Effects Of Temporal And Spatial Configuration Changes On Soil Water And Carbon Sequestration Rate Of Apple And Crop Intercropping System

The Loess Plateau is the largest area in the world where apples are planted continuously.Apple planting has become an effective measure to deal with the problem of large-scale reduction of cultivated land after the “Grain for Green Project” and a leading industry to promote regional economic development.The precipitation characteristics and unreasonable farming system lead to the deterioration of the soil water environment of the local dry farming apple orchard and the shortage of soil organic carbon pool.The agroforestry system has both the functions of soil water regulation and carbon sequestration,but the high-water consumption growth period of the components of the composite system in this region basically coincides,which will inevitably increase the probability of soil water competition.According to these above problems,this study took dry farming apple orchards in the Loess Plateau as the research object,established a new type of fruit farmer composite system by changing the time and density of intercropping,and systematically studied the compound by using field positioning observation and field sampling characteristics of soil water and soil organic carbon comprehensively.The study set up four treatments: apple interrow intercropping high density rape(AHR),apple interrow intercropping medium density rape(AMR),apple interrow intercropping low density rape(ALR),and apple with clearing tillage(CK).The main conclusions of this study are as follows:(1)The effects of various treatments on soil water and the interannual regulation and control effects are explored.For the intercropping period in the normal precipitation year(2018),the soil water effect value of apple trees is AHR(0.9%)> AMR(-1.9%)> ALR(-4.2%);the soil water effect value of the edge of intercropping is AHR(1.8%))> AMR(-2.2%)> ALR(-5.6%);the effect value of soil water between rows is AHR(-3.5%)> AMR(-6.1%)> ALR(-6.6%).For the intercropping period during the wet year(2019),the soil water effect value of apple trees is ALR(2.3%)> AMR(-1.2%)> AHR(-2.8%);the soil water effect value of the intercropping edge is AMR(1.0 %)> ALR(-0.1%)> AHR(-0.7%);the effect value of soil water between rows is ALR(2.0%)> AHR(-0.3%)> AMR(-2.6%).For the non-intercropping period,the three intercropping treatments have positive effects,and the positive effect of AHR significantly greater than ALR and AMR.The negative effects are mainly concentrated in the 0-100 cm soil layer,and the 100-200 cm soil layer shows more positive effects.The spatial distribution of soil water shows that the consumption of soil water between rows of crops is mainly concentrated in the 0-100 cm soil layer,and the AHR intercropping treatment significantly reduces the loss of soil water storage during the dormant period of apple trees.(2)Clarified the inter-species soil water competition relationship.The fluctuation of the RSWD value in the normal precipitation year is greater than that in the wet year,and the minimum value of the normal precipitation year is much smaller than that in the wet year.The normal precipitation year will produce more intense competition.The three treatment competitions mainly occur when the 0-100 cm soil layer is consistent with the root overlap layer,while the 100-200 cm soil layer is more of a promotion effect.Among the three intercropping densities,ALR has the highest competition,followed by AMR,and AHR has the smallest competition.For ALR,the main competition area is the intercropping edge,and for AMR and AHR,intercropping is the main competition occurrence location.(3)Clarified the characteristics and influencing factors of soil organic carbon content in the composite system.Compared with CK,the three intercropping treatments significantly increased the soil organic carbon content of the 0-10 cm soil layer.At the same time,the organic carbon storage in the 0-100 cm soil layer was significantly increased.The growth rate of soil organic carbon content in different intercropping densities show big discrepancy,the growth rate increased with the intercropping density.The growth rate of soil organic carbon content is positively correlated with aboveground biomass,underground biomass,rape root density,silt content,and clay content,and is negatively correlated with soil p H,soil sand content,and soil water content.The above ground biomass explained growth rate of soil organic carbon most and significantly,at 41.9%.In summary,considering the soil water effect,soil water competition relationship and soil organic carbon change of the three intercropping systems,the implementation of a compound system model of high-density rapeseed intercropping in dry farming apple orchards on the Loess Plateau can ameliorate the soil water environment and increase the soil organic content.But intercropping density should be appropriately reduced in wet year to avoid the negative effects of soil water.