Effects Of Different Application Of Nitrogen And Phosphorus On Phosphorus Forms Of Typical Farmland In The Dry Farming Area Of The Loess Plateau

Long-term unreasonable fertilization in agricultural production will lead to the accumulation of ineffective phosphorus in the soil,which not only reduces the effectiveness of phosphorus,but also affects the utilization rate of phosphorus fertilizer,and leads to the risk of waste and loss of phosphorus resources.Combined application of nitrogen and phosphorus fertilizers is one of the important measures to improve the effect of fertilization.This experiment uses factorial experiment design.There are four levels of nitrogen and phosphate fertilizers(0,75,115,190 kg·hm^-2),16 orthogonal treatments in total.The treatment experiment is arranged in random blocks and repeated three times.In 2019 Soil samples of 0-20 cm cultivated layer were collected after crop harvest on July 28.The forms of inorganic phosphorus and organic phosphorus in each treated soil were studied by the Jiang Baifan-Gu Yichu and Bowman-Cole methods.Effects of total nitrogen,total phosphorus,available phosphorus,microbial biomass carbon,nitrogen,phosphorus,alkaline phosphatase,wheat yield,apparent phosphorus fertilizer utilization rate and water use efficiency on inorganic phosphorus and organic phosphorus components.The main findings are as follows:（1）From the perspective of the composition of phosphorus forms,the soil in this study is dominated by inorganic phosphorus,which accounts for about 78%of the total phosphorus content of the soil,the soil organic phosphorus accounts for about22%of the total phosphorus content,and the soil inorganic phosphorus is mainly Ca₁₀-P,Accounting for about 50%of the total inorganic phosphorus,the order of the content of each inorganic phosphorus form is Ca₁₀-P>Ca₈-P>OP>Fe-P>Al-P>Ca₂-P.The composition of organic phosphorus is dominated by MLOP,accounting for about 70%of the total organic phosphorus,followed by HROP,MROP,and the least is LOP.（2）Nitrogen application increased the content of O-P and decreased the content of Ca₂-P,Ca₈-P,Al-P,Fe-P and Ca₁₀-P.Phosphorus application significantly increased the content of inorganic phosphorus in all forms,and all inorganic phosphorus forms increased with the increase of phosphorus application.With the increase of nitrogen application rate,Ca₈-P and total inorganic phosphorus decrease first and then increase and then decrease,Al-P,Fe-P and Ca₁₀-P decrease and then increase,Ca₂-P decreases and O-P increases.The effect of phosphorus application on soil total inorganic phosphorus,Ca₂-P,Ca₈-P,Al-P,Fe-P,O-P is the most significant.The effect of nitrogen application on soil Ca₁₀-P is the most significant;Ca₈-P,Fe-P,O-P reached the maximum in N1P4 treatment,Al-P reached the maximum in N1P3treatment,and Ca₁₀-P reached the maximum in N1P2 treatment.Ca₂-P has a positive effect on soil available phosphorus and has the largest contribution rate.（3）Nitrogen application reduced the content of LOP,MLOP and MROP,and increased the content of HROP.Phosphorus application can increase the content of LOP,MLOP,MROP,and reduce the content of HROP.As the amount of nitrogen applied increased,LOP,MLOP,and MROP decreased first and then increased.The N3 level was the smallest and the N1 level was the largest.The total organic phosphorus decreased.The HROP increased first and then decreased.As the amount of phosphorus applied increases,the total amount of LOP,HROP,and organic phosphorus increases,and MROP decreases.The effects of phosphorus application on soil LOP,MROP,and HROP are the most significant.The effects of nitrogen application on soil MLOP and total organic phosphorus are the most significant.Reaching maximum,HROP reaches maximum in N3P3 processing.LOP has a positive effect on soil available phosphorus and has the largest contribution rate.（4）Nitrogen application significantly increased SOC,TN,WUE,grain yield,above-ground biomass,stem total phosphorus,leaf total phosphorus,grain total phosphorus,MBC,MBN,MBP,ALP,phosphate fertilizer utilization rate,phosphorus fertilizer partial productivity,reduced TP,Olsen-P,pH,harvest index,apparent surplus of phosphorus.Phosphorus application significantly increased TN,TP,Olsen-P,WUE,grain yield,above-ground biomass,stem total phosphorus,leaf total phosphorus,grain total phosphorus,MBN,MBP,ALP,phosphorus apparent surplus and reduced SOC.（5）Redundancy analysis results showed that Al-P and phosphate fertilizer utilization ratio,Fe-P and ALP and MBN,Ca₈-P and TP,Ca₁₀-P and MBP were significantly related.SOC is the most important factor affecting the change of inorganic phosphorus composition.LOP and TP,MROP and pH,HROP were significantly correlated with grain yield,WUE and MBP.MBP is the most important factor influencing the change of organic phosphorus composition.In conclusion:the order of inorganic phosphorus forms in spring wheat farmland combined with nitrogen and phosphorus is Ca₁₀-P>Ca₈-P>O-P>Fe-P≈Al-P>Ca₂-P,mainly Ca₁₀-P;the order of organic phosphorus forms is MLOP>HROP>MROP>LOP,mainly MLOP.Ca₂-P and LOP are more effective for soil available phosphorus.Combined application of nitrogen and phosphorus increased the contents of Ca₂-P,Ca₈-P,Fe-P,O-P,LOP,MLOP,and HROP,and decreased the contents of Ca₁₀-P and MROP.MBP is the key factor affecting the distribution and transformation of organic phosphorus components;SOC is the key factor affecting the distribution and transformation of inorganic phosphorus forms.From the perspective of fertilizer utilization,this study recommends a nitrogen application rate of 115kg·hm^-2 and a phosphorus fertilizer of 115 kg·hm^-2 as the fertilizer application efficiency for the region.