As the available agricultural land per head of population dwindles, countries must plan how best to use their land. Sound methods of preventing land degradation must then be applied so that production can be maximized without jeopardizing future fertility.
THE PER CAPUT availability of agricultural land in developing countries is projected to nearly halve between the late 1980s and 2010, from 0.65 to about 0.4 hectares. Even this figure will shrink further by 2050.
It is critically important to optimize the uses to which land is put, assisted by sophisticated techniques of land-use planning. Land that is designated for agricultural use will have to be carefully protected, using a range of conservation techniques, from the degradation that now results in the loss of an estimated 5 to 7 million hectares of good land each year.
Most land users do not have the time, the resources or the inclination to adopt new, and perhaps risky, practices to tackle problems that they probably cannot even see. So emphasis must be placed on involving farmers from the start in developing and adopting measures that not only conserve the soil but also offer short-term, tangible benefits - such as increased yields or easier work.
SOUND LAND-USE planning has been made much easier by the advent of micro-computers, the development of databases and the use of Geographic Information Systems (GIS, see diagram right).
The diagram below summarizes the essential steps in optimizing the choice of crop for any given plot of land, down to a 1 0-km square. These steps involve matching the requirements of individual crops (step 1) with existing conditions on the ground: climatic requirements (2a) and soil requirements (2b). Overlaying these two inventories then creates a land inventory which includes information on both climate and soil (3). Constraints on crop yield are then added on, together with information about pests and harvesting difficulties (4). Finally, data on soil constraints are added, resulting in a land-use recommendation about what crop should be grown, what inputs will be required, and what crop management techniques should be used.
Five steps to sound land use
A figitalized Geographic Information System (GIS)
In a modern GIS, the exact geographical location of each piece of data stored in a database is recorded. For each geographical location, the required data can then be called up, and layers of information built up one over the other. The resulting map can then either be viewed on screen or printed out.
Global status of soil degradation
'If the soil on which all agriculture and all human life depends is wasted away, then the battle to free mankind from want cannot be won:
Lord John Boyd Orr first Director-General of FAO, 1948
HUMAN ACTIVITIES have often led to degradation of the world's land resources. Damage has occurred on 15 percent of the world's total land area 13 percent light and moderate, 2 percent severe and very severe. There are four main types of land degradation.
· Water erosion
The commonest form of degradation, water erosion is causing massive damage in nearly all developing countries (see map above). It occurs where steep land is being unwisely farmed and where gently sloping land is left exposed to the effects of heavy rain. In the United States the annual loss of topsoil still averages 12 tonnes per hectare, and an estimated 50 million tonnes a year of plant nutrients are washed away with it.
· Wind erosion
Land stripped of vegetation and exposed to strong winds can be quickly blown away - as much as 150 tonnes can be blown off one hectare in an hour. Wind erosion caused the famous dust bowls in the Great Plains of the United States in the 1 930s. The cure for wind erosion is to ensure good ground cover and windbreaks (such as hedges).
· Physical and biological damage
Soil may be damaged if it is worked with heavy equipment in wet weather or when it is compacted round water holes in pasture land. Biological damage occurs when soils are deprived of their nutrients, organic matter or humus. Deep-rooting crops are needed to cure physical damage, and crop rotation and good farming practices to cure biological damage.
· Salinization and waterlogging
When poorly drained land is irrigated, the sun evaporates the water, leaving behind its salts. After several years, the soil becomes highly saline and affects plant growth. If drainage is very poor, the soil may also become waterlogged. It is estimated that about 40 million out of 200 million irrigated hectares are waterlogged, affected by salt, or both. The area of land being abandoned every year for these reasons is roughly equal to the amount of land being reclaimed and irrigated.
CHECKING LAND degradation depends on two simple ideas: first, the prevention of degradation carries with it its own motivating force - the increase in production that accompanies well protected land: and. second. that land users can and will organize and implement the necessary measures themselves, given a little catalytic help.
These are bold new ideas, contrasting starkly with traditional conservation techniques which were imposed from above and required expensive and exhausting physical labour. Today the emphasis is on biological techniques - such as preserving ground cover and choosing the right crop for the right land - and crop management methods that avoid degradation from the start.
For further information, please contact:
Food and Agriculture Organization of the United Nations
Viale delle Terme di Caracalla, 00100 Rome, Italy
Information Division, Tel: (39-6) 5225-3276/5225-4781/5225-4243
Land and Water Development Division, Tel: (39-6) 5225-4702
Internet, http://www.fao.org or gopher.fao.org
United Nations Environment Programme, P.O. Box 30552 Nairobi, Kenya
Information and Public Affairs
Tel: (254-2) 621234; Fax: (254-2) 226831;
Telex: 22068 UNEP KE