Effect of density and time of growth suppression of cowpea on weed management in sorghum

In order to study the effect of living mulch on cowpea weed management in sorghum, a factorial experiment was carried out in the research farm of Islamic Azad University, Karaj Branch based on randomized complete block design with three replications. First factor was density of cowpea on three levels, optimum density (160,000 plants per hectare), 33% and 66% more than optimum density. The second factor was time of suppression of growth of cowpea in four levels, 6, 8, 10 and 12 leaves stages of sorghum(using herbicide 2,4-D) plus control treatment(weed free). Weight of weeds in the first and second harvests was measured. The result of ANOVA showed that effect of cowpea density and suppression time of cowpea growth on total dry weight of weeds was significant in both harvests. The interactions between density and suppression time of cowpea growth on total weight of weeds were not significant in first sorghum harvest but were significant in second harvest. Results of mean comparison showed that cowpea density of 66% more than optimum, has the lowest total dry weight of weeds in the first and second harvests. The result of suppression time of cowpea growth showed that the best time in terms of decreasing dry weight of weeds is until 10 leaves stage of sorghum for both first and second harvests. The interactions between density and suppression time of cowpea growth showed that lowest total dry weight of weeds is in the cowpea density of 66% more than optimum and until 10 leaves stage of sorghum. Therefore, if cowpea with plant population of about 260,000 per hectare is used as cover crop, and then converted to mulch at 10 leave stage of sorghum, it can be effective in the integrated weed management system.