Allelopathic effects of crops (sorghum, sunflower and brassica) on weeds, productivity and rhizosphere of mung bean (Vigna radiata L.)

Abstract

The present research work was conducted to evaluate the effect of allelopathic crops like sorghum (Sorghum bicolor L.), sunflower (Helianthus annuus L.) and brassica (Brassica compestris L.) on weeds, productivity and rhizosphere of mung bean during 2014 and 2015. Laboratory trials were conducted in Plant and Microbial Ecology Lab, Department of Agronomy, University of Agriculture, Faisalabad. Three sets of field experiments were conducted and repeated at Student Research Farm, Department of Agronomy, University of Agriculture, Faisalabad. In all three field experiments, crop water extracts (10 and 20 L ha-1) were foliar applied at 15 DAS and residues incorporation (4 and 6 tons ha-1) was done before sowing. Among all the treatments residue incorporation at 6 tons ha-1 showed the highest suppression of weed density, fresh and dry weight (sorghum; 62, 67, 65%, sunflower; 57, 66, 61% and brassica; 52, 61, 56% respectively). In case of soil properties significant improvement was observed by the application of crop residues at 6 tons ha-1 as compared with control. In all three field experiments maximum mung bean seed yield was improved (37%, 36% and 33%) by the application of sorghum, sunflower and brassica crop residues, respectively at 6 tons ha-1 as compared with control. Sorghum, sunflower and brassica residues incorporation at 6 tons ha-1 had higher net benefits (306, 339 and 347 $ ha-1, respectively) followed by 4 tons ha-1 during both years. In the fourth experiment the bacterial strains 4-17HM, C-14HM, C-17HM and 10-10M isolated from rhizosphere soil of mung bean which was amended by allelopathic crop water extracts and residues, showed the highest resistance against synthetic allelochemicals and allelopathic crop water extracts and the maximum nitrogen fixing, zinc and phosphate solubilization activity. So, the whole study was concluded that the residues incorporation of different allelopathic crops (sorghum, sunflower and brassica) was more effective than their water extracts application in weed suppression, improvement in soil health and productivity of mung bean. Application of crop residues at 6 tons ha-1 was the most effective and economical treatment with highest net benefit and marginal rate of returns. Due to their resistance and active role of bacterial strains in the rhizosphere, as nitrogen fixer, zinc and phosphate solubilizer, they could be applied with the allelopathic crop water extracts and residues to manage weeds and improve soil health.