Phosphorus use efficiency, uptake and apparent balance response to substituting long-term chemical fertilizer with organic fertilizer in a double-rice cropping system

Abstract The overuse of chemical phosphorus (P) fertilizer commonly practiced in southern China can reduce P use efficiency and threaten environmental safety. To greatly exploit organic manure and reduce the rate of chemical fertilizer; a 35-year fertilization study was conducted under continuous double-rice cropping system to assess the long-term effects of replacing chemical fertilizer by organic fertilizer on grain yield, P use efficiency, uptake and balance. Treatments involved an unfertilized control (CK), chemical phosphorus and potassium fertilizer (PK), chemical nitrogen and phosphorus fertilizer (NP), chemical NK fertilizer (NK), chemical NPK fertilizer (NPK), and 30% NPK fertilizer with 70% organic manure (NPKM). The results revealed that the grain yield was more than 11.0 t ha-1 with NPK and NPKM treatments during 1984-2018. The grain yield with NPKM treatment was significantly (p<0.05) higher than with NPK treatment, except during 1984-1995. The soil P contents and P uptake were significantly (p<0.05) increased under manure amended treatment. The mean P use efficiencies under PK, NP, NPK and NPKM treatments were 10.7%, 20.2%, 36.1% and 44.2%, respectively. Phosphorus balance was positive under treatments with P addition, and negative in the without P addition treatments. Soil properties and P input were the key factors regulating P uptake and balance, and P activation coefficient. The results suggested that relatively high grain yield and P use efficiency can be achieved through rational chemical fertilizer, but, substituting 70% of the chemical fertilizer with manure might be the promising strategy seeing the increases in the soil fertility and P use efficiency.