Regulation of the product stoichiometry of denitrification in intensively managed soils

Abstract

Abstract Crop residue amendment in conjunction with synthetic nitrogen (N) fertilization is a common agricultural practice that increases soil fertility and crop yield. However, such a practice may also change soil denitrification process. Here, we conducted an incubation experiment with a robotized continuous flow N 2 free incubation system [using helium (He) and oxygen (O 2 )] and measured fluxes of N 2 O and N 2 at a high resolution in an intensively managed soil to examine the interaction effect of straw amendment and N fertilization on soil denitrification. Four treatments were set consisting of (a) a nonamended treatment (Control); (b) a Straw treatment (2 g straw kg −1 dry soil); (c) a KNO 3 treatment (KNO 3 , 15 mM KNO 3 ); and (d) a Straw + KNO 3 treatment (2 g straw kg −1 dry soil and 15 mM KNO 3 ). During the oxic phase (80% He plus 20% O 2 ) of the experiment (initial 2 days), flux rates of N 2 O were 0.54 and 0.38 kg N/ha day −1 in the Control and KNO 3 treatments, respectively. Meanwhile, straw amendment triggered N 2 O fluxes immediately after the onset of treatments, which was more evident in the Straw + KNO 3 treatment. During the anoxic phase (100% He), both N 2 O and N 2 emissions increased in all treatments, with the effect being more pronounced in the Straw and Straw + KNO 3 treatments. In line with the observed differences in gas fluxes, the abundances of nirK , nirS , and nosZ genes increased clearly in these treatments. Overall, the mean N 2 O/(N 2 O + N 2 ) ratio (0.69 ± 0.03) in the Control treatment was significantly lower compared to the KNO 3 treatment (18.8%) and higher than the straw‐amended soils (31.9% and 17.4% compared to the Straw and Straw + KNO 3 treatments, respectively). Taken together, our results suggest straw amendment significantly altered N 2 O and N 2 fluxes by decreasing the N 2 O/(N 2 O + N 2 ) ratio; however, the effects of straw amendment depended on soil nitrate content.