The influence of N-fertilization regimes on N2O emissions and denitrification in rain-fed cropland during the rainy season

Abstract

The effects of nitrogen fertilization regimes on N₂O emissions and denitrification rates were evaluated by in situ field incubation experiments with intact soil cores and the acetylene block technique. Intact soil cores were collected from long-term field experiments involving several N fertilization regimes, including single synthetic N fertilizer (N), organic manure (OM), synthetic N, P, K fertilizer (NPK), organic manure with synthetic fertilizer (OMNPK), crop straw residue with synthetic fertilizer (SRNPK) and no nitrogen fertilizer (NF). N₂O was sampled from the head space of the cylinders to determine the daily N₂O emission and denitrification rate. The results showed that the N₂O emissions were greatly influenced by the specific fertilization regime even when the same nitrogen rate was applied. The mean N₂O emissions and denitrification rates from the N, OM, NPK, OMNPK and SRNPK treatment were 2.22, 2.66, 1.94, 2.53, 1.67 and 4.63, 5.96, 4.15, 5.41, 3.65 mg per m² per day, respectively. The application of OM significantly increased the N₂O emission and denitrification compared to the application of NPK because of the high soil organic carbon (SOC) content of OM. However, SRNPK increased the SOC content and decreased the N₂O emissions significantly compared to the OM and OMNPK treatments because the addition of crop straw with a high C/N ratio to soil with a low inorganic N content induced N immobilization. The contents of soil nitrate and ammonium were the main limiting factors for N₂O emissions in a positive regression as follows: Ln (N₂O) = 2.511 + 1.258 × Ln ([NH₄⁺] + [NO₃⁻]). Crop straw residue combined with synthetic fertilizer is recommended as an optimal strategy for mitigating N₂O emissions and denitrification-induced N loss in rain-fed croplands.