Abstract: The yield responses of naked oats to phosphorus fertilizer and organic fertilizer,the balance between P input and output,and the changes in soil Olsen-P and inorganic phosphorus fraction pool were studied in 8-year experiments on chestnut soil at arid plateau region.The results showed that P fertilization in combination with N fertilizer could help raise naked oats yield,single application of P(N0P1) and N(N1P0) fertilizers brought about 30.8% and 109.4% of oats yield,respectively.Combined application of N and P fertilizers(N1 and P1) gave an increase of 314.0% compared with the control.There was an significant positive interaction effect of N and P fertilizers on yield which resulted in an increase of 86.9% of oats yield.Application of 22.5 t/ha and 45.0 t/ha of organic fertilizer alone gave an increase of 115.1% and 220.1% compared with N0P0,respectively,however,applying P fertilizer after the application of organic fertilizer did not show a yield-enhancing effect.The content of soil Olsen-P and inorganic phosphorus fractions were changed by applying P fertilizer and organic fertilizer on different treatments,The content of soil OlsenP decreased by 3.3 mg/kg in no P fertilizer treatment after 7-years cropping.All phosphorus fraction pools addressed with P and organic fertilizers were enhanced at varying degreess.Most of residual P were inorganic phosphorus,among which Ca2-P and Ca5-P were accounted for 19.2% and 25.3%;Al-P and Fe-P were accounted for 23.4% and 15.3%,respectively;and O-P and Ca10-P were accounted for 13.5% of total inorganic P.According to the balance between P input and output,45.0 (kg/ha) was figured out as the critical rate of P2O5 that could maintain the P balance in soil.The recommended application rates of P fertilizer for maximum yield combined with 0 or 22.5 t/ha organic fertilizer using regression equations were 98.4 kg/ha,87.4 kg/ha respectively.