Sensitivity of legumes and soil microorganisms to residue of herbicide mixture of atrazine and mesotrione

Mixing of herbicide compounds in one formulation is oneway to prevent weed resistance, but itmay increase herbicide persistence in the soil and cause eco-toxicity. The research was aimed to evaluate the sensitivity of legumes and the response of soil microorganisms to the residue of the herbicide mixture of atrazine and mesotrione. Herbicide mixture was applied on the soil surface in polybags at 0, 0.125, 0.25, 0.5, 1.0, and 2.0 x field rate (FR). Seeds of soybean, yard long bean, peanut, and mung bean were planted 2 weeks after herbicide application and grown in greenhouse for 4 weeks. Planting legumes was repeated in the same polybag at 8 and 14 weeks after herbicide application. The trials were arranged in a completely randomized design with three replications. Data observed were subjected to analysis of variance and means were further separated by LSD test (P ≤ 0.05). Harmful effects of herbicide residues on legumes seedlings identified ascrop injury (CI), decreased greenness level of leaves (GLL), and decreased dry biomass weight (DBW) were observed at 2 and 8 weeks after application. After 14 weeks, CI and decreased GLL wereevident only on soybean, but DBW of legume seedlings was remaining depressed. Similarly, a population of soil bacteria and fungi enumerated as colony forming unit (CFU) per gram of soil were inhibited up to 18 weeks. Efficacy of herbicide residues (EHR)counted as percent of reduction of DBW and CFU on legumes and microorganisms, respectively, were stronger by increasing the rates of herbicide applied andthe EHR persisted until 18 weeks after herbicide application.