Oilseed Meals as Bioherbicides and Organic Fertilizers.

Oilseed crops are being widely evaluated for potential biodiesel production. Seed meal (SM) remaining after extracting oil may have use as a bioherbicide or organic fertilizer. Brassicaceae SM often contains glucosinolates that can hydrolyze into biologically active compounds. Jatropha curcas SM does not contain glucosinolates but contains curcin, a known phytotoxin (toxalbumin). A 14 d greenhouse study was conducted to determine how Sinapis alba (S. alba), Brassica juncea (B. juncea), Camelina sativa (C. sativa) and Jatropha curcas (J. curcas) applied to soil at varying application rates and incubation times affected seed germination and seedling survival of cotton [Gossypium hirsutum (L.)], sorghum [Sorghum bicolor (L.) Moench], Johnsongrass (Sorghum halepense), and Redroot pigweed (Amaranthus retroflexus). Seed meals applied at 0, 0.5%, 1.0% and 2.5% (w/w) were incubated in Darco fine sand soil for 1, 7 and 14 d prior to planting. A second greenhouse study was conducted to determine the availability of nutrients in SM (S. alba and B. juncea) for cotton and sorghum crops. With each weed species, germination and survival was most reduced by 2.5% S. alba SM incubated 1-d for Johnsongrass and 14 d for pigweed. Cotton and sorghum seedlings showed strong negative effects to S. alba SM applications of 2.5% at any incubation time. The nutrient uptake study included SM of S. alba and B. juncea applied at 1% and 2.5% and incubated for 56 days prior to planting. Nutrient uptake by cotton and sorghum was determined for SMs compared to inorganic nutrients. Results suggested that the type, rate, and timing of SM applications should be considered before land-applying SMs in organic cropping systems in order to successfully manage weeds while producing a profitable crop.