Effects of imidacloprid and chlorpyrifos on transformation of urea nitrogen in soil

In order to assess the effects of pesticides on transformation of urea nitrogen in soil, indoor incubation experiments with 8 treatments including control, urea (200 mg/kg, a.i.,N dry soil), urea (200 mg/kg, a.i.,N dry soil)+imidacloprid (5, 10 and 50 mg/kg, a.i.,dry soil) and urea (200 mg/kg, a.i.,N dry soil)+chlorpyrifos (5, 10 and 50 mg/kg, a.i., dry soil) were investigated. The dynamic variations of NH4+-N, NO3-N and denitrification loss in soil were measured. Results showed that imidacloprid and chlorpyrifos had significant boost on the urea hydrolysis. Both imidacloprid and chlorpyrifos had positives effects on soil nitrification at 5 mg/kg treatment. The nitrification rate of the soil increased by 5.63 and 4.33 percent points, respectively, compared with which by urea treatment at the 8th day. When the concentration reached 10 mg/kg, imidacloprid had no effect on soil nitrification, but chlorpyrifos had negative effect; both of the two kinds of pesticides inhibit soil nitrification when the concentration reached 50 mg/kg. Compared with urea treatment, the nitrification rate of the soil decreased by 5.18 and 8.69 percentage points, respectively at the 8th day. The imidacloprid application significantly decreased the nitrogen loss of soil denitrification (P<0.01), compared with urea treatment. The 3 concentration treatments reduced denitrification loss of 36.98%, 39.92% and 68.54%, respectively. The chlorpyrifos had no effect on soil denitrification at 5 and 10 mg/kg concentration treatments but showed significant negative effect at 50 mg/kg, reducing denitrification loss of 39.69%.