Evaluating the soil evaporation loss rate in a gravel-sand mulching environment based on stable isotopes data

In order to cope with drought and water shortages,the working people in the arid areas of Northwest China have developed a drought-resistant planting method,namely,gravel-sand mulching,after long-term agricultural practices.To understand the effects of gravel-sand mulching on soil water evaporation,we selected Baifeng peach(Amygdalus persica L.)orchards in Northwest China as the experimental field in 2021.Based on continuously collected soil water stable isotopes data,we evaluated the soil evaporation loss rate in a gravel-sand mulching environment using the line-conditioned excess(lc-excess)coupled Rayleigh fractionation model and Craig-Gordon model.The results show that the average soil water content in the plots with gravel-sand mulching is 1.86%higher than that without gravel-sand mulching.The monthly variation of the soil water content is smaller in the plots with gravel-sand mulching than that without gravel-sand mulching.Moreover,the average lc-excess value in the plots without gravel-sand mulching is smaller.In addition,the soil evaporation loss rate in the plots with gravel-sand mulching is lower than that in the plots without gravel-sand mulching.The lc-excess value was negative for both the plots with and without gravel-sand mulching,and it has good correlation with relative humidity,average temperature,input water content,and soil water content.The effect of gravel-sand mulching on soil evaporation is most prominent in August.Compared with the evaporation data of similar environments in the literature,the lc-excess coupled Rayleigh fractionation model is better.Stable isotopes evidence shows that gravel-sand mulching can effectively reduce soil water evaporation,which provides a theoretical basis for agricultural water management and optimization of water-saving methods in arid areas.

砾石覆盖对坡面产流产沙的影响

采用人工模拟降雨试验的方法,试验中设置降雨强度为30mm/h和60mm/h,坡度为10°和20°,地表砾石覆盖度为0,10%,20%,30%,40%和50%,对北京山区褐土坡面产流产沙特征进行研究。研究结果表明:(1)坡面产流时间随砾石覆盖度的增大而延迟,且两者有着较好的线性关系。(2)坡面总产流量随砾石覆盖度的增大呈线性减小,在雨强为30mm/h,坡度为10°和20°条件下,砾石覆盖度为50%的坡面总产流量比砾石覆盖度为0时的坡面产流总量减少45.19%和49.87%;在雨强为60mm/h时,坡度为10°和20°条件下,砾石覆盖度为50%的坡面总产流量比砾石覆盖度为0时的坡面产流总量减少24.33%和33.46%。(3)坡面土壤侵蚀量随砾石覆盖度的增加呈负指数减小,在雨强为30mm/h,坡度为10°和20°条件下,砾石覆盖度为50%的坡面总侵蚀量比砾石覆盖度为0的坡面总侵蚀量减少92.40%和68.21%;在雨强为60mm/h时,坡度为10°和20°条件下,砾石覆盖度为50%的坡面总产流量比砾石覆盖度为0时的坡面总侵蚀量减少69.65%和65.62%。(4)降雨强度和坡度不影响砾石覆盖影响坡面产流产沙的趋势。

Effects of Different Gravel Mulched Years on Soil Microbial Flora and Physical and Chemical Properties in Gravelsand Mulched Fields

Soil microbial flora and influencing factors of soil microbes in soil and gravel-sand mixed layer（ SGSML）,roots denseness layer（ RDL）,eluviate layer（ EL） and calcium accumulation layer（ CAL） in gravel-sand mulched fields（ GSMFs） with different gravel mulched years（ 1,6,12,19 and 25 years） were studied. The results showed that in the composition of soil microbes in the GSMFs,the quantity of bacteria was the largest,followed by actinomycetes,while the number of fungi was the smallest. The total quantity of soil microorganisms in the GSMFs dropped rapidly with the increase of soil depth,which was related to the sudden decrease in the quantity of bacteria. The number of microbes in the RDL was larger than that in the SGSML with few roots due to the effects of root distribution. The number of bacteria and actinomycete in the growing season was larger than that in the non-growing season,while the quantity of fungi in the growing season was smaller than that in the non-growing season. The quantity of bacteria and fungi was the largest in the GSMFs which had been mulched with gravel for 6-12 years. With the increase of mulching time,the GSMFs aged gradually,so their quantity reduced gradually. The quantity of actinomycetes was the smallest in the GSMFs which had been mulched with gravel for 6-12 years and increased with the increase of mulching time. The number of soil microbes in the GSMFs had a good correlation with soil moisture content,p H and mulching time. Soil total carbon content was an important factor restricting the quantity of soil microbes in the GSMFs.

DEM investigation of strain behaviour and force chain evolution of gravel-sand mixtures subjected to cyclic loading

The strain characteristic and load transmission of mixed granular matter are different from those of homogeneous granular matter.Cyclic loading renders the mechanical behaviours of mixed granular mat-ter more complex.To investigate the dynamic responses of gravel-sand mixtures,the discrete element method(DEM)was used to simulate the cyclic loading of gravel-sand mixtures with low fines contents.Macroscopically,the evolution of the axial strain and volumetric strain was investigated.Mesoscopi-cally,the coordination number and contact force anisotropy were studied,and the evolution of strong and weak contacts was explored from two dimensions of loading time and local space.The simulation results show that increasing fines content can accelerate the development of the axial strain and vol-umetric strain but has little effect on the evolution of contact forces.Strong contacts tend to develop along the loading boundary,presenting the spatial difference.Weak contacts are firstly controlled by confining pressure and then controlled by axial stress,while strong contacts are mainly controlled by axial stress throughout the whole cyclic loading.Once compression failure occurs,the release of axial stress causes the reduction of strong contact proportion in all local regions.These findings are helpful to understand the dynamic responses of gravel-sand mixtures,especially in deformation behaviours and the Spatio-temporal evolution of contact forces.