Sustaining soil
Michael Stocking Dr Michael Stocking is a Senior Lecturer in the Natural Resources Development Department at the University of East Anglia, Norwich, UK. He is also an FAO consultant on soil erosion and productivity. Soil conservation is undergoing a revival. Projects and programmes containing measures designed to protect soil resources are burgeoning throughout Africa, the Caribbean and the Pacific. No longer is the soil seen as a passive medium, responsive only to chemical inputs but which otherwise remains unaltered throughout the lifetime of agricultural development schemes. Much better understood now are erosion processes and the dynamic nature of soil fertility, structure and chemistry. The time was ripe for views to change. In reviewing the food self sufficiency of 117 of the poorest countries of the world, FAO's 'Potential Population Supporting Capacities' project concluded that unchecked soil degradation is the single greatest threat to food production. Erosion undermines both indigenous and introduced farming systems; people are having to change their staple crops in response to declining fertility brought on by erosion; land is being abandoned and populations are migrating; and whole regions are becoming increasingly susceptible to droughts as the soil no longer can maintain an adequate capacity to supply plant-available water Cases abound throughout ACP countries. Ethiopia has seen a massive flight from the countryside aggravated by war and unreliable rain, but caused, I argue, by accelerated erosion and the consequent inability of the soil to produce. In Barbados, sugar cane plantations are responsible for displacing people to the hills, where soils are thin and erosion hazard is great. Is soil conservation really the answer? Logic might suggest it is: if soil is moving, let us stop it! However, if by conservation we mean a package of technical remedies, designed by agricultural engineers and land use planners, applied to the land as the optimum solution for arresting further loss of soil, the record is far from convincing. Time and again such packages have failed. The now-classic Sukumaland Development Scheme of the 1950s in Tanzania (then Tanganyika) exemplifies the pitfalls. Impressive lists of rules covering all aspects of land preparation, cultivation and grazing were devised; ridging practices and manuring were enforced; tree cutting was forbidden; and strict controls were placed on cattle numbers. All the ingredients were there for stopping erosion. However, there was so much resentment against these measures that riots ensued and, when the Scheme failed in 1958, contour banks, terraces and hedges were all physically destroyed. There is no evidence to support the suggestion that it would have helped if the measures had been enforced less autocratically, as can be seen from present attempts in Tanzania to destock and reforest. My concern is that 'soil conservation' is the wrong term, with misleading connotations, targeting the wrong problem in the wrong way. US agronomists of the 1920s and 1930s recognized erosion correctly for what it is: a threat to the productivity of the soil, making it more costly to gain yields because those lost nutrients have to be replaced, thus involving disruption and difficulties to farmers. Today, for developing country farmers, we could add that erosion threatens their whole ability to survive. Early experiments showed how yield levels of crops plummet with only small amounts of erosion. We know that these declines are far more dramatic on susceptible tropical soils. Because the reduction in yield is non-linear, a unit quantity of erosion on a good soil is proportionately far more serious than on the same soil already degraded. This has two implications. First, erosion rates are meaningless. The massive research effort into predictive techniques of soil loss estimation (e.g., the Universal Soil Loss Equation) is wasted. Not only does a soil loss rate in tonnes per hectare tell us nothing about the effect of erosion on the land user but it also diverts attention from the real seriousness of erosion, making it impossible to integrate the assessment with other measures in economic planning. Secondly, the focus of attention is drawn to the soil that is lost, not the soil remaining. We forget the land user that has to eke a living out of the sand and gravel that remain. This emphasis on eroded sediments has, I believe, separated soil conservation from where it should be -- as part of land management, integrated with the farming system, reinforcing societal goals and needs and, above all, providing an assured sustainable livelihood for the land The best way of conserving soil is to prevent its initial detachment by layers of living or dead vegetation which intercept rain drops. It is no coincidence that farming systems with good cover tend to yield better or that plants grown with a ground cover of mulch survive droughts better. In short, good soil conservat~on is a matter of providing good vegetal cover which not only protects the soil but also, most importantly, provides benefits to the farmer in the form of better yields. Physical conservation measures incur costs in labour, money and resources without any commensurate short-term benefits. Only exceptionally, as with the 'Fanya Juu' terraces in the high erosion potential areas of Kenya, are mechanical measures accepted as an integral part of the farming system, maintained over long periods and taken up by adjacent farmers. Land users in the Third World would be committing economic suicide in accepting many of the techniques we promote as 'soil conservation'. Maybe it is time to ditch the term 'soil conservation' entirely. Its record is poor. It is inextricably linked with unloved, unwelcome and inappropriate techniques. Malawi has done so, renaming its 'Soil Conservation Branch', 'Land Husbandry'. But more radical solutions are needed now, where measures to protect soil resources take their rightful place in agricultural development alongside and within plant-breeding programmes, farming systems analysis, adaptive research, intercropping, agroforestry, and so on. In short, within sustainable development which must be our ultimate goal: without soil resources it is but a pipe-dream. The views expressed are those of the author, not necessarily those of CTA.
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| Format: | News Item biblioteca |
| Language: | English |
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Technical Centre for Agricultural and Rural Cooperation
1988
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| Online Access: | https://hdl.handle.net/10568/44876 |
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