Nitrapyrin addition mitigates nitrous oxide emissions and raises nitrogen use efficiency in plastic-film-mulched drip-fertigated cotton field

Nitrification inhibitors (NIs) have been used extensively to reduce nitrogen losses and increase crop nitrogen nutrition. However, information is still scant regarding the influence of NIs on nitrogen transformation, nitrous oxide (N(2)O) emission and nitrogen utilization in plastic-film-mulched calcareous soil under high frequency drip-fertigated condition. Therefore, a field trial was conducted to evaluate the effect of nitrapyrin (2-chloro-6-(trichloromethyl)-pyridine) on soil mineral nitrogen (N) transformation, N(2)O emission and nitrogen use efficiency (NUE) in a drip-fertigated cotton-growing calcareous field. Three treatments were established: control (no N fertilizer), urea (225 kg N ha(-1)) and urea+nitrapyrin (225 kg N ha(-1)+2.25 kg nitrapyrin ha(-1)). Compared with urea alone, urea plus nitrapyrin decreased the average N(2)O emission fluxes by 6.6–21.8% in June, July and August significantly in a drip-fertigation cycle. Urea application increased the seasonal cumulative N(2)O emission by 2.4 kg N ha(-1) compared with control, and nitrapyrin addition significantly mitigated the seasonal N(2)O emission by 14.3% compared with urea only. During the main growing season, the average soil ammonium nitrogen (NH(4)(+)-N) concentration was 28.0% greater and soil nitrate nitrogen (NO(3)(-)-N) concentration was 13.8% less in the urea+nitrapyrin treatment than in the urea treatment. Soil NO(3)(-)-N and water-filled pore space (WFPS) were more closely correlated than soil NH(4)(+)-N with soil N(2)O fluxes under drip-fertigated condition (P<0.001). Compared with urea alone, urea plus nitrapyrin reduced the seasonal N(2)O emission factor (EF) by 32.4% while increasing nitrogen use efficiency by 10.7%. The results demonstrated that nitrapyrin addition significantly inhibited soil nitrification and maintained more NH(4)(+)-N in soil, mitigated N(2)O losses and improved nitrogen use efficiency in plastic-film-mulched calcareous soil under high frequency drip-fertigated condition.