Evaluation of Three Animal Powered Weeding Implements in Cotton Based Systems of the Zambezi Valley in Zimbabwe.
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This thesis reports the results of a survey carried out in Muzarabani, through use of a questionnaire administered to a total of 83 farmers in Gutsa, Muringazuva, Mfudzi and Kapembere villages to determine the condition of animal powered implements. It also assesses the performance of three animal powered mechanical weeding implements using the mother-baby approach through various options for land preparation, crop establishment and weed management. The assessments were done during the 2000/01 and 2001/02 seasons. The thesis concludes by discussing the merits and demerits of using the different weeding options. Mould board ploughs (OP+Ds) and cultivators (OCs) were generally found to be in a condition average to good as most farmers interviewed had fairly new implements (less than 6 years). More than 50% of the OP+Ds had their hitch assembly removed and cultivators had the two front tines removed. About 40% of OP+Ds had worn out landsides, shares, regulator hakes, wheels and wheel axles while between 30-45% OCs had worn out wheels and axles. More than 80% of farmers rarely replaced their draw bar hitch assembly, frog, regulator hakes, u-piece and screw, u-clamp, plough handles and stays. Only 16-22% of farmers claimed that they replaced the wheel axles, wheels and tines once in three years in cultivators. The rest of the parts for the OCs were rarely replaced. Most farmers (63%) were not aware of the depth of cut adjustment options in cultivators like positioning the wheel arms and adjusting the length of the chain. The use of winter followed by spring ploughing (wp + sp) resulted in reduced subsequent, draft force requirements, supplementary hand weeding requirements and weed density. At the same time wp + sp increased work rates, field efficiency, soil moisture retention levels throughout the season. When practised, it resulted in a better crop stand and increased cotton yield by 33% compared to spring ploughing only. There was no significant difference between using the open plough furrow planting technique and the ripper tine for crop establishment for the various parameters looked at. The use of an OC for weed control resulted in significantly (P<0.001) more draft force requirements than the mould board plough with mould board (OP+D) or without (OP-D). The use of OC in some instances resulted in draft capabilities greater than 12% of the body weight of draft animals, which is considered to be higher than what a span of oxen can comfortably pull for a working day. However, it was noted that the OC had significantly (P<0.001) higher field efficiency of more than 90% compared to OP+D and OP-D of less than 70%. The use of OP + D resulted in significantly (P<0.001) higher weeding efficiency and soil moisture retention at 6 and 9 weeks after crop emergence (wace) while the OC gave the least. The use of the different weeding implements did not result in a significant yield variation, but carrying out winter ploughing in addition to spring ploughing resulted in significantly (P<0.05) higher yields than spring ploughing only. The economic studies revealed that the cost of banded pre-emergence herbicide was lower than the supplementary hand weeding cost. In a season with good rainfall pattern (2000/2001) of at least 450mm distributed over 4 months the additional cost incurred in winter ploughing for wp + sp portions was easily offset by the increase in cotton yield. At the same time in a drought/bad season (2001/2002) though with 540mm of rainfall poorly distributed over 2 ½ months the additional cost incurred in winter ploughing for wp + sp portions was lower than the increase in cotton yield. The study also showed that the highest returns to labour are obtained by using OP+D whilst the lowest overall weeding cost and greatest productivity is achieved with OC, in both cases with a band application of pre-emergence herbicide.