Phosphorus Fractions Transformation And Availability Of Varying Synthetic Phosphorus Varieties In Loess Soil

Synthetic phosphorus fertilizers may vary in their behavior when applied to soil because of their inherent differences in nature.In order that the phosphate fertilizers could well match the crops’P requirement,the selection of appropriate types of P sources are of paramount importance in practice.To achieve this,it is necessary to make a thorough investigation on phosphorus distribution among different soil P fractions and their bioavailability when P applied to soil in various varieties of synthetic phosphate fertilizers.In this paper,pot experiment and long-term fertilizer localization experiment were used to study:1)The difference of phosphorus form transformation and availability of varying synthetic phosphorus varieties in Loess soil;2)Transformation and accumulation of inorganic phosphorus forms in soils with long-term application of two synthetic phosphorus varieties.Eight treatments were established in pot experiment:no phosphate fertilizer（control）,superphosphate（SSP）,calcium magnesium phosphate（Ca Mg P）,mono-ammonium phosphate（MAP）,di-ammonium phosphate（DAP）,ammonium poly-phosphate（Poly P）,urea phosphate（Urea P）and superphosphate plus ammonium sulfate（SSP+ASA）.Long-term fertilizer localization experiment includes long-term application of calcium superphosphate and di-ammonium phosphate.In this study,two treatments were selected:no fertilization（CK）and nitrogen and phosphorus fertilizer application（NP）.The inorganic phosphorus fractions in soil were determined with a P fractionation method modified by Jiang&Gu.The main results of this study are as follows:（1）Results showed that the contents of soil available P（Olsen P）and its dynamics varying with treatments.The average Olsen P contents followed an order of DAP>Urea P≥Poly P>MAP>SSP+ASA>SSP>Ca Mg P>Control based on their statistical significance during the experimental period of two months.（2）Compared with the control treatment,all treatments receiving P significantly increased the above-ground biomass,phosphorus uptake and phosphorus use efficiency of maize by 64.8%-221.3%,114.1%-593.0%and 2.1%-11.0%,respectively.The largest increase was observed in treatments receiving DAP and poly P.Both the phosphorus uptake and above-ground biomass of maize were positively and significantly correlated with soil Olsen P.（3）Phosphorus fractions of Ca₂-P,Ca₈-P,Al-P and Fe-P were enhanced by36.9%-610.0%,21.7%-85.5%,57.2%-83.0%,28.5%-77.8%in all phosphorus application treatments except O-P and Ca₁₀-P,which remained unchanged except in Ca Mg P treatment.Of which,the greatest increases in Ca₂-P and Ca₈-P were observed in treatments given MAP,DAP,poly P and Urea P;the largest increases in Al-P and Fe-P were found in SSP+ASA and SSP treatments;significant increases in O-P and Ca₁₀-P were only obtained in Ca Mg P treatment.The Poly P treatment had the significantly greater Ca₂-P than MAP and Urea P treatments,only lower that DAP treatment,but it contained a significantly lower Ca₈-P relative to DAP,MAP and Urea P treatments.Compared with SSP,SSP+ASA significantly increased the contents of Ca₂-P and Al-P by 24.9%and 11.9%,respectively,and the available phosphorus content increased by 11.4%.The inorganic P fractions of Ca₂-P,Ca₈-P and Al-P showed a significant and positive correlations with soil available phosphorus and phosphorus uptake by plants.（4）Compared with initial,the contents of available P,total P and P activation coefficient were significantly increased by 22.25 mg·kg^-1,490.30 mg·kg^-1and 1.65%,respectively;Long term application of DAP significantly increased soil total P content by272.70 mg·kg^-1,but decreased available P and P activation coefficient by 3.16 mg·kg^-1and0.87%,respectively.（5）Compared with initial,the total inorganic phosphorus content of long-term application of SSP fertilizer increased by 84.95%,and the increase rates of Ca₂-P,Ca₈-P,Al-P,Fe-P,O-P and Ca₁₀-P were 228.76%,467.45%,253.35%,249.30%,45.01%and17.02%,respectively;the total inorganic phosphorus content of long-term application of DAP increased by 22.01%,and the contents of Ca₈-P,Al-P,Fe-P and O-P increased by181.50%,60.66%,72.55%and 31.14%respectively,while the contents of Ca₂-P and Ca₁₀-P decreased by 34.33%and 15.71%respectively.（6）Compared with the long-term application of two synthetic phosphorus fertilizer varieties,the average annual amount of inorganic phosphorus components converted from unit superphosphate was higher than that from di-ammonium phosphate,but the transformation from di-ammonium phosphate fertilizer to fixed phosphorus Ca₁₀-P was less.In conclusion,it is recommended to apply diammonium phosphate fertilizer under winter wheat summer maize system in Lou soil area of Guanzhong Plain.It can not only ensure the demand of crops for phosphorus,but also increase the most labile P and moderately labile P fraction in soil,weaken the accumulation of the least labile P fraction,so as to improve the utilization rate of phosphorus fertilizer.