In-vitro evaluation of rice and wheat straw biochars’ effect on pyrazosulfuron-ethyl degradation and microbial activity in rice-planted soil

A pot-culture evaluation of 0.5% wheat (WBC600) and rice straw (RBC600) biochar amendments on degradation of pyrazosulfuron-ethyl (PYRAZO) in rice-planted sandy loam soil was undertaken. Results suggest that PYRAZO and its metabolites persisted for longer in biochar-amended soils and degradation followed biphasic dissipation. Three metabolites of PYRAZO viz. 5-(aminosulfonyl)-1-methyl-1 H-pyrazole-4-carboxylic acid, ethyl 5-(aminosulfonyl)-1-methyl-1 H-pyrazol-4-carboxylate and 2-amino-4,6-dimethoxy pyrimidine (AP) were detected in soil. There was no significant difference in the amounts of metabolites recovered from no-biochar and biochar-amended soils except the metabolite AP, which was less persistent in the biochar-amended soils. The half-life of pyrazosulfuronethyl residues (calculated using amount of parent PYRAZO and persistent AP metabolites) during the first and second phase in the no-biochar control, 0.5% WBC600 and 0.5% RBC600 treatments were 4.7 and 9.2, 5.8 and 12.6, and 7.0 and 14.5 days respectively. Biochars did not have any inhibitory effect on the soil microbial biomass, soil dehydrogenase, fluorescein diacetate and acid/alkaline phosphatase activity, but slightly increased microbial biomass carbon content. This study suggests that even at 0.5% dose the rice and wheat biochars had a marginal effect on persistence of PYRAZO residues, thus, agronomic application of these biochars can be suggested.