Kinetics and isotherm modeling of azoxystrobin and imidacloprid retention in biomixtures

Linear and Nonlinear Isotherm Models and Error Analysis for the Sorption of Kresoxim-Methyl in Agricultural Soils of India

Kresoxim methyl sorption in soils of five agro-climatic zones of India varied from 41.6% to 84.7%. Highest sorption was recorded in organic carbon rich Almora soil. Isotherm parameters for linear and non-linear Freundlich and Temkin models were almost same, whereas Langmuir parameter Q₀, for linear (1.60 to 9.434 μg g^-1) and non-linear (8.48 to 17.129 μg g^-1) models were quite different. For isotherms optimization different error functions such as sum of squares error (SSE), root mean square error (RMSE), Chi square error, hybrid fractional error (HYBRID) and average relative error (ARE) were calculated. Lowest error function values were obtained for Freundlich isotherm in all the soils except inceptisol (Kolkata) for which Langmuir isotherm gave the best fit. Statistical analysis using SAS 9.3 software and Tukey's HSD test revealed the significant effect (p < 0.001) of soil type on sorption. Sorption correlated positively with the organic carbon and clay contents of the soil.

Parameters affecting azoxystrobin and imidacloprid degradation in biobed substrates in the North Indian tropical environment

This study reports degradation of azoxystrobin (AZOXY) and imidacloprid (IMIDA) in the rice straw (RS)/corn cob (CC) and peat (P)/compost (C)-based biomixtures. The effect of biomixture preconditioning (10 days incubation prior to pesticide application), pesticide concentration and moisture content was evaluated. Results suggested that conditioning of biomixture greatly affected IMIDA degradation where half-life (t_1/2) was reduced by 5-9 times. This was attributed to higher microbial biomass carbon content and dehydrogenase activity in the conditioned biomixtures. Pesticide application in the conditioned biomixture did not show any negative impact on soil microbial parameters. Both pesticides degraded at faster rate in the rice straw-based biomixtures than in the corn cob-based biomixtures. Degradation slowed down with increase in initial concentration of pesticides in biomixture and 1.6-3.0 (AZOXY) and 2.4-3.6 (IMIDA) times increase in t_1/2 values was observed. The moisture content of biomixture showed positive effect on degradation which increased when moisture content was increased from 60 to 80% water holding capacity. The effect was significant for IMIDA degradation in the corn cob-based biomixtures and AZOXY degradation in the peat biomixtures. The rice straw-based biomixtures were better in degrading AZOXY and IMIDA and can be used in biopurification systems.