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Tilling and timing

Cutting a narrow groove in the soil, just where you need to plant your seed, seems like a good idea if time is short and the alternative is to turn the whole field over with a plough. In much of sub-Saharan Africa, time for land preparation is indeed short. Conservation tillage in Brazil. Horse drawn roller-cutterOne of the major constraints to agricultural production in the Sahel is the shortage of rainfall, its uneven distribution and the unpredictable onset of the rainy season. Elsewhere too, in southern Zambia for example, the optimum time for planting may be as little as one to two weeks. Tilling and timing is a constant challenge and making best use of farm power is important.

For countless millions of farmers, draught animal power is the best option for land preparation. Schemes to encourage mechanization by tractor, introduced in the 1960s and 1970s, have largely failed and draught animals, which can complement both tractor and hand power, have taken their place. Animal traction is increasing in most African countries, and in Tanzania, for example, the number of draught animals has nearly doubled in the last twenty years. Nevertheless, many farming households do not own draught animals and must hire or borrow animals for preparing land before sowing. Ploughing takes a long time and is hard work and draught animals are in their weakest condition at the end of the dry season. Naturally the animals' owners select the optimum time for their own land work which means, of course, that the hirers must wait, often until the rains are well established. By this time planting will be late, with knock-on effects that may be disastrous on yields.

Conservation tillage addresses some of these problems but raises others. It can take a number of forms but the common factor is that the land is not completely turned over by plough. Seed is sown directly, usually in a narrow planting line cut with a ripper implement attached to a beam harnessed to a horse, a donkey or a pair of oxen (or cows). This offers two advantages for timing. The first is that much less labour is required and land can therefore be prepared more quickly, or more land can be prepared in the given time. The second is that, unlike ploughing, it is not necessary to wait until the soil is friable. This means that there is a longer window for land preparation. This makes better use of draught animals and is particularly useful for people dependent on hiring or indeed those who wish to hire out their animals. It may also help women, who are usually responsible for growing food crops, to plant earlier and, possibly, larger plots with obvious advantages for household food security.

...and tillage...
Ploughing bares the soil and exposes it to splash, sheet and wind erosion. Furthermore, if ploughed to the same depth year after year, a hard pan may develop through which rain and roots cannot easily penetrate. In contrast, conservation tillage helps to reduce soil erosion because organic matter - crop residues - are retained in the soil. There is less soil compaction and so water penetration and soil moisture retention are enhanced. And the draught requirement may be less than that required for ploughing. In parts of Honduras, El Salvador, Nicaragua and Bolivia, conservation tilling along the contours, combined with strip planting of food and fodder crops, is controlling erosion on the hillsides.

So far so good, but the disadvantages are equally obvious. If crop residues are normally fed to animals, including working animals, what is to replace them? If farmers cannot afford chemical herbicides to control weeds - and neither do they have sufficient mulch available to suppress them -Horse drawn seeder in Honduras how is the weed problem to be solved? One point of ploughing is, of course, to bury the weeds. Conservation tillage - as practised where herbicides are unaffordable - can give weeds full rein.

...and tools
Whereas land preparation, especially if it involves animals, is usually men's work, weeding is usually done by women and children - and by hand. And if more land is cultivated because the tillage technology has provided that option, weeding can be a very daunting task indeed. Every farmer knows that there is no point sowing if you cannot weed. Increasingly, therefore, animal drawn cultivators are being used to control weeds. Farmers in the Chungu district of Tanzania, where the land preparation window is too short to plough by ox, have tripled their area under cotton using ox drawn weeders after planting in holes hand dug by hoe. In much of the world, sowing is also done by hand but animal drawn seeders are easily made and used, and save labour and seed. Hundreds of thousands of factory-made seeders are now used in West Africa, while in Central America and Bolivia metal-working artisans have been assisted to make seeders. The challenge is to develop a critical mass of potential users so that workshops A seeder from Brazil being demonstrated in Ugandabecome interested in supplying the market. Training and financial support may be required for jigs, technical drawings and early production.

Farmers in Paraná in the south of Brazil have used conservation tillage continuously for the last ten years, thanks to a close partnership between Brazilian researchers (Embrapa - Empresa Brasileira de Pesquisa Agropecuária) and smallholder farmers. Over 100,000 hectares in Paraná are now planted direct with animal power. At a workshop held in Uganda last year under the auspices of ATNESA and partner organisations, participants were able to see some of the equipment that has been developed in Brazil - an interesting example of intercontinental technology transfer. Conservation tillage technology for smallholder farmers is now being evaluated in several countries in Africa and Asia, through a project coordinated by DMC-Cirad.

Conservation tillage does not, of course, provide all the solutions to soil and water conservation and timely land preparation. There are good and bad elements in all farming systems and farmers must base their decisions on what is best in their circumstances and with the farm power at their disposal.

For further information
ATNESA (Animal Traction Network for Eastern and Southern Africa)
African Conservation Tillage Network
RELATA (Animal Traction Network for Latin America)
DCM (Direct sowing, mulch-based and conservation agriculture)
Federação Brasileira de Plantio Direto na Palha
See also New Agriculturist 01-6 Focus On Soil: Giving ploughs the push

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1st July 2003