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The use of reclaimed water (RW) for irrigation alleviates agricultural water shortages. However, N 2 O 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 ( 15 N-labeled KNO 3 and (NH 4 ) 2 SO 4 ), and soil moisture contents at 40, 60, and 90 % water-filled pore space (WFPS) on N 2 O emissions and N fertilizer transformations in intact soil cores. The results showed that cumulative N 2 O emissions ranged from 3.78 to 36.30 mg N m −2 , and fertilizer-derived N 2 O losses accounted for 0.14-2.44 % of N fertilizers, while fertilizer-derived N residues (NO 3 − -N + NH 4 + -N) accounted for 10.16-26.95 % of N fertilizers. The N 2 O 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 N 2 O losses at 60 % WFPS in soils irrigated with RW were 10.26 % higher than those irrigated with FW. The N 2 O emissions and fertilizer-derived N 2 O losses in soils amended with (NH 4 ) 2 SO 4 at 40 and 60 % WFPS were significantly (26.61-178.84 %) larger than those amended with KNO 3 , while fertilizer-derived N residues in soils amended with KNO 3 were significantly (41.47 %) higher than those amended with (NH 4 ) 2 SO 4 . The N 2 O 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 N 2 O 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 KNO 3 can reduce N 2 O emissions and fertilizer-derived N 2 O losses, and correspondingly increase fertilizer-derived N residues, which can contribute to climate change mitigation.

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Reclaimed water is an alternative water source which could alleviate the shortage of water resources in agricultural systems. Many researchers have studied the effect of reclaimed water on soil environment, crop yield, etc. However, carbon sequestration in reclaimed water irrigated agricultural systems is less studied. This study investigates methane uptake and photosynthesis in reclaimed water irrigation systems contributing to carbon sequestration estimation and analyzes the important factors impacting them. The results show that CH4 uptake is related to soil water-filled pore space (WFPS) with a quadratic and it has the highest uptake when WFPS is between 40 and 50%. Long-term reclaimed water irrigation could significantly decrease (p < 0.05) CH4 uptake and macroaggregate stability in the topsoil. However, reclaimed water had no significant impact on photosynthesis in comparison. The type of fertilizer is an important factor which impacts CH4 emission from soil; urea had a lower CH4 uptake and a higher CO2 emission than slow-released fertilizer. Overall, reclaimed water irrigation could effectively decrease soil carbon sequestration. A soil wetted proportion level of 40–50% was recommended in this study for favorable methane oxidation. Slow-released fertilizer in reclaimed water irrigated agriculture could better control soil carbon emission and soil carbon absorption.