Abstract:

To investigate the effects of nitrogen fertilizer reduction combined with organic fertilizer on rice-wheat rotation system，a field experiment was conducted in Sanmen County，Zhejiang Province，from 2023 to 2024. Seven treatments were set up：no fertilizer control（CK），no phosphorus（NK），conventional fertilization（N100），15% nitrogen fertilizer reduction based on conventional fertilization（N85），30% nitrogen fertilizer reduction based on conventional fertilization（N70），15% nitrogen fertilizer reduction with organic fertilizer（MN85），and 30% nitrogen fertilizer reduction with organic fertilizer（MN70）. The effects of different treatments on crop yield，phosphorus uptake，and soil phosphorus content were analyzed. The results showed that fertilization significantly （p<0.05） increased yield，with increases of 59.5%-64.9% for rice and 130.8%-167.0% for wheat compared with CK， and MN85 performed best among treatments. Compared with N100，MN85 significantly increased wheat grain phosphorus content by 13.7%，grain phosphorus uptake by 21.6%，and straw phosphorus uptake by 105.3%. The soil available phosphorus and soluble phosphorus contents under MN85 were increased by 57.7% and 61.6%，respectively，compared with N100，and the apparent phosphorus balance shifted from deficit to surplus. However，compared with MN85，N100 significantly increased the partial factor productivity of phosphorus fertilizer by 325.5% for rice and 306.6% for wheat. In conclusion，reducing nitrogen by 15%-30% combined with organic fertilizer can effectively improve soil phosphorus availability，promote crop phosphorus uptake，and stabilize yield，but the ratio of organic fertilizer to chemical fertilizer needs to be optimized to balance phosphorus use efficiency.

Key words: nitrogen fertilizer reduction, organic fertilizer, apparent phosphorus balance, partial factor productivity of phosphorus fertilizer, rice-wheat rotation