Effects of organic material amendment and water content on NO, N2O, and N2 emissions in a nitrate-rich vegetable soil

Amending vegetable soils with organic materials is increasingly recommended as an agroecosystems management option to improve soil quality. However, the amounts of NO, N2O, and N2 emissions from vegetable soils treated with organic materials and frequent irrigation are not known. In laboratory-based experiments, soil from a NO 3 − -rich (340 mg N kg−1) vegetable field was incubated at 30°C for 30 days, with and without 10 % C2H2, at 50, 70, or 90 % water-holding capacity (WHC) and was amended at 1.19 g C kg−1 (equivalent to 2.5 t C ha−1) as Chinese milk vetch (CMV), ryegrass (RG), or wheat straw (WS); a soil not amended with organic material was used as a control (CK). At 50 % WHC, cumulative N2 production (398–524 μg N kg−1) was significantly higher than N2O (84.6–190 μg N kg−1) and NO (196–224 μg N kg−1) production, suggesting the occurrence of denitrification under unsaturated conditions. Organic materials and soil water content significantly influenced NO emissions, but the effect was relatively weak since the cumulative NO production ranged from 124 to 261 μg N kg−1. At 50–90 % WHC, the added organic materials did not affect the accumulated NO 3 − in vegetable soil but enhanced N2O emissions, and the effect was greater by increasing soil water content. At 90 % WHC, N2O production reached 13,645–45,224 μg N kg−1 from soil and could be ranked as RG > CMV > WS > CK. These results suggest the importance of preventing excess water in soil while simultaneously taking into account the quality of organic materials applied to vegetable soils.