Abstract:

【Objective】 In this study, the changes of phosphorus profit and loss as well as various forms of inorganic phosphorus in fluvo-aquic soil under long-term fertilizer application, and the effect of soil phosphorus profit and loss on inorganic phosphorus were discussed, which provided a theoretical basis for the rational application of phosphorus fertilizer in fluvo-aquic soil.【Method】 Based on the “National Long-term Monitoring Station for Soil Fertility and Fertilizer Benefit in Fluvo-aquic Soil”, the four fertilization modes in North China including NPK (single chemical fertilizer), SNPK (straw return), MNPK (organic-inorganic combined application), 1.5 MNPK (high amount of organic-inorganic combined application), were studied with the control of NK (non-phosphate fertilizer) to study the changes of apparent phosphorus profit and loss, cumulative phosphorus profit and loss, the content and relative content of each form of inorganic phosphorus, and the effect of soil phosphorus profit and loss on each form of inorganic phosphorus.【Result】 Under the condition of not applying phosphate fertilizer for 25 years, the phosphorus in the soil was always in a state of deficit, the cumulative deficit of phosphorus in soil was 431.8 kg·hm ^-2, after 25 years, the cumulative surplus of soil phosphorus on four phosphate fertilizer models (NPK, SNPK, MNPK, and1.5MNPK) was 291.2, 398.4, 1 742.4, and 2 676.9 kg·hm ^-2, respectively. When phosphorus fertilizer was not applied for a long time, Ca₂-P decreased most in soil inorganic phosphorus by 49.0%. In the first 13 years, the soil Ca₂-P of the above four fertilizer models increased by 1.2-5.4 times, with an average annual increase of 1.26-5.73 mg·kg ^-1. In the latter 12 years, the growth rate of soil Ca₂-P decreased by 99.2%-112.6% by applying chemical fertilizer single, straw returning and organic-inorganic combined application model; and the content of Ca₂-P in the soil decreased by 2.0 mg·kg ^-1 per year. The relative content of soil Ca₂-P increased by 1.0%-3.5% in 25 years above four fertilizer models. After 25 years of application of phosphate fertilizer, the content of Ca₈-P, Al-P, and Fe-P in soil increased 1.4-6.5, 1.8-3.3, and 1.1-2.2 times, respectively, with an average annual increase of 4.69-19.81, 1.67-3.10, and 1.23-2.37 mg·kg ^-1, respectively; the relative content increased 8.4%-3.0%, 3.3%-4.0%, 1.8%-3.3%, respectively. The contents of Ca₁₀-P and O-P were oscillatory between 350-410 and 100-160 mg·kg ^-1 for a long time, but their relative contents decreased by 11.4%-29.7% and 3.1%-8.9%, respectively. Under the condition of not applying phosphate fertilizer for 25 years, for every 100 kg P·hm ^-2 cumulative deficit, Ca₂-P, Ca₈-P, Al-P, Fe-P, Ca₁₀-P, and O-P in soil decreased by 1.2, 2.7, 1.1, 1.5, 0.8, and 7.5 mg·kg ^-1, respectively. Under the mode of single fertilizer and straw returning for 25 years, for every 100 kg P·hm ^-2 cumulative surplus, Ca₂-P, Ca₈-P, Al-P, Fe-P, Ca₁₀-P, and O-P in soil increased by 3.9-5.0, 21.5-21.6, 6.5-7.4, 4.8-5.6, 4.0-7.5, and 2.4-7.2 mg·kg ^-1, respectively. Under the mode of organic and inorganic combined application for 25 years, for every 100 kg P·hm ^-2 cumulative surplus, Ca₂-P, Ca₈-P, Al-P, Fe-P, Ca₁₀-P, and O-P in soil increased by 1.8-2.8, 14.2-16.4, 2.5-3.2, 1.9-2.6, -0.2-1.2, and 0.3-1.9 mg·kg ^-1, respectively. 【Conclusion】 The long-term application of phosphorus fertilizer could increase the surplus of phosphorus and the content and its relative content of Ca₂-P, Ca₈-P, Al-P, and Fe-P in fluvo-aquic soil, and the effect of organic and inorganic combined application was higher than that of single chemical fertilizer and straw returning. When the surplus of phosphorus in fluvo-aquic soil was the same, the increment of Ca₈-P was the most in all fertilizer models, followed by Al-P and Fe-P, and the increment of Ca₂-P, Ca₈-P, Al-P, and Fe-P in soil with single chemical fertilizer was higher than that of straw returning and organic and inorganic combined application.

Key words: long-term located fertilization, fluvo-aquic soil, phosphorus profit and loss, inorganic phosphorus