Activating Fixed P And Controlling P Fertilizer Invalidation In Typical Soils Of Northern China

Reducing the fixation of phosphorus fertilizer in the soil and improving its utilization rate has always been a key issues for further research in soil science and plant nutrition.In this study,two strategies have been used to overcome this problem:(1)Activation and reuse of accumulated phosphorus in the soil;(2)Scientific and reasonable application of phosphate fertilizer.A pot experiment was conducted to study the effects of m monoammonium phosphate(MAP),ammonium polyphosphate(APP)and calcium superphosphate combined with ammonium sulphate(N:P=2:1)on phosphorus retention and fixation in nine different soil types(Black soil,White clay soil,Brown soil,Brown calcareous soil,Chestnut calcareous soil,Tidal soil,Cinnamon soil,Lou soil and Grey desert soil)of Northern China,and two common organic acids(oxalic acid and humic acid)were selected as activators.The effect of different organic acids on the accumulation and activation of phosphorus in different soils was aimed to select a suitable phosphorus fertilizer for typical soils in North China,to alleviate phosphorus fixations in soils and to reuse the bound phosphorus in soils.The main results are as follows:(1)Compared with the control,different phosphatic fertilizers increased the soil available phosphorus.In the whole incubation study,soil available phosphorus content in black soil was higher in ammonium polyphosphate treatment,phosphorus fixation was lowest,and the effect of phosphorus retention and control was good.The white soil has highest phosphorus fixation rate,and about 80%of phosphorus was fixed after 30 days of fertilization,however the effect of superphosphate combined with ammonium sulfate was relatively good.There was no significant difference in three kinds of phosphate fertilizers are in brown soil.Overall,ammonium polyphosphate has a good effect in brown soil;In brown calcium soil and chestnut soil,available phosphorus content in monoammonium phosphate treatment was highest,but p H showed a significant decrease,and the resistance and control effect was good.In grey desert soil,available phosphorus content was higher and p H was reduced significantly,which shows that the main resistance and control of phosphorus fixation in alkaline soil was due to acidification effect.Under high p H,the solubility of insoluble nutrients increased through acid-base neutralization.Monoammonium phosphate had the best effect in Chao Soil and Lou soil,while ammonium polyphosphate had better effect in brown soil.(2)In the whole incubation study,the application of ammonium polyphosphate,monoammonium phosphate and calcium superphosphate combined with ammonium sulfate can improve the soil p H to a certain extent,which can make the soil p H close to neutral.Soil phosphorus fixation mainly occurs within 10 days after fertilization,so the phosphorus fertilizer should be applied at the same time of sowing,and proper measures should be taken to prevent and control the fixation of phosphorus.(3)Soil available phosphorus was changed significantly after the application of exogenous organic acids into nine soils.During the whole incubation period,available phosphorus content was increased in early stages and then decreased during incubation period,and soil p H value was decreased in the early stage and then increased with incubation time.Generally,Lowest soil p H was observed during 10-20 days of incubation,and the effect was gradually disappeared after 35 days of incubation.After 60 days of incubation,there was no significant difference among each treatment and the control.The total activated amount of available phosphorus in Albic soil was highest(93.1 mg/kg),which is the best one among the nine tested soils;followed by black soil(91.9 mg/kg)and brown calcium soil(22.29 mg/kg).(4)In black soil and albic soil,humic acid has a stronger ability to activate soil phosphorus than oxalic acid and mixed acid(Mixed acid>oxalic acid>humic acid).Oxalic acid application in alkaline calcareous soil,such as Chao soil,cinnamon soil,chestnut soil,brown calcium soil and grey desert soil,has higher phosphorus activation rate than other treatments,and the p H reduction in these soils was also significant,which shows that oxalic acid has strong complexation ability with calcium ion,and can ionize H~+to dissolve part of phosphorus absorption matrix and activate soil phosphorus.In general,the activation effect of oxalic acid and mixed acid is better in calcareous and neutral soil,and humic acid is better in Northeast acidic soil.