Effects Of Phosphate Fertilizer Regulation Measures On Phosphorus Transformation And Availability In Black Soil

Phosphate fertilizer is one of the important agricultural fertilizers in China.In recent years,unreasonable application of phosphate fertilizer has led to the decrease of black soil fertility in Northeast China,resulting in the accumulation of phosphorus in the soil,low utilization rate of phosphate fertilizer,increased the risk of black soil phosphorus loss and led to a series of agricultural pollution problems.Therefore,it is necessary to select suitable phosphate fertilizer types,reasonable proportion of combined application and phosphorus reduction control measures for the black soil area in Northeast China.In this paper,indoor simulation experiments and field experiments were used to explore the effects of phosphate fertilizer types on the form and availability of phosphorus in black soil.Effects of combined application of phosphorus fertilizer on soil phosphorus form and availability;effects of phosphorus reduction regulation on soil phosphorus forms and transformation.Four treatments were set up in the indoor simulation experiment:no phosphate fertilizer（CK）,diammonium phosphate（DAP）,calcium magnesium phosphate（FCMP）and ammonium polyphosphate（APP）.Six treatments were set up in the field experiment:no phosphate fertilizer（CK1）,100%diammonium phosphate （CK2）,25%calcium magnesium phosphate+75%diammonium phosphate（T1）,50%calcium magnesium phosphate+50%diammonium phosphate（T2）,75%calcium magnesium phosphate+25%diammonium phosphate（T3）,ammonium polyphosphate: diammonium phosphate=2:1（T4）.A total of 8 treatments were set up in the field experiment of phosphorus reduction regulation:no phosphorus fertilizer（CK）,farmer conventional fertilization（FP）,25%phosphorus reduction（R1）,50%phosphorus reduction（R2）,50%phosphorus reduction+regulation measure 1（R2C1）,50%phosphorus reduction+regulation measure 2（R2C2）,50%phosphorus reduction+regulation measure 3（R2C3）,50% phosphorus reduction+regulation measure 4（R2C4）.The main results are as follows:（1）The results of indoor simulation test showed that the contents of organic phosphorus,available phosphorus and phosphorus components in soil increased first and then decreased with the prolongation of culture time until equilibrium was reached.Among them,APP（ammonium polyphosphate）had the best effect on the increase of available phosphorus content in black soil;among the different phosphorus fractions,the content of medium active phosphorus（Na OH-Pi and Na OH-Po）was the highest,and the content of active phosphorus（H₂O-Pi and H₂O-Po） was the lowest.APP（ammonium polyphosphate）treatment increased the content of active phosphorus in black soil and reduced the proportion of active phosphorus in total phosphorus.（2）The results of field experiment on combined application of phosphate fertilizer showed that combined application of phosphate fertilizer could increase the contents of total phosphorus,available phosphorus and organic matter in black soil.The total phosphorus content increased by 4.87%-7.45%,the organic matter content increased by 0.23%-7.84%,and the available phosphorus content increased by 33.6%-57.64%.T1 treatment（25%calcium magnesium phosphate+75%diammonium phosphate）performed best.The combined application of phosphate fertilizer reduced the proportion of medium active phosphorus（Na OH-Pi and Na OH-Po）and residual phosphorus to total phosphorus,and increased the content of active phosphorus（H₂O-Pi,H₂O-Po and Na HCO₃-Pi and Na HCO₃-Po）and low active phosphorus（HCl-Pi and HCl-Po）.Among them,T1 treatment had the best effect,which reduced medium active phosphorus and residual phosphorus by 5.64%and 1.91%,respectively,and increased active phosphorus and low active phosphorus by 6.00%and 1.54%,respectively.（3）The results of field experiments on phosphorus reduction regulation showed that all treatments of phosphorus reduction regulation increased the total phosphorus and organic matter content of black soil to a certain extent.The total phosphorus content of black soil increased by0.78%～4.7%,and the organic matter content increased by 0.25%～7.84%.The regulation of each treatment（R2C1,R2C2,R2C3 and R2C4）significantly increased the available phosphorus content in black soil,among which R2C4 treatment was the best,followed by R2C3treatment.Compared with CK treatment,the increase was 38.22%～80.46%,while compared with FP treatment,the increase was 1.59%～32.62%.From the perspective of phosphorus component content,Res-P,Na OH-Pi and Na OH-Po accounted for the main proportion of each treatment,while active phosphorus（H₂O-Pi,H₂O-Po,Na HCO₃-Pi and Na HCO₃-Po）and low active phosphorus（HCl-Pi and HCl-Po）accounted for a small proportion of total phosphorus.Among the treatments of phosphorus reduction regulation,R2C4 treatment had better effect on the improvement of each phosphorus component than other treatments,increased the content of active phosphorus and low active phosphorus,and reduced the proportion of medium active phosphorus and residual phosphorus in total phosphorus.The results of ³¹P NMR spectra showed that the content of organic phosphorus components was higher than that of inorganic phosphorus components.In the inorganic phosphorus components of black soil,orthophosphate content is higher than pyrophosphate;the content of orthophosphate monoester in organophosphorus components is higher than that of phosphate diester.In summary,under the conditions of this experiment,single application of ammonium polyphosphate,25%calcium magnesium phosphate fertilizer+75%diammonium phosphate,and phosphate fertilizer control measures based on 50%phosphorus reduction combined with application of phosphate solubilizing bacteria and start-up phosphorus technology have the most significant effect on the improvement of available phosphorus in black soil,and the effect of improving the content of active phosphorus in black soil is the best,which reduces the fixation of phosphorus in black soil and is more conducive to the conversion of invalid phosphorus to available phosphorus in black soil.