Effects of Brassicaceae Seed Meal-Amended Soil On Germination and Growth of Weed Seeds.

The need for sustainable agricultural production systems has generated demand for effective non-synthetic alternative weed control strategies.  For some vegetable crops there are few herbicide options available, and there is little prospect of new herbicides being registered for vegetable crops.  Brassicaceae seed meal, a residue product of the seed oil extraction process, can provide a resource for supplemental nutrients, disease control and weed suppression.  The objective of this study was to evaluate the effect of different Brassicaceae seed meals and application rates on the emergence of wild oat, Italian rye grass, prickly lettuce and pigweed which are some of the major weeds in vegetable production systems.  Sinapis alba ‘IdaGold’,  Brassica juncea ‘Pacific Gold’ and Brassica napus ‘Dwarf Essex’ seed meals were used with or without a functional myrosinase  enzyme.  Seed meal amendments reduced weed seedling emergence by between 7-19%, 15-22%, 50-65% and 50-64% in Italian rye grass, wild oat, prickly lettuce and pigweed, respectively, at application rates of 1-2 Mt ha^-1. Dry weed biomass was reduced by between 55-77% and 63-79% for prickly lettuce and pigweed, respectively, at seed meal application rates of 1-2 Mt ha^-1.  Intact S. alba seed meals applied at a rate of 2 Mt ha^-1 significantly reduced weed seedling emergence and weed dry biomass compared to intact B. napus seed meal amended treatments.  B. juncea showed significantly better herbicidal efficacy on the grassy weeds than S. alba which was most effective in controlling broadleaf weeds.   In all instances, a 1 Mt ha^-1 application rate of either B. juncea or S. alba exhibited greater herbicidal effect relative to a 2 Mt ha^-1 application rate of B. napus seed meal.  These results demonstrate that all glucosinolates are not equal in herbicidal effects.  The herbicidal effects of the mustard seed meal could offer vegetable growers a new option for weed control, particularly in organic production systems.  In a real life practical situation it would perhaps seem feasible to treat soils with a blend of B. juncea and S. alba seed meals so that both grassy and broad leaved weeds can be effectively controlled.