on only 4% slope land. Section b) of Chart 2 shows how, with less or no tillage, machinery was able to go into the field and work, much sooner following a storm, while at the same time much more rain water infiltrated into the soil for the less-tillage case. It is common knowledge that machinery can be highly destructive of soil structure when used especially under soil conditions that are beyond the liquid limit.
2.5 Regional efforts towards conservation tillage and case studies
There have been several concentrated efforts towards eventual introduction of conservation tillage at farm level in the SSA region. These efforts have been in research stations and institutions while more recently, and on some cases they are reported to have moved to the farmers farms, adopting more participatory approaches. The efforts have seen various degrees of success. In turn the efforts have taken various forms of localized and national ventures with minimal regional integration for dissemination. Duplication of efforts has not been absent.
Work carried out in introducing conservation tillage research and management at both stations and farms includes that by: International
Institute of Tropical Agriculture (IITA) in Ibadan, Nigeria; International Centre for Research in Semi-arid Tropics (ICRISAT) Sahelian Centre, Niamey, Niger; Zimbabwe's Agricultural and Technology Extension Services (AGRITEX) in collaboration with various European institutions such as Silsoe Research Institute; works of Kenya Agricultural Institute (KARI) and Regional Land Management Unit (RELMA), formerly Regional Soil Conservation Unit (RSCU) in Kenya, the Palabana, Zambia work on CONTIL equipment, the Improved Maresha prototype Contil project by University of Nairobi and Swedish University of Agricultural Sciences (Gebresenbet and Kaumbutho, 1997) among others.
At an FAO/FARMESA led meeting in Harare (June, 1998), the idea of forming a regional network on Contil was floated and intensely discussed. Where Contil studies have persisted in the ESA region and even better, gone from the research station to the farmers' fields, real progress has been recorded although mass adoption of technologies is yet to follow. Various technological advances have been made, with greatest impact where introduction of equipment has been backed by multi-disciplinary research teams looking at:
Box 4: Striking the balance
Although a comparatively large amount of research and development work has gone into various conservation tillage systems in Zimbabwe, farmers in both large and small scale sectors have been slow to adopt them. This reluctance can be attributed primarily to conservatism, rather than to technical or socio-economic factors, though the latter obviously play a part. It must be recognised that none of the currently available conservation tillage techniques are truly sustainable in terms of preserving soil, rainwater, nutrients, soil structure and the ecosystem. Nevertheless, some hesitant steps have been taken locally to reduce the environmental damage resulting from annual ploughing combined with mono-cropping and over-reliance on chemicals. Tine planting into residues has the potential to reduce losses of soil, rainwater and nutrients to levels close to sustainable ones, and significant improvements in soil structure have been recorded under this treatment; but the technology still depends on large inputs of chemicals and has been tested for only a limited number of crop rotations. The locally developed system called no-till tied-ridging is particularly suited to the communal areas as hardy residues are recommended to be fed to the cattle and would be a hindrance in land preparation if left on the surface. Losses of soil, rain and nutrients are reduced to very low levels under this system but no significant improvement in soil structure has been recorded. The experiment no-till strip-cropping system is the closest approximation to a sustainable low-external-input system yet devised locally. Negligible soil, rainwater and nutrient losses have been recorded with soil structure being maintained at levels similar to virgin ground.
Tillage increases water holding and transmitting properties of the soil. The more open the tillage- induced structure the greater are these increases. However, at high rainfall intensities the effect of tillage in enhancing these properties is undermined by the structural breakdown of the surface layer which results in greatly reduced water intake rates. The finer the tillage-induced surface structure, the more vulnerable it is to structural damage. The effect of tillage on evaporation depends on the surface structure and the level of atmospheric demand. At lower evaporation demands rougher than smoother surfaces. However, at high evaporativities, tillage tends to induce more evaporation losses. It appears that the argument that tillage reduces evaporation losses through the “soil mulch” theory tends to hold at relatively low evaporativities.
This paper is published in: Kaumbutho P G and Simalenga T E (eds), 1999. Conservation tillage with animal traction. A resource book of the
Animal Traction Network for Eastern and Southern Africa (ATNESA). Harare. Zimbabwe. 173p. A publication supported by French Cooperation, Namibia. For details of ATNESA and its resource publications, see http://www.atnesa.org