Bio-availability of phosphorus fertilizers in acid paddy soils with different P status.

Pot experiments on three acid paddy soils with different P status were conducted to investigate the effects of P fertilizers on ryegrass growth and changes of soil P fractions after ryegrass planting.The results show that application of P fertilizers increased dry matter weight and P uptake of ryegrass on low-P status soils(NK and CK)by 32.7%-53.0% and 82.4%-151.9%,respectively;on high-P status soil(NPK)by 11.0%-14.0% and 51.1%-65.0%,respectively.Dry matter weight and P uptake of ryegrass on NPK soil were higher than that on NK and CK soil under the same fertilizer treatment.Average agronomic efficiency of P fertilizer(AEP)for KPR500,KPR1000 and SSP22 on three soils were 5.6,2.5 and 124.2,respectively;average recovery efficiency of P fertilizer(REP)for KPR500,KPR1000 and SSP22 on three soils were 1.0,0.7 and 21.1,respectively.Compared with the control(no P application),soil available P(Resin-P,NaHCO3-Pi and NaHCO3-Po)increased at different grade on the three soils after P fertilizers application.Soil NaOH-Pi also increased,while soil NaOH-Po was stable and less affected by addition of P fertilizers.Phosphate rock application increased soil HCl-P and Residual-P fractions substantially.