MULCHES INCREASE YIELD AND IMPROVE WEED CONTROL IN NO-TILL ORGANIC BROCCOLI (BRASSICA OLERACEA VAR. BOTRYTIS)

Weeds are a major limiting factor in organic vegetable production systems. The objective of this study was to determine the effects of tillage, cover crop and mulch on weed control and yield of organic broccoli. The experiment was a split plot with four replications, where tillage (conventional or no-till) was the main plot, cover crop [pearl millet (Pennisetum glaucum), cowpea (Vigna unguiculata), or soybean (Glycine max)] was the subplot, and mulch (black plastic film, wheat straw and unmulched) was the sub-sub plot. The cover crops were sown in the summer of 2005 and the broccoli plants were grown in the spring of 2006. Weed control over the season was 84.8 and 71.6% for the conventional tillage and no-till, respectively. Among cover crops, pearl millet tended to provide the highest weed control. Wheat straw and plastic film mulch both had higher levels of weed control compared to unmulched soil. Broccoli top biomass was higher in conventional tillage than in no-till, was not affected by cover crop and was highest in plastic mulch and lowest in unmulched soil. The marketable and total number of florets was unaffected by tillage, cover crop and mulch. Marketable and total floret yields and individual floret weight were highest on wheat straw and lowest on unmulched soil, and were unaffected by tillage and cover crop. Weed control was probably the main factor that explained the increased yields of plants grown on mulches. In conclusion, although cover crops residue alone partially inhibited weed growth, use of mulches (wheat straw or plastic film mulch) in combination with cover crop residue provided the best weed control.