| Abstract: | Most published studies related to crop effects on denitrification are not continuous and are based on the growing period. The objective of this work was to evaluate the effect of different amounts of soybean stubble, under different soil moisture contents, on gaseous nitrogen (N) losses by denitrification from an agricultural soil. The following soil moisture treatments were reached by adding distilled water to soil cores of a typic Hapludoll: 50 and 100% of water‐filled porosity space (WFPS). Residue treatments included no application of residues, amendment with 2600 kg ha?1 of soybean residues, and amendment with 5200 kg ha?1 of soybean residues. Cumulative nitrous oxide + dinitrogen (N2O + N2) emissions displayed great variability, ranging between 0 and 581.91 µg N kg?1, which represented 0 to 3.93% of the N residue applied. Under 50% WFPS moisture conditions, statistical differences in cumulative N2O + N2 emissions between residue treatments were not detected (p = 0.21), whereas at saturation conditions, cumulative N2O + N2 emissions decreased with the application of increasing amounts of soybean residues (p = 0.017). Daily and cumulative N2O + N2 emissions significantly increased as soil moisture increased, except at soils amended with 5200 kg ha?1 of soybean residues; this lack of statistical difference was probably due to the immobilization of native mineral N. Under 50% WFPS soil moisture contents, aeration seemed to be the main factor controlling redox conditions, limiting the denitrification process, and preventing differences in N emissions between residue treatments. The application of soybean residues to saturated soils notably decreased N2O + N2 emissions by denitrification through a strong mineral N immobilization into organic and nondenitrifiable forms. |
