Manganese oxide affects nitrification and N2O emissions in a subtropical paddy soil with variable water regimes

Abstract

SummaryCrop management‐induced redox cycles lead to the formation of distinct soil layers that characterize manganese (Mn) distribution or redistribution in rice (Oryza sativa L.) based ecosystems. We studied the effect of Mn oxides on soil nitrification and N2O emissions to validate the hypothesis that Mn oxides affect the soil's nitrification and denitrification processes. Subtropical paddy soil with three different water regimes (50, 100 and 200% of soil water‐holding capacity (WHC)) was treated with 3% birnessite (Mn oxide) or left untreated. The nitrification process was simulated with zero‐ or first‐order kinetic models and N2O emissions were also measured. The maximum net rates of soil nitrification (Va1) decreased significantly with increasing soil moisture contents (F = 184.8; P < 0.001), and so did the average net rates of soil nitrification (Va2) (F = 6.96; P = 0.008). Manganese oxide significantly decreased Va1 (F = 474.7; P < 0.001), whereas it had no significant effects on Va2 (F = 0.26; P = 0.62). Manganese oxide changed the best fitting nitrification kinetic model from first‐ to zero‐order for both 50 and 200% WHC, but it had no effect at 100% WHC. The maximum rates of emission of N2O significantly increased with increasing soil water contents (F = 15 007; P < 0.001). Manganese oxide retarded the maximum rate of N2O emission at 100% WHC, whereas it depressed the rate from 1084 to 225 μg N kg−1 day−1 at 200% WHC (F = 7494; P < 0.001). The results indicate that the effects of Mn oxide on regulating nitrification and N2O emissions are associated with water regime‐dictated redox potential, and might have important implications for regulating N cycling in rice‐based ecosystems.Highlights Effect of manganese oxide on nitrification and denitrification in a paddy soil. Mn oxide retarded nitrification in oxic conditions and enhanced it in anoxic conditions. Mn oxide decreased rate of emission of nitrous oxide in anoxic conditions. Manganese oxide might be able to regulate N cycling in rice paddy soil.