Dissimilatory nitrate reduction to ammonium in a soil under greenhouse vegetable cultivation as affected by organic amendments
2015
Lü, Weiwei | Zhang, Hailin | Min, Ju | Shi, Weiming
PURPOSE: Excessive nitrate (NO₃⁻) accumulation in greenhouse vegetable soils often results in nitrogen (N) loss through leaching or gaseous emission as a result of denitrification. Dissimilatory NO₃⁻reduction to ammonium (NH₄⁺) (DNRA) as affected by organic amendments in a greenhouse vegetable soil was studied. MATERIALS AND METHODS: Soil incubations were carried out following the amendment of rice straw (RS), Chinese milk vetch (CMV), and a control (CK) without organic amendment using two¹⁵ N isotope methods in the laboratory. RESULTS AND DISCUSSION: Gross DNRA rates were 15.2–26.2 and 0.21–1.06 mg N kg⁻¹ day⁻¹when estimated by the recovery of¹⁵NO₃⁻in NH₄⁺and organic N (ON) pools (M1) and by mean residence time (MRT) of NH₄⁺(M2), respectively. Microbial NO₃⁻assimilation might occur due to high NO₃⁻content in the tested soil (1.27 g N kg⁻¹), and thus, M1 probably overestimated gross DNRA rates. Gross DNRA rates estimated by M2 were higher in RS and CMV treatments than those in CK and were significantly (p < 0.05) correlated with soil dissolved organic carbon (DOC) content and the ratio of DOC to NO₃⁻–N. CONCLUSIONS: Therefore, the DNRA rate was promoted by organic amendments attributed to the enhancement of soil DOC to NO₃⁻–N ratio. Further studies on DNRA in more soil types under different conditions are required in order to better understand the potential contribution of DNRA to N transformation and conservation in vegetable soils.
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