Analysis Of Phosphorus Fertilizer Availability Loss And Forms Transformation In Meadow Soil-cotton System

This study is based on the irrigated meadow soil-cotton field system in northern Xinjiang.Two parts of the experiment are meadow soil cultivation and cotton pot cultivation.In order to provide scientific basis for rational phosphorus application in cotton field,the effects of phosphorus fertilizer varieties and application methods on available phosphorus,total phosphorus and inorganic phosphorus forms in meadow soil and phosphorus absorption and biomass of cotton were quantitatively analyzed,and the law of phosphorus transformation in meadow soil-cotton system was explored.The meadow soil culture experiment set up six treatments:triple super phosphate base application（TSP-B）,mono-ammonium phosphate base application（MAP-B）,ammonium polyphosphate base application（APP-B）,mono-ammonium phosphate drip application（MAP-D）,ammonium phosphate drip application（APP-D）and no phosphate fertilizer（CK）.The cotton pot cultivation was divided into two groups:base application and drip application.In the basal application test,there were four treatments:triple super phosphate base application（TSP-B）,mono-ammonium phosphate base application（MAP-B）and no phosphate fertilizer（CK）.In the drip application test,there were three treatments:mono-ammonium phosphate drip application（MAP-D）,ammonium phosphate drip application（APP-D）and no phosphate fertilizer（CK）.And all pot experiments were conducted with cotton（C-）and no cotton（N-）as controls.The main results and conclusions are as follows:In the experiment of meadow soil cultivation:（1）Ca₁₀-P and O-P were the highest inorganic phosphorus forms in meadow soil,accounting for36.7%～38.4%and 35.1%～36.9%of total inorganic phosphorus,respectively.The other forms of Ca₈-P were 13.6%～14.3%,Al-P was 6.1%～6.5%,Fe-P was 4.7%～5.1%,Ca₂-P was at least 1.7%～1.8%.The correlation between Ca₂-P and available P was the strongest,followed by Ca₈-P,Al-P and O-P.TSP,MAP and APP could increase the contents of Ca₂-P,Ca₈-P,Al-P and Fe-P in soil in a short term,but had little effect on the contents of Ca₁₀-P and O-P.（2）Base application of P fertilizer could increase the contents of available P and inorganic P in 0～20cm soil layer of irrigated meadow,while drip application could only increase the contents of available P and inorganic P in 0～5 cm soil layer;Thus,for deep root crops,base application should be the main phosphate fertilizer,and TSP with relatively low price should be selected;for shallow root crops（<5 cm）,the drip application of phosphorus fertilizer can be used,and the effect of APP drip application is better than map.In the experiment of meadow soil-cotton pot cultivation:（1）Ca-P was the main component of inorganic P in soil,accounting for more than 70%of total inorganic P.Ca₁₀-P was the most and Ca₂-P was the least in Ca-P.For cotton,Ca₂-P is the most effective phosphorus source,followed by Ca₈-P.In addition,cotton also significantly affected the content and proportion of Fe-P in meadow soil（P<0.05）.（2）In terms of soil P pool,base application of P fertilizer could significantly（P<0.05）increase the contents of available P Ca₂-P and Ca₈-P,drip application of P fertilizer significantly（P<0.05）increased soil available P and Ca₂-P contents.And APP has stronger effect than MAP over time.The cotton roots activated TSP,MAP and APP to a certain extent,and the available P content and phosphorus activation coefficient of cotton planted soil were higher than those of non-cotton planted soil under P application.（3）From the perspective of cotton growth and development,high input of phosphorus fertilizer could not promote the growth and development of cotton.The dry matter quality of cotton treated by TSP and MAP was higher than that treated by APP at budding,flowering and Bolling stages under base application,and significantly higher than that treated by MAP at flowering and bolling stages（P<0.05）There was no significant difference between MAP and APP under drip application.From the economic point of view,TSP and MAP should be selected under base application and drip application respectively.