Persistence of Herbicides in Rice–Maize Cropping System in Telengana and Andhra Pradesh

Abstract

A long-term field experiment was conducted at Hyderabad during 2008–2013 in rice–zero tillage maize system to study the persistence of herbicides in crops, soils and also to assess the impact of herbicides on soil properties. Butachlor was applied to transplanted rice as pre-emergence herbicide at 1.0 kg/ha at 3 days after transplanting and cyhalofop-P-butyl was applied as post-emergence herbicide at 20 days after transplanting at 100 g/ha. In maize, atrazine was applied as pre-emergence herbicide at 1.0 kg/ha. The herbicide residues were estimated in soil at 0, 15, 30, 45 days after application and at harvest. Soil properties (pH, EC, organic C, cation exchange capacity, texture, available N, P and K) were analyzed using standard procedures. Application of butachlor and cyhalofop-P-butyl to the rice crop or atrazine to zero-till maize did not cause any significant change in physico-chemical properties of the soil. There was no effect of butachlor or cyhalofop-p-butyl on the rotational zero-till maize crops germination, growth and yield. Growth of the rice seedlings was not affected by the atrazine residues and no herbicide phytotoxicity symptoms were observed in the rice crop. Butachlor and cyhalofop residues persisted in the soil up to 30 days after application, beyond which, the concentration of both herbicides was below the detection limits (0.025 mg/kg). The herbicide residues in grain and straw were found below the detection limit. Atrazine persisted in the soil up to 45 days and the residues in soil were found below the detection limit at 60 days and at harvest. In maize grain and straw, the atrazine residues were below the detection limit throughout the period of study.