Accumulation of excess salts in the root zone resulting in a partial or complete loss of soil productivity is a worldwide phenomenon. The problems of soil salinity are most widespread in the arid and semi-arid regions but salt affected soils also occur extensively in sub-humid and humid climates, particularly in the coastal regions where the ingress of sea water through estuaries and rivers and through groundwater causes large-scale salinization. Soil salinity is also a serious problem in areas where groundwater of high salt content is used for irrigation. The most serious salinity problems are being faced in the irrigated arid and semi-arid regions of the world and it is in these very regions that irrigation is essential to increase agricultural production to satisfy food requirements. However, irrigation is often costly, technically complex and requires skilled management. Failure to apply efficient principles of water management may result in wastage of water through seepage; over-watering and inadequate drainage result in waterlogging and salinity problems which reduce the soil productivity, eventually leading to loss of cultivable land.
Buringh (1979) calculated from various available data that the world as a whole is losing at least ten hectare of arable land every minute, five because of soil erosion, three from soil salinization, one from other soil degradation processes and one from non-agricultural uses. The problem of soil degradation is a serious threat to the welfare of mankind. Although degradation of the land has always characterized mans systematic use of it, the process has accelerated in recent decades and precisely at a time when population growth and rising expectations have begun to demand enormous increases in food production. The problem is of overwhelming urgency. As the soil is subject to degradation, the cost of reclaiming it becomes higher, rising sharply until the threshold is passed beyond which reclamation is no longer economically feasible. Nearly 50 percent of the irrigated land in the arid and semi-arid regions have some degree of soil salinization problems. This figure indicates the magnitude of the problem that must be tackled in order to meet future global food needs.
It is generally agreed that the future food needs of increasing population will be met by directing the efforts of all concerned towards:
- improving the level of management of soils already under cultivation, andSoil salinity is a major impediment in achieving increased crop yields by either of the above approaches. It is in realization of this that the United Nations Conference on Desertification held in Nairobi in 1977 adopted the following recommendations: It is recommended that urgent measures be taken to combat desertification in the irrigated lands by preventing and controlling waterlogging, salinization and sodication by modifying farming techniques to increase productivity in a regular and sustained way; by developing new irrigation and drainage schemes where appropriate always using an integrated approach; and through improvement of the social and economic conditions of people dependent on irrigated agriculture (United Nations 1977).
- by bringing under plough the potentially arable soils which are presently uncultivated.
The problems of salt-affected soils are old but their magnitude and their intensity have been increasing fast due to large-scale efforts to bring additional areas under irrigation in recent decades. The problems have been made worse by development of irrigation systems without adequate provision for drainage and are being aggravated by poor water management practices and unsound reclamation procedures.
The general characteristics and basic principles involved in the identification, reclamation and management of salt-affected soils are the same throughout the world. However, differences from place to place in soil characteristics, climate, water availability, farm management capability, financial resources, available inputs and economic incentives lead to differences in method, extent and rapidity of soil reclamation. Although technical literature abounds with sound information on the subject, nonetheless, there are far too many partial or complete failures of efforts to reclaim salt-affected soils. These failures, due largely to lack of proper identification and subsequent use of incorrect reclamation methods, result in losses of both money and potential increases in crop production. This publication presents a brief summary of information which will be particularly useful in the proper identification, reclamation and management of soils with problems caused by the presence of excess salts.