Cypermethrin persistence and soil properties as affected by long-term fertilizer management
AbstractLittle is known about the effects of long-term fertilization on pesticide persistence. A long-term field experiment was thus conducted to study the influence of fertilization on soil physicochemical properties, microbial biomass carbon, microbial quotient, enzyme activities, and cypermethrin dissipation. Five fertilization treatments were arranged: organic manure (OM), NPK fertilizer, PK fertilizer, NK fertilizer, and no fertilizer (control). Soil organic C, N, P contents and enzymatic activities were higher in soils with balanced fertilization as opposed to those with unbalanced fertilization, especially fertilization with organic manure. The longest half-life of cypermethrin was in the NK treatment (15.1 d), the least in the PK treatment (9.6 d). Pesticide dissipation in non-sterilized and sterilized soils showed that changes of cypermethrin persistence were caused by biodegradation. Soil N/P ratio (ratio of soil-available N to available P) and available N content positively correlated with half-life ( p< 0.05), and could limit cypermethrin dissipation greatly. These results indicate that in agricultural practice, oversupplying N should not be advocated. P application may be an efficient way to decrease N/P ratio and enhance cypermethrin dissipation in soil with high available N content. Based on a comprehensive consideration of soil fertility, crop yield, and environment, a mixed application of organic manure and inorganic fertilizers is recommended in the region, although balanced fertilization results in slower cypermethrin dissipation than does N-deficiency treatment.