Posted June 1996
Soil and water, the functions they have and the substances they carry, underlie all agriculture. Soil is the indispensable resource for adequate crop production. It is the medium in which plants grow and contains or stores both the nutrients and the water needed for biosynthesis, a process for which sunlight normally provides the energy.
The ultimate potentials of land resources for arable agriculture are not known precisely. What is known is that in some developing countries available agricultural production technology now or soon will not be able to sustain their populations. About 90 percent of available arable land in populous countries of the Far East is already used for food production. Increases must come from more intensive cultivation of and higher yields from the land.
Arable agricultural lands differ greatly in quality. With similar inputs, crops grown on land that is only marginally suited for arable agriculture will yield perhaps half as much or less than those grown on neighbouring good land. In general, and particularly in densely populated rural areas of developing countries, the quality of remaining undeveloped land is inferior to most land now in use for agriculture.
On all continents, farmers have made local improvements in soil quality to increase productivity. Globally, however, the productivity of land under crops (and pasture) has declined for various reasons, including greater use of land that is only marginally suitable for the kind of agriculture practiced on it. Dramatic increases in the populations of developing countries have placed pressure on the land to produce additional food. This pressure has been among the causes of misuse or poor management of soils, exacerbating other processes that lead to soil degradation.
The combination of land scarcity and the threat of land degradation represents the most serious problem for the growth of agriculture in the Third World. New as well as existing farmland must be carefully conserved and managed so as to preserve and enhance its productive potential.
Water is needed for the growth and maintenance of plants and animals. On a planetary basis enough water exists to meet all needs, but water can still prove to be a serious constraint to agriculture. Its availability at some stages of plant growth, and hence at specific periods, is a prerequisite for good crop development and yields. As with soils, the quality of water is of great importance. It, too, is under threat of degradation from several causes, including agricultural practices themselves.
Irrigation is among the oldest means that man has used to harness nature's resources. About four-fifths of the developing world's potential arable land is in areas with sub-humid or semi-arid climates with erratic rainfall. Well-managed irrigation schemes can do much to improve reliability of production in these areas, but accessible surface and groundwater resources are sufficient to irrigate only a small fraction of the total area.
Too much water can be as serious a problem for agricultural production as too little. Floods can wash away newly-planted crops or drown livestock. Some 20-30 million hectares of irrigated farmland are severely degraded by waterlogging or salinity or both, and a further 60 to 80 million hectares suffer to some extent from these conditions. The problems are frequently made worse by high and rising groundwater levels caused by poor water supply management and drainage, and by salts in the irrigation water.
In large areas of the world, however, too little water per se or when needed is a major constraint to agricultural production. Some groundwater levels are low and falling, and agricultural productivity then depends largely on the amount, distribution and reliability of rainfall. In these conditions, every effort must be made to harness rainwater: soil preparation for rapid infiltration or minimal run-off, well-timed crop sowing and fertilizer application, collecting and holding excess rainwater for future supplementary irrigation.
Agricultural productivity is minimal under desert-like conditions. Close to one-quarter of the land surface of the earth is desert or at an advanced stage of desertification. In recent times, mismanagement of resources has been a prime source of desertification which is accelerating in many areas. Among the causes, direct or indirect, are increasing human and livestock populations, overgrazing, bush fires, forest fires and deforestation, and inappropriate practices in agriculture. Efforts to counter desertification have so far failed to prevent the substantial net loss of rangeland and cropland observed in recent years.
Technologies for land with high potential for agricultural production have benefited from research but knowledge on how to improve production on marginal land remains inadequate. Some so-called improved technologies tend to expose farmers to greater risks and so have met with only limited acceptance and use, especially by poor farmers in marginal areas. Recent research and development efforts have led to better technologies that can also help reverse soil degradation. However, the correct use of land has emerged as the best means of avoiding the problem. Better tools have been created to provide the information essential for planning and monitoring the proper use of land.
Good land management calls for the employment of specific techniques in specific locations, e.g. suitable crops and cropping sequences, contour cultivation, strip cropping, terraces and protected waterways, and fertilizer application related directly to crop requirements. Impaired rangelands can be reclaimed by controlling grazing, by pasture improvement and by judicious application of fertilizers; and croplands by improving drainage, adopting better cropping patterns or introducing new crops, and by adding residues for soil fertilizing, conditioning and nutrient replenishment. Knowledge of these technologies has grown substantially in the past decades, but the ability to put it to use in local situations is still weak in many areas of the developing world.
Science and technology have done much to improve the management of irrigation systems. Computerization and linked automatic control of water delivery can increase tremendously the efficiency of water use. Devices for measuring the rate of crop evapotranspiration and soil moisture depletion have been refined and adapted to serve the needs of developing countries. Monitoring of these rates assists in deciding when water should be applied for irrigation, and how much. This is particularly important to reduce excessive water application, environmental hazards and negative effects of drought.
The allocation of water from complex canal systems with multiple users requires frequent adjustments which can be most efficiently made through computer automated controls. Electronic sensors and telemetered, computer-controlled monitoring are also used for real-time synoptic information on water levels, water discharges and state of gates in irrigation water distribution systems. To design better irrigation schemes, software is now available for optimization of distribution networks and for efficient on-farm surface irrigation systems. These applications of advanced technology allow for more intensive use of the water management infrastructure and of limited water resources. Also, prevention of flood disasters and flood management through computerized early warning systems have become an important tool to save crops, environment, infrastructure and lives.
Although scientists are unlikely to find ways of controlling the supply of rainfall in the foreseeable future, scientific soil management and crop management have much to contribute to efficient water use where irrigation is not possible. Rainwater can be conserved through various methods of "water harvesting": by holding the water on the land in small basins or tied ridges or by collecting runoff. Improved knowledge of rainfall patterns can be used to direct research on production, especially where rainfall varies over relatively small areas. Probability analysis improves the predictability of field trial results. Together with modern plant breeding techniques, this essentially agro-meteorological approach could be used more widely to exploit the full production potential of areas with low and erratic rainfall and to reduce fluctuations in production caused by drought.
On a global scale, FAO has worked with Unesco to produce the Soil Map of the World-an outstanding achievement which involved collaboration between scientists from all parts of the world over a period of 20 years. This map locates the different dominant types of soils of the world, but more information is required to evaluate their agricultural potential. FAO therefore developed a method of combining information on soils and climate so as to define agroecological zones. When this information was further combined with data on the requirements of major crops grown in the zones, the food producing potential of different areas could be assessed. FAO elaborated and tested this methodology to calculate the potential population-supporting capacities of the lands in the developing world.FAO continues to lead in extending the use of methodologies for determining land use and population-supporting capacity to different regions and countries, as well as to areas and localities. It supports training and efforts to support planning and action to increase the efficiency of use of land and water resources in a sustainable way.
With computers becoming more widely available, the methodology developed by FAO is being used or adapted in software which allows for the storage, retrieval and appraisal of data on land resources. FAO has also made use of computers to develop and install its own Geographic Information System (GIS) in which soils data are stored. The system's special usefulness derives from its capacity to "overlay" map layers featuring a locale's different characteristics such as topography, land use, infrastructure, soil types, water availability and population. Advances in soil science, surveying, photogrammetry and remote sensing underlie the evolution of the GIS.
Development of FAO's GIS had four main objectives: to provide global and regional data bases incorporating map coverages relevant to FAO work plus statistical data; to combine this data to provide outlook and other types of studies; to provide a tool for backstopping projects; and to train staff. The integration of socioeconomic data bases into the GIS and the linkup of the GIS with international data bases outside FAO is proceeding. Global and regional-level applications of FAO's GIS are carried out at headquarters. FAO helps member countries to develop a GIS capability.
Land will produce well only if it is properly managed, and FAO has been among the leaders in introducing new and improved techniques of land management to developing countries. Assistance has been given to establish laboratories in which analyzes of soils and plant materials are conducted with up-to-date techniques. Such data are essential for proper management which first requires identification of constraints if effective recommendations on fertilizer application are to be made. The need to conserve and improve soil fertility has led FAO to develop and apply integrated plant nutrition systems.
A considerable amount of information is now available on soil erosion: erosion processes, the susceptibility of different soils to erosion, amounts of soil loss and measures to reduce erosion. But surprisingly, little is known as yet about the effects of erosion on soil productivity-the characteristic of erosion of greatest importance to the farmer.
FAO has developed a research design to obtain this important information. The design is under test in 12 research institutes in 10 countries. The Organization is seeking to foster and support a collaborative research network on the effects of erosion on soil productivity and is also working on an internationally acceptable and practical ways of mapping soil erosion. Developing countries face many additional problems in the agricultural use of their soils and water, e.g. overcoming soil salinity and waterlogging, developing alternatives to shifting cultivation, managing acid-sulphate and other problem soils, devising suitable tillage techniques, improving the use of crop residues, etc. FAO has been active in seeking solutions to these problems, but has in particular sought to strengthen the pertinent national capabilities in research and extension. Scientists and technicians from developing countries have been trained in soil conservation and research on various land degradation problems.
The work of FAO on water use centres on resources for irrigation and on techniques for water management. In many parts of the world, water is a limiting factor for agricultural development, not only because of inadequate quantity, but also because of low quality. FAO has been gathering information and disseminating it and guidelines on technologies for using low quality water such as saline water, drainage effluents and treated wastewater, and promoting technologies for efficient use of water.
Any climate change towards global warming will affect the amount and the seasonal pattern of both available water resources and irrigation water demand. FAO is supporting studies on the effects of climate change on existing irrigation schemes and on how to adapt to changing climate conditions. Climate change might also result in salt-water intrusion in coastal aquifers. The deterioration of groundwater quality could have dramatic consequences for local irrigated agriculture.
Information collected by instruments in satellites is increasingly used in field studies on the engineering, economic and environmental aspects of surface and groundwater development, on utilization of poor quality water for agricultural purposes, and on social and institutional aspects of irrigation water management. In one FAO study, satellite remote sensing data on vegetation cover, soil characteristics and the hydrographic network is analyzed together with statistical hydrological data to estimate annual runoff in small ungauged basins. This study may lead to the possibility of mapping annual runoff in small basins automatically to guide planners on the overall distribution of surface water resources. Another application may use data over a large river basin to improve forecasts of flows into reservoirs so that seasonal agricultural planning and water releases from a reservoir system can be optimized.
An irrigation management model capable of being run on a personal computer has been devised by FAO. Using the model, indicative irrigation schedules can be derived from average climatic (rainfall) and agricultural field data, taking into account the specific requirements of the irrigated crop. Key to the model is the daily assessment of the water balance. Soil moisture status is determined from calculated evapotranspiration and water supply from rainfall and irrigation. FAO methodologies for determining crop water requirements and yield response to water application are used.In its field programmes, FAO participates in the evaluation and design adaptation of water lifting devices that use renewable sources of energy, i.e. wind or water turbines. Guidelines for site selection are made available. FAO supports training in water use techniques and in the management of large irrigation schemes, in community irrigation and in water use at the farm level. Information on proven technologies and training materials has been assembled in a catalogue designed to promote the transfer of agricultural water technology.