Rhizosphere effect of herbicides on nitrogen fixing bacteria in relation to availability of nitrogen in rice soil

A field experiment was conducted with four herbicides viz. butachlor [N-(butoxymethyl)-2-chloro-2´,6´-diethyl-acetanilide], fluchloralin [N-(2-chloroethyl)-2-6-dinitro-N-propyl-4-trifluoromethyl) aniline], oxadiazon [5-terbutyl-3-(2, 4-dichloro-5-isopropoxyphenyl)-1, 3, 4-oxadiazol-2-one] and oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenyl)-4-(trifluoromethyl) benzene] at rates of 2.0, 1.5, 0.4 and 0.12 kg a.i. ha⁻¹, respectively, to investigate their effects on the growth and activities of non-symbiotic N2fixing bacteria in relation to mineralization and availability of nitrogen in the rhizosphere soil as well as yield of the rice crop (Oryza sativa L. variety IR-36). Application of herbicides stimulated the population and activities of non-symbiotic N2-fixing bacteria, mineralization of total nitrogen and availability of inorganic nitrogen in the rhizosphere soil resulting in greater yield of the crop. Among the herbicides oxyfluorfen was more stimulative followed by fluchloralin and butachlor. Oxadiazon also highly accentuated the mineralization and availability of nitrogen in the rhizosphere soil. The yield of the crop was significantly increased due to the application of oxyfluorfen and fluchloralin.