An investigation of tillage systems and implement design for water conservation in semi arid conditions in Botswana

摘要

Botswana, as a semi arid country, is faced with serious shortage of moisturefor crop production. Its challenging climatic condition makes the little moisturereceived from summer rainfall insufficient. The development of appropriate tillage systems can assist with sustainable crop production. The aim of this project was to come up with a tillage system to improve the suitability of the physical conditions of soil for effective seeding in rain fed farming in Botswana. Strip, Reservoir (depression) and no tillage systems (control) were therefore investigated. Laboratory investigation of the tillage systems for soil water conservation and erosion was undertaken under different slopes (5 and 10°) and rainfall intensities (55 and 95 mm/hr). Energy requirements andwork rates of the systems were analysed. The results showed that slope has effects on the capability of strip tillage to harvest water from rainfall of low intensity. It managed to harvest 69.12% of rainfall from 55mm/hr rainfall at a slope of 5° whereas at 10°slope it harvested about 49%. The effects of slope were not significant for the reservoir tillage and no tillage systems. Under ahigher intensity rainfall of 95mm/hr the effects of slope were insignificant. Theonly source of variance was due soil disturbances and the strip soildisturbance performed better than the other treatments.When eroded soil was investigated under low intensity rainfall (55 mm/hr), there was no significant difference between strip and depression. Depression and strip soil disturbances reduced soil erosion similarly by 47 and 46 % respectively. Under high intensity rainfall eroded soil was still high under undisturbed soil disturbance. This is due to the fact that when the soil surface is bare, there is a higher risk of soil erosion. But when strips and depressionare created, the risk of soil erosion is localised especially at high rainfallintensities.The evaporation analysis showed no significant difference among the tillagesystems. This means that the power of water conservation in semi arid environment lies more on water harvesting than reduction of evaporation.The analysis of power and work rates showed big advantage of strip tillagesystem over reservoir tillage in the sense that it required less energy and power to complete a hectare of land. Its work rate is almost double of strip tillage.From the results it can be concluded that, at low slope and low rainfallintensity strip tillage harvest more water than reservoir tillage and zero tillagesystems. When slope is elevated there is no difference between strip andreservoir tillage. The strip tillage system harvest more water than bothreservoir tillage and zero tillage at high intensities. Strip and reservoir tillagereduce soil erosion similarly at both low rainfall and high rainfall intensity. Theenergy requirements and work rate were more positive for strip tillage thatreservoir tillage. Therefore with these results a conceptual design of striptillage system was developed.