Distribution and availability of phosphorus in black soil water-stable aggregate under different long-term fertilizations

The distribution and availability of P in black soil water-stable aggregates were studied in a long-term fertilization field experiment. The field is located at Hailun Station of Agro-ecology Research, Chinese Academy of Sciences. The experiment included a control with no fertilization (CK), treatments with only chemical (N and P) fertilization (NP) and with chemical and pig manure (NP+OM) fertilization. The results show that fertilization increases total P content in the soil water-stable aggregates. Total P in the soil water-stable aggregates under NP treatment increases by 28.9%～37.8% compared with CK, whereas that under NP+OM treatment increases by 44.0%～63.9% over NP treatment. Available P content is significantly different for different treatments. Available P in the soil water-stable aggregates under NP treatment increases by 146%～183% compared with CK, whereas that under NP+OM treatment is 3.4～5.3 times as much as treatment NP. Though total P and available P for all the treatments are evenly distributed in the >0.053 mm soil water-stable aggregate, a significantly drop is noted in the soil water-stable aggregates which are smaller than 0.053 mm. Calculated percent values of available P in total P indicate that fertilization favors P availability in soils. This is especially the case under NP+OM treatment. Percent values of available P in total P in the soil water-stable aggregates under treatment NP are 1.94～2.32 times as much as treatment CK, while those of treatment NP+OM are 2.13～2.83 times as much as treatment NP.