Study On The Characteristics Of Phosphorus Depletion In Topsoil Of Lou Soil

In order to provide a basis for the assessment of phosphorus reduction potential and the effective utilization of accumulated phosphorus in high phosphorus farmland,the characteristics of phosphorus depletion and phosphorus morphological changes in Lou soil with different phosphorus levels were studied.A long-term experiment was conducted to study the winter wheat-summer maize system,The law of soil phosphorus depletion and the characteristics of phosphorus change under different phosphorus levels were studied,and the phosphorus depletion model of Lou soil was established by using the data obtained from the experiment;Pot experiment was conducted to study the characteristics of phosphorus depletion in soil with different phosphorus fertility.In the field experiment,six treatments were selected,including low amount of organic fertilizer（M1）,low amount of organic fertilizer combined with low amount of nitrogen and phosphorus fertilizer（M1N1P1）,low amount of organic fertilizer combined with high amount of nitrogen and phosphorus fertilizer（M1N2P2）,high amount of organic fertilizer（M2）,high amount of organic fertilizer combined with low amount of nitrogen and phosphorus fertilizer（M2N1P1）,high amount of organic fertilizer combined with high amount of nitrogen and phosphorus fertilizer（M2N2P2）.All treatments stopped applying organic fertilizer and phosphorus fertilizer,and only applied nitrogen fertilizer.In the pot experiment,five phosphorus application levels of five phosphorus fertility gradients（F1,F2,F3,F4,F5）were selected from the previous phosphorus application rates of 60 and 120 P₂O₅（kg/ha）:F1P60,F2P60,F3P60,F4P60,F5P60,F1P120,F2P120,F3P120,F4P120,F5P120,all treatments stopped fertilization.The main findings are as follows:（1）At the beginning of the depletion experiment,the higher the content of soil Olsen-P and Ca₂-P,the greater the annual consumption rate of soil Olsen-P and Ca₂-P,and there was a significant linear relationship between them.Only in the high phosphorus level treatment,the higher the content of soil total phosphorus,active organic phosphorus（L-OP）and medium active organic phosphorus（ML-OP）,the greater the annual consumption rate,and there was a significant linear relationship between the two.（2）Among the inorganic phosphorus fractions,Ca₂-P decreased the most（37.6%-74.0%）,followed by Ca₈-P（5.3%-48%）.The reduction of Al-P and Fe-P in M2,M2N1P1and M2N2P2 treatments was also relatively high.The reduction of Ca₈-P accounted for18.6%-152.7%of the total inorganic phosphorus（TPi）reduction.The contribution rate of Ca₂-P was only 6.8%-12.0%in five years.（3）L-OP decreased by 20%-35.1%,ML-OP decreased by 2.6%-27.9%.The reduction of labile organic phosphorus（ML-OP）accounted for about 55.6%-99.1%of the total organic phosphorus（TPo）reduction,while the reduction of labile organic phosphorus（L-OP）accounted for only 2.1%-11.1%of the total organic phosphorus（TPo）reduction.The contents of O-P、Ca₁₀-P、MR-OP and HR-OP were relatively stable.（4）The effect of each phosphorus component on available phosphorus was:Ca₂-P>Ca₈-P>L-OP>Fe-P>ML-OP>Al-P>O-P>Ca₁₀-P>MR-OP>HR-OP.（5）Soil Olsen-P content and soil Olsen-P variation were significantly positively correlated with crop yield and phosphorus uptake.Under the current conditions,the critical soil available phosphorus for wheat yield has been proved to be only 35.1 mg/kg in actual production.Therefore,continuous and reasonable application of phosphorus fertilizer can maintain the appropriate phosphorus fertility level of Lou soil,which is a means to improve the utilization rate of phosphorus fertilizer.The results provide a theoretical basis for the development of specific phosphorus fertilizer management strategies in the Lou soil area of the Guanzhong Plain.