WEED-CONTROL IN SOYBEAN (GLYCINE-MAX) WITH GREEN MANURE CROPS

Greenhouse and field experiments were initiated to evaluate rapeseed a nd mustard species as green manure crops for weed suppression. Under g reenhouse conditions incorporating 20 g fresh wt leaf and stem tissue of rapeseed, two white mustards, and brown mustard into 450 g Sharpsbu rg, silty clay loam soil resulted in significant reductions in weed em ergence, biomass, and height. Kochia, shepherd's-purse, and green foxt ail emergences were reduced by all green manure crops. Redroot pigweed emergence was reduced by all green manure crops except brown mustard, and velvetleaf emergence was reduced by white mustards only. Kochia a nd shepherd's-purse fresh weights were reduced by all green manure cro ps, while redroot pigweed and velvetleaf fresh weights were reduced by brown mustard and white mustard var. Salvo. Green foxtail fresh weigh t was reduced by all green manure crops except rapeseed. With the exce ption of shepherd's-purse, no relationship between glucosinolate conte nt of the incorporated green manure and suppression of weed growth was found. Under field conditions, early spring-planted green manure crop s reduced early season weed biomass in soybean at one of the two locat ions. Mustard species as green manure crops reduced total weed biomass in soybean by 40% 4 weeks after emergence (WAE) and 49% 6 WAE. Soybea n biomass and yield were sometimes reduced by the incorporation of gre en manure crops in treatments containing weeds; however, hand-weeded p lots with green manure treatments yielded similar to hand-weeded plots without green manure.