Liming accelerates the NO3 − removal and reduces N2O emission in degraded vegetable soil treated by reductive soil disinfestation (RSD)

Abstract

Reductive soil disinfestations (RSDs), as an alternative to chemical fumigations, have been widely applied to improve degraded greenhouse vegetable soils. However, high nitrous oxide (N2O) emission and nitrate (NO3 −) leaching would occur during RSD treatment. The aim of this study was to investigate the effect of pH on the removal of NO3 − and its transformed products during RSD treatment. A 15N tracing incubation experiment was conducted in a degraded vegetable soil under 30 °C for 360 h. There were five treatments: control (flooding only, noted as CK), flooding + alfalfa (RSD0), and RSD0 + lime at three application rates, which adjusted soil pH to 6.7, 7.7, and 8.4, noted as RSD1, RSD2, and RSD3, respectively. Increase in pH accelerated the removal of NO3 − under flooding condition, with the decrease in Eh. It took 120 and 72 h for RSD0 and RSD0 + lime treatments, respectively, when soil NO3 − content dropped from initial 147 to below 25 mg N kg−1, but NO3 − content in the CK was still 32.1 mg N kg−1 even after 360-h incubation. Liming inhibited dissimilatory NO3 − reduction to ammonium (DNRA) process and immobilization of NO3 − into organic nitrogen (N). After 360-h incubation, the ratios of 15N transformed into NH4 + and organic N pools accounted for 0.46–1.20 % and 3.11–9.48 % of added K15NO3 in RSD treatments, being lower than 2.17 and 16.8 % in CK, respectively. The ratio of cumulative N2O emissions to NO3 − disappeared from soil was greatly lower in RSD treatments (0.80–2.29 %) than in CK (5.20 %). RSD associated with liming accelerated the NO3 − removal and reduced the N2O emission but decreased the conversion rates of NO3 − to NH4 + and organic N.