with respect to rainfall was most important, more so for farmers who relied on contract cultivation. It was shown that even with optimum soil moisture conditions at sowing, subsequent conditions, if hot and dry, still reduced establishment. Seed soaking was shown to be one method of speeding up early growth and enhancing establishment and merits further investigation.
Agro-climatology studies were also conducted to provide an understanding of the spatial temporal variability of rainfall. While large differences in seasonal rainfall were evident between sites, the differences between years at a given site were much greater.
Among other points, the study concluded that:
Net runoff losses from cultivated fields were small and inconsequential in comparison with the effects on crops of inefficient management.
Runoff losses could be substantial from rangeland with sparse vegetation cover. Grazing could be managed to minimise runoff or to maximise runoff for use in a downslope crop area. The latter would however degrade the land.
Redistribution of rainfall within fields as a result of widespread micro-topography was a far more serious problem for arable agriculture. Large asymmetries in the system had important consequences for crop production because they reduced the level of control exercised by farmers over their operations.
Systematic variations in the micro- topography were associated with termite activity. These formed an environmental mosaic with large interactions between surface water mobility, available water- holding capacity, fertility and the destructive habits of the termites themselves. The system was extremely dynamic and relative cropping outcomes depended on a further interaction between rainfall pattern and sowing date.
Soils varied widely in the major components of available water holding capacity influenced by depth and texture. This variation was loosely correlated with position in the landscape, but also influenced by the nature of parent material.
Current cropping strategies involved minimal inputs by farmers who perceived arable farming to be a high-risk occupation. Crop production was not viewed as a high priority. Such an outlook was possible in
Botswana because the buoyant economy offered alternative sources of income.
Levels of land management and crop husbandry were very low. Consequently, production was “sustainable” because off- takes were small. Improved management, which was a prerequisite for improving crop yields needed to be addressed.
Working at Makoholi Experiment Station in semi-arid Zimbabwe Mashavira et al. (1997) described yield responses of commercial cotton to reduced tillage systems and the evaluation of innovative combinations of low-input tillage and weeding systems. The tillage practices adapted farmer practices and implements that were available to the communal area farmer, namely the mouldboard plough and the five-tine cultivator and ripper tine for maize production.
They concluded that open plough furrow planting (OPFP) with an ox-plough and ripping a planting line to a depth of 30 cm offered alternative crop establishment options that could be successfully implemented on ploughed or fallowed (reduced tillage) land without any yield reduction. In fact, for the scenarios they described, maize yield increased between 20 and 300% over hand planting. Although ripping to 30 cm required more labour than OPFP, the grain yield returns more than compensated.
Adding efficiency to current animal traction systems
Mbanje (1997) analyzed implement and selection factors with an aim of achieving practical opportunities to reduce draft demand. He did this by exploiting ways of having a multi- operation single pass, correct implement adjustment for right orientation, whereby, orientation referred to the position of implement in relation to the direction of movement of work animals (Gebresenbet, 1991). Other factors considered were ploughing speed and equipment hitching and harnessing, maintenance, and cleaning. Soil factors were such as choosing when and how to plough.
Caring for the soil, involved the way it was cultivated and the nutrients that were added to it. For example, addition of manure and organic matter helped reduce draught demand. The author however did not reach any quantifiable gains and recommended further work on this, much neglected subject of efficient tillage and use of animal traction.
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