Influence of post emergence application of glyphosate on crop phytotoxicity and soil microbial status in transgenic maize

Abstract

Field experiments were conducted at Tamil Nadu Agricultural University, Coimbatore to study the weed and crop phytotoxicity and soil weed seed bank of transgenic stacked maize hybrids named Hishell and 900 M Gold and the treatments were, glyphosate as early post emergence application (POE) at 900, 1800 and 3600 g a.e ha-1 compared with non-transgenic counterpart maize hybrids applied with pre-emergence (PE) atrazine at 0.5 kg ha-1 followed by one hand weeding (HW) on 40 DAS and with and without insect management. The results revealed that the rate of phytotoxicity development and time to destruction of weeds was increased over the increase of glyphosate doses from 900 g a.e ha-1 to 3600 g a.e ha-1 without affecting the crop growth. Post emergence application of glyphosate at 900 and 1800 g a.e ha-1 in herbicide tolerant transgenic maize resulted in more number of bacteria, fungi and actinomycetes. Whereas, in higher dose (3600 g a.e ha-1) initial reduction of microbial population was observed and it recovered within 45 days after glyphosate spraying. PE application of atrazine exerted a significant detrimental effect on soil bacteria, fungi and actinomycetes and reduced the microbial count in herbicide treated plots upto 30 DAHS. Thereafter, microbial population started to recover slowly.