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The developing countries (excluding China, Mongolia, Viet Nam, the Democratic People's Republic of Korea and the Republic of Korea) cover an area of nearly 6500 million hectares. Somewhat more than one-tenth of this is currently cultivated. This results in an average of 3.2 people living off every cultivated hectare of land.
In itself, this statistic is not alarming. Yet over the last 20 years of this century, the population of the developing countries is expected to increase by 50 percent. It is expected to triple before it stabilizes. What is the potential of the agricultural resource base that must support this population?
Much of the land in developing countries is not well suited to rainfed agriculture. Nearly four-fifths of it is covered by soils that limit crop production. Climatically, much of it is too dry, some too wet and some too cold for crop production. As a result, a maximum of about 2000 million ha of land in the developing countries is potentially cultivable - about three times the currently cultivated area.
Globally, this figure appears almost reassuring. It confirms that it might be possible to triple population without greatly increasing the number of people living off each cultivated hectare - but only if all suitable land is brought under cultivation.
The situation is much more alarming when analysed regionally or nationally. Little more than seven percent of land in Southwest Asia, for example, is suitable for rainfed agriculture. And more land is already being cultivated there than is theoretically suitable for cultivation. In Southeast Asia, the limits of rainfed agriculture are also close at hand. Only in parts of South America and Africa are there large reserves of agricultural resources. Even these resources may be difficult to exploit because they are often remote and difficult to manage.
This situation therefore demands careful land-use planning. Agriculture must be developed over the long term in such a way that all available land is put to its optimum but sustainable use. Unhappily, planning on this dimension is hampered by a long list of unknowns:
• Exactly how much potentially arable land is available, and where is it?
• What crops could be grown on it, and what would. they yield?
• What level of farming inputs is needed to produce required yields?
• What is the risk of degrading this land through cultivation, and how can the risk be minimized?
• Which areas and which crops would produce the highest returns given more resources?
• What would it cost to realize these returns?
• What are the maximum returns attainable?
• Where should future research be concentrated?
Our inability to answer such questions has frequently led to disaster in the past. Millions of hectares of good land were destroyed in the United States of America in the 1930s when the soil was left exposed to wind erosion. Bad planning led to the groundnut disaster in East Africa in the 1950s, in the course of which huge sums were invested, and lost, in a cash crop which was grown under unsuitable conditions. In Africa today, some of the drier areas are being degraded at such a rate that the term 'desertification' has come into use. Yields here, as in other over-exploited areas, are declining.
The Agro-Ecological Zones (AEZ) study was conceived by the Food and Agriculture Organization of the United Nations (FAO) to help prevent this kind of disaster and answer these questions. With the help of computers and many man- and woman-years of painstaking work, details of the moisture, temperature and soil requirements of the major crops have been compiled, and the soil and climatic conditions that exist in most parts of the developing world have been quantified.
The AEZ Study views the developing countries' land area as a mosaic of about 650000 grid squares (10 x 10 km), each with a specific climate, growing period and association of soils. From these the area of each soil within each climate and length-of-growing-period zone has been calculated for each country. These defined agro-ecological cells constitute the data base which is stored on computer.
This data base can then be used by a series of computer programs to answer questions about potential cultivation on a regional or national level. The first regional studies were completed in 1978. More detailed studies, particularly at the country level, have been continuing since.
The methodology has now reached the stage where it can be of practical assistance in long-term planning at the subregional, national or district level. This publication is designed to explain the technique, and its potential, to those charged with this responsibility.
How soil limits crop production (percentage of total area)
