------------------------------------------------------------------------------------------21
4.3.2. Soil Electrical Conductivity (EC) -------------------------------------------------------------22
4.3.3. Soil Organic carbon -----------------------------------------------------------------------------22
4.3.4. Available Phosphorous -------------------------------------------------------------------------24
v
4.4. Relation of Soil Organic carbon and other soil properties of the different Land Uses and
Soil Fertility-------------------------------------------------------------------------------------------------25
4.5. Soil Fertility Status in Different Land Uses Using VS Approach -----------------------------27
4.5.1. Soil Fertility Status in Agricultural Land ----------------------------------------------------28
4.5.2. Soil Fertility Status in Pasture Land ----------------------------------------------------------29
4.5.3. Soil Fertility Status in Eucalyptus Plantation -----------------------------------------------30
Chapter V. Conclusions and Recommendations---------------------------------------- 32
5.1. Conclusions--------------------------------------------------------------------------------------------32
5.2. Recommendations ------------------------------------------------------------------------------------32
6. References -------------------------------------------------------------------------------- 34
7. Appendices ------------------------------------------------------------------------------- 40
Appendix 1. Record format for results of soil laboratory analysis ---------------------------------40
Appendix 2. Soil Visual Assessment Score Card-----------------------------------------------------41
Appendix 3. Soil Visual Assessment Check List ----------------------------------------------------41
Appendix 4. Laboratory results of Soil Particle size distribution -----------------------------------45
Appendix 5. Standard values of some topsoil chemical properties --------Error! Bookmark not
defined.
Appendix 6. Results of Soil Laboratory Analysis ---------------- Error! Bookmark not defined.
vi
Abstract
The study was conducted at Tiyo District near Adama University, Asella School of Agriculture,
which is part of central Ethiopia on three different land uses, namely: pasture land eucalyptus
plantation and agricultural land. Soil fertility varies under different land use systems due to the
influence of the land use practices on soil nutrient differently. The research was conducted with
objectives to evaluate the effect of different land uses on soil properties and to assess the
influence of different land use on soil fertility. The three land use systems under rainfed
environment in central Ethiopia were considered as treatments for test of soil fertility by
considering some selected soil properties. Soil samples were collected from three different land
uses under each land use the soil samples were collected at 15 sampling points and two depths
(0-15 cm and15-30 cm) by taking 300m by 500m larger plot by using grid or systematic sampling
and a total of 90 soil samples were collected. Results indicated that in the selected soil
properties were significantly different (P<0.05). Soil bulk density of the land uses were
0.92g/cm3, 1.02g/cm
3 and1.04g/cm
3 for pasture land, eucalyptus plantation and agricultural
land, respectively at the surface soil, and 0.99g/cm3, 1.01g/cm
3 and 1.09g/cm
3 the subsoil. Soil
texture was almost similar for the three land uses and it was clayey. The result also revealed that
the soil chemical properties such as; soil pH were 5.09, 5.01 and 5.00 for pasture land,
eucalyptus plantation and agricultural land respectively for the surface soil and 5.03, 5.01 and
4.94 for sub soil. The EC5 of the soil were 19.2, 19.0 and 16.2µs/cm for the surface soil and 15.8,
18.1 and 13.7µs/cm for subsoil in pasture land eucalyptus plantation and agricultural land,
respectively. The soil organic carbon and available phosphorous were also significantly different
among the three land uses and depths. Soil OC (%) was 5.19, 4.76 and 2.78 on the surface soil
and 4.37, 3.81 and 2.02 in the subsoil for pasture land, eucalyptus plantation and agricultural
land respectively. Available phosphorous (ppm) was 14.2, 13.33 and 10.8 in surface soil and
11.73, 10.27 and 7.8 in subsoil for pasture land, eucalyptus plantation and agricultural land,
respectively. Generally, pasture land was better than the other land uses in terms of soil fertility
from these results.
vii
Acknowledgement
First of all, Glory is to Jesus the Christ-Justified, Examined, Sacrificed, and Utmost Savior-who
helped me at every moment of my life. First and foremost, my heart felt appreciation and
gratitude to my advisors Dr. Fassil Kebede and Dr. Charles Yamoah, for their enthusiastic effort,
invaluable and stimulating guidance, moral support, and unbounded constructive comments
starting from selection the title to final thesis reporting.
I would like to acknowledge Kulumsa Agricultural Research Center staff; specially the Soil and
Water Section; Mr. Kassu Tadese, Ms Rut Duga and Mr. Sidelil Asfaw for their material and
laboratory facility support and I would also like to thank the Ministry of Agriculture and Rural
Development for funding the research and sponsoring the scholarship. And also, I would like to
extend my deepest appreciation to my dearly lovely wife Soreti Shiferaw and my father Lemi
Sori and my mother Tiru Hunda and my brothers; Fanta and Akuma Lemi and sisters; Gonfe,
Kisi and Desistu Lemi for their love, continual moral and material support, and encouragement. I
am also grateful to my friends Ashenafi Atomsa, and other my classmates. Finally, I would like
to extend my deepest appreciation to my friends at work place; Damtew Fufa, Abebe Terefe,
Birhanu Mamo, Mulugeta Dula, Mulugeta Kebede, Masfin Benti and his wife Hiwot Teshome,
for their moral support and encouragement.
viii
Acronyms
AGL Agricultural land
C: N Carbon to Nitrogen ratio
C: P Carbon to Phosphorous ratio
C/Po Carbon to Organic Phosphorous ratio
EC Electrical Conductivity
EFAP Ethiopian Forest Action Plan
EUP Eucalyptus Plantation
FAO Food and Agricultural Organization
g cm-3
Gram per centimeter cube
g kg-1
Gram per kilogram
g m-2
Gram per meter square
GPS Geographic Positioning System
ha Hectare
KARC Kulumsa Agricultural Research Center
km Kilometer
m Meter
masl Meter above sea level
mm Millimeter
OC Organic Carbon
OM Organic Matter
P Phosphorous
Pi/Po Inorganic to organic phosphorous ratio
ρb Bulk density
PL Pasture land
SO Soil organic carbon
t ha-1
Ton per hectare
VS Visual Scoring
VSA Visual Scoring Approach
ix
List of Tables
Table 1. The mean values of soil bulk density, pH and electrical conductivity. ........................... 19
Table 2. The mean values of soil ocarbon and available phosphorous ......................................... 22
Table 3. Soil visual assessment values of agricultural land .......................................................... 28
Table 4. Soil visual assessment values of pasture land ................................................................. 29
Table 5. Soil visual assessment value of eucalyptus plantation .................................................... 30
x
List of Figures
Figure 1.Location map of Tiyo...................................................................................................... 14
Figure 2. Experimental layout of the research site ........................................................................ 17
Figure 3. Correlation of available phosphorous with organic carbon of the different land uses... 25
Figure 4. Correlation of soil electrical conductivity with organic carbon of the different land uses
........................................................................................................................................ 26
Figure 5. The correlation relation of Soil pH with soil organic carbon of the different land use
system. ............................................................................................................................ 26
Figure 6. The correlation relation of soil bulk density with soil organic carbon of the different
land use system............................................................................................................... 27
Figure 7. Soil profile pit of agricultural land................................................................................. 28
Figure 8. Soil profile pit of pasture land........................................................................................ 29
Figure 9. soil profile pit of eucalyptus plantation......................................................................... 30
1
Chapter I. Introduction
1.1. Background
The increasing world population is now confronted with recurrent famine particularly in the third
world countries. Agricultural research through out the world which is supposed to increase yield
is beset with several constraints such as poor soil fertility inadequate fertilizers, lack of pests and
diseases control, as well as introduction of new varieties that are able to make good use of added
inputs. High productivity can only be achieved if the plants are properly fed. i.e. if the availability
of nutrients from the soil meets the demand of crop for its maximum growth (Sheleme and
Gashaw, 1994).
In this regard knowledge of the nature and properties of soils is vital in regions where soil
productivity is often limited by poor soil fertility and where the need for food production is large.
In addition to the low soil fertility, soil degradation is an increasing threat in many parts of
Ethiopia. There is an urgent need to understand the processes involved so that remedial actions
can be put in place with a view to achieving sustainable land management (Mitiku et al, 2006).
There is general agreement, that N-fertilizer application has had by far the most important
fertilizer in increasing crop production. Phosphorous is also very important since most arable
lands in Ethiopia are deficient in phosphorous (Sheleme and Gashaw, 1994).
In Ethiopia it is also a common practice to change natural forest and grazing lands to agricultural
practice and monoculture plantation. This may cause variability of different plant nutrients in the
soil and land degradation. To reduce land degradation, and satisfy the demand for timber and
non-timber products of the local population, extensive afforestation with fast-growing exotic tree
species has been carried out on degraded agricultural lands (Pohjonen and Pukkala, 1990);
Ashagrie (2003). Deforestation and cultivation of agricultural crops result in reduction in organic
C, total N and C:N ratios but no significant changes in total and available P levels (Hasmot et al,
1998).
2
Soil carbon content was highly affected by different land use and management practices,
particularly in the surface horizon. Considering the surface soil layers, the highest and the lowest
Organic Carbon contents were recorded on the virgin land and cultivated fields respectively
(Heluf and Wakene, 2006).
In agreement with organic carbon, the content of total nitrogen, and C: N ratio is also varied
markedly due to changes in land use and soil management practices especially in surface horizon.
Considering the surface soil layers, the highest total N and C: N was obtained land whereas the
lowest total N and C: N on cultivated research and farmers’ field (Heluf and Wakene, 2006).
Compared to forest soil mineralization of organic phosphorous was about four times as great as in
the agricultural soil, and the amount of phosphorous lost to stream was eight times as great
(Brady and Weil, 2002).
Unlike annual crops, pastureland continuously maintain a cover of vegetation on the soil, reduce
soil temperature, and sometimes have high productivity and turnover rates that add organic
matter, particularly from below ground, to the surface soil (Brown & Lugo, 1990) since
pastureland is generally not cultivated. The loss of carbon from pasture soil is usually less than
25% of the initial carbon contained in the top 100 cm under forest. But extensive grazing of the
pasture land causes deterioration of soil properties (Brown & Lugo, 1990).
Fast growing tree species such as Eucalyptus plantations are also sometimes influences the soil
nutrient status due to maximum utilization of nutrients as they are fast growing and adversely
affect the under story vegetations. Properties of the top 30 cm of soil under plantations of 1-yr to
8-yr old Eucalyptus and in adjacent natural mixed broad-leaved forest were compared in the sub-
tropical zone of the central Himalaya. Various soil-physical characteristics decreased with
increasing age; soil-chemical properties, notably organic carbon, total N, P and K decreased as a
result of reforestation with Eucalyptus and further decreased with increasing age of the plantation
(Bargali, 1993).
3
1.2. Statement of the Problem
Soil fertility matters on the productivity of the land and the management practices required.
Economic development, burgeoning cities and increasing rural populations, are driving
unprecedented land use changes. In turn, unsustainable land use is driving land degradation a
long-term loss in ecosystem function and productivity which requires progressively greater inputs
to recoup the situation. Its symptoms include soil erosion, nutrient depletion, salinity, water
scarcity, pollution, disruption of biological cycles, and loss of biodiversity. To understand and
revise the necessary solution for this devastating problem requires assessment and evaluation of
the fertility status of the soil and the land.
So the knowledge quantitative and qualitative and up-to-date information about the fertility of the
soil under different land use is needed, to support policy development for sustainable land
management and security of economic, social and environmental issues. And the assessment of
soil fertility may serve as yardstick for the necessary management option to be taken for
sustainability of the different land uses.
Further more the purpose of this research was to assess the fertility of different land uses by
taking more samples at the same area rather than replicating at different site, which is not
commonly practiced in our country. This research tried to answer what soil fertility of the area
looks and can be a base for further studies since there are limited research activities in the area
specially on the farmers land which might be used for betterment of livelihood of the farming
community.
1.3. Hypothesis
� There is no significant difference in soil fertility status under tree, crop and pasture land
use systems in rainfed environments.
4
1.4. Objectives
1.4.1. General Objective
� The general objective of the study is to assess the status of soil fertility under trees,
agricultural crops and pasture land use systems in rainfed environments in central
Ethiopia.
1.4.2. Specific Objectives
Specific objectives of the study are:
� To evaluate the effect of different land uses on soil properties and;
� To assess the influence of different land use on soil fertility.
5
Chapter II. Literature Review
2.1. Land Uses of Tiyo District
Arsi zone in generally have a total land area of 23,060ha from this 60.5% cultivated land 0.63%
grass land 17.6% forest land 0.16%wet land and 1.03% lakes and reservoirs (Bezuayehu et al
2002). The zone is characterized by diverse agro-climatic condtion. From this Tiyo district is
found in high altitude range. The district has a total area of 665km (3.09% of the Zone), out of
this 41.57%, 13.73%, 4.23%, 14.98%, 9.51% and 15.98% are covered with cultivated land,
pasture land, forestland, and bush and shrubs, construction and others (mountains ), respectively.
From the cultivated land, 82.86%,15.29% and 1.85% are covered with cereals, pulses and oil
crops, respectively (AZARDO,2008/09). The major cultivated crops in the order of area coverage
are wheat (11805 ha), barley (6311 ha), Faba bean (1677.5 ha), Teff (1502.9 ha), field pea (1330
ha), linseed (244.4) and rapeseed (193 ha) (AZARDO, 2008/9). The district is one of the potential
areas for livestock and crop production.
2.2. Soil Properties under Different Land Use
Soils have many variables, which have multiple types of characteristics that ultimately affect crop
production and land productivity. Therefore, in order to understand the similarities, dissimilarities
and relationships among different land uses, it is important to study the effects of land use on the
vital physical and chemical properties of soil Brady and Weil, (2002). Changes in land use and
soil management can have a marked effect on the soil organic matter (OM) stock. Several studies
in the past have shown that deforestation and cultivation of virgin tropical soils often lead to
depletion of nutrients (N, P, and S) present as part of complex organic polymers. Bernoux et al.
(1998), indicated that long practices of deforestation and/or replacement of natural forests by
crops and uncontrolled overgrazing have been the major causes for soil erosion and low quality
of soil.
6
2.2.1. Soil Physical Properties
The physical properties of soils determine their adaptability to cultivation and the level of
biological activity that can be supported by the soil. Soil physical properties also largely
determine the soil's water and air supplying capacity to plants. Many soil physical properties
change with changes in land use system and its management such as intensity of cultivation, the
instrument used and the nature of the land under cultivation, rendering the soil less permeable
and more susceptible to runoff and erosion losses (Sanchez, 1976).
2.2.1.1. Bulk Density
Measurement of soil bulk density is required for the determination of compactness, as a measure
of soil structure, for calculating soil pore space and as indicator of aeration status and water
content (Barauah and Barthakulh, 1997). Bulk density also provides information on the
environment available to soil microorganisms. White (1997), stated that values of bulk density
ranges from < 1 g/cm3 for soils high in organic matter 1.0 to 1.46 g/cm3 for well- aggregated
loamy soils and 1.2 to 1.8g/cm3 for sands and compacted horizons in clay soils. Bulk density
normally decreases as mineral soils become finer in texture. Soils having low and high bulk
density exhibit favorable and poor physical conditions, respectively (White, 1997).
Bulk densities of soil horizons are inversely related to the amount of pore space and soil organic
matter (Brady and Weil, 2002; Gupta, 2004). Any factor that influences soil pore space will also
affect the bulk density. For instance, intensive cultivation increases bulk density resulting in
reduction of total porosity.
The study results of Mulugeta (2004), revealed that the bulk density of cultivated soils was higher
than the bulk density of forest soils. Soil bulk density increased in the 0-10 and 10-20 cm layers
relative to the length of time the soils were subjected to cultivation. Similarly, Ahmed (2002)
reported that soil bulk density under both cultivated and grazing lands increased with increasing
soil depth. On the other hand, Wakene (2001) reported that bulk density was higher at the surface
than the subsurface horizons in the abandoned and lands left fallow for twelve years. The changes
7
in the physical soil attributes on the farm fields can be attributed to the impacts of frequent tillage
and the decline in organic matter content of the soils.
2.2.1.2. Soil texture
Soil texture is the most fundamental quantitative soil physical property controlling water,
nutrient, and oxygen exchange, retention, and uptake. It is a master soil property that influences
most other properties and processes. It has major effect on forest growth, but these effects are
indirect. Manifested through its effect on features such as water holding capacity, aeration and
organic matter retention (Fisher and Binkley, 2000).
Soil texture determines a number of physical and chemical properties of soils. It affects the
infiltration and retention of water, soil aeration, absorption of nutrients, microbial activities,
tillage and irrigation practices (Foth, 1990; Gupta, 2004). It is also an indicator of some other
related soil features such as type of parent material, homogeneity and heterogeneity within the
profile, migration of clay and intensity of weathering of soil material or age of soil (Miller and
Donahue, 1995; Lilienfein et al., 2000).
Soil texture is one of the inherent soil physical properties less affected by management. The rate
of increase in stickiness or ability to mould as the moisture content increases depend on the
content of silt and clay, the degree to which the clay particles are bound together into stable
granules and the OM content of the soil (White, 1997). Over a very long period of time,
pedogenic processes such as erosion, deposition, eluviations and weathering can change the
textures of various soil horizons (Foth, 1990; Brady and Weil, 2002).
2.2.2. Soil Chemical Properties
2.2.2.1. Soil pH
Soil pH is generally referred to as a “master variable” because it regulates almost all biological
and chemical reactions in soil (Brady and Weil 1996). Distribution of soil pH may provide a
useful index of the weathering status, potential nutrient holding capacity and fertility of soil
types. Soil pH is mostly related to the nature of the parent material, climate, organic matter and
8
topographic situation (Tamirat, 1992). The soil in high altitude and those higher slopes had low
pH values, probably suggesting the washing out of solutes from these parts (Belay, 1996;
Abayneh, 2001; Mohammed et al., 2005).
Continuous cultivation practices, excessive precipitation, steepness of the topography and
application of inorganic fertilizer could be attributed as same of the factors which are responsible
for the reduction of pH in the soil profiles at the middle and upper elevation zone (Mokwunye,
1978).
Descriptive terms commonly associated with certain ranges in pH are extremely acidic (pH <4.5),
very strongly acidic (pH 4.5-5.0), strongly acidic (pH 5.1-5.5), moderately acidic (pH5.6-6.0),
slightly acid (pH 6.1-6.5), neutral (pH 6.6-7.3), slightly alkaline (pH 7.4-7.8), moderately alkaline
(pH 7.9-8.4), strongly alkaline (pH 8.5-9.0), and very strongly alkaline (pH > 9.1) (Foth and
Ellis, 1997). The degree and nature of soil reaction influenced by different anthropogenic and
natural activities including leaching of exchangeable bases, acid rains, decomposition of organic
materials, application of commercial fertilizers and other farming practices (Brady and Weil,
2002).
2.2.2.2. Soil Electrical Conductivity (EC)
The electrical conductivity indicates the amount of soluble (salt) ions in soil. In addition to
overcoming some of the ambiguities of total dissolved salts measurements, the EC measurement
is quicker and sufficiently accurate for most purposes (Bohn et al., 2001). Excessive
accumulation of soluble salts convert soils to salt affected soils and the process leading to
accumulation of salts are common in arid and semi arid regions where rainfall amount is
insufficient to leach soluble salts.
2.2.2.3. Soil Organic Carbon
Soil organic matter (SOM) content is probably the most useful single indicator of the
sustainability of the soil resource. It is associated with key functions in both chemical and
physical aspects of a soil’s overall function. Chemically, it supplies nutrients and also mediates
their uptake by roots, as well as attenuating the impact of many toxic chemicals added to the soil.
9
Physically, it encourages a well-structured medium for root growth as well as easing tillage
operations. Of the main constituents that make up soil solids, SOM is most open to change, as it
is maintained by the balance of soil processes, which themselves are governed in part by land
management. Changes in SOM content, as indicated by soil Organic Carbon (SOC) content, can
therefore potentially be used as an indicator of changes in the ability of soils to maintain current
crop yields and other functions (King et al, 2005).
Agricultural soils may function as either a source or a sink of atmospheric CO2 (Al-Kaisi et al,
2005). Land misuse and soil mismanagement can cause depletion of soil Organic Carbon(SOC)
with an attendant emission of CO2 into the atmosphere (Lal, 2004), whereas, appropriate land-use
and soil management can lead to an increase in SOC, thereby potentially mitigating the current
increase in atmospheric CO2 (Paustian et al., 2000).
In most tropical environments, the conversion of forest vegetation to agricultural land results in a
decline of the soil OM content to a newer, lower equilibrium (Woldeamlak and Stroosnijder,
2003). Most cultivated soils of Ethiopia are poor in OM contents due to low amount of organic
materials applied to the soil and complete removal of the biomass from the field (Yihenew,
2002), and due to severe deforestation, steep relief condition, intensive cultivation and excessive
erosion hazards (Eylachew, 1999). Biological degradation is frequently equated with the
depletion of vegetation cover and OM in the soil, but also denotes the reduction of beneficial soil
organisms that is important indicator of soil fertility (Oldman, 1993).
Uncultivated soils have higher in soil Organic Carbon(both on surface and in soil) than those
soils cultivated years (Miller and Gardiner, 2001). In the forest, there is a continuous growth of
plants and additions to the three pools of organic carbon: standing crop, forest floor and soil. In
the grassland ecosystems, much more of the Organic Carbon is in the soil and much less occurs
in the standing plants and grassland floor. Although approximately 50% of the total organic
matter in the forest ecosystems may be in the soil, over 95% may be in the soil where grasses are
the dominant vegetation (Foth, 1990). This means land management practices, which reduce soil
fertility, will seriously decrease its chemical activity and also its ability to hold plant nutrients
(Assefa, 1978). Soluble and exchangeable aluminum in acid soils are substantially reduced by
organic amendments (Hoyt and Turner, 1975; Hue and Amien, 1989).
10
When forest is cleared to establish pasture, considerable aboveground C in vegetation is lost, but
is not necessary that there be declines in soil organic C (Post & Kwon 2000). Pasture established
following clearing of forest has greater potential soil organic c stock than it has following crop
and, in the long term, grass management systems have nearly equivalent potential to store soil
organic C as forest Franzluebbers et al. (2000). Stevenson (1982) indicated that the organic
matter content of grassland soils was substantially higher than for forest soils if other factors were
remains constant. Hence, soil carbon stocks could be higher under natural grasslands than under
natural forest. For example, Tate et al. (2000) reported that total soil profile C stock was 13% in
the grassland than in the forest as they studied (19.9 & 16.7 kg m-2
), respectively.
Sharma et al., (2009) stated Organic C (OC) was significantly influenced under different land-use
systems when compared with arable land. On a weighted-mean basis, its contents varied from
3.66 g kg-1
in arable land to 9.60 g kg-1
in an agroforestry system. Based on the weighted-mean
values of all the four profile layers, the enrichment of agrihorticultural, agroforestry, and pastoral
systems in OC content over the arable land was 2.19, 2.62, and 2.22 times greater, respectively.
This enrichment in OC content under tree-based systems could be due to several factors such as
contribution by litter fall, root biomass, and root exudates, whereas under a pasture system, it
could be through root biomass contribution and recycling of aboveground plant parts in a natural
process. Decrease in OC content was recorded with soil depths in almost all the land-use systems.
It has been well understood that the deep-rooted systems contained higher OC content than the
shallow-rooted systems. When root residues decompose, they supply nutrients as a result of
mineralization and also contribute C in the process of humification. It has been reported that the
oxidation loss of C and N during humification is less than that from decomposition of
aboveground litter.
Soil Organic Carbon and total nitrogen stocks in the top 20 cm varied widely with different land
use and different site Soil organic-C stocks ranged from 14.45 to 81.18 Mg ha–1
under plow
tillage, from 17.11 to 81.87 Mg ha–1
under reduced tillage, and from 30.03 to 106.37 Mg ha–1
under grass land, respectively. Soil organic-C stocks were significantly higher under grass land
than under plow tillage. Soils under reduced tillage had significantly higher soil Organic Carbon
stocks than under plow tillage. Trends in total nitrogen stocks were similar to those of the soil
11
Organic Carbon stocks. Grass lands had significantly higher soil Organic total nitrogen stocks
than plow tillage or reduced tillage (Chen et al 2009).
2.2.2.4. Available Phosphorous
Phosphorus (P) is known as the master key to agriculture because lack of available P in the soils
limits the growth of both cultivated and uncultivated plants (Foth and Ellis, 1997). Following N,
P has more wide spread influence on both natural and agricultural ecosystems than any other
essential elements. In most natural ecosystems, such as forests and grasslands, P uptake by plants
is constrained by both the low total quantity of the element in the soil and by very low solubility
of the scarce quantity that is present (Brady and Weil, 2002). It is the most commonly plant
growth-limiting nutrient in the tropical soils next to water and N (Mesfin, 1996).
Variability of the level of available P is related to land use, altitude, slope position and other
characteristics, such as clay and calcium carbonate content (Mohammed et al., 2005). Many
study shown that soil devoted to crop production lost far more P to steams than do those covered
by relatively undisturbed forest or natural grass land (Brady and Weil, 2002).
The main sources of plant available P are the weathering of soil minerals, the decomposition and
mineralization of soil OM and commercial fertilizers. Most of the soils in Ethiopia particularly
Nitisols and other acid soils are known to have low P contents, not only due to the inherently low
available P content, but also due to the high P fixation capacity of the soils (Murphy, 1968;
Eylachew, 1987). Oxisols, Ultisols, Vertisols and Alfisols are generally low in total P while
Andosols are generally high in P content (Mesfin, 1996).
In the sub-humid highlands of southern Ethiopia, clear-cutting of the indigenous forests and their
conversion into agricultural fields or plantations significantly reduced (P<0.05) the amount of
total P. Total soil P declined by 31% at the Wushwush and 39% at the Munesa sites due to
clearing and long-term cultivation. Compared to the continuously cropped fields, smaller losses
of total soil P were found in the tea (21%) and Cupressus (22%) plantations (Solomon, et al,
2002).
12
Stewart and Tiessen (1987) state that under temperate regimes, the decline in total soil organic
matter level will be accompanied by a smaller decline in organic P compared to C. However,
under tropical conditions where organic matter and associated materials are frequently stabilized
in biomass and recent dead materials, the breakdown of this organic matter will cause C, N and P
losses in equal proportions). The depletion of organic P (49% and 55%) as a result of cultivation
was, however, smaller than the losses of organic C (55% and 63%) and N (52% and 60%) at the
Wushwush and Munesa sites (Solomon, et al, 2002).
Sharma, et al. (2009) reported Total P content varied from 473.5 mg kg-1
in arable land to
880.0 mg kg-1
in the pastoral system. As soil depth increased, P content tended to decrease. In the
pasture system, the buildup in total P in the surface soil layer could be attributed to accumulation
and recycling of higher biomass. In agroforestry and agrihorticultural systems, the greater P
content could be due to recycling of P through mining by the tree species and subsequently
recycling by way of surface litter fall.
The greater loss of organic P observed in the continuously cropped fields compared to the
plantations may be attributed to the increase in mineralization of organic P following forest
clearing and continuous cropping and to the export of P along with crop or animal products. On
the contrary, lower depletion of organic P in surface soils of the plantations may be ascribed to
the active biocycling of P due to the presence of a perennial plant cover with deeper-reaching
plant roots and to the better crop residue management through the use of pruned tea plant parts as
a mulch and to surface litter accumulation after senescence observed in the Cupressus
plantations. The C/Po and Pi/Po ratios in the bulk soils were also influenced by changes in
management practices The average C/Po ratio of these soils decreased in the order: natural forests
(160 and 169)>plantations (141 and 153)>cultivated fields (138 and 140), while the average
Pi/Po ratio increased in the order: natural forest (1.4 and 1.3)<plantations (2.4 and 1.5)<cultivated
fields (2.6 and 2.2) at the Wushwush and Munesa sites, respectively (Solomon, et al, 2002).
2.3. Visual Soil Assessment Techniques
Visual Soil Assessment is based on the visual assessment of key soil “state” of soil quality,
presented on a score card. Soil quality is ranked by assessment of the soil indicators alone. Plant
13
indicators require knowledge of crop growing history in a given farm. The knowledge of this
information will facilitate the satisfactory completion of the plant indicator score card (Shepherd,
2000).
VSA is based on evaluation of soil properties and soil quality indicators, mainly morphological,
physical, biological and partly chemical which are visible or possible to distinguish without
laboratory analyses. VSA can be used as support tool in: Soil survey, Soil quality assessment;
and Soil conditions evaluation. Plant cover, single plants and their stand are supporting
indicators- plant indicators for soil conditions and quality evaluation (Houšková, 2005).
Each indicator is given a visual score (VS) of 0 (poor), 1 (moderate), or 2 (good), based on the
soil quality observed when comparing the soil sample with in the field guide manual. The scoring
is flexible, so if the sample you are assessing does not clearly align with any one of guides but
sits between two, a score in between can be given. Because some soil factors or indicators are
relatively more important for soil quality than others, VSA provides a weighting factor of 1, 2,
and 3. The total of the VS rankings gives the overall ranking score for the sample you are
evaluating. Compare this with the score ranges at the bottom of the page to determine whether
your soil has good, moderate, or poor quality. Placing the soil and plant indicator scores of soil
quality side by side at the bottom of the plant indicator, score card should prompt you to look for
reasons if there is a significant discrepancy between the soil and plant indicators (Shepherd,
2000).
14
Chapter III. Materials and Methods
3.1. Description of the Study area
3.1.1. Location of the Study Site
This research was conducted around Asella located in Oromia National Regional State, Arsi
Administrative Zone, Tiyo district, Ethiopia. It is at about 175Km south of Addis Ababa. The
Addis Ababa – Asella all-weather road provide the primary access to the area. Geographically
Tiyo district is approximately found between 70 45' 55'' and 8
0 02' 02'' N latitude and 38
o 56' 42''
to 39o 18' 31”E longitude. It is located just on the top of the eastern edge of the Ethiopian Rift
Valley (Fig. 1).
Figure 1.Location map of Tiyo
15
3.1.2. Topography
The topography of the area is part of the Arsi- Bale Mountains chain in general and the Chilalo-
Galama Mountains in particular with the altitude of around 2400masl. The area is also
characterized by flat to very steeply topographic features (personal observation).
3.1.3. Climate
The site has a bimodal rainfall pattern with a mean annual precipitation of about 787 mm
(KARC, 2008). The main rainy season extends from June to September with a maximum rainfall
in August, while the short rainy season is between February to April. The mean minimum and
maximum temperatures of the experimental site were 8.28oC and 23.3
oC, respectively (KARC,
2008).
Generally, the study area experiences temperate type major agro ecology and warm temperate
pre-humid sub agro-ecology with warm summer and dry winter season KARC (2005).
3.1.4. Vegetation
The vegetations of the area are high altitude natural forest including trees such as: Podocarpus
falcatus, Hagenia abyssinica, Juniperus procera, Ficus species Acacia abissinica ,Mesea
lensolata Vernonea species, and other broad leaved trees and shrubs. However, a large part of the
original natural vegetation has been cleared for agriculture, construction and fire wood purposes.
As a result, old remnant trees were found only as scattered trees on farm lands, small patch of
forests and in the very high altitude parts where cultivation expansion is limited (personal
observation).
The most common plantations are different species of eucalyptus with dominant of Eucalyptus
globulus, E. grandis and E. camandulesis, Pinus patula, cupperesus lustanica and some acacia
species (Personal observation).
16
3.1.5. Geology and Soil
In the Arsi highlands, rocks of the Mesozoic and Cenozoic era are identified. Most of the
volcanic rocks in the Arsi were formed during the Cenozoic era of the tertiary period because of
the wide spread volcanism induced by extensive fracturing and subsequent faulting. During this
period, the outpouring of lava along fissures covered the present highland parts of Arsi. This has
created thick lava basalt rocks of the trap series Mohr (1971).The soil type of the area is Nitisols
(KARC, 2005).
3.1.6. Land Use
The land use system of the area is mixed farming characterized as crop-livestock production.
Cattle are important in the agricultural production system as they provide inexpensive and easily
accessible inputs required for crop production and power for plowing and threshing. In turn, crop
production supplies crop residue as feed supplement to the livestock. The district has a total area
of 665km2 out of this 41.57%, 13.73%, 4.23%, 14.98%, 9.51% and 15.98% are covered with
cultivated land, pasture land, forestland, and bush and shrubs, construction and others
(mountains), respectively. From the cultivated land, 82.86%,15.29% and 1.85% are covered with
cereals, pulses and oil crops, respectively(AZARDO,2008/09).
3.2. Methods
3.2.1. Study site selection criteria
To carry out the research from three different land uses systems namely; pasture land Eucalyptus
plantation, and Agricultural land were systematically selected. All the three land use systems
were chosen in such away that all are under rainfed practice. The representative land uses were
selected systematically, by considering similarity in topography and proximity to each other.
17
3.2.2. Experimental Design and Layout
By taking a rectangular plot of 300m by 500m from the three land uses, within each land use15
samples were taken at 0-15cm and 15-30cm depth each sample 100m distant from one another.
Systematic or grid sampling was used in each land uses independently in sample collection.
Agricultural land Pasture land Eucalyptus plantation
X is the sampling point and 100m from one another
Figure 2. Experimental layout of the research site
3.2.3. Soil Fertility Assessment Using VS Approach in the Field
The soil condition assessment was made using visual soil field assessment approach. VSA was
based on evaluation of soil properties and soil indicators, mainly morphological, physical, and
biological. VSA was based on the visual assessment of key soil “state” of soil fertility, presented
on a score card. Soil fertility was ranked by assessment of the soil physical and biological
indicators alone (Appendix 2). Each soil fertility indicator was given a visual score (VS) of 0
(poor), 1 (moderate), or 2 (good), based on the soil quality observed when comparing the soil
sample with in the field guide manual (Appendix 3).
3.2.4. Soil sampling and sample preparation
Within each representative site of the three land uses systems area of 300m by 500m 15samples
were taken at 0-15 cm and 15-30 cm depth each. Once the samples are collected at the two
depths, the debris were removed, the soil samples were air-dried, ground and passed through a 2
N
300m
m
500m
X X X X X
X X X X X
X X X X X
300m
m
500m
X X X X X
X X X X X
X X X X X
300m
500m
X X X X X
X X X X X
X X X X X
18
mm sieve and taken to Kulumsa Agricultural Research Center soil laboratory for chemical
analysis of organic carbon, available phosphorous, pH and EC
3.2.5. Determination of Soil Physico-Chemical Properties
Soil Organic Carbon was determined by Walkley and Black method (1934). Phosphorous was
determined by Mehlich No.3 Extraction method (Mehlich 1984) Soil pH was measured in soil
and water solution at ratio of 1:2 by electrode pH meter as described by Rhoades (1982). EC of
the soil was measured in 1:5 soil and water solution using EC meter. Bulk density of soil under
trees/forests, pasture land and agricultural field were determined by core method as described by
Gupta (2004). Particle size distributions was determined by pipette method according to Gupta
(2004)
3.2.6. Statistical Analysis
The SAS statistical package institute output software JMP 5 Statistical Package was used for the
data analysis. The significance of changes in soil physicochemical properties between different
land use types was tested by one-way ANOVA. Significance of differences between means of
soil physicochemical properties under each land use and depths was compared by using LSD
comparison method at 0.05 significance level. The correlation analysis was made by taking soil
organic carbon as independent variable and the other properties as dependent variable the
correlation analysis was made for determining the relation of some selected soil properties with
organic carbon of the three land use systems.
19
Chapter IV. Results and Discussions
4.1. Effect of Land Use on Soil Properties
Results of some physical and chemical soil properties under the three land uses; namely
Eucalyptus plantation(EUP), Agricultural land (AGL) and Pasture land (PL) are presented and
discussed here under.
4.2. Effect of Land Use on Soil physical properties.
4.2.1. Bulk Density
The soil bulk density of the three land uses were statistically significantly different (P<0.0001).
Table 1. The mean values of soil bulk density, pH and Electrical conductivity.
Land uses Property Depth
PL EUP AGL
0-15 0.92c 1.02b 1.04ab Bulk density
15-30 0.99b 1.01b 1.09a
0-15 5.09a 5.01ab 5.00ab pH
15-30 5.03ab 5.01ab 4.94b
0-15 19.24a 18.99a 16.17ab EC
15-30 15.80ab 18.10a 13.73b
PL= pasture land, EUP = Eucalyptus plantation, AGL= agricultural land
Means followed by different letters are significantly different
The change in the mean value of soil bulk density in Eucalyptus plantation and Agricultural land
was positive as compared to pasture land. The mean Bulk density was also significantly different
at two different depths (P<0.01) (Table 1).
20
Comparing the three land use systems, pasture land had lower bulk density than eucalyptus
plantation and agricultural land, because in the pasture land plenty of grasses are available as
surface cover, which are easily decomposable to enrich the soil organic carbon pool that increase
the soil pore space. This is in comply the study results of Mulugeta (2004), which revealed that
the bulk density of cultivated soils was higher than that of forest soils. Soil bulk density increased
in the 0-10 and 10-20 cm layers in relation to the length of time the soils were subjected to
cultivation.
Similarly the bulk density of soil with increasing depth of soil; the bulk density of the sub soil
was higher than surface soil. In the same way, Ahmed (2002) reported that soil bulk density
under both cultivated and grazing lands increased with increasing soil depth. This is may be more
soil organic matter usually found in the upper surface than the lower soil layer due to
decomposition of the surface cover on surface soil than the sub soil (Table 1).
The reason for the increasing of soil bulk density in agricultural land may be the compaction of
soil surface during agricultural practices. In most cases agricultural land contain low organic
matter than pasture land and eucalyptus plantation. And also the reason why bulk density of soil
of eucalyptus plantation was higher than pasture land is the plantation is near to Asella town and
the society frequently collects the litter from eucalyptus for fuel purposes and no much litter left
for decomposition (personal observation). Wakene (2001) stated the changes in the physical soil
characteristics on the farm lands could be attributed to the excessive tillage and deterioration of
SOM.
4.2.2. Soil texture
Soil textures of study site had no as such variation. The result of textural analysis showed that the
soil particle size distribution was clay in the three land use systems (Appendix 4). As stated by
White (1997), soil texture is one of the inherent soil physical properties less affected by
management.
21
4.3. Effect of Land Use Type on Soil Chemicals Properties
4.3.1. Soil pH
The mean soil pH value the three land use systems (Pasture land, Eucalyptus plantation
Agricultural land) is not statistically different (P<0.05) (Table 1). In all cases the soils are acidic.
From the observed mean value it indicated decreasing trend in pH as the land use is converted
from pasture land to Eucalyptus plantation and Agricultural land. Comparing depth with of the
three land uses the lower pH was found at the subsoil.
The lower pH value of the agricultural land may be due continuous cultivation, high annual
rainfall and application of commercial fertilizers because the agricultural land is under
continuous cultivation for more than 10 years (personal interview). As Mokwunye, (1978) stated
continuous cultivation practices, excessive precipitation, steepness of the topography and
application of inorganic fertilizer could be attributed as some of the factors which are responsible
for the reduction of pH in the soil profiles at the middle and upper elevation zone.
Sharma, et al (2009), showed significant influence of different land-use systems on soil pH in all
the soil profile layers. On the basis of weighted means, pH varied from 5.4 in agrihorticulture
system to 7.5 in agroforestry system. More or less, the pH values in most of the land-use systems
tended to decrease with soil depth. Interestingly, except for the agrihorticulture system, all the
land-use systems showed greater pH than the arable land. The greater pH values in different land-
use systems could be attributed to the release of bases and their deposition over a long period of
tree growth. Earlier results also revealed that trees continuous grass cover have the capacity to
moderate the effects of leaching by way of contribution of bases to the soil. The greater pH level
in some of the tree-based land-use systems could also be due to humic matters released as a result
of tree and grass root exudates that complex the aluminum (Al+3
) and consequently result in
greater soil pH.
22
4.3.2. Soil Electrical Conductivity (EC)
The mean soil electrical conductivity (EC) values among the three land uses were statistically
different (P<0.05). The laboratory analysis of soil EC showed the mean value of EC of
Eucalyptus land was significantly different from Agricultural land but there was no significant
difference between pasture land and Eucalyptus land and between Pasture land and agricultural
land (Table 1).
The EC of eucalyptus land was higher than the other land uses. The depth wise comparison of the
mean EC value was significantly different between the two depths (p<0.001); (Table 1). In this
study there was higher electrical conductivity of the soil under eucalyptus plantation and pasture
land than agricultural land which confirms the study of Sharma, et al (2009), that states electrical
conductivity in soil was significantly greater under the agroforestry system (110µS cm-1
) and
pastoral system (70µS cm-1
) than under arable land and agrihorticultural systems (40µS cm-1
).
However, with soil depth, no consistent trend was observed. But from this study the electrical
conductivity of the soil decreases with depth.
4.3.3. Soil Organic carbon
The mean Soil OC (%) contents of the soils under pasture land Eucalyptus plantation and
agricultural land were significantly different (P< 0.05). Pasture land had the highest organic
carbon content.
Table 2. The mean values of soil Organic carbon and Available phosphorous
Land uses Property Depth
PL EUP AGL
0-15 5.19a 4.76ab 2.78d Organic carbon (%)
15-30 4.37b 3.81c 2.02e
0-15 14.2a 13.33ab 10.8c Available Phosphorous
(ppm) 15-30 11.73bc 10.27c 7.8d
PL= pasture land, EUP = Eucalyptus plantation, AGL= agricultural land
Means followed by different letters are significantly different
23
The OC content of the soil was also statically different at depths 0-15cm and 15-30cm (p<0.001).
The results showed that the pasture land contains more OC than both eucalyptus plantation and
agricultural land and soil of eucalyptus plantation contains more OC than agricultural land.
Similarly, the higher soil OC content was in the upper soil depth than in the subsoil.
The less organic carbon content of the agricultural land may be the effect of continuous farming
and utilization of the crop residue for different domestic purposes and disturbance of the naturally
existing vegetation. As stated by Woldeamlak and Stroosnijder (2003), in most tropical
environments, the conversion of natural vegetation to agricultural land results in a decline of the
soil organic matter content to a newer, lower equilibrium.
In this study PL was more fertile than eucalyptus plantation and agricultural land in terms of its
organic matter content. And agricultural land was the least fertile among the tree land uses. King
et al, (2005) also reported changes in SOM content, as indicated by soil organic carbon (SOC)
content, can therefore potentially be used as an indicator of changes in the ability of soils to
maintain current crop yields and other functions.
Similarly in the study of Yihenew, (2002), most cultivated soils of Ethiopia are poor in organic
matter contents due to low amount of organic materials applied to the soil and complete removal
of crop residue from the field. Moreover, Eylachew, (1999) alleged that low soil carbon in
Ethiopian soils may be due to severe deforestation, steep relief condition, intensive cultivation
and excessive erosion hazards. Biological degradation is frequently equated with the depletion of
vegetation cover and OM in the soil, but also denotes the reduction of beneficial soil organisms
that is important indicator of soil fertility (Oldman, 1993).
This result is also similar to the study of Sharma, et al, (2009), which states organic carbon was
significantly influenced under different land-use systems when compared with arable land. On a
weighted-mean basis, its contents varied from 3.66 g kg-1
in arable land to 9.60 g kg-1
under tree
based land use system. This enrichment in OC content under pasture and tree based systems
could be due to several factors such as contribution by surface cover and litter fall, root biomass,
and root exudates, whereas under a pasture system, it could be through root biomass contribution
and recycling of aboveground plant parts in a natural process. Decrease in OC content was
24
recorded with soil depths in almost all the land use systems because most of the surface cover
decomposes on the surface soil.
4.3.4. Available Phosphorous
Soil available phosphorous content (ppm) varied significantly (P < 0.01) among the three land
use systems. Pasture land had the highest and agricultural land the lowest amount of available P.
The soil available phosphorous content is significant between pasture land and agricultural land
and between eucalyptus plantation and agricultural land but there was no significant difference
between pasture land and eucalyptus plantation (Table2).
Depth-wise, comparison of soil available phosphorous content was also significantly different;
higher available Phosphorous in 0-15cm depth than 15-30cm depth.
Sharma, et al. (2009) reported that total P content varied from 473.5 mg kg-1
in arable land to
880.0 mg kg-1
in the pastoral system. As soil depth increased, P content tended to decrease. In the
pasture system, the buildup in total P in the surface soil layer could be attributed to accumulation
and recycling of higher biomass. In agroforestry and agrihorticultural systems, the greater P
content could be due to recycling of P through mining by the tree species and subsequently
recycling by way of surface litter fall.
With the confirmation to this in the study area pasture land had better surface cover than
Eucalyptus plantation and agricultural land. Even if the Eucalyptus land was covered with
plantation there was no as such surface cover under the plantation which may be the probable
cause for low phosphorous content than the pasture land. Stewart and Tiessen (1987), stated that
under temperate regimes, the decline in total soil organic matter level will be accompanied by a
smaller decline in organic P compared to C. However, under tropical conditions where organic
matter and associated materials are frequently stabilized in biomass and recent dead materials, the
breakdown of this organic matter will cause C, N and P losses in equal proportions.
25
4.4. Relation of Soil Organic carbon and other soil properties of the different
Land Uses and Soil Fertility
The results from correlation analysis of soil properties in relation to organic carbon except the
bulk density of the soil showed that, positive relation with the carbon content of the soil. But in
all cases almost the R-square is low. This may shows that the relationship of organic carbon and
other selected soil properties may not be linear.
The correlation of available phosphorous with Organic carbon was positive with as shown in this
equation: Av. P (ppm) = 5.8865 + 1.2174 OC (%) and R2
=0.44
4
6
8
10
12
14
16
18
20
AvP
(p
pm
)
1 2 3 4 5 6 7 8
OC(%)
Figure 3. Correlation of available phosphorous with organic carbon of the different land uses
In the same way soil Electrical Conductivity and pH was also positively correlated with Organic
carbon. Figure 5 show there was a slight increase of soil pH as the Organic carbon content of the
soil increases.
26
10
15
20
25
30
35
EC
(µs/c
m)
1 2 3 4 5 6 7 8
OC(%)
Figure 4 Correlation of Soil Electrical Conductivity with organic carbon of the different land
uses
4.2
4.4
4.6
4.8
5
5.2
5.4
5.6
5.8
pH
1 2 3 4 5 6 7 8
OC(%)
Figure 5. The correlation relation of Soil pH with Soil organic carbon of the different land use
system.
Bulk density with organic carbon showed the negative relation (Figure 6)
27
pb (g/cm3) = 1.1350.028 OC(%), R2 = 0.24.
0.8
0.9
1
1.1
1.2
1.3
pb
(g
/cm
3)
1 2 3 4 5 6 7 8
OC(%)
Figure 6. The correlation relation of soil Bulk density with Soil organic carbon of the different
land use system
From Figure 5 it is clear that soil with high organic carbon had low bulk density that means more
porous and less compactness.
In general from the correlation analysis of selected soil properties with organic carbon indicates
soil/ land use with high organic matter content is also better in other soil properties. And from the
result above the organic carbon content of pasture land was higher than the other land uses so,
pasture land under this study can be considered as better in soil fertility than the other land uses.
According to Gete, (2000) classification (appendix 5) the soil of the study area under the three
land uses, pasture land had medium organic carbon, high available phosphorous and low pH.
Eucalyptus plantation had medium organic carbon, medium available phosphorous and low pH.
Agricultural land had low organic carbon medium available phosphorous and low pH.
4.5. Soil Fertility Status in Different Land Uses Using VS Approach
The soil quality by using soil visual assessment (SVA) method is presented as the following for
the three land uses. The sum of scoring < 10 poor, 10-25 moderate and > 25 good (Appendix 2.)
28
4.5.1. Soil Fertility Status in Agricultural Land
Land Use: Agricultural Land
Site location Name: Tulu Kuche Kebele
Date: 12/01/2010
Soil Type: Nitosols
Textural Qualifier: Clayey
Moisture Conditions: Moist
Seasonal Weather Conditions: Average
Table 3. Soil visual assessment values of agricultural land
Visual indicator of Soil
Quality
Visual Score (VS)
Weighting VS Ranking
structure and consistence 1 X 3 3
Soil porosity 1 X 2 2
Soil color 2 X 2 4
No. and color of soil mottles 2 X 1 2
Earthworm counts 0 X 2 0
Tillage pan 0 X 1 0
Soil cover 1 X 3 3
Soil depth 2 X 2 4
RANKING SCORE (Sum of VS Ranking) 18
NB: 0 = Poor, 1 = Moderate, 2 = Good condition
Figure 7. Soil profile pit of Agricultural land
29
4.5.2. Soil Fertility Status in Pasture Land
Land Use: Pasture Land
Site location Name: AME Dairy Farm
Date: 12/01/2010
Soil Type: Nitosols
Textural Qualifier: Clayey
Moisture Conditions: Moist
Seasonal Weather Condition: Average
Table 4. Soil visual assessment values of pasture land
Visual indicator of Soil
Quality
Visual Score (VS)
Weighting VS Ranking
Structure and consistence 2 x 3 6
Soil porosity 2 x 2 4
Soil color 2 x 2 4
No. and color of soil mottles 2 x 2 4
Earthworm counts 1 X2 2
Tillage pan 2 x 1 2
Soil cover 2 x 3 6
Soil depth 2 x2 4
RANKING SCORE (Sum of VS Ranking) 32
Figure 8. Soil profile pit of pasture land
30
4.5.3. Soil Fertility Status in Eucalyptus Plantation
Land Use: Eucalyptus Plantation
Site location Name: SIDA Plantation
Date: 12/01/2010
Soil Type: Nitisols
Textural Qualifier: Clayey
Moisture Conditions: Moist
Seasonal Weather Conditions: Average
Table 5. Soil visual assessment value of eucalyptus plantation
Visual indicator of Soil
Quality
Visual Score (VS)
Weighting VS Ranking
Structure and consistence 2 x 3 6
Soil porosity 2 x 2 4
Soil color 2 x 2 4
No. and color of soil mottles 2 x 1 2
Earthworm counts 0 x 2 0
Tillage pan 1 x 1 1
Soil cover 0 x 3 0
Soil depth 2 x 2 4
RANKING SCORE (Sum of VS Ranking) 21
NB: 0 = Poor, 1 = Moderate, 2 = Good conditions
Figure 9. soil profile pit of eucalyptus plantation
31
The results of VS soil fertility assessment (Tables 3, 4 & 5), revealed that pasture land was
better in soil fertility than Eucalyptus plantation and agricultural land. Under each land use
except for pasture land the earth worm count was zero. This was might be because of agricultural
land is poor in moisture status and surface cover, under eucalyptus plantation the acidic nature of
the soil might not be conducive for earth warms. The structure and consistence of the
agricultural land was poor due to the reason that continuous cultivation and cultivating wet soil
might be distorted the structural properties of the soil. The visual assessment also supports the
laboratory analytical data. From the results the soils of the study site were good in most soil
physical properties but the biological properties such as the presence of earth worm were poor.
Under this study eucalyptus plantation and agricultural land were grouped under moderate
conditions and pasture land was grouped under good condition according to Shepherd (2000)
visual soil assessment field guide.
32
Chapter V. Conclusions and Recommendations
5.1. Conclusions
This study revealed that soil fertility varies among the three land use systems. Under this
condition pasture land was more fertile than the two land use systems both in physical and
chemical soil properties. Soil bulk density was lower on pasture land than eucalyptus plantation
and agricultural land. Agricultural land had the highest bulk density from the three land uses.
The pH and soil particle distribution were almost similar in the three land uses, which were
acidic and clayey, respectively. Electrical conductivity was higher for eucalyptus plantation than
the two land use systems.
Soil organic carbon and available phosphorous were higher under pasture land than the two land
uses systems. Furthermore, as expected, surface soil was more fertile than subsurface under the
three land uses. With the exception of bulk density, other soil properties correlated positively
with organic carbon.
From the result of VS soil fertility assessment pasture land was good but eucalyptus plantation
and agricultural land were moderate in fertility. Under agricultural land and eucalyptus
plantation, earthworm as biological soil fertility indicators of the soil was found to be poor. This
might be due to low soil pH and poor surface cover. Generally the VS soil fertility assessment
supported the results of laboratory analysis.
5.2. Recommendations
In light of this study, the following recommendations have been made.
� The high rate of variability in soil fertility was mainly due to the agricultural practice and
proper management of the agricultural land is important for wellbeing of the society.
� To appropriately use the fertility potential of pasture land, it is better to introduce
improved grasses and manage the grassing method of the area.
33
� Since the area has great agricultural potential improved soil fertility management system
is recommended so as to avoid further fertility deterioration.
� In order to understand the effect of different land use practices in the zone, this study
recommends upscaling of similar research activities so that more geographical coverage
is addressed which eventually will serve for creating/enriching the regional database for
policy making and proper utilization of land use systems.
34
6. References
Abayneh Esayas, 2001. Some Physicochemical Characteristics of the Raya Valley Soils.
Ethiopian J. Natural Resources, Vol. 3, issue 2, Pages 179-193
Ahmed Hussein, 2002. Assessment of Spacial Variability of Some Physicochemical Property of
Soil Under Different Elivation and Land Use systems in the Western slops of Mount Chilalo,
Arisi. MSc Thesis, Alemaya University, Ethiopa.
Al-Kaisi, M. M., Yin, X. H., Licht, M. A. (2005): Soil carbon and nitrogen changes as influenced
by tillage and cropping systems in some Iowa soils. Agric. Ecosys. Environ. 105, 635–647.
Ashagrie, Y., Zech, W., Guggenberger, G., Teketay, D. (2003) Changes in soil organic carbon,
nitrogen and sulphur stocks due to the conversion of natural forest into tree plantations (Pinus
patula and Eucalyptus globulus) in the highlands of Ethiopia. World Resour. Rev. 15, 462−482.
Assefa Kuru, 1978. Effects of humus on water retention capacity of the soil, and its role in fight
against desertification. M.Sc. Thesis, Department of Environmental Science, Helsinki
University. 68p..
AZARDO, 2008/9. Arsi Zone Agricultural and Rural Development Official annual report.
AZARDO, 2008/9. Arsi Zone Finance and Economics Development Office annual report.
Barauah, T.C. and H.P. Barthakulh, 1997. A textbook of soil analysis. Viskas Publishing House.
New Delhi, India. 334p.
Bargali, S.S., Singh, R. P. and Joshi, M. 1993. Changes in soil characteristics in eucalyptus
plantation replacing natural broad leaved forests. IAVS; Oppulus press Uppsala journal of
vegetation science, 4:25-28
Belay Tegene, 1996. characteristics of Landscape Relationships of Vertisol and Vertic Luvisols
of Melbe, Tigray, Ethiopia. SINET: Ethiopian J. Sci. Vol.20 issue 2, Pages 151-175.
Bernoux, M., C.C. Cerri, C. Neill and J.F.L. De Moraes, 1998. The use of stable carbonisotopes
for estimation of soil organic matter turnover rates. Geoderma. 82: 43-58.
Bezuayehu T., Gezahegn A., Yigezu A., Jabbar, M.A. and Paulos D. 2002, Nature and causes of
land degradation in the Oromiya Region: A review: Socio-economics and Policy Research
Working Paper 36.
Blake, G.R., and K.H. Hartge, 1986, Bulk Density, in A. Klute, ed., Methods of Soil Analysis,
Part I. Physical and Mineralogical Methods: Agronomy Monograph no. 9 (2nd ed.), pp. 363-375.
35
Bohn, H.L, B.L. McNeal and G.A. O'Connor, 2001. Soil chemistry, 3rd Ed. John Wiley and
Sons, Inc., New York. 307p.
Brady, N. C. and Weil, R. R . 2002. The nature and properties of soil.13th Ed. New Jersey:
Prentice-Hall, Inc. Page 960.
Brady, N. C. and Weil, R. R. 1996. The nature and properties of soil (11th Edition). New Jersey:
Prentice-Hall, Inc. Page 740..
Chen, H., Marhan, Billen, N., and Stahr, K., 2009. Soil organic-carbon and total nitrogen stocks
as affected by different land uses in Baden-Wurttemberg (southwest Germany); Journal of Plant
Nutr., 172, 32–42
EFAP (1994) Ethiopian Forest Action Plan, The challenge for development, vol. 2, Ministry of
natural resources development and environmental protection, Addis Ababa, Ethiopia
Engda Mersha (2003) Classification of Ethiopia into thermal zones. Ethiopia. J. Nat. Res. 5(1):
143-154.
Eylachew Zewdie, 1987. Study on phosphorus status of different soil types of Chercher
highlands, south-eastern Ethiopia. Ph.D. Dissertation, University of Jestus Liebig,
Germany.168p.
Eylachew Zewdie, 1999. Selected physical, chemical and mineralogical characteristics of major
soils occurring in Chercher highlands, eastern Ethiopia. Ethiopian Journal of Natural Resource.
1(2): 173-185.
Fisher, R.F. and D. Binkley, 2000. Ecology and management of forest soils, 3rd Ed. John Wiley
and Sons, Inc., New York. 489p.
Foth, H.D. and B.G. Ellis., 1997. Soil fertility, 2nd Ed. Lewis CRC Press LLC., USA. 290p.
Foth, H.D. and Ellis, B.G. 1996. Soil Fertility. 2nd Ed. Department of Crop and Soil Science,
Michigan, Lewis Publisher, New York. Page 290.
Foth, H.D., 1990. Fundamentals of soil science, 8th Ed. John Wiley and Sons, Inc., New York,
USA. 360p.
Franzluebbers, A.J., Stuedemann, J.A., Schomberg, H.H and Wilkinson, S.R. (2000) soil organic
C and N pools under long term pasture management in the southern piedmont USA. Soil Biology
and Biochemistry, 32, 469-478.
Gete Zeleke, 2000. Landscape dynamics and Soil Erosion process Modelling in the northwestern
Ethiopia highlands. Geographical Bernensia, Switzerland
36
Goovaerts, P., 1999. Geostatistics in soil science: state-of-the-art and perspectives. Geoderma 89,
pp. 1–45.
Guo, L.B. and Gifford (2002) Soil carbon stocks and land use change: a Meta analysis, Australia,
cooperative research centre for green house accounting, Australia, Global Change Biology 8,
345-360
Gupta, K.P. (2006) Soil, plant, water and fertilizer analysis. Agrobis (India).
Gupta, P.K., 2004. Soil, plant, water and fertilizer analysis. Shyam Printing Press, Agrobios,
India. 438p.
Hasmot Saikh, Chandrika Varadachari and Kunal Ghosh 1998. Changes in carbon, nitrogen and
phosphorus levels due to deforestation and cultivation: A case study in Simlipal National Park,
India Springer Netherlands Plant and soil 198,2:137-145
Heluf G. and Wakene N. 2006. Impact of land use and manangement practices on chemical
properties of some soils of Bako area western Ethiopia. Ethiopian Journal of Natural resources
8:177-197
Houšková Beata ,2005. 3rd European Summer School On Soil Survey; Visual Soil
Assessment: Co-Organized By Taiex, Jrc And Sziu
Hoyt, P.J. and Turner, R.C. 1975. Effect of organic material added to very acid soils on pH,Al,
exchangeable NH4+ and crop yields. Soil Sci. 19: 119-237.
Hue, N.V. and Amien, I. 1989. Aluminum deterioration with green manures. Commun. Soil Sci.
Plant and Anal. 20: 1499-1511.
KARC (2005). Annual report. Kulumsa Agricultural Research Center, Asella, Ethiopia.
King, J.A., Bradley, R.I., Harrison, R., 2005. Current trends of soil Organic Carbonin English
arable soils; Soil Use and Management (21), 189–195
Lal, R. (2004): Soil carbon sequestration to mitigate climate change. Geoderma 123,1-22.
Lilienfein, J., W. Wilcke, M.A. Ayarza, L. Vilela, S.D.C. Lima and W. Zech, 2000. Chemical
fractionation of phosphorus, sulphur, and molybdenum in Brazilian savannah Oxisols under
different land uses. Geoderma. 96: 31-46.
Lugo, A. E., Sanchez, M. J. and Brown, S. (1986) Land use and Organic Carboncontent of some
subtropical soils, Plant and Soil 96, 185−196.
McGarry, D. (2004). A Methodology of a Visual Soil-Field Assessment Tool to Support,
enhance and Contribute to the LADA program; FAO
37
Mehlich, A. 1984. Mehlich 3 soil test extractant: A modification of Mehlich 2 extractant. Comm.
Soil Sci. Plant An. 15: 1409-1416
Mesfin Abebe, 1996. The challenges and future prospects of soil chemistry in Ethiopia. pp. 78-
96. In: Teshome Yizengaw, Eyasu Mekonnen and Mintesinot Behailu (Eds.). Proceedings of the
3rd Conference of the Ethiopian Society of Soil Science (ESSS). Feb. 28-29, 1996. Ethiopian
Science and Technology Commission. Addis Ababa, Ethiopia. 272p.
Miller, R.W. and D.T. Grardiner, 2001. Soils in our environment, 9th Ed. Prentice-Hall Inc.,
Englewood Cliffs, New Jersey. 671p.
Miller, R.W. and R.L. Donahue, 1995. Soils in our environment, 7th Ed. Prentice Hall Inc.,
Englewood Cliffs, New Jersey. 649p.
Mitiku, H, Herweg, K, and Stillhardt, B. 2006. Sustainable land management-A new approach to
soil and water conservation in Ethiopia. Mekelle, Ethiopia: Land Resources Management and
Environmental Protection Department, Mekelle University; Bern, Switzerland: Centre for
Development and Environment (CDE), University of Bern, and Swiss National Centre of
Competence in Research (NCCR) North-South.
Mohammed Assen, P.A.L., Leroux, C.H., Barker, Heluf Gebrekidan, 2005. Soil of Jelo Micro-
Catchment in the Central Highlands of Eastern Ethiopia. I. Morphological and Physiochemical
Propertyies. Ethiopian J. Natural Resource, Vol. 7, issue 1, Pages 55-81.
Mohr, P.A. (1971) The geology of Ethiopia. University college of Addis Ababa press, Addis
Ababa.
Mokwunye, A.U., 1978. The Role of in Organic Fertilizers in the Chemical Degradation of
Nigerian Savannah Soil. Samaru Conference Paper 14. Expert consultation on Methodology for
Assessing soil Degradation. FAO, Rome.
Mulugeta Lemenih, 2004. Effects of land use changes on soil quality and native flora
degradation and restoration in the highlands of Ethiopia: Implication for sustainable
landmanagement. PhD Thesis Presented to Swedish University of Agricultural Sciences,
Uppsala. 64p.
Mulugeta, L., Bekele, L. and Demel T. (2005) Changes in soil carbon and total nitrogen
following reforestation of previously cultivated land in the highlands of Ethiopia, Ethiopian
Journal of Science, Volume 28, Number 2, Faculty of Science, Addis Ababa, Ethiopia. 10, 99-
108
Murphy, H.F., 1968. A report on the fertility status and other data on some soils of Ethiopia,
Experiment Station Bulletin No. 44, College of Agriculture Haile Sellassie I University, Dire
Dawa, Ethiopia. 551p.
38
Oldman, L.R., 1993. The extent of human induced soil degradation. Annex 5- World map ofthe
status of human induced soil degradation. An explanatory note ISRIC. Wageningen. Cf: Steiner,
K.G., 1996 (Ed.). Cause of soil degradation and soil development approach to soil management.
Margrafvelag, Weikersheim, Germany. 95p.
Olsen, S.R., C.V. Cole, F.S. Watanable and L.A. Dean, 1954. Estimation of avariable
phosphorus in soil by extraction with sodium bicarbonate. USDA Circular. 939: 1-19.
Paustian, K., Six, J., Elliott, E. T., Hunt, H. W. (2000): Management options for reducing CO2
emissions from agricultural soils. Biogeochem. 48, 147–163.
Pohjonen, V. and Pukkala, T. (1990) Which Eucalypt grows best in Ethiopian Highlands?
Journal of biomass and bioenergy 1, 193-195
Post, W.M., Kwon, K.C. (2000) soil carbon sequestration and land use change processes and
potential. Global Change Biology, 6, 317-327.
Rhoades, J.D., 1982. in methods of soil analysis part 2. second edition; American Society of
Agronomy. Madison USA.
Sanchez, P.A., 1976. Properties and management of soils in the tropics. John Wiley and Sons,
Inc., New York, USA. 618p.
Sharma, K. L., Ramachandra Raju K., Das S. K., Prasad Rao B. R. C, Kulkarni B. S., Srinivas
K. J., Kusuma Grace J., Madhavi M., and Gajbhiye Pravin N.; 2009. Soil Fertility and Quality
Assessment under Tree-, Crop-, and Pasture-Based Land-Use Systems in a Rainfed
Environment; Communications in Soil Science and Plant Analysis, V. 40, 1436 – 1461.
Sheleme Beyene and Gashaw Meteke 1994. the evaluation of nutrient status of soils of selected
site in Mid and southern regions of Ethiopia.)
Shepherd, T. G. 2000: Visual Soil Assessment. Volume 1. Field guide for cropping and pastoral
grazing on flat to rolling country. Horizons.mw & Landcare Research, Palmerston North. 84p)
Simpson, J.A., Smith, T.E., Keay, P.T., Osborne, D.O., Xu, Z.H. and Podberscek, M.I. (2004)
Impacts of Inter-rotation Site Management on Tree Growth and Soil Properties in the First 6.4
Years of a Hybrid Pine Plantation in Subtropical, Site Management and Productivity in Tropical
Plantation Forests: CIFOR.
Stevenson, F.J. (1982) humus chemistry – genesis, composition, reactions. John Wiley & Sons
Inc, New York.
Stewart and Tiessen, 1987. Dynamics of soil organic phosphorus. Biogeochemistry 4 (1987), pp.
41–60.
39
Tamirat Tsegaye, 1992. Vertisol of Central Highlands of Ethiopia: Characterization and
Evaluation of Phosphorus Statues. MSc Thesis, Alemaya University, Ethiopa.
Tate, K. R. 1992. Assessment, based on a climosequence of soils in tussock grasslands, of
soilcarbon storage and release in response to global warming. Journal of Soil Science. 43: 697-
707.
Tate, K.R., Scott, N.A., Ross, D.J., Parshotam, A. and Claydon, J.J. (2000) Plant effect on soil
carbon storage and turnover in a montane beech (Nothofagus) forest and adjacent tussock grass
land in New Zealand. Australia Journal of Soil Research, 38, 685–698.
Turner, J. and Lambert, M. (2000) Change in Organic Carbonin forest plantation soils in eastern
Australia, Forest Ecology and Management 133, 231−247.
Wakene Negassa, 2001. Assessment of important physicochemical properties of Dystric Udalf
(Dystric Nitosols) under different management systems in Bako area, western Ethiopia. M.Sc.
Thesis Submitted to School of Graduate Studies, Alemaya University, Ethiopia. 93p.
WalKley, A. and Black, C. A. (1934) an examination of digestion of Degtjareff methods for
determining soil organic matter and proposed modification of the chromic acid titration method.
Soil science: 29-38.
Walkley, A. and I.A. Black, 1934. An examination of the Degtjareff method for determining soil
organic matter and a proposed modification of the chromic acid titration method. Soil Sci. 37:
29-38.
White, R.E., 1997. Principles and practices of soils science: The soil is the natural resource.
Cambridge University Press, UK. 348p.
Woldeamlak Bewket and Stroosnijder, L. 2003. Effects of agro-ecological land use succession
on soil properties in the Chemoga watershed, Blue Nile basin, Ethiopia. Geoderma. 111: 85-98.
Yihenew Gebreselassie, 2002. Selected chemical and physical characteristics of soils Adet
Research Center and its Testing Sites in North-Western Ethiopia. Ethiopian Journal ofNatural
Resources. 4(2): 199-215.
Yost, R.S., Uehara, G. and Fox, R.L., 1982. Geostatistical analysis of soil chemical properties of
large land areas: I. Semivariograms. Soil Sci. Soc. Am. J. 46, 1028–1032
40
7. Appendices
Appendix 1. Record format for results of soil laboratory analysis
Name of Laboratory: Kulumsa Agricultural Research center Soil Laboratory
Soil properties
Geo. Position
Land use
X Y Z
Sampl
e No
Sample
code
De
pth
OC
(%)
Av. P
(ppm)
pH EC
(µs/cm
)
Pb
(g/cm3
)
Text
ure
41
Appendix 2. Soil Visual Assessment Score Card
Visual indicator of Soil Quality Visual Score (VS) 0 = Poor,1 = Moderate,2 =
Good
Weighting VS Ranking
Soil structure and consistence x 3
Soil porosity x 2
Soil color x 2
Number and color of soil mottles x 1
Earthworm counts x 2
Tillage pan x 1
Soil cover x 3
Soil depth x 2
RANKING SCORE (Sum of VS Ranking)
Fertility rating
Soil Quality Assessment Ranking score
Poor <10
Moderate 10-25
Good >25
Source: (Shepherd, 2000)
Appendix 3. Soil Visual Assessment Check List
(Source: Shepherd, 2000)
Soil Structure and Consistence
GOOD CONDITION VS: 2
Good distribution of friable finer aggregates with
no significant clouding
MODERATE CONDITION VS: 1
Soil contains significant proportions of both
coarse firm clods and friable, fine aggregates
42
POOR CONDITION VS: 0
Soil dominated by extremely coarse, very firm clods with very few finer aggregates
Soil Porosity
GOOD CONDITION VS: 2
Soils have many macro pores between and within
aggregates associated with readily apparent good
soil structure
MODERATE CONDITION VS: 1
Soil macro pores between and within aggregates
have declined significantly but are present on close
examination of clods showing a moderate amount
of consolidation
43
POOR CONDITION VS: 0
No soil macro pores are visually apparent within compact, massive structureless clods. The clod surface is
smooth with few cracks or holes, and can have sharp angles
Earthworm Counts
Visual score(VS) Earthworm counts (per 20 cm cube of soil)
2 > 8
1 4 – 8
0 < 4
Number and Color of Soil mottles
Visual score(VS) Earthworm counts (per 20 cm cube of soil)
2 Mottles are generally absent
1 Soil has common (10-25%) fine and medium
orange and grey mottles
0 > 50% medium and coarse orange and
particularly grey mottles
PRESENCE OF A TILLAGE PAN
44
GOOD CONDITION VS: 2
No tillage pan with a friable, clearly
apparent structure and soil pores throughout
the topsoil
MODERATE CONDITION VS: 1 Firm, moderately developed tillage pan in
the lower topsoil showing clear zones of
consolidation but including areas with
weakly developed structure, cracks, fissures
and a few macro pore
POOR CONDITION VS: 0
Very firm to hard, well-developed tillage pan in the lower topsoil, showing severe consolidation
with no structure, no macro pores and few or no cracks
SOIL COVER
45
GOOD CONDITION VS: 2
Soil surface totally covered by plant residues
MODERATE CONDITION VS: 1
Soil surface partially covered (30 to 50%)
by plant residues
POOR CONDITION VS: 0
Soil surface with completely absence of residue
SOIL DEPTH
Visual score (VS) Soil depth
2 > 60 cm
1 30 – 60
0 < 30
Source: (Shepherd, 2000)
