Weed suppression in Vigna unguiculata with a spring-seeded brassicaceae green manure

A spring-seeded commercial blend of Brassica juncea L. and Sinapis alba L. was evaluated for biomass production, glucosinolate content, and weed suppression in Vigna unguiculata in Kibler, AR; Bixby, OK; and Pendleton, SC in 2003. Brassica biomass at termination prior to planting Vigna unguiculata was 272-752 g/m2. Total glucosinolate production at mechanical termination of the green manure ranged from 8600-26,700 μmol/m2. Glucosinolate production and type varied among locations, with the major glucosinolates in Brassica shoots being 2-propenyl and p-hydroxybenzyl. 2-Phenylethyl comprised 35-48% of the total glucosinolates in roots at each location. Weed suppression also varied across locations, with a high level of suppression at Pendleton only. At 8 weeks after planting Vigna unguiculata at Pendleton, weed biomass was 118 g/m2 in green manure plots compared with 413 g/m2 in non-amended plots. The weed suppression from the green manure at Pendleton improved Vigna unguiculata yields by an average of 415 kg/ha over non-amended plots. These results illustrate the potential for using Brassicaceae green manures as weed suppressants in Vigna unguiculata. However, reasons for variability in weed suppression and glucosinolate production among environments need further investigation before wide-spread adoption of this integrated weed management strategy.