| As an important reserve resource of cultivated land,barren rocky beach can be used for comprehensive harnessing and development.After transforming into cultivated land via relevant optimization engineering measures,it is not only of great benefit for flood control and disaster reduction,but also has enormous argicultural output efficiency.When comprehensively improve barren rocky beach,how to rebuild the plough layer,ensure its stability and satisfy crops growing requirements is a great concern.Soil structure,as a basic characteristic of soil,direct effects the growth and development of plants through its effects on soil fertility.It is not only an important indicator of land productivity,but also an important basis for identification of soil erosion extent.Based on the results of simulation experiment,model simulation and laboratory experiment in a desert rocky beach area from 2011 to 2014,aiming at the problems of bare gravel,shallow soil layer and large riverbed gradient,this paper studies the thickness of soil,the construction of plough layer.the settlement of soil and the erosion of surface layer of this area and analyzes the correlation among crop output and thickness and capacity of overbarden via RZWQM2 mode stimulated crop yield after plough layer construction.The main conclusions drew as fol ows:(1)Revealing the characteristics of water seepage and particle migration with different soil thickness treatments.With the increase of soil thickness,soil water leakage and leakage rate will decrease.Compared with 5cm thick soil layer,the cumulative water leakage and averageeakage rate of 20cm thick soil layer are about 35.60%and 33.63%of it.There was a negative correlation between the amount of soil patrticles removed and the thickness of soil layer.The greater the thickness of soil layer,the smaller the amount of soil particles removed.The soil particles in the leachate tend to be stable at the later stage of 100 min.The content of silt(>0.005 mm)was the highest and gradually reduced.With the increase of soil thickness,the concentration of clay in the leachate gradually increased.The change of soil particle size in the leachate showed that the particle size of powder particles tends to be stable after increasing with the increase of leakage time,while the sand grains tend to be stable after decreasing.The thinner the soil layer is,the more unstable the soil structure is,the thicker the soil layer is,the stronger the soil water and fertilizer conservation ability is.(2)The leakage and erosion characteristics of soil water fertilize with different bulk density treatments are revealed.The soil bulk density,initial leakage capacity and average leakage rate are negatively correlated.However,the total nutrient leakage decreases with increasing capacity at a capacity of not more than 1.5 g/cm3,and the difference of nutrient leakage is small when the isolation layer capacity is greater than 1.5-1.7 g/cm.It is shown that the core soil layer is 1.5 g/cm3 for optimal fertilizer capacity reconstructive structure.Soil erosion,sediment yield and soil bulk density are positively correlated.The greater the soil bulk density,the greater the sediment yield.Based on the analysis of the stability of the tillage layer structure and the characteristics of water and fertilizer retention,the optimum volume combination was obtained:the bulk density of the bottom layer was 1.5 g/cm',the thickness was 10 cm,the bulk density of the bottom layer was 1.3 g/cm,,the thickness was 20 cm,the bulk density of the tillage layer was 1.2 g/cm3,and the thickness was 20-30 cm.(3)The variation characteristics of soil quality under different soil cover thickness and plow layer construction mode are clarified.After the construction of different overlying soil thickness plots,the settlement depth of the soil and the thickness of the overlying soil are positively correlated,that is,the greater the thickness of the overlying soil,the greater the settlement depth,and the lowest settlement rate is when the thickness of the soil cover is 50 cm.Soil bulk density,compactness and overlying soil thickness were positively correlated,,and soil porosity and overlying soil thickness was negatively correlated.However,the bulk density and compactness of the upper soil(0-20 cm)and their increasing amplitude with the thickness of overlying soil were smaller than those of the lower soil(20-40 cm),but the porosity of the upper soil was greater than that of the lower soil,when the thickness of overlying soil was higher.The porosity of the two layers increases with the covering time when the thickness of the overlying soil is less than 50 cm,and the thickness of the overlying soil decreases with the covering time when is greater than 50 cm.When the thickness of overlying soil is 50 cm,the difference between bulk density,porosity and compactness of the lower and upper layers is the largest,and the variation amplitude with time is small,forming a soil structure of water and fertilizer conservation.Except for the crops in the fifth season,the soil nutrients of 0-30 cm in each season were higher when the soil thickness was 50 cm and 60 cm.The nutrient content of each index increased steadily with the time when the thickness of overlying soil was 50 cm,and reached the highest in the seventh season,and the soil quality index reached the highest,about 0.84.When the soil thickness is 50 cm,the physical and chemical properties of soil are relatively stable,which is beneficial to root growth and water and fertilizer conservation.(4)Based on the simulation results of RZWQM2 model,the influence of different plough layer construction patterns on crop yield is clarified.When the soil cover thickness was 50 cm and 60 cm,the plant height of summer maize and winter wheat was overall high,the yield of crops was the largest,and the number of ears,grains per ear and 1000-grain weight were larger.Based on RZWQM2 model,it is shown that the soil water-holding capacity and water-supplying capacity to crops are stronger and the crop yield is the highest when the covering soil thickness is 50-60 cm.The crop yield increases with the increase of the covering soil thickness,but the increase of crop yield slows down when the covering soil thickness is more than 50 cm.When the bulk density of the core soil layer is 1.5 g/cm3,the relative water content of the soil is higher and the water supply capacity to crops is stronger.Yet the bulk density of the core soil layer is 1.5-1.6 g/cm3,and the yield of the crop is the highest.(5)Combining with the engineering cost,the optimum model for constructing the barren rocky beach plough layer is as follows:the thickness of the overlying soil is 50 cm,the bulk density of the bottom-up soil layer is 1.5-1.6 g/cm,the thickness is 10 cm,the bulk density of the plough bottom layer is 1.3 g/cm3,the thickness is 20 cm,the bulk density of the plough layer is 1.2 g/m3,and the thickness is 20-30 cm. |
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