Organic carbon and nitrogen mineralization in a poorly‐drained mineral soil under transient waterlogged conditions: an incubation experiment

SUMMARY: In poorly‐drained mineral soils, little interest has been shown on the effects of the duration and frequency of water saturation periods on carbon (C) and nitrogen (N) mineralization. This study investigates C and N mineralization rates in a poorly‐drained mineral soil in response to transient and permanent waterlogged conditions. Soil samples were incubated for 43 days at 20°C under three treatments: field capacity (T0), transient waterlogged conditions (T1) and permanent waterlogged conditions (T2). The carbon dioxide (CO₂)‐C and nitrous oxide (N₂O)‐N emissions, soil mineral N content (NH₄⁺, NO₂⁻and NO₃⁻) and contents of organic acids were measured. Soil C mineralization rate during transient waterlogged periods (68.7 mg kg⁻¹after 38 days) was not significantly different to that at field capacity (58.6 mg kg⁻¹after 38 days) and was twice that of permanently waterlogged soil. In contrast, the N mineralization rate in soil under transient waterlogged conditions was half that of permanently waterlogged soil or soil at field capacity. An accumulation of acetate and formate was measured in the soil during waterlogged periods in treatments T1 and T2; in treatment T1, de‐saturation resulted in a significant decrease in their concentrations. Mineralization of C and N under transient waterlogged conditions was related to aerobic and anaerobic mineralization processes. Rapid mineralization under oxidizing conditions of labile transient organic compounds from anaerobic processes resulted in pulses of CO₂‐C and N₂O‐N emissions. This study shows that in poorly‐drained mineral soil, C and N mineralization rates at a given time depend not only on the current soil redox status, but also on that of previous soil conditions. Further investigation comparing different durations of waterlogged conditions could allow better understanding of the impact of previous redox conditions on the dynamics of organic acid, C and N mineralization during transient conditions.