| Slope land as an important land resource in China is the main part of agricultural land resources in China.The cultivated area of cultivated land is 2/5 of cultivated land,and the grain yield of sloping land accounts for 1/5~1/3;purple soil is mainly distributed in the upper reaches of the Yangtze River,accounting for about 18% of the total land area of the upper reaches of the Yangtze River,concentrated in Sichuan Province and Yunnan Province,the two provinces of purple soil accounted for 75%the above.Purple soil has obvious high productivity,rapid weathering and strong erosion.Purple soil slope farmland shallow soil,more stone,bedrock depth shallow,only 40 ~ 100 cm,high soil porosity,soil saturated high water conductivity,hydraulic characteristics of the spatial variability.The soil profile,soil and chemical characteristics and tillage characteristics of sloping land are the root causes of the soil quality of sloping land.The paper analyzes the soil quality change and stability characteristics of slope farmland,establishes the minimum data set of soil quality evaluation of sloping farmland,The optimization method of quality is the quantitative evaluation of soil quality of sloping farmland and the prerequisite of soil quality improvement of slope farmland.In this paper,Chongqing Hechuan,Jiangxi,Yunnan and three locations in Chuxiong purple soil as the research object,the soil physical and chemical characteristics and the characteristics of soil fertility were analyzed in different areas,the soil physical and chemical characteristics of purple soil were studied in different areas through field investigation and laboratory test combining.Soil infiltration and reservoir characteristics were determined by indoor ring detection method,analysis of different regional slope cropland of purple soil infiltration and water retention properties;at the same time,the soil stability and corrosion resistance were studied by soil dry sieve and wet sieve,soil disintegration and water stability in different areas;The establishment of minimum data evaluation indicators of soil quality in purple soil set by the method of principal component analysis(MDS),analyzes the influence on slope cropland of purple soil quality in different regions of soil erosion;and through the data access and data analysis of the survey results,the suitability evaluation indexes of the regional threshold of purple soil quality,put forward the optimization approach of slope farmland soil quality;Finally,the changing characteristics of slope protection measures-biological ridge under dry and wet alternation were analyzed.The main conclusions:(1)The distribution of crop roots in the sloping land decreased from top to bottom with the soil profile,and there were differences in soil physical properties at different levels.The crop root mainly distributed in surface soil(more than accounted for the entire crop root 60%),a small amount of the distribution in the subsoil(accounting for about 20% of the crop root),and the bottom layer of almost no crop roots exist;The mechanical composition of soil in different locations was mainly composed of sand content and silt content,and soil cosmid(<0.001 mm)content of 0-20 cm was significantly higher than that of 20-40 cm and 40-60cm;The soil bulk density was 0-20 cm <20-40 cm <40-60 cm with the vertical depth of slope soil;The soil total porosity and capillary porosity of the three sites were consistent with the vertical depth of soil,which was characterized by tillage layer(0-20 cm)> soil layer(20-40 cm)> bottom layer(40-60 cm);The physical quality of cultivated land in Hechuan slope farmland of Chongqing is poor,mainly in the highest soil bulk density(1.43g/cm3),the total porosity(45.97%)and capillary porosity(34.36%)is the smallest;The soil physical properties of purple soil slope land at the same location changed with the vertical depth.From the perspective of soil quality,the soil physical quality of 0-20 cm tillage is better than that of 20-40 cm soil layer and 40-60 cm soil bottom layer.(2)The soil nutrient and tillage characteristics of purple soil slope land in different places were different.There were significant differences in soil organic matter content in purple soil slope at different locations,and there were significant differences in soil total nutrients and available nutrients in purple soil;The content of soil organic matter in purple soil slope was from high to low order in Yunnan(28.80 g/kg),Jiangxi Xingguo(9.03 g/kg),Chongqing,Hechuan(8.80 g/kg);There was a significant difference in soil nutrient content with soil depth in different sites;The content of total nitrogen in 0-20 cm soil was higher than that of 20-40 cm and 40-60 cm soil layer in different sites;The available nutrient changes in different vertical levels of slope farmland were basically the same,and the available nutrient was mainly concentrated in 0-20 cm layer,while 20-40 cm and 40-60 cm soil layers were not significantly different;The soil shear strength and soil penetration resistance of the plow layer in the purple soil slope landed in different locations were expressed as Chongqing Hechuan> Yunnan Chuxiong> Jiangxi Xingguo,and the soil shear strength and soil penetration resistance increased with the vertical depth of soil layer;The soil shear strength of the sloping land in different locations was 15.39,14.74 and 10.66 kg/cm2,respectively,and the soil penetration resistance was 424.83,252.50 and 188.87 kPa.The results show that the cultivated soil of purple soil slope in Chongqing Hechuan can better resist the shear failure ability of rainfall and tillage,as well as the compaction ability of tillage machinery.(3)The results showed that the soil infiltration characteristics of the cultivated land in different sites were consistent with the vertical depth of the tillage layer,that is,the soil infiltration decreased with the depth of the soil.The characteristics of soil infiltration in slope land in different locations were consistent with the vertical depth of the plough layer;The Kostiakov model is suitable for fitting different locations 0~20cm slope cropland of purple soil infiltration process;and the depth of 20~40cm Horton in Chongqing Hechuan and Yunnan Chuxiong area model is suitable;the Philip model with a physical base,but in different locations in the purple soil soil to the effect is poor,therefore,the Philip model is suitable;The total storage capacity of soil water is manifested as Yunnan Chuxiong(1052.52 t/hm2)> Jiangxi Xingguo(974.15 t/hm2)> Chongqing Hechuan(867.30 t/hm2);The change law of soil water dead storage capacity is consistent with the change of soil water total storage capacity.The Reservoir capacity of purple soil slope cultivated land are in HeChuan,Chongqing(293.02 t/hm2)> Chuxiong,Yunnan(291.89 t/hm2)> Xingguo,Jiangxi,(182.28 t/hm2);The soil retention capacity is the largest in theXingguo,JiangXi((458.776 t/hm2),which is 2.54 times of that of Hechuan,Chongqing soil.The maximum effective storage capacity of purple soil slope is the highest in Yunnan Chuxiong(873.311t/ hm2);Total storage capacity,dead storage,utilizable capacity,flood detention capacity,the maximum effective capacity of Cultivated topsoil are 0-20 cm tillage layer was larger than 20-40 cm soil layer and 40-60 cm soil layer;There was a significant positive correlation between soil infiltration and soil bulk density,while the infiltration rate and average infiltration rate were positively correlated with soil bulk density.The correlation coefficients were 0.540 and 0.525,respectively;There was a significant positive correlation between total porosity and soil infiltration rate and soil infiltration rate,and the correlation coefficients were 0.604 and 0.635,respectively;The correlation between soil infiltration performance and mechanical composition was positively correlated with 1 ~ 0.05 mm,and negatively correlated with 0.05 ~ 0.001 mm and <0.001 mm.There was a negative correlation between soil bulk density and soil bulk density,and the correlation coefficient was between 0.021~0.451,soil reservoir characteristics were positively correlated with soil water content,soil porosity and soil organic matter.(4)The distribution characteristics of different aggregates are shown in different sites.>0.25 mm dry aggregate content from high to low is Chongqing Hechuan(97.716%)> Yunnan Chuxiong(94.430%)> Jiangxi Xingguo(90.875%);The content of >0.25 mm water stable aggregates in purple soil was significantly lower than that of air dried aggregates;The specific content of >0.25 mm water stable aggregates is Chuxiong,Yunnan(86.118%)>Hechuan,Chongqing(83.769%)> Xingguo,Jiangxi(65.805%);The destruction rate of soil aggregate structure in cultivated land of purple soil slope is Jiangxi Xingguo(34.195%)> Chongqing,Hechuan(16.231%)> Yunnan,China(13.882%);The content of >0.25 mm air dried aggregates and >0.25 mm water stable aggregates in 0~20cm soil layer was less than 20~40cm and 40~60cm soil layer;The fractal dimension of soil dry aggregates in purple soil slope in different locations,Chongqing Hechuan area between 1.79 ~ 2.38,Jiangxi Xingguo area in the range of 2.01 ~ 2.30 changes,Yunnan Chuxiong numerical value between 2.16 ~ 2.52;The fractal dimension of soil wet sieve aggregate is Yunnan Chuxiong > Jiangxi Xingguo > Chongqing;The soil aggregate stability index for Yunnan Chuxiong(average of 3.620)> Jiangxi Xingguo(average 2.796)> Chongqing Hechuan(average of 2.528),the same place in different layers of soil aggregate stability index of the overall performance of 0~20cm>20~40cm>40~60cm,namely 0~20cm soil and structural stability is relatively good,with strong soil erosion ability.The results showed that geometric mean diameter(GMD)and mean weight diameter(MWD)has the same variation,the specific performance of Chongqing Hechuan(GMD: 4.975,MWD: 1.014)>Yunnan Chuxiong(GMD: 3.977,MWD: 1.012)> and Jiangxi Xingguo(GMD: 2.808,MWD: 1.008);The GMD and MWD in different soil layers at different locations were generally realized as dry sieve aggregates larger than those in wet sieve aggregates;The final breakage rate of soil aggregates in purple soil slope in different locations is Jiangxi Xingguo(86.667%)> Chongqing Hechuan(78.333%)>Yunnan Chuxiong(45.333%);The numerical stability index of different sites is the largest(0.686)in YunNan Chuxiong area,the second(0.550)in Chongqing Hechuan and the lowest in Jiangxi Xingguo(0.211);When the soil water content is constant,the shear strength increases linearly with the increase of the vertical pressure of the soil.Different places purple soil of the vertical pressure on the shear strength of the effect size differences in soil in Yunnan area of Chuxiong has the largest increase,increases more than 300;in the Chongqing Hechuan region,between the increase range of 273~299;Jiangxi Xingguo area stress increases with the increase of 130~299.With the increase of moisture content,the shear strength of soil decreased,and the effect of water content on shear strength is mainly to reduce the cohesion of soil,and the influence of internal friction angle is smaller;The cohesion of soil decreased with the increase of water content in different locations,but the change of water content to the internal friction angle was relatively small,in general,the internal friction angle decreased with the increase of water content.(5)The minimum data set of soil quality assessment of purple soil slope farmland was soil bulk density,field water holding capacity,soil penetration resistance,soil organic matter,> 0.25 mm water stable aggregate content.The difference of soil quality of cultivated land in purple soil slope shows that the plough layer of Hechuan slope in Chongqing has the characteristics of large soil bulk density,low porosity,low permeability and water storage capacity,the soil quality of the cultivated land is poor;The average value of soil tillage index in the cultivated land of slope land in different places is in the range of suitable cultivated land of cultivated land,while the evaluation index of 20-40 cm and 40-60 cm exceeds the range of 20-40 cm and 40-60 cm individual index value is beyond the suitable range of tillage;Good tilth index level will be directly related to the level of crop yield,so it can take appropriate measures(such as local farming in general 22-24 cm following subsoiling,deep soil fertility etc.)of topsoil soil quality improvement,such as the choice of subsoiling,organic fertilizer,straw and other suitable cultivation measures,in order to the soil quality slope farmland effectively improve;There are four main ways to control the quality of cultivated land in Sloping Farmland based on DPSIR,one is to control the dynamic balance of total cultivated land and maintain the quantity and quality of cultivated land.Second,strengthen the construction of agro-ecological environment of slope farmland and protect the ecological environment of slope farmland;Third is to increase investment to ensure the benefits of slope farmland and quality and safety;four for the development of arable land protection standards to ensure the long-term efficiency of arable land protection.(6)The distribution of biological ridge root space are different in different soil layers.the soil layer of 0~10cm,biological roots have fine root distribution of <1mm root diameter,1 mm< root diameter class <2 mm roots to 20~30cm of soil layers at most,2 mm <root diameter ? 5mm root system in the distribution of soil more uniform;Biological ridge soil bulk density,porosity characteristics and field capacity difference with wet and dry time changed significantly.In the time before rainfall,the level of mulberry biological ridge soil bulk density in 1.19~1.38 g/cm3,and increases with the increase of soil depth;After the rainfall,the soil bulk density increased gradually and then decreased with the change of dry and wet level;The changes in the number of pores and non-capillary pores occurred mainly from day 0 to 1 day of wet and dry.The cohesion and internal friction angle are approximately linearly attenuated with the increase of water content,and the correlation coefficients of cohesion and internal friction angle are 0.6820 and 0.7251 respectively;The soil cohesion and internal friction angle at each level under the effect of dry and wet before the first decline after the recovery of the "V" type change trend;The soil cohesion degree is 30 ~ 40cm(18.11Kpa)> 0 ~ 10cm(15.80Kpa)> 10 ~ 20cm(15.28Kpa)> 20 ~ 30cm(6.99kpa),the soil friction angle is 0 ~ 10 cm layer Soil attenuation degree of the largest,is 14.69°,30 ~ 40 cm the minimum degree of attenuation,is 12.84°;During the wet and dry cycle,the soil cohesion and internal friction angle were recovered,but did not reach the level before the rainfall,the cohesion recovery degree of 30 ~ 40cm(14.24Kpa)the largest,20 ~ 30cm(0.99Kpa)is the smallest,and the degree of recovery of the internal friction angle is in the order of 0~10 cm(13.33 °)> 10~20 cm(11.71 °)> 20~30 cm(11.02 °)> 30~40 cm(9.54 °);There were significant positive correlations with cohesion,internal friction angle and shear strength of root layer density and root surface area density of different root diameter soil mulberry ridge.The correlation coefficient was between 0.301 and 0.793.The agroforestry systems biological ridge slope land and slope land surface field crop composition,to slope cultivated crop growth,increase the yield and create favorable conditions. |
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