Dynamic of phosphorus accumulation in anthropogenic-alluvial soil of Yellow River irrigation area in Ningxia

The Second Soil Census of Ningxia showed that the content of available phosphorus(FRP) in anthropogenic-alluvial soil of irrigation areas was improved obviously,and the average content of FRP was increased from 16.3 mg/kg to 28.0 mg/kg in 1985.Fertilization experiments in Dongta village of Wuzhong showed that application of phosphate fertilizer did not affect the crops in the soil containing 50～60 mg/kg FRP.The more fertilizer used,the lower fertilizer efficiency produced.The maximum fertilizer efficiency was of 4.4 kg.It had little impact on crop yield when applying P2O5 combined with organic manure.However,P2O5 should be applied with the amount of 90 kg/hm2 to keep the soil nutrient in balance.Though there was a negative effect of phosphate fertilizer applied in paddy fields,P2O5 should be applied with an amount of 92 kg/hm2 to keep the paddy soil available phosphorus in balance.Reasonable application amount of P2O5 in paddy field was better when the soil phosphorus content was in middle or lower level.The yield of rice was decreased with the amount of P2O5 applied higher than 64 kg/hm2 and fertilizer efficiency on crops was at 23.3 kg.