Agronomic performance of wild mustard in an intercropping with green beans.

Abstract

Wild mustard (Brassica spp.) is used as an edible wild leafy vegetable by indigenous people in South Africa. The potential of wild leafy vegetables in agriculture is not well understood, because there is generally no agronomic research on their production practices. The objective of this study was to examine the performance of three wild mustard species (herein referred to as I, K and M) over four cropping seasons in an intercropping system with green beans (Phaseolus vulgaris L. cv. Imbali). The crops were grown with and without organic fertiliser under dryland conditions at two sites (The University of KwaZulu-Natal Research Farm, Ukulinga and in a rural area of Umbumbulu, KwaZulu-Natal within the farmers' locality) during autumn, winter, spring and summer of 2004 to 2005. Plant development (leaf number, plant height and fresh biomass) during the first six weeks after sowing and seed yield were used to determine agronomic performance of each species. Nutrient status of the rhizosphere soil was determined at 42 days after sowing for each species to determine what effect growing the species would have on mineral availability. Wild mustard production significantly (P < 0.01) performed better at Ukulinga than Umbumbulu. Polyculture was beneficial for wild mustard leaf accumulation and green bean production as determined by land equivalent ratios greater than one for all species combinations, regardless of fertiliser application. Cool environmental conditions occurring in autumn and spring were more favourable (P < 0.05) for wild mustard and green bean biomass accumulation than summer and winter conditions. However, wild mustard seed yield was highest in winter compared with autumn and spring, and there was no measurable seed production in summer. Soil analysis results at 42 days after sowing showed an increase in P, K, Cu and Mg in the rhizosphere of wild mustard without organic fertiliser. Polyculture improved Zn, Cu, Mn and K in wild mustard leaf tissue. It is concluded that wild mustard can be grown as a leafy vegetable throughout the year, but it requires cool environmental conditions to enhance seed yield. Species M significantly yielded better biomass and seeds than species I and K during all the seasons. However, species K performed the least in all aspects.