Effects of Different Irrigation Water Types, N Fertilizer Types, and Soil Moisture Contents on N2O Emissions and N Fertilizer Transformations in Soils

Abstract

The use of reclaimed water (RW) for irrigation alleviates agricultural water shortages. However, N2O emissions and N fertilizer transformations in soils irrigated with RW under different N fertilizer types and soil moisture contents are poorly understood. A 216-h laboratory incubation experiment was conducted to evaluate the effects of irrigation water types (RW and fresh water, FW), N fertilizer types (15N-labeled KNO3 and (NH4)2SO4), and soil moisture contents at 40, 60, and 90 % water-filled pore space (WFPS) on N2O emissions and N fertilizer transformations in intact soil cores. The results showed that cumulative N2O emissions ranged from 3.78 to 36.30 mg N m−2, and fertilizer-derived N2O losses accounted for 0.14–2.44 % of N fertilizers, while fertilizer-derived N residues (NO3 −-N + NH4 +-N) accounted for 10.16–26.95 % of N fertilizers. The N2O emissions at 40 % WFPS and fertilizer-derived N residues at 60 % WFPS in soils irrigated with RW were significantly (10.98 and 20.95 %, respectively) higher than those irrigated with FW, while fertilizer-derived N2O losses at 60 % WFPS in soils irrigated with RW were 10.26 % higher than those irrigated with FW. The N2O emissions and fertilizer-derived N2O losses in soils amended with (NH4)2SO4 at 40 and 60 % WFPS were significantly (26.61–178.84 %) larger than those amended with KNO3, while fertilizer-derived N residues in soils amended with KNO3 were significantly (41.47 %) higher than those amended with (NH4)2SO4. The N2O emissions significantly increased with increasing soil moisture content. Our results indicate that N fertilizer types and soil moisture contents are the two important factors regulating N2O emissions and N fertilizer transformations. When RW irrigation is used, controlling soil moisture contents within 41 and 60 % WFPS (the optimum is 46 % WFPS) and application of KNO3 can reduce N2O emissions and fertilizer-derived N2O losses, and correspondingly increase fertilizer-derived N residues, which can contribute to climate change mitigation.