Drip irrigation affects N2O emission differently depending on soil moisture status in an intensive vegetable production system

Plastic-shed vegetable production system is becoming the main type of vegetable production in China, while excessive irrigation and fertilization input lead to significant N loss by leaching, runoff, and gaseous N. The current study established a field experiment to investigate the effects of drip irrigation and optimized fertilization on vegetable yield, water and fertilizer efficiencies and N₂O emission in a typical intensive plastic-shed tomato production region of China. The treatments include CK (no fertilization, flood irrigation), FFP (farmers’ conventional fertilization, flood irrigation), OPT1 (80% of FFP fertilization, flood irrigation), OPT2 (80% of FFP fertilization, drip irrigation). N₂O isotopocule deltas, including δ¹⁵N^bulk, δ¹⁸O and SP (the ¹⁵N site preference in N₂O), have been used to investigate microbial pathways of N₂O production under different treatments. Our results showed: i) optimized fertilization and drip irrigation significantly improved the fertilizer and water use efficiency without reducing tomato yield, ii) compared with flood irrigation, drip irrigation decreased soil WFPS and soil ammonium content, but increased soil nitrate content. When soil moisture was higher than 60%WFPS, drip irrigation led to a decrease of N₂O emission with lower N₂O SP signature observed than that of food irrigation, suggesting a reduction of denitrification derived N₂O. In contrast, drip irrigation significantly increased N₂O emission and N₂O SP value when soil moisture status was lower than 55% WFPS, which may be due to the enhanced nitrification or fungal denitrification derived N₂O.