In Situ Dissimilatory Nitrate Reduction to Ammonium in a Paddy Soil Fertilized with Liquid Cattle Waste

Most studies on dissimilatory nitrate reduction to ammonium (DNRA) in paddy soils were conducted in the laboratory and in situ studies are in need for better understanding of the DNRA process. In this study, in situ incubations of soil DNRA using N-15 tracer were carried out in paddy fields under conventional water (CW) and low water (LW) managements to explore the potential of soil DNRA after liquid cattle waste (LCW) application and to investigate the impacts of soil redox potential (Eh) and labile carbon on DNRA. DNRA rates ranged from 3.06 to 10.40 mg N kg(-1) dry soil d(-1), which accounted for 8.55%-12.36% and 3.88%-25.44% of consumption of added NO3-N-15 when Eh at 5 cm soil depth ranged from 230 to 414 mV and -225 to -65 mV, respectively. DNRA rates showed no significant difference in paddy soils under two water managements although soil Eh and/or dissolved organic carbon (DOC) were more favorable for DNRA in the paddy soil under CW management 1 d before, or 5 and 7 d after LCW application. Soil DNRA rates were negatively correlated with soil Eh (P < 0.05, n = 5) but positively correlated with soil DOC (P < 0.05, n = 5) in the paddy soil under LW management, while no significant correlations were shown in the paddy soil under CW management. The potential of DNRA measured in situ was consistent with previous laboratory studies; and the controlling factors of DNRA in paddy soils might be different under different water managements, probably due to the presence of different microfloras of DNRA.