Total-P and Olsen-P dynamics of long-term experiment without fertilization

Dynamics of total phosphorus and Olsen-P of soils without fertilization were studied with long-term experiment on eleven typical soils. The results indicated that changes of Olsen–P were more significant than that of total P over time in all soils. Soil total P decreased linearly with time for gray desert soil, paddy soil and fluvo-aquic soil, but did not change significantly for other soils. Decreases in soil total P was not significantly correlated with crop P uptake. Tendency of soil Olsen-P decrease differed with initial Olsen-P content in the soils. When initial Olsen-P was greater than 20mg/kg, it decreased quickly and reduced 30 mg/kg in 5 years and reduced 40.5mg/kg in 25 years. When initial Olsen-P was between 10 mg/kg and 20 mg/kg, they decreased slowly and reduced 15 mg/kg in 5 years and 19mg/kg in 15 years. When initial Olsen-P was less than 10 mg/kg, there was no obvious change over time. The ratios of Olsen-P to total-P and avail-N to Olsen-P were two important factors influencing Olsen-P change. Olsen-P decreased linearly with ratio of Olsen-P to total-P.