Influence of Various Agrochemicals on Dynamics of Applied Urea-Nitrogen in Flooded Soils

摘要

Laboratory incubation experiments were conducted to study kinetics and regulation of nitrification in moist aerobic soils and nitrate disappearance from the soils on subsequent submergence, simulating the conditions of aerobic-anaerobic sequence prevailing in the rainfed lowland rice ecosystem. A separate laboratory study was also conducted to evaluate the inhibitory effect of different agrochemicals on enzymatic hydrolysis of urea in aqueous solutions. Results revealed that the rate of nitrificationof applied urea in moist aerobic soil i.e. at 60% water holding capacity (WHC) was slow up to 14 days of incubation after which it sharply increased. The extent of nitrification was higher in laterite soil than in alluvial soil during the initial periodof 3-4 weeks of incubation. Between two nitrification regulators, hydroquinone (HQ) was significantly more effective in inhibiting the nitrification than nimin, the efficacy of HQ being higher in alluvial soil than in laterite soil. Nitrate disappearance from soil on flooding followed first order reaction kinetics with the rate constants varying from 0.049 to 0.064 d~(-1) and the half life from 10.8 to 14.1 days. Among several agro-chemicals and other chemicals screened, HQ at a concentration of l mg L~(-1)and copper sulphate and N (n-butyl) thiophosphoric triamide (NBPT) at a concentration of 100 mg L~(-1) inhibited enzymatic hydrolysis of urea, the extent of inhibition being 92.0, 79.8 and 60.2%, respectively.