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6. Obtaining more facts about resources
Start
with soil surveys
Soil Map of the World and other aids to
assessment
Making land capability assessments
Further
research needed
German researchers study erosion
Forest crops and other possibilities
There is still a lack of information in many countries on the condition of land resources just as there is inadequate knowledge about farming and grazing systems that combine satisfactory production with resource protection.
To know where to begin with a land use policy and a soil conservation programme, a country will need to know the answers to several basic questions about its resources:
Water is another basic resource that must be taken into account, but as the subject is vast enough to warrant a separate publication of its own, it will not be treated here. However, its interactions in any conservation work must be borne in mind.
Answers to these important questions will help guide a country's efforts to develop new or improved soil conservation programmes. A good place to start is with soil surveys. Soil surveys describe and evaluate the various types of soil in a country, locating them on maps. They describe each soil's susceptibility to erosion and its limitations for different uses. For example, one soil might be excellent for growing trees but subject to severe erosion if planted in maize. Another might make good cropland if the water table were lowered slightly. Soil surveys guide planners and farmers to alternatives for making land use decisions .
Surveys also predict crop yields for different soils and tell what crops, grasses, and trees are best suited to each soil. They also describe the soil and water management needed to use each soil on a sustained basis. Soil surveys are a basic tool of modern agriculture, as well as of many other enterprises involving land use, like highway construction.
But making a scientific soil survey requires time, the services of professional soil scientists, and a considerable investment. Thousands of separate ground observations are required for a survey, and these have to be delineated on aerial photographs of the area being mapped. Help in making soil surveys and assessments of land conditions is available to developing countries from a number of sources, including FAO, the USA, the Federal Republic of Germany, the United Kingdom, and others.
Soil Map of the World and other aids to assessment
On a world scale, important contributions in mapping and assessments have already been made by agencies of the United Nations. FAO and Unesco have completed a Soil Map of the World, a highly generalized but extremely useful look at the planet's soil resources. More recently, FAO completed an Agro-Ecological Zones Project, to obtain "a more precise assessment of the production potential of the world's land resources, and so provide the physical data base necessary for planning future agricultural development".
To carry out the latter project, FAO compiled data on those areas of land in the world suited to the rainfed production of 12 major crops. The study, which takes into account soils, climate, length of growing period for crops, and other factors affecting agriculture, presents its findings, not by country, but by agro-ecological zones. In this way, the food-producing potential can be determined for various regions. The project employs the principles of the FAO Framework for Land Evaluation, including the concept that suitability for growing a particular crop assumes use of the soil on a sustained basis and without risk of environmental degradation. Findings of this 1981 project should be of great help to agricultural planners and developers in every country.
More detailed guidance for countries on surveys is available in several FAO Soils Bulletins, including the following: A framework for land evaluation, No. 32; Assessing soil degradation, No. 34; and Prognosis of salinity and alkalinity; No. 31. These are available from FAO Distribution and Sales Section, Rome, and certain authorized sales agents.
Expert soil survey assistance is also available to developing countries through the Soil Management Support Services ( SMSS), a programme of the US Agency for International Development (AID) which is executed by the Soil Conservation Service. SMSS is also refining Soil Taxonomy, a system of soil classification developed in the USA, to make it more useful in the tropics. Similar facilities are available through the British Land Resources Division of the Overseas Development Administration (ODA).
In the absence of surveys by trained scientists, it is possible for a lay person with brief training to observe signs of serious land degradation and to record his observations in a methodical manner. During a rainstorm, for example, or immediately after it has ended, rills appear clearly as small channels in cultivated cropland, most often near upper slopes. Gullies are obvious, and it is not hard to learn to estimate their dimensions. A less obvious but tell-tale sign of erosion is a stream of water that turns muddy just after rain, especially when the muddy stream is seen entering a larger stream that is clear. The muddy stream is carrying recently eroded soil. Erosion is also signalled by deposits of gravel, sand, or silt in stream channels.
Sometimes a field is covered with gravel or stones, indicating that the fine soil has been washed away. Exposed roots of trees and shrubs are also evidence of erosion from water, as are washed-out fence posts. On sloping land, eroded soil accumulates above trees, stones, and fences. Deposits of soil at the bottom of slopes are another sign of erosion. So are light and dark patches in a field, indicating the cover of topsoil is uneven.
Signs of wind erosion, apart from the obvious experience of a dust storm, are deposits of white sand on the surface of the soil, ripple designs on sandy soil, and the formation of hummocks and dunes. Another sign is an accumulation of sand against grass stems, tree trunks, fences and sheds in the direction of prevailing winds.
Marks of salinity or alkalinity include salt crust on the surface of the soil or along the edges of irrigation furrows. Barren spots in a field of crops or unhealthy looking plants are another sign.
It does not take a professional soil scientist or an agronomist to spot these danger signals, and when carried out in a planned way, such assessments can provide a good, working appraisal of resource conditions.
Making land capability assessments
A number of simple guides for determining land capability are being used by farmers and conservationists in different countries today. Canada, Great Britain, and New Zealand all have their own schemes of classification, but most are adaptations of a system developed in the USA. The idea behind all of them is that proper use of the land is the best means of erosion control. The US system divides the rural landscape into eight capability classes, with Class I the best suited for growing crops and Class VIII unsuited for any agricultural purpose at all.
Despite the great advances in agricultural research made in most developed countries, much more needs to be learned about managing tropical soils and other aspects of farming in the tropics and subtropics.
Promising research is under way to develop alternatives to shifting cultivation. Among these are various forms of mulch tillage, mixed cultures of crops and forest trees, and intercropping. It seems likely that no single satisfactory answer will be found, but that different agricultural systems will be developed for different soil types and to meet the needs of different societies and cultures.
An example of the kind of practical research that is desperately needed was announced recently by the International Crops Research Institute for the Semi-arid Tropics ( lCRISAT), at Hyderabad, India. The problem is that the deep black soils that cover much of India are too wet and sticky to cultivate during the monsoon rains. Left fallow during the rainy season, the fields are eroded and depleted by runoff, reducing the chance or good crop yields when the monsoon is over.
Now ICRISAT has developed technology that permits such crops as sorghum and pigeonpeas to be grown on deep black soils during the rainy season. The system has many facets. It involves shaping the land into broadbeds and furrows to facilitate cultivation and drainage. The system uses bullocks and a new two-wheeled tool carrier developed at ICRISAT. According to the inventors, the animal-drawn vehicle can do anything a tractor-powered vehicle can do.
Seedbeds are prepared during the dry season with the tool carrier and sowed just ahead of the monsoon before the soil becomes too sticky to cultivate. Improved crop varieties and combinations of crops are used with adequate amounts of fertilizer. Excess water is stored to be used for irrigation during the dry season. ICRISAT predicts that this farming system, which will permit farmers to harvest two crops a year instead of one, will have "tremendous impact on food production in India".
German researchers study erosion
Another example of helpful research was undertaken in 1978 and 1979 in Paraná, Brazil, by scientists from the German Agency for Technical Cooperation (GTZ) working with staff of the Fundaçào Instituto Agronômico do Paraná. The state of Paraná. has suffered an alarming increase in soil erosion since its tree cover was reduced from 84 percent to 9 percent and the forests were replaced with large-scale, mechanized farming. With double-cropping of wheat and soybeans, annual soil losses on 6 percent slopes ranged from 700 tons per hectare on unprotected land to slightly less than 100 tons per hectare where terraces were combined with good tillage practice. But losses were still much too high to maintain soil fertility and to use the soil for crops on a permanent basis.
The German scientists conducted trials at two sites in Paraná. and found that the root structure of cover crops increased water infiltration rates up to 416 percent on one type of soil and up to 629 percent on another. Erosion rates decreased significantly. They also found that wheat yields from non-tilled plots were higher in dry years than those from conventionally tilled plots, probably because of higher soil moisture content, lower soil temperature, and increased biological activity. Non-tilled soybeans, they learned, can be sown with lower risks than those conventionally planted.
Findings such as these offer hope that more protective agricultural systems can be found for this valuable farming area and for areas in other countries with similar soils and erosion rates.
Forest crops and other possibilities
In a number of countries, new and improved forest crops, like the fast-growing ipil-ipil tree (Leucaena leucocephala (Lam.)) in the Philippines, lay the groundwork for innovations in commercial forestry, releasing more land for crops. In a number of tropical countries, degraded forests have been transformed in just a few years into successful man-made plantations.
Much of current research on improving unproductive grazing land is directed toward finding hardier, more nutritious forage plants.
Research is also needed to find more productive ways for people to work with one another toward common goals of resource management, particularly at the village level.
A major research objective is to determine the relationship between soil loss and crop yields for major agricultural soils, so that the costs of conservation can be measured accurately against the benefits to individual farmers and to countries.
There have been encouraging experiments and field work in all of these areas, but they need to be multiplied many times around the world.