Herbicide-Mediated Effects on Soil Microbes, Enzymes and Yield in Direct Sown Rice

An investigation was undertaken to study the response of soil microbes, soil enzymes and yield of wet direct sown rice on application of different herbicide mixtures for controlling weeds. The treatments consisted of nine different combinations of herbicides involving azimsulfuron, bispyribac sodium, flucetosulfuron, penoxsulam, cyhalofop-butyl, fenoxaprop-p-ethyl, ethoxysulfuron, XR-848 benzyl ester, bensulfuron methyl and pretilachlor, with a herbicide check and two controls. Soil enzymes, viz. fluorescein diacetate hydrolase, dehydrogenase, urease, acid and alkaline phosphatase, and population of soil microbes, viz. bacteria, fungi, actinomycetes, diazotrophs, phosphate-solubilizing bacteria and Pseudomonas, were studied. Fenoxaprop-p-ethyl + ethoxysulfuron recorded the highest populations (86.07 × 106 cfu/g soil) among all herbicidal treatments at 10 DAHA, while flucetosulfuron + bispyribac sodium recorded the highest population at 30 DAHA (116.40 × 106 cfu/g soil). Also flucetosulfuron + bispyribac registered the highest PSB population (119.40 × 103 cfu/g soil and 178.98 × 103 cfu/g soil) and actinomycetes population (134. 4 × 104 cfu/g soil and 174.97 × 104 cfu/g soil) at both 10 DAHA and 30 DAHA. Application of XR-848 benzyl ester + cyhalofop-butyl and flucetosulfuron + bispyribac sodium recorded the highest soil microbial activity. Among herbicidal treatments, fenoxaprop-p-ethyl + ethoxysulfuron recorded the highest yield of 4.88 t/ha; however, it was at par with penoxsulam + cyhalofop-butyl (4.75 t/ha), azimsulfuron + bispyribac sodium (4.68 t/ha), flucetosulfuron + bispyribac sodium (4.57 t/ha) and bispyribac sodium + ethoxysulfuron (4.46 t/ha). Considering the response of soil microbial activity and the grain yield of rice, flucetosulfuron + bispyribac sodium may be recommended in direct sown rice.