Effects Of Long-term Different Fertilization Measures On Phosphorus Form Change And Accumulation In Dryland Red Soil Profile

Soil phosphorus is one of the essential nutrient elements for crop growth and development.The availability of phosphorus is an important index to evaluate soil quality and fertility.However,phosphorus is easily fixed in the soil,and the utilization rate of phosphorus fertilizer is low.Therefore,it is of great significance to study the effects of single application of inorganic phosphorus fertilizer and combined application of organic and inorganic phosphorus fertilizer on soil phosphorus forms.Based on the long-term(1989～)positioning experiment of red soil ecological experimental station of Chinese Academy of Sciences in Yingtan City,Jiangxi Province,this study discussed the effects of long-term different fertilization measures on the morphological changes and accumulation characteristics of phosphorus in dry land of red soil profile,and analyzed the evolution characteristics of clay minerals and iron oxide in red soil by X-ray diffraction(XRD).Five treatments were set up in the field experiment:NPK,NPK+peanut straw(NPK+PS),NPK+green fertilizer(NPK+FR),NPK+rotten pig manure(NPK+PM)and only nitrogen and potassium(CK).The main results obtained are as follows:(1)Long term application of phosphorus fertilizer significantly improved the basic physical and chemical properties of red soil,such as p H,organic matter,total nitrogen,total phosphorus and available phosphorus content.The effect of NPK+PM treatment was the most significant,and there was no significant difference among NPK,NPK+PS and NPK+FR treatments.(2)Long term application of phosphorus fertilizer can improve the phosphorus activation coefficient(PAC)of the plough layer(0～20 cm).The soil PAC of no phosphorus fertilizer treatment was only 1.62%.The soil PAC of NPK,NPK+PS and NPK+FR treatment could be increased to 6%～10%,and the soil PAC of NPK+PM treatment was the most significant,up to 38.91%.(3)The long-term application of phosphorus fertilizer had a great effect on the form of soil phosphorus.The inorganic phosphorus in red soil treated with CK was mainly in closed storage state,but under different phosphorus fertilizer treatments,exogenous phosphorus was more likely to accumulate in the form of aluminum phosphate(Al-P)and iron phosphate(Fe-P),and NPK+PM treatment was the most obvious.The organic phosphorus components are mainly moderately active organic phosphorus(MAOP)and moderately stable organic phosphorus(MSOP),and the contents of active organic phosphorus(AOP)and highly stable organic phosphorus(HSOP)were lower.Compared with CK treatment,the MAOP content of NPK,NPK+PS and NPK+FR treatment increased slightly,and NPK+PM treatment increased the most significantly.The content of MSOP in NPK+PM treatment increased significantly,and there was little difference between other treatments and CK treatment.Correlation analysis showed that aluminum phosphate(Al-P)and iron phosphate(Fe-P)in moderately active organic phosphorus(MAOP)and inorganic phosphorus were significantly correlated with the content of available phosphorus(P<0.05).(4)The effect of long-term fertilization on phosphorus in red soil is mainly concentrated in the plough layer,with the increase of soil depth.In the 20～40 cm soil layer,compared with CK,the total phosphorus content of NPK,NPK+PS,NPK+FR and NPK+PM treatments increased by 76.18%,80.53%,81.84%and 184.93%respectively;The content of available phosphorus increased by 72.40%,77.60%,97.39%and 2308.17%respectively.In the soil layer below 40 cm,the contents of total phosphorus and available phosphorus in NPK,NPK+PS and NPK+FR treatments had no significant change compared with CK treatment,but there was still a small amount of available phosphorus accumulation in the bottom layer(60～100 cm)soil in NPK+PM treatment.Phosphorus fertilizer and its combined application with organic fertilizer significantly promoted the accumulation and activation of soil phosphorus,especially the rotten manure with pig manure as raw material.(5)The correlation between soil p H,organic matter content and phosphorus form of red soil shows that p H and organic matter are positively correlated with the proportion of Al-P and Fe-P in inorganic phosphorus,and negatively correlated with the proportion of O-P and Ca-P;PH and organic matter were negatively correlated with the proportion of AOP in organic phosphorus,and organic matter was significantly positively correlated with MSOP.(6)The contents of clay minerals and iron oxides have a certain correlation with phosphorus forms in red soil.1.4 nm transition minerals,hydromica and kaolinite are positively correlated with the contents of Al-P,Fe-P and O-P in inorganic phosphorus,respectively.There was no significant relationship between free iron oxide(Fe_d)and inorganic phosphorus in red soil,while amorphous iron oxide(Fe_o)was positively correlated with the contents of Fe-P and Ca-P;1.4 nm transition minerals and kaolinite are negatively correlated with the proportion of AOP and MSOP in organic phosphorus,and positively correlated with the proportion of MAOP.Hydromica has no significant relationship with the components of organic phosphorus.Free iron oxide(Fe_d)was positively correlated with HSOP content,while amorphous iron oxide(Fe_o)was negatively correlated with AOP content.