关键词: 无机磷形态, 冬小麦-夏玉米体系, 14李若楠（校样）, 土')">土, 磷有效性, 有效磷梯度

Abstract:

【Objective】 Investigating the contribution of inorganic phosphorus (P) fractions to soil available phosphorus under equivalent soil organic matter content might be helpful in development of phosphate fertilizer management strategy whereby to improve phosphorus use efficiency in a given soil.【Method】 We collected and screened the soils with a gradient of Olsen P level but the quite similar soil organic matter content (SOC ranges from 10.03 to 10.68 g·kg ^-1) in a Tier soil under winter wheat-summer maize cropping in Guanzhong Plain of Shaanxi Province. The Olsen P contents of the selected soil samples were 10.73 mg·kg ^-1, 18.06 mg·kg ^-1, 20.61 mg·kg ^-1, 24.01 mg·kg ^-1, 30.73 mg·kg ^-1, 43.69 mg·kg ^-1, and 58.58 mg·kg ^-1, respectively. We then analyzed the soil inorganic phosphorus forms with the phosphorus fractionation method developed by Chang & Jackson and modified by Jiang & Gu.【Result】 The results showed that the calcium bounded phosphorus fraction was the dominant form in the cultivated soil in the northwestern winter wheat-summer maize planting area, accounting for 66.67% of the total amount of inorganic phosphorus, of which dicalcium phosphate (Ca₂-P), octa-calcium phosphate (Ca₈-P) and apatite (Ca₁₀-P) account for 2.80%, 16.80% and 47.09%, respectively, on average; and aluminum bounded phosphate (Al-P), iron bounded phosphate (Fe-P) and occluded phosphate (O-P) composed of 16.28%, 5.23% and 11.81%, respectively. Soil Olsen P was increased significantly and linearly with the increasing content of Ca₂-P, Ca₈-P, Ca₁₀-P, Al-P, Fe-P and O-P; while the phosphorus activation coefficients, defined as the ratio of soil Olsen P to total P, were correlated significantly positively and linearly to the content of Ca₂-P, Ca₈-P, Al-P, Fe-P and O-P. The results of path analysis showed that the contribution of inorganic phosphorus to soil available phosphorus (Olsen P) in Guanzhong Plain area of Shaanxi Province was in the order of Ca₂-P (0.974)＞Al-P (0.186)＞Ca₈-P (0.182)＞Fe-P (0.150)＞Ca₁₀-P (0.007)＞O-P (-0.074), the contribution of inorganic phosphorus to phosphorus activation coefficient (PAC) was Ca₂-P (0.768)＞Al-P (0.082)＞Ca₈-P (0.071)＞Fe-P (-0.018)＞Ca₁₀-P (-0.055)＞O-P (-0.388), which was consistent with the contribution of soil phosphorus component to available phosphorus. The results of stepwise regression analysis showed that Ca₂-P and Ca₈-P were the major two contributors to Olsen P, but the Ca₂-P contributed the most to PAC.【Conclusion】 Under the same or similar soil organic matter condition, Ca₂-P was the most effective phosphorus source in Tier soil of wheat-maize growing area in Guanzhong Plain of Shaanxi Province. The increase of soil phosphorus availability was mainly achieved by increasing the proportion of phosphorus forms of readily available and relatively high availability such as Ca₂-P, Ca₈-P and Al-P, and reducing the proportion of very low availability forms, i.e. Ca₁₀-P. Generally, under current cropping system, the application of phosphate fertilizers mainly kept the soil phosphorus in pools of available forms in the Guanzhong Plain.

Key words: forms of inorganic phosphorus, winter wheat summer maize cropping, tier, phosphorus availability, Olsen P gradient