Aim: To elucidate the influence of non target Arbuscular Mycorrhizal (AM) fungi on glyphosate dissipation in okra cultivated sodic soil of Tamil Nadu. Methodology: A field experiment was carried out during Rabi 2017-18 to study the interactive effect of glyphosate and Arbuscular mycorrhizal fungi (AM) on glyphosate dissipation in sodic soil from okra (A. esculentus) grown field. Experiment was laid adopting Randomized Block Design (RBD) with different rates of glyphosate and with and without AM fungi. Glyphosate was applied as pre-plant herbicide 20 days before sowing, and AM biofertilizer was applied as basal before sowing of okra. Soil samples were collected from the field at different time interval after glyphosate application and analysed for glyphosate and Amino Methyl Phosphonic Acid (AMPA) residues. Results: Glyphosate persistence decreased with time and degraded with the mean half-life ranging from 5.09 to 10.35 days by following first order reaction kinetics. AMPA was witnessed from day 1 and increased up to 15th day and followed first order reaction kinetics dissipation with the mean half-life of 8.62 to 13.06 days. Glyphosate and AMPA residues were recorded below detection limit (0.01 mg kg-1) on 45th and 60th days, respectively, in soil. Interpretation: The higher rates of glyphosate showed enhanced persistence of glyphosate and its metabolite AMPA in soil, hence application of AM fungi 100 kg ha-1 with lower glyphosate rate of 6 ml/L can be recommended for okra cultivated sodic soil with the safer waiting period of after 45 days harvest.
Currently more than 20 per cent of the world's irrigated land is salt affected. Of that about 60 per cent are sodic soils, warranting attention for efficient, inexpensive and environmentally feasible amelioration. An incubation study was performed to study the influence of amendments on physico-chemical and biological properties of sodic soil. Gypsum + Green manure @ 6.5 t ha -1 , Distillery spentwash (DSW)@ 5 lakhs liter -1 , Green leaf manure (GLM) @ 12.5 t ha -1 were used as amendments for the reclamation of sodic soil by adopting standardized reclamation procedure. The results of the incubation study revealed that application of amendments decreased the pH of the soil. The pH declined from the initial level of 10.2 to 8.37, 8.42 and 9.21due to application of DSW, Gypsum + GM, and GLM respectively. Maximum reduction in soil pH was recorded in DSW applied treatments. The soluble salt concentration was found to be slightly increased in the DSW applied treatments, but the extent of increase was within the permissible limit (<4 dS m -1 ). Soil ESP was significantly reduced on reclamation to the level of 13.1, 13.5 and 24.2 per cent on account of application of DSW, Gypsum + GM, and Green leaf manure respectively from the initial level of 31.8 per cent with increased exchangeable Ca, Mg and K and reduced exchangeable Na content of the soil. The application of amendments significantly improved microbial population and soil enzyme activity of the soil in the order of DSW>Gypsum + GM>GLM>control.
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