Comparative Efficacy of White Mustard (<i>Sinapis alba</i>L.) and Soybean (<i>Glycine max</i>L. Merr.) Seed Meals as Bioherbicides in Organic Broccoli (<i>Brassica oleracea</i>Var. Botrytis) and Spinach (<i>Spinacea oleracea</i>) Production

Abstract

White mustard and soybean seed meals were compared for weed control and yield of organically grown broccoli and spinach. The meals were incorporated into the soil 2 weeks before crop planting at two rates (1.24 and 4.48 t ha−1). Weed densities and hand-weeding time were recorded twice during the growing seasons and weed biomass was measured at crop harvest. Compared to the 1.24 t ha−1 soybean treatment, weed densities were 52 to 95% and 41 to 45% less at 3 and 6 weeks after planting, respectively, in both crops with the 4.48 t ha−1 white mustard seed meal treatment. Time required for hand weeding at these times was also reduced by up to 82% and 48%, respectively. Broccoli yield was similar in all the treatments, but spinach yield was greatest in the 4.48 t ha−1 treatments for both seed meals. Petiole nitrate and nutrient concentrations in both crops were generally similar in all the treatments.