Effect of herbicides on soil microorganisms in direct-seeded rice

The use of herbicides in direct-seeded rice may affect the biological equilibrium of the soil and thus influence the nutrient status, health and productivity of the soil. To study the effect of herbicides on soil microbial population of direct-seeded rice, field experiment was conducted at Punjab Agricultural University, Ludhiana (Punjab) during Kharif 2009 and 2010. Sixteen weed control treatments, viz. pendimethalin 0.75, butachlor 1.50, thiobencarb 1.50, anilofos 0.375, pretilachlor 0.75, oxadiargyl 0.09 and pyrazosulfuron-ethyl 0.015 kg/ha applied as pre-emergence and each followed by bispyribac 0.025 kg/ha at 30 days after sowing; two hand weedings and unweeded control were tested. The results revealed that viable microbial population was influenced to varying degrees with different weed control treatments during both the years. The herbicides, viz. pendimethalin, butachlor, thiobencarb, anilofos, pretilachlor, oxadiargyl and pyrazosulfuron-ethyl as pre-emergence and bispyribac as post-emergence were safe for soil microbial populations at recommended rate.