Cap 01 Salinity Problems

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Integrated approach to address salinityproblems in irrigated agriculture

Julian Martinez Beltrn1

1Centro de Estudios Hidrogrficos del CEDEX, Madrid, Espaa

Manejo da salinidade na agricultura: Estudos bsicos e aplicados

ISBN 978-85-7563-489-9

Fortaleza - CE2010

IntroductionSoil and water salinity in irrigated agricultureIntegrated approach for salinity managementConclusions

References


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INTRODUCTION

Irrigated agriculture is essential for crop production.

Although the area under irrigation (277 million hectares)

is only about 20 percent of the total cropped area, it

contributes approximately 40 percent of the total food

production. Therefore, the productivity of the irrigated

lands is approximately three times the productivity of rain-

fed areas (FAO, 2006).

It is expected that in 2030 the contribution of irrigated

agriculture to food production could be close to 50

percent. To achieve this target there are two needs: to

increase the area under irrigation and to increase the

productivity of the currently irrigated lands. The irrigationexpansion has important constraints: the scarcity of good

quality water and of lands with irrigation suitability; the

resources needed to finance the investments; and the

need of legal and institutional development and capacity

building, especially in those countries with less irrigation

tradition. Therefore, consolidation and modernization of

current irrigation schemes, in order to increase water

productivity, is being a priority action in many countries,

as usually less financial resources are required and no

new natural resources need to be mobilised.

Improvement of existing irrigation schemes has two

major components: increasing water productivity and

conservation of the quality of land and water resources,

which frequently are affected by salinity in the arid and

semi-arid regions.

This paper is focused on the latter mentioned issue.

The overall objective of this paper is to describe an

integrated approach to manage soil and water salinity in

irrigated lands. An overview of global salinity problems

was described by Martnez Beltrn and Licona Manzur

(2005). Details on the control of soil and water salinity

Integrated approach to address salinityproblems in irrigated agriculture

and on reclamation of saline soils can be consulted in the

Annex of the TRAGSA-publication La ingeniera enlos procesos de desertificacin (Martnez Beltrn,

2003).

SOIL AND WATER SALINITY IN IRRIGATED

AGRICULTURE

Approximately 40 percent of the world s irrigated

land is located in arid and semi-arid regions (FAO, 2006),

as it can be observed in the FAO global map of irrigation

areas (Figure 1).

In those regions, secondary salinity is common in

irrigated agriculture because of the salts added with theirrigation water and the build up of saline groundwater in

lands lacking of natural drainage (Figure 2).

Figure 2B shows that adjacent to a well cropped field

there is a plot where salt accumulates in the soil surface

due to capillary rise of saline groundwater (Figure 2A).

This illustrates the man made character of secondary

salinity.

Consequences of soil salinity are the progressive

decrease of crop yields and the loss of land productivity.

If the salt accumulation process continues, the retirement

of land from cultivation is the following phase that drives

to land desertification (Figure 2B).

In 2002, FAO (2002a) estimated that about 20-30

million hectares of irrigated land were seriously damaged

by soil salinity and 0.25-0.50 million hecta res were

estimated to be lost from production every year as a

result of salt build-up.

Figure 3 shows the world map of saline soils. By

comparing with the global map of irrigation (Figure 1),

some coincidence between the areas affected by salinity

and the areas under irrigation can be observed.


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4 Julian Martinez Beltrn

Figure 1. The FAO digital global map of irrigation areas (February, 2007)

A.

Figure 2. A) Capillary rise of shallow saline groundwater. B)Land degradation due to salt accumulation. Mendoza,Argentina

B.

Figure 3. The world map of saline soils (FAO/UNESCO 2003)

in < 1% of areain < 1-10% of area

in < 11-20% of areain < 21-30% of areain < 31-40% of areain < 41-50% of areain < 51-60% of areain > 60% of area

The economic impact of soil salinity on irrigatedagriculture has been estimated in some cases, in thecontext of plans to reclaim salt affected soils forproductive agriculture and to prevent the further salinityhazard. For example, this type of assessment was madein the Ro Fuerte Irrigation District, Sinaloa, Mexico,where soil salinity has limited the agricultural production

of some irrigated lands mapped in Figure 4 according toits salinity level.

In this case, the annual production losses due to soilsalinity were estimated as difference between the valueof the potential production in the irrigation district and theactual production. The potential production wasdetermined from: the land use distribution, the averagecrop yields in salt free soils and crop prices. The actualproduction of the salt affected soils was estimated byapplying to each mapping salinity class, whose area isknown, the crop yield losses due to soil salinity (Table 1).


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5Integrated approach to address salinity problems in irrigated agriculture

INTEGRATED APPROACH FOR

SALINITY MANAGEMENT

A first step for salinity management is the estimation

of the magnitude of the socio-economic problem. For this

purpose, mapping the sa lt af fected ar eas and the

characterization of the salinity problem is needed. Maps

similar to that of Figure 4 can be obtained by remote

sensing and field work. Methods for soil salinityassessment can be consulted in the FAO Irrigation and

Drainage Paper No 57 (1999). In addition to this, the

impact of salinity on the economy of the farmers involved

should be done. For this purpose a method similar to that

described in the previous section could be applied.

Reclamation of salt affected soils and the continuous

control of soil salinity in irrigated lands need an integrated

approach. Such approach includes technical (hydraulic,

mechanical, chemical and agronomic), economic and

environmental measures, as it can be observed in Figure 5.

A first distinction should be made between rain-fedagriculture, where soils generally have natural salinity

(primary salinity), and irrigated agriculture where

secondary salinity is due to inadequate water

management.

In dry lands of the arid and semi-arid regions, in the

absence of rainfall and irrigation water to leach salts from

the root zone, the economic use of slightly and moderately

saline soils is limited to growing salt tolerant crop varieties

and to the application of agronomic practices adapted to

the salinity conditions (saline agriculture). Generally, soils

affected by severe primary salinity are not cultivated and

natural vegetation, adapted to salinity conditions,

develops.

The availability of effective precipitation or/and good

quality irrigation water permits the leaching of salts, if the

lands have natural drainage or are provided with drainagesystems to control surface water and a shallow

groundwater table.

Figure 6 highlights the above mentioned concepts:

sustainable irrigated agriculture is possible in salt affected

soils if the root zone is free of salts by leaching with

irrigation water and the water table is controlled by a

Figure 6. Irrigation and drainage of a soil affected by primarysalinity (Lower Guadalquivir River, Spain)

Figure 5. Integrated management of saline soils (Adaptedfrom FAO, 2005)

Hydraulic aspects:IrrigationDrainageLeaching

Chemical aspects:Soil amendments

Mineral fertilization

Socio-economic,enviromental andlegal aspects

Mechanical aspects:Land levelling and smoothingDeep plowingSubsoilingSanding

Agronic aspects:Sowing techniques

MulchingGreen manure

Saline agriculture

Integratedmanagement of

salt affected soils

Table 1. Estimation of production losses due to soil salinity in the Ro Fuerte Irrigation District, Sinaloa, Mexico (adaptedfrom Pulido et al., 2000)

Figure 4. Salt affected lands in the Ro Fuerte IrrigationDistrict, Sinaloa, Mexico (Pulido et al., 1998)

Color ClassedSm-1

Area(ha)

0-4

4-88-12

12-16> 16Total

181,631

69,31627,42814,90926,692

319,976

Area(%)

56.8

21.78.64.68.3

100.0


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6 Julian Martinez Beltrn

subsurface drainage system. In this case, the subsoil is

still saline as the natural vegetation of the ditch bank

indicates.

Subsurface drainage systems have been installed in

many irrigated areas of the world in large scale projects

to reclaim lands affected by salinity and to control soil

salinity, for example, in most of the lands of the Nile

Delta in Egypt.The relevance of irrigation and drainage for salinity

management is also highlighted in Figure 7, which shows

the contact between an irrigation scheme and the dry

lands in an area with an arid climate (Mendoza,

Argentina).

Figure 7. Irrigated lands and dry lands in an area affected bysalinity (Mendoza, Argentina)

In this arid zone, agriculture is only possible under

irrigation. Dry lands are severely affected by salinity, as

it can be observed in the right part of the above picture.Irrigation makes agriculture possible as the left part of

the picture shows. However, lands with insufficient

natural drainage are affected by secondary salinity.

Therefore, land productivity is clearly below the potential

productivity obtained in the lands where subsur face

drainage systems have been installed (central part of the

picture).

Surface drainage and subsurface drainage are key

factors for successful salinity management. FAO (2007)

has provided guidelines and computer programs for the

planning and design of land drainage systems. Details onsalinity control can also be consulted in this FAO

Irrigation and Drainage Paper.

Land leveling and smoothing are needed in irrigated

fields to prevent surface water accumulation and in order

to achieve sound surface drainage. In addition to this,

other mechanical measures, such as deep plowing and

subsoiling, are needed to increase the hydraulic

conductivity of the top soil in order to improve the

infiltration and percolation of the irrigation water.

If the sodium content of the soil is high, gypsum

amendments are recommended to maintain soil structure

stability and the infiltration rate of the soil.

Crop selection is a key factor in the integrated

management of salinity in irrigated agriculture.

Differences in crop tolerance to soil salinity permit the

selection of the appropriate crops and the most resistant

crop varieties according to the salinity levels of the soil.Good agronomic practices adapted to soil salinity

should also be considered if the topsoil is still saline.

Sound mineral fertilization is needed to prevent the

increase of salinity due to nitrates application. Sowing

techniques should also be adapted to the saline

environment to prevent the location of seeds in ground

pa tches where sa lts accumulate, as the top of the

irrigation furrows.

Finally, a third aspect in salinity management under

irrigated agriculture is sound agricultural drainage water

management. Irrigation and drainage are essential for

salinity management in irrigated lands. However,

deterioration of the quality of drainage water due to

salinity cause major problems for the safe disposal of

drainage flows, especially if water resources situated

downstream of the outlets of the drainage systems are

affected. Therefore, an overall view of drainage water

management is needed by considering the three levels

involved: the irrigated field, the irrigation scheme and the

river basin. FAO has also provided guidelines for

agricultural drainage water management in arid and

semi-arid areas (FAO, 2002b). In this publication

measures for water conservation at the field level, reuseof drainage water at the scheme level, safe disposal and

in some cases water treatment have been described.

CONCLUSIONS

Irrigated agriculture is essential for food production

and it will be in the future to reduce food insecurity in

developing countries. To cover the medium term food

needs, the irrigated acreage in the developing countries

should be increased, especially in those with current low

irrigation development. In addition, land and water

productivity of existing irrigation schemes needs to be

increased.

In many irrigated areas of the arid and semi-arid

zones land and water productivity is seriously affected by

soil and water salinity. Therefore, reclamation of the

affected lands should be an essential component of

projects for the rehabilitation and modernization of

irrigation schemes. Besides, in order to ensure the

sustainability of the new projects, which are needed to

expand the present irrigation acreage, control of


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7Integrated approach to address salinity problems in irrigated agriculture

secondary salinity of the irrigated soils has also to be

taken into account. In addition, agricultural drainage

water management is needed to reduce the

environmental impacts of irrigated agriculture.

Soil and water salinity management needs an

integrated approach by considering different technical,

socio-economic and environmental aspects which are

very specific of each agricultural development project.Also several geographic levels should be considered in

the approach from the irrigated field to the river basin.

There is enough knowledge and expertise on soil and

water salinity to address this challenge. Frequently, this

knowledge and expertise have been applied successfully

in pilot projects. However, commonly in developing

countries farmers affected by salinity problems have not

enough economic resources to finance the investments

needed to reclaim their salt-affected lands, although costs

generally are recovered in a short term. For this reason,

governments have the responsibility to provide the initial

resources and technical advice for up-scaling the goodresults obtained at the pilot level. In order to formulate

an appropriate reclamation policy, it is useful to start with

a sound evaluation of the socio-economic and

environmental impact of salinity on the project area.

REFERENCES

FAO. Soil salinity assessment, methods and interpretation of

electrical conductivity measurements. By J.D. Rhoades, F.

Chanduvi & S. Lesh. FAO Irrigation and Drainage Paper

No. 57. Rome. 1999. 150 pp.

FAO. Crops and drops: making the best use of water foragriculture. Rome. 2002a. 22 pp.

FAO. Agricultural drainage water management in arid and semi-

arid areas. In: Tanji, K. K.; Kielen, N. C. (ed) FAO Irrigation

and Drainage Paper No. 61. Rome. 2002b. 188 pp.

FAO. Management of irrigation-induced salt-affected soils. Joint

publication of CISEAU, IPTRID and FAO, Rome. 2005.

FAO. Water in agriculture; opportunity untapped. Rome: Food

and Agriculture Organization of the United Nations, 2006.

FAO. Guidelines and computer programs for the planning and

design of land drainage systems. In: van der Molen, W. H.;

Martnez Beltrn, J.; Ochs, W. J. (ed) FAO Irrigation and

Drainage Paper No. 62. Rome. 2007. 228 pp.

FAO/UNESCO. Digital soil map of the world and derived soilproperties. Rome: Land and Water Digital Media Series rev.

1. 2003.

Martnez Beltrn, J. Control de la salinizacin de suelos y

aguas, y recuperacin de suelos salinos. In: La ingeniera

en los procesos de desertificacin. Annex, pp. 1003-1045.

Edited by TRAGSA and published by Mundi-Prensa,

Madrid. 2003.

Martnez Beltrn, J.; Licona Manzur, C. Overview of salinity

problems in the world and FAO strategies to address the

problem. In: Proceedings of the International Salinity

Forum, Riverside, California, United States of America.

2005. p.311-314.Pulido Madrigal, L.; Gonzlez Meraz, B. J. Robles Rubio, J.L.

Lpez de Santa Ana & O.X. Cisneros Estrada.

Identificacin con imgenes de satlite y sistemas de

informacin geogrfica, de la salinidad del suelo y de los

problemas de drenaje del distrito de riego 075 Ro Fuerte.

Informe final del proyecto convenido entre el IMTA y la S.

de R. L. del distrito de riego 075 Ro Fuerte, segn Anexo

Nmero Uno IMTA-ANUR DR 075, del 21 de enero de

1998. Instituto Mexicano de Tecnologa del Agua, Jiutepec,

Morelos, Mxico. 1998.

Pulido Madrigal, L., J.L. Lpez de Santa Ana, O.X. Cisneros

Estrada & B. Robles Rubio. Estimacin de cosechas por

medio de imgenes de satlite en el Distrito de Riego 075Ro Fuerte, Sinaloa. Memorias de la XI Reunin Nacional

SELPER-Mxico, Sociedad de Especialistas

Latinoamericanos de Percepcin Remota y Sistemas de

Informacin Espacial. Cuernavaca, Morelos, Mxico. 2000.

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Cap 01 Salinity Problems