Temporal And Spatial Distribution Of Soil Phosphorus In Plough Layer On A Typical Black Soil Slope

The Mollisol region is the important commodity grain basket of China.However,in this area,soil fertility was seriously reduced because of the landscape,long-term unreasonable farming increased soil erosion.This enhances the heterogeneity of soil nutrients in the space,and which is more difficult to the management of soil nutrient,and threats to the local ecological environment and the sustainable development of agriculture.Phosphorus(P)is necessary for plant growth,that affect crop growth,yield and grain quality.P,at the same time,as a closely correlated with environmental factors,and is directly related to the environment quality of surface water and groundwater.Since the whole management process in spring,such as cultivation,sowing,fertilizing,weeding,row,influence the spatial heterogeneity of P.Crop growth and soil erosion under slopes,has dynamically changed the soil P distribution.Thawing-freezing phenomenon is a common and covered of winter-spring and autumn-winter period freeze in Mollisol region,as well as freezing--thawing process also significantly affected the soil structure,soil erosion,P conversion process,and then change the spatiotemporal distribution of soil P.Therefore,it is very importance to clarify the the spatial distribution of soil P during the growth stages before and after freezing and thawing and its main driving mechanism in black soil area,which is also the important evidence for accurately evaluating soil fertility,guiding fertilization and environmental governance.The experiment was carried for two years in a typical black soil in Northeast China.Both of classical statistics and geo-statistics were used to study the spatial and temporal distribution characteristic of soil total phosphorus(TP)and available phosphorus(AP)during the crop growth stages,and the period before and after freezing and thawing.Soil nitrogen(N),water,heat,indictors of crop growth were measured to analyze the main driving mechanism of P spatial distribution.These results can provide a theoretical evidence and technical support for the management of soil P from the farmland in black soil area.The main results and conclusions are as below:Spatial and temporal pattern of AP and the main driving mechanism in the growth stages and the period of freezing and thawing process.(1)During the crop growth stages,the AP content ranged from 3.11 to 315.09 mg kg-1,15.26 to 340.52 mg and 1.01 kg-1-60.07 mg kg-1 in seedling stage,growth period and mature period,respectively.AP ranged from 1.96 to 42.60 mg kg-1 before the freezing and thawing,and was between 4.68 to 156.20 mg kg-1 after freezing and thawing.(2)Due to the influences of rainfall,temperature,erosion and crop growth on P uptake,the dynamic changes in AP are similar between various slope positions under different treatments,but greatly differ between the years.The soil AP contents at various slope positions under various treatments are significantly higher in the early growth period than in the seedling and maturity periods,but the different between slope positions and between treatments are not significant.The residue return and crop rotation treatments have the weak effects on the spatial and temporal distribution of AP during the crop growth stages.(3)During the seedling stage,growth stage and maturity stage,the heterogeneity of AP is mainly affected by the structural factors except that after fertilization.The heterogeneity is mainly affected by random factors,exhibiting strong spatial autocorrelation.In the autumn,the soil AP heterogeneity is mainly affected by random factors during freeze-thawing process.After this process,treatments without residues in 0-20 cm soil layer or treatments with residues in 0-5 cm soil layer are mainly affected by the random factors,and treatments with residues in 5-10 cm soil layers were mainly affected by random factors.(4)After freeze-thawing process,the soil AP contents are generally higher than before the freeze-thawing.The AP content in the 10-20 cm soil layer without bucket mulching is 58.94%significantly higher than that before freeze-thawing under corresponding treatment,while the AP content in the 5-10 cm soil layer with bucket mulching is 40.31%significantly higher than that before the freeze-thawing.Temporal and spatial pattern of TP and its main driving mechanism during the freeze-thaw process:(1)The soil TP content is between 0.20-1.01 g kg-1 before freeze-thawing,whereas is between 0.04-1.84g kg-1 after freeze-thawing.During the freeze-thaw process,increase of evaporation capacity and appropriate soil moisture content are beneficial to the upward movement of soil P.(2)During freeze-thawing process,the higher bulk density of soil at the slope back resulted in the P migration towards the topsoil.After freeze-thawing process,TP migration towards topsoil got the maximum at the slope crest of the treatments,while it was lower at the bottom slope.(3)Although mulching(residue return and bucket mulching)reduced evaporation,reduced erosion,and was beneficial to increasing the surface soil P content.After the freeze-thawing process,maximum TP(no straw return in the treatments of soybean-maize rotation)significantly increased by 56.05%than before the freeze-thawing.Despite the large evaporation capacity increased P upward migration in the treatments without mulching,but the erosion reduced the P content in the topsoil layers.(4)The influence from cropping rotation,e.g.maize-soybean rotation and maize continuous cropping,has little effect on the dynamic change of TP in plow layer during the freeze-thaw period.(5)Before freeze-thawing process,TP is mainly affected by structural factors.After freeze-thawing process,TP in the treatment with the mulched is mainly affected by structural factors,while that in the unmulched 0-5 cm and 10-20 cm topsoil layers is mainly affected by random factors.