Abstract:

To investigate the effect of nitrogen fertilizer reduction on double-cropping rice yield，phosphorus（P）fertilizer efficiency and soil P supply capacity after returning Astragalus sinicus L. to the field，this study focused on the southern double-cropping rice system and established five treatments：no-fertilizer plot（CK），100% nitrogen application（N100），80% nitrogen application（N80），60% nitrogen application（N60），and 40% nitrogen application（N40），to examine the impacts of these different fertilization treatments on rice yield，P uptake，P balance，and soil available P content. The results showed that fertilization increased crop yield，with N100 treatment increasing grain yield significantly （p<0.05） by 47.5% compared with CK. Among the N reduction treatments，the yields of N80 and N60 showed no significant difference from N100，but the N40 treatment significantly reduced yield by 8.94%. The aboveground P uptake in the N100 treatment increased by 58.5% compared to CK. As N application decreased，plant P uptake and partial factor productivity of P fertilizer（PFP）showed a declining trend，with the N40 treatment reducing P uptake significantly by 16.1% and 15.3% compared with N100 and N80. The PFP of N40 treatment significantly decreased by 8.95%，7.32%，and 6.13% than N100，N80 and N60 treatments. Fertilization treatments significantly improved P balance，with the deficit in the N100 treatment reduced to 8.1 kg·hm^-2. N reduction treatments further alleviated the P deficit，with the N40 treatment showing a surplus of 7.7 kg·hm^-2. The soil available P content in fertilization treatments significantly increased by 52.8% to 79.0% compared with CK，with N reduction treatments demonstrating more pronounced improvements. In conclusion，under Astragalus sinicus L. incorporation，reducing N fertilizer application by 20% is a feasible optimization strategy. This level of N reduction maintains high rice yield（yield reduction <3%）while improving soil P status.

Key words: nitrogen fertilizer reduction, Astragalus sinicus L., rice yield, phosphorus utilization efficiency, soil phosphorus balance