Response of Olsen-P to P balance in cinnamon soil under long-term fertilization

【Objectives】 The study on the relation of soil phosphorus availability with phosphorous balance under long-term fertilization will provides theoretical basis for scientific application of phosphorus and keep sustainable high production efficiency in the dry farming area of loess plateau. 【Methods】 The study was based on the long-term fertilizer experiment of cinnamon soil in Shouyang County, Shanxi Province. Soil samples were collected from nine treatments: without fertilization(CK), four single chemical fertilizer treatments(N1P1, N2P2, N3P3 and N4P4 ),three organic and inorganic fertilizer combination treatments(N2P1M1, N3P2M3 and N4P2M2), and one single manure treatment (N0P0M6). The soil phosphorus contents in 0-20 cm layer were determined every 5 years, plant biomass was investigated in the same year after harvest, and the P contents in plants were determined. The amount removed by maize and the cumulative surplus of phosphorus were calculated. 【Results】 In the long-term without P fertilizer input, the soil phosphorus is in a deficit state with annual decline rate of 0.02 mg/(kga). With only chemical fertilizer input, soil available phosphorus contents have been increased with the increased exogenous P input, the annual increment in treatments (N1P1, N2P2, N3P3 and N4P4 )are 1.04, 1.08, 1.70 and 2.13 mg/(kga). With combined use of manure and chemical fertilizers (treatments N2P1M1, N3P2M3 and N4P2M2), the annual soil Phosphorus increments are 1.70, 3.73 and 4.72 mg/(kga), that with only manure is in 5.63 mg/(kga). Long-term no fertilizer input leads to the deficit of soil phosphorus, every annual deficit of P 100 kg/hm2 will result in an average decrease of available phosphorus content of 0.5 mg/kg. With the continuous manure input, soil P is in state of accumulation, every increase accumulation of P2O5 100 kg/hm2 will lead to average increase of 4.3 mg/kg of available P2O5. Manure and chemical fertilizers have synergistic effect, the every P increase of 100 kg/hm2 will lead to average increase of available P of 9.1 mg/kg. The fastest increase in available P content is obtained in treatment N2P1M1, i.e. the annual P2O5 input is 65 kg/hm2, with the soil P2O5 accumulation of 100 kg/hm2, the content of soil available phosphorus will be averagely increased by 17.1 mg/kg. 【Conclusions】 Soil available phosphorus content is affected by the surplus and deficit of soil phosphorus, and also by the P2O5 input amount. The annual P2O5 input of 37.5-65 kg/hm2 will basically meet the demand for the growth of crops, and produce high phosphate fertilizer efficiency and less accumulation in the soil. The annual P2O5 inputs of 112 kg/hm2, will lead to a large amount of phosphorus surplus in soil, which not only results in low response of crop yields but, also causes harm to farmland environment.