LAUSR

Abstract Long-term field fertilization trials have suggested that reduced chemical nitrogen (N) plus organic fertilization can effectively reduce N loss without sacrificing crop yield, while the knowledge of how organic fertilizers regulate soil microorganisms and their function in N transformation are limited. In this study, the response of net nitrification rate and the ammonia-oxidizer community within soil aggregates to long-term combined organic N and reduced chemical N fertilization was evaluated to understand the underlying mechanism of the practice in mitigating soil N loss. The fertilization experiment included an unfertilized control; chemical N fertilizer (N), superphosphate (P) and potassium sulfate (K) fertilizer (NPK); NPK plus straw (NPKS); and NPK plus manure (NPKM). The results showed that the large macro-aggregates mass (>2 mm) in soil significantly increased from 34.1% in NPK to 47.2% in NPKS (P