[Effects of the blended nitrogen fertilizers combined with inhibitors on soil nitrogen pools.]

Pot experiment with winter wheat was conducted to investigate the effects of blended nitrogen (N) fertilizer (slow-release fertilizer-N:urea-N=1:1) combined with N fertilizer inhibitor NAM on soil ammonium (NH ₄ ⁺ -N), nitrate (NO ₃ ^- -N), microbial biomass nitrogen (MBN) and fixed-ammonium (FN) contents. We analyzed dynamic characteristics of soil mineral N, MBN, FN pools under different treatments. There were six treatments, including no N fertilizer (CK), conventional urea (U), blended N fertilizer (MU), MU plus 2.5‰ NAM (MUN ₁ ), MU plus 5‰ NAM (MUN ₂ ), and MU plus 7.5‰ NAM (MUN ₃ ). Our results showed that, compared to that of MU treatment, MUN ₂ and MUN ₃ delayed the appearance time of NH ₄ ⁺ -N peak. Averaged across the whole wheat growing period, soil mineral N content for NAM treatments decreased by 5.3%-11.7%. From tillering to maturity stage, MBN mineralization and mineralization rates were 38.96 mg·kg ^-1 and 91.5%, which was higher than that of U treatment; MBN mineralization and mineralization rates for MUN ₁ , MUN ₂ and MUN ₃ treatments were 58.73 mg·kg ^-1 , 83.3%, 94.20 mg·kg ^-1 , 94.6%, 104.46 mg·kg ^-1 and 96.3%, respectively. The FA mineralization release for NAM treatments were higher by 2.83-9.19 mg·kg ^-1 than that of MU treatment. The results of path analysis showed that NAM addition weakened the direct effect of soil NH ₄ ⁺ -N pool on NO ₃ ^- -N pool but enhanced the indirect effects of FN pool on NO ₃ ^- -N pool through affecting NH ₄ ⁺ -N pool. The wheat grain yields of the MUN ₁ , MUN ₂ and MUN ₃ treatments were significantly higher by 31.6%, 21.5% and 22.9% than that of MU treatment. Nitrogen use efficiencies were increased by 8.1%, 13.5% and 3.1%, respectively. In summary, through double regulation for N release and transformation in soil, NAM delayed the appearance time of soil NH ₄ ⁺ -N peak and retarded its transformation into NO ₃ ^- -N, and increased the roles of MBN and FN in supplying N, thereby increased crop yield and N-fertilizer use efficiency.