[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-N), nitrate (NO-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), MU plus 5‰ NAM (MUN), and MU plus 7.5‰ NAM (MUN). Our results showed that, compared to that of MU treatment, MUN and MUN delayed the appearance time of NH-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 and 91.5%, which was higher than that of U treatment; MBN mineralization and mineralization rates for MUN, MUN and MUN treatments were 58.73 mg·kg, 83.3%, 94.20 mg·kg, 94.6%, 104.46 mg·kg and 96.3%, respectively. The FA mineralization release for NAM treatments were higher by 2.83-9.19 mg·kg than that of MU treatment. The results of path analysis showed that NAM addition weakened the direct effect of soil NH-N pool on NO-N pool but enhanced the indirect effects of FN pool on NO-N pool through affecting NH-N pool. The wheat grain yields of the MUN, MUN and MUN 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-N peak and retarded its transformation into NO-N, and increased the roles of MBN and FN in supplying N, thereby increased crop yield and N-fertilizer use efficiency.