Response of phosphorus components to phosphate surplus in cinnamon soil under long-term fertilization

Objectives The effects of different P source inputs on soil P composition and accumulation in maize feild of cinnamon soil under long-term fertilization were studied, and the correlation between different P components and soil P surplus was analyzed, which will provide basis for regulating the utilization efficiency of P fertilizers.

Methods The long-term experiment, located in Beiping plateau, Shouyang County of Shanxi Province, was started since 1992.There were 9 fertilization treatments in the experiment, they were: no fertilizer control (CK), N₁P₁, N₂P₂, N₃P₃, N₄P₄, N₂P₁M₁, N₃P₂M₃, N₄P₂M₂, N₀P₀M_6. Among them, N₁, N₂, N₃ and N₄ represent urea N application rates of 60, 120, 180, 240 kg/hm²; P₁, P₂, P₃, P₄ represent super calcium phosphate rates of P 16, 33, 49, 66 kg/hm²; M was manure compost, the followed digital of M₁, M₂, M₃, M₆ represent the manure P application rates of 14, 28, 42 and 83 kg/hm². Soil samples were taken from 0−20 cm topsoil during 1992 to 2016 after harvest. The contents of different soil P fractions were analyzed, and the surplus amount of P in top soil and the correlation between it and the P fractions were calculated.

Results After 25 years of continuous fertilization, the P composition in the soil changed differently. Except for H₂O-Pi and Residual-P, P contents in different forms were lower than that at the beginning of the experiment. The application of inorganic fertilizer mainly increased the HCl-P in the soil, and N₄P₄ treatment increased the most, which was 127.7% higher than that of the initial experiment. The application of organic fertilizer could significantly improve the active P in soil. After applying high rate of organic fertilizer, the total content of H₂O-P was 8 times higher than that at the beginning of the experiment, and the annual increase rate of NaHCO₃-Pi was 11.50 mg/(kg·a).The surplus amount of soil P in different fertilization treatments was in order of N₀P₀M₆ > N₃P₂M₃ > N₄P₄ > N₄P₂M₂ > N₃P₃ > N₂P₂ > N₂P₁M₁ > N₁P₁ > CK. P surplus was an important factor influencing the change of P composition in soil, and the response order of various P component to P accumulation in the season was NaHCO₃-Pi > NaOH-Pi > HCl-P > NaHCO₃-Po > Residual-P > H₂O-Po > NaOH-Po > H₂O-Pi.

Conclusions Long-term fertilization has significantly changed the contents of different fraction of soil P. Combined application of organic and inorganic fertilizer is conducive to the conversion of active P in soil. Excessive application of phosphorus results in a large surplus of phosphorus in the soil, and the highest surplus of phosphorus is obtained in high application rate of organic fertilizer. When inorganic fertilizer is applied, P 33 kg/(hm²·a) of superphosphate can basically meet the requirements of plants. When inorganic and organic fertilizers are applied with superphosphate P 16 kg/(hm²·a) and manure P 14 kg/(hm²·a) , the surplus of phosphorus in soil is the least.