Effects Of Continuous Combined Application Of Organic And Inorganic Fertilizers On Soil Phosphorus Fractions

The combined application of phosphate fertilizer and organic fertilizer is a common measure to reduce fertilizer application and improve soil phosphorus supply.However,the proportion of the two types of fertilizers applied,and the effects of soil phosphorus fractions,utilization efficiency and yield of crop after consecutive fertilizer application for years are still unclear.Therefore,it is of great significance to investigate the effects of the single application of phosphate fertilizers and the combined application of phosphate fertilizers with different organic fertilizers on soil phosphorus fractions for years to improve the efficiency of phosphate fertilizer utilization.This study set up eight treatments with no fertilizer control,single fertilizer application,15%pomace phosphorus+85%fertilizer phosphorus（low amount）,30%pomace phosphorus+70%fertilizer phosphorus（medium amount）,45%pomace phosphorus+55%,chemical Fertilizer Phosphorus（High）,15%Cow Manure Phosphorus+85%Fertilizer Phosphorus（Low）,30%Cow Manure Phosphorus+70%Fertilizer Phosphorus（Medium）and 45%Cow Manure Phosphorous+55%Fertilizer Phosphorous（High）.Field experiments and mathematical statistics were conducted for four consecutive years to study dynamic change characteristics of volatile water-soluble phosphorus（H₂O-P）,sodium bicarbonate（NaHCO₃-P）,moderately stable sodium hydroxide（NaOH-P）,hydrochloric acid（HCl-P）and stable residual phosphorus（Res-P）;And this study also investigated the relationship between different fertilization treatments with phosphorus use efficiency,the phosphorus fractions,soil pH and organic matter,aiming to provide a theoretical basis for the rational application of phosphate fertilizer with organic fertilizer.The main conclusions are as follows:（1）After 4 years of consecutive fertilization,the phosphorus content in soil under different fertilization treatments was 0.61-213.14 mg kg^-1.The content of volatile phosphorus and phosphorus was 3.37-26.58 mg kg^-1,accounting for 0.61-4.33%of total phosphorus;medium stability of phosphorus was 34.47-193.72 mg kg^-1,accounting for6.27-28.91%of total phosphorus;the contents of steady phosphorus was 191.38-204.95mg kg^-1,accounting for 28.92-34.81%of total phosphorus.The soil phosphorus fractions were dominated by Res-P and HCl-P,and the content of H₂O-P was the lowest,ranging from 10.21 to 16.49 mg kg^-1.（2）During the process of consecutive fertilization,the content of changeable phosphorus and moderate-stable phosphorus in soil all showed an upward trend,and the change of steady-state phosphorus was slight.The increases of soil changeable phosphorus content under the combined application of fungicides,cow dung and chemical fertilizers were significantly higher than those of single-fertilizer treatments.The combined applications of middle-level organic fertilizer and chemical fertilizer were significantly higher than those of other treatments（P<0.05）.The increases of soil changeable phosphorus under the same proportion of chemical fertilizers was higher than that of the microbial residue.The proportions of NaHCO₃-P and NaOH-P in total phosphorus were higher than those before fertilizations,while the proportion of HCl-P was decreasing.The results showed that the appropriate amount of slag,cow dung and chemical fertilizer increased the content of phosphorus components in the soil that was easily absorbed by plants and promoted mineralization and decomposition of phosphorus components that were difficult to be absorbed by plants.（3）After 4 years of consecutive fertilization,the crop yield and phosphate fertilizer use efficiency under the combined application of medium amount of microbial residue,cow dung and chemical fertilizer were significantly higher than those of single application of chemical fertilizer（P<0.05）.The yields of wheat and maize under the combined application of medium-dose cow dung and chemical fertilizers were increased by 885 kg hm^-2 and 975 kg hm^-2,respectively;the ratio of chemical fertilizer with cow manure was superior to that of chemical fertilizer;Phosphate fertilizer physiological utilization was performed as cow dung combined chemical fertilizers>single application of chemical fertilizers>microbial residue combined chemical fertilizers.（4）The surplus of soil phosphorus under the combined application of fungicides,cow dung and chemical fertilizers showed a downward trend with the growth of fertilization years,while the treatment with single chemical fertilizer showed an upward trend.From 2013 to 2016,the surplus of phosphorus in soil was increasing under the treatment of single chemical fertilizer,and the treatment with fungicides,cow dung and chemical fertilizers showed a downward trend,and the middle amount of cow dung and fertilizer had the lowest phosphorus surplus.With the increase of fertilization time,the positive correlation between the changeable components of phosphorus and pH was gradually decreased.The treatment with cow manure,fungicides and fertilizers showed the opposite trend.With the increase of fertilization time,the positive correlation between organic matter and phosphonate components,NaOH-P,and the negative correlations between HCl-P and steady-state phosphorus showed an upward trend in the treatment of cow manure,microbial slag and chemical fertilizer.The positive correlation of volatile phosphorus components increased with the increase of the organic fertilizer ratio.（5）The results of correlation analysis of different soil phosphorus components showed that there was a certain degree of mutual transformation between different phosphorus components.There was a significant positive correlation between soil available phosphorus and soil available phosphorus（P<0.05）.There was a significant negative correlation between moderately stable and stable phosphorus and soil available phosphorus（P<0.05）;There were also a negative correlation between varible phosphorus component,NaOH-P,HCl-P and stable phosphorus components;While there was a positive correlation only between HCl-Po and Res-P.