Impact of glyphosate and chlorpyriphos on chemical and biological properties of a lateritic soil

The impact of glyphosate and chlorpyriphos on the non-target organisms in the soil namely, earthworms, bacteria, fungi and the major chemical properties of the soil is reported. Laboratory studies were conducted in plastic containers(earthworm avoidance test) and in pots filled with lateritic soil and field studies in the banana ratoon plots and established lawns. Maximum avoidance by earthworms and micro flora was observed with the application of Roundup 12 mL L⁻¹ followed by Glycel 12 mL L⁻¹ and Dursban 8 mL L⁻¹. In pot culture study, neither glyphosate nor chlorpyriphos at recommended doses had deleterious effect on the multiplication of earthworms. However, both fungal and bacterial populations in soil were temporarily affected. Higher concentration of Roundup (12 mL L⁻¹) showed the maximum decline whereas Glycel at lower concentration showed the minimal decline at both sampling intervals. In the field study, application of glyphosate caused short term inhibitory effect on soil fungi up to 30 days of application. Soil bacteria count and dehydrogenase enzyme activity were unaffected by glyphosate application. Application of chlorpyriphos in lawn caused a short term inhibitory effect on soil bacteria (at 30 DAS) but no effect was observed on soil fungi and dehydrogenase activity. Application of glyphosate in the banana field and chlorpyriphos in lawns did not produce any significant effect on chemical characteristics of the soil namely pH, organic carbon and available nutrients.