An experiment was conducted to evaluate the effects of zero tillage and conventional tillage and amount of soybean residue on weed emergence and wheat yield at the University of Zimbabwe campus and farm. Conventional tillage significantly (P<0.05) reduced weed emergence when compared to zero tillage at the two sites. The distribution of weed seeds in the soil profile explained why more weeds emerged in the zero tillage treatment with 72, 23 and 5% of viable weed seeds found in the 0-5, 5-10 and 10-15cm soil layers, respectively, in the zero tillage treatment; this contrasted with almost equal distribution of viable weed seeds in the soil profile of the conventional tillage treatment. There was a significant soybean mulch x tillage interaction (P<0.05); soybean mulch significantly suppressed weed emergence in the zero tillage treatment but not under conventional tillage. Conventional tillage had significantly (P<0.05) higher wheat yield at the University of Zimbabwe campus where weed infestation was high; yield was similar under both tillage systems at the University of Zimbabwe farm where weed infestation was relatively lower. High weed pressure in the zero tillage treatment was responsible for the yield reduction at the University of Zimbabwe campus.
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