Dynamics of phosphorus in Fluvo-aquic soil under long-term fertilization

【Objectives】 In order to provide theoretical basis for agricultural production and soil fertility improvement, this study tried to investigate effect of a long-term (1989-2010) compost and mineral fertilizer application on dynamics of soil phosphorus in the North China Plain under condition of equal input of phosphorus fertilizer. 【Methods】 The long-term experiment consisted of seven treatments, organic compost (OM), half-organic compost plus half-NPK mineral fertilizer (1/2OM), NPK, NP, PK, NK, and control (CK). Soil total P and available P under different fertilization treatments were determined, and then the ratios of available P to total P were calculated. Impact factors on the phosphorus dynamics were investigated. 【Results】 There was a significant positive linear correlation between the soil total P contents under the P applied treatments and the years of the experiment. The average annual increments of total P under the 1/2OM, OM and NPK treatments were 0.0083 g/kg, 0.0081 g/kg and 0.011 g/kg, respectively. The order of 2008-2010 average soil available P in the different fertilization treatments was PK OM 1/2OM NPK NP CK NK. The soil available P contents were increased quickly in the first 11 years, while the available P contents were relatively stable in the latter 10 years. The ratios of available P to total P of OM and 1/2 OM were significantly higher than that of NPK, and the ratios of OM and 1/2 OM were 1.9 and 1.4 times of that under NPK. The P balance was correlated significantly with total P and available P, and the correlation coefficients were 0.981 and 0.886, respectively. Each 100 kg/hm2 increase in the P balance associated with 0.04 g/kg in soil total P content and 2 mg/kg in available P content. Other soil physico-chemical properties such as organic matter did not significantly relate to total P and available P. However, soil organic matter and total N significantly related to the ratio of available P to total P. 【Conclusions】 The P balance had strong influence on dynamics of soil total P and available P. In comparison with the compost, the chemical fertilizer can improve accumulation of total P when the application amount of P fertilizer is P2O5 135 kg/hm2 per year. The available P content is about 7 mg/kg after 21 years mineral fertilizer application, and still unable to meet the requirement of crop growing. The compost application can activate soil P and increase the availability of soil P when the input of phosphorus fertilizer is equal. Therefore, increasing the compost portion in the total P input should be recommended to improve soil fertility and protect environment in the North China Plain.