Enriching organic carbon bioavailability can mitigate soil acidification induced by nitrogen fertilization in croplands through microbial nitrogen immobilization

Excessive application of ammonium-based N fertilizers promote nitrification, which is mainly responsible for intensive acidification in cropland soils. Thus, there is an urgent need for the development of control measures to manage soil acidification induced by N fertilization. In this study, we investigated the potential of enriching organic C bioavailability to mitigate acidification induced by N fertilization through microbial N immobilization using an indoor incubation experiment. Results showed that the sole application of ammonium sulfate [(NH4)(2)SO4] or urea to a cropland soil promoted nitrification of fertilizer N, and subsequently soil pH decreased by 0.48-1.00 units after 45-d incubation. The combined application of glucose with N fertilizers induced microbial immobilization of almost all fertilizer N within 1 d and gradually induced mineralization of soil organic N after 1 wk of incubation. More than 65% of immobilized total extractable N was returned to soil solution and mainly existed as NH4+-N and extractable organic N, with the pH decrement being <0.10 units after 45-d incubation. These results indicated that (a) enriching organic C bioavailability in cropland soils intensified microbial N immobilization, (b) intensification of microbial N immobilization induced a buffering effect to regulate soil inorganic N supply, and (c) microbial N immobilization had great potential to inhibit soil acidification and retard aluminum mobilization. The results obtained in this study provide a theoretical strategy to control soil acidification and increase N use efficiency in croplands.