Effects of long-term fertilization on the transformation of cypermethrin in soils

A long-term field experiment was conducted to study the influence of fertilization on cypermethrin persistence. Five fertilization treatments were arranged: organic manure(OM), NPK fertilizer, PK fertilizer, NK fertilizer and no fertilizer(CK). Transformation rates were determined by cypermethrin residues and its metabolite 3-phenoxybenzoic acid formation in soils. Results show that cypermethrin transformation varies significantly in soils with different fertilization treatments. Pesticide dissipates fast in PK and CK treatments and the lowest in NK treatment. The DT50 values(disappearance time of 50% of the initial concentration) are 9.6 days, 10.7 days and 15.1 days respectively. Transformation rate is higher in OM treatment than that in NPK treatment, but can not reach the significant level. The DT50 value is 10.8 days in OM treatment and 11.8 days in NPK treatment. Soil available nitrogen content is significantly positively correlated with DT50(p<0.05). Long-term unbalance fertilization with nitrogen can increase soil available nitrogen content, which in turn inhibited the dissipation of cypermethrin. Reduced transformation in OM and NPK treatments may be attributed to the high organic matter content, which can increase the adsorption of cypermethrin in soils.