Address causes, not symptoms

Soil conservation must address the causes and not just the symptoms of water run-off and erosion. This is the opinion of the senior land husbandry advisor to a joint Zambia Government-Swedish Development Agency (SIDA) project in Zambia, which has been launched to return eroded and fertility-depleted land to productivity as quickly as possible.

One of the largest countries in Southern Africa, Zambia, has vast areas yet to be developed for commercial agriculture. Yet much of this land, together with land in regions of high population, that has been developed (Copperbelt, Lusaka, Central and Southern Provinces), is suffering from serious degradation. Deforestation is a major problem, with commercial logging, charcoal production and bush clearance for illegal settlements all contributing. However, agriculture is the most serious culprit.

Despite rainfall of less than 800mm in most parts of the country, run-of erosion is all too common. "Everyone thinks that soil conservation is the best way of controlling run-off", says Lars ov Jonsson, the senior land advisor to the programme. "But this is a very conservative view, because when you concentrate on the run-off you're dealing with the symptoms, not the problem." So, the programme is focusing on building the organic content of soils and enhancing fertility through the incorporation of green and animal manures and crop residues. Whereas mineral fertilizers are expensive and do nothing for soil condition, organic matter (biomass) initially protects the soil surface from the force of heavy rainfall, slows infiltration and, as it decomposes, provides nutrients and increases the water-holding capacity of the soil.

Training is crucial since nothing less than a change in farmers' attitude is necessary, as well as acquisition of new skills. To keep soil disturbance to a minimum, they are trained to use a soil ripper instead of the ox-plough, with seed planted in the slots cut through the soil and biomass overlay by the ripper. Water harvesting is another new concept being taught. And rotations and the use of more leguminous nitrogen-fixing crops for consumption and for green manure are being introduced. Because it can take several seasons to recover fertility in depleted soils, farmers are introduced to fish farming and agroforestry as supplementary sources of income.

Monitoring and evaluation to assess the impact of the programme has been conducted in four provinces, focusing on soil erosion levels, water-holding capacity of soils and fertility. Production output has shown significant gains with yields in many instances up more than threefold, compared with yields achieved before the land management and conservation programme was introduced.

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