| Purple soil slope farmland is an important cultivated land resource for agricultural production in the southwest region,and is an important area for local agricultural production and an important erosion zone in the Yangtze River Basin.The concentration of cultivated layer quality in purple soil slope farmland is characterized by severe erosion and low yield and unstable crop yield.Soil erosion is the main cause of degraded sloping land,soil erosion and productivity,and it has great potential danger to the ecological safety and sustainable use of sloping farmland.Sloping ploughed soil is not only the basis of agricultural production,but also the object of soil erosion.To understand the soil profile and physicochemical properties of sloping arable land,study the effects of soil erosion on soil moisture,drought resistance and soil stability of plough layer,and establish a minimum data set for rational plough evaluation of purple soil sloping land,and analyze crop-plough layer The relationship between soil suitability and the identification of soil quality barriers in sloping farmland can provide an important basis for the evaluation and regulation of rational tillage in slope farmland.In this paper,purple sloping arable land is taken as the research object.Through the investigation of small sloping farmland in the field,the simulated erosion community in the field,and the data review,the structural characteristics of the plough layer of purple soil slope with different erosion degrees are analyzed.Through field investigation and indoor physical and chemical properties test,the changes of soil physical and chemical properties of purple soil slopes with different erosion degrees were analyzed,and the influence of soil erosion on the geochemical properties of purple soil slopes was explained.Through soil moisture characteristic curve,soil infiltration and soil reservoir characteristics,the soil water retention and drought resistance performance of sloping farmland with different erosion degrees were analyzed.Based on the soil water stability index,disintegration and mechanical stability characteristics,the stability and erosion resistance of the ploughed soil in different sloping fields were analyzed.Based on principal component analysis and Norm value method,the minimum data set?MDS?for soil quality evaluation of purple soil slope farmland was established,and the soil quality of purple soil slope farmland was evaluated.Using the soil quality barrier factor diagnosis model,the obstacles of each soil index were analyzed.By constructing the crop-plough layer coupling coordination degree model,the coordination degree and suitability of crop-plough layer coupling in purple soil slope farmland with different soil fertility levels were analyzed,and the control methods were proposed according to the type of obstacles.The main conclusions are as follows:?1?On the plot scale,there are significant differences in soil profile and soil erosion properties of sloping farmland in purple soil slope.The soil structure of the purple soil slope arable land is better,and the soil structure is granular.The soil is loose.The texture shows that the soil structure changes to sandy soil and heavy soil with the decrease of soil fertility grade.The soil structure is blocky and the soil is slightly compact.Or compact,the mother layer is due to disturbances that cause the soil to be massive,firm or extremely tight.As the degree of soil erosion increases,the soil texture of sloping farmland gradually becomes“roughly ossified”.The soil particles of S-0 slope farmland are mainly concentrated in the powder content of 50.67%;S-5,S-1010 and S-1515 are mainly composed of sand content and powder content,which are 41.83-44.33%and 38.67-43.33%respectively.The change in S-2020 soil particles is mainly concentrated at 1-0.05 mm.The average soil bulk density of sloping farmland with different erosion degree is S-5?1.44 g/cm3?>S-15?1.43g/cm3?>S-0?1.41 g/cm3?>S-20?1.40 g/cm3?>S-10?1.36 g/cm3?;The soil nutrient of purple soil slope farmland with different erosion degree is generally low,which belongs to the middle and lower level.Among them,soil organic matter,total nitrogen and alkali nitrogen were all at the five-level level,and the available potassium level was four levels.The total phosphorus and available phosphorus showed the third level and the total potassium level.?2?Different soil erosion degree The soil moisture characteristic curve,pore characteristics,infiltration and reservoir characteristics of sloping arable land and different soil depths are obviously different.Under the same suction,the soil water content of the soil decreases with the increase of erosion degree.When the degree of erosion is increased from 0 cm to 20 cm,the rate of decline of soil volumetric water content is 7.8-24.32%,and the average decline rate is 17.80%.The increased soil erosion can reduce the volumetric water content of the soil under the same suction,which is not conducive to the water storage of the slope farm soil.The pores of sloping farmland with different erosion degree are concentrated in the storage pores with diameter of<0.03 mm,which accounts for24.47-31.83%,followed by ventilated pores with a diameter of>0.1 mm,accounting for11.88-22.13%,and finally The water-conducting pores with a diameter of 0.10.03mm are only between 0.15 and 3.31%.There are significant differences in pores at different diameters at different vertical depths.The soil pores of the soil in the plough layer?0-10 cm and 10-20 cm?are generally larger than the layers of 20-30 cm and 30-40 cm.The total soil storage capacity is S-10?422.65t/hm2?>S-5?413.12 t/hm2?>S-15?408.20 t/hm2?>S-0??404.92 t/hm2>S-20?403.46 t/hm2?,As the degree of erosion increases,the ineffective water in the soil and soil of purple soil slope farmland has increased to varying degrees.Among them,S-1010 slope farmland soil ineffective reservoir increased the most,increasing by 7.3%.There is little difference between the water storage characteristics of0-40 cm layer soil in different eroded slope farmland.The maximum water storage capacity varies between 139-144mm,the maximum retained water volume varies between 42-50mm,the saturated water storage varies between 182-194mm,the slope of different erosion degrees under the same soil depth,the maximum suction The water storage capacity accounts for 75%of the saturated water storage.Under the same suction,the percentage of cumulative loss of water in the sloping farmland soil increased with the increase of erosion degree,which was S-10>S-20>S-15>S-5>S-0.Under the same soil suction,the soil of S-0 slope farmland lost the least water,and the soil of S-10 slope farmland lost the most water.With the degree of erosion,the soil drought resistance of slope farmland deteriorated.?3?There are significant differences in soil water stability and soil mechanical stability between different sloping fields and different vertical depths.The water stability index of sloping farmland with different erosion degree is S-15?47.35%?>S-5?36.47%?>S-10?31.20%?>S-0?27.44%?>S-20?23.37%?;It indicates that when erosion occurs on purple soil slope farmland,the first resistance to soil erosion is enhanced,and then weakened.When erosion continues to occur,the erosion resistance is enhanced and then weakened.For different erosive sloping land plots,the soil water stability index of S-00 and S-2020 sloping arable land is different at different vertical depths,which are18.88%-32%and 13.48%,respectively.28.44%change.The soil shear strength of sloping farmland with different erosion degrees is S-15?7.94 kg/cm2?>S-0?7.57 kg/cm2?>S-20?6.88 kg/cm2?>S-5?6.82kg/cm2?>S-10?6.73 kg/cm2?;The degree of compaction is generally manifested as the degree of erosion increases,showing a trend of decreasing first,then increasing and then decreasing;Among them,S-00 slope farmland had the highest soil compactness?average 167.12 N/cm2?,S-15?average value 151.93 N/cm2?and S-10minimum?average value 96.25 N/cm2?.The soil erodibility K value of the sloping arable land was as follows:S-0?0.0410?>S-10?0.0406?>S-15?0.0399?>S-5?0.0389?> S-20?0.0377?.The soil stability of the ploughed ploughed soil was in the middle and lower level with different erosion degree.The soil stability increased first and then decreased with the degree of erosion.With the increase of soil erosion,the soil stability is S-15>S-10>S-5>S-20>S-0;This indicates that the soil stability is the weakest at the beginning of soil erosion,and the soil stability is gradually increased with the degree of erosion.When the erosion degree is 15 cm,the soil stability reaches the strongest,and then the soil stability begins to decline.As the degree of soil erosion increased,the soil penetration resistance first decreased and then increased,which was S-20?8.77kPa?>S-0?8.37 kPa?>S-5?7.71 kPa?>S-15?7.51 kPa?>S-10?4.72 kPa?.?4?The minimum data set for quality evaluation of purple soil slope farmland consists of tillage thickness,silt,clay,soil organic matter,soil compaction,soil shear strength,and six soil attribute indicators.The soil barrier factors of sloping farmland are mainly divided into three categories.The soil quality of the purple soil slope arable land was lower than the middle and low grade,and the soil quality index?SQI-MDS?under the minimum data set of the small sloping farmland was between0.28 and 0.58.The soil quality index of sloping farmland with different erosion degree showed S-10?0.63?>S-0?0.59?>S-15?0.54?>S-5?0.52?>S-20?0.47?.The soil barrier factors of the three types of purple soil slope farmland are:The first category is nutrient-limited,with an obstacle degree between 0.065 and 0.083,including soil available phosphorus,saturated hydraulic conductivity,organic matter,particle content,shear strength,and total nitrogen;The second type is soil thickness limitation type,the degree of obstacle is between 0.047-0.057,including pH value,available potassium,slope,sand content,tillage thickness,bulk density,total porosity,effective soil thickness;The third category is the arable limit,and the degree of obstacle is between 0.032 and 0.041,including natural moisture content,penetration resistance,firmness,and clay content.The direct effect of soil compaction is the largest and negative?-0.716?,which has an inhibitory effect on the quality of cultivated soil.The direct diameter coefficients of organic matter,shear strength,tillage thickness and clay content on the soil quality index of the cultivated layer were 0.409,0.393,0.335and-0.282,respectively.The ranking parameters of the soil quality index and the minimum data set index of the plough layer are:R2?X6?>R2?X4?>R2?X3?>R2?X1?>R2?X2?>R2?X5?,compactness and organic matter As the main decision variable of the soil quality index of the plough layer,the shear strength is the main limiting variable.?5?The suitable relationship between crops and plough layer in purple soil slope farmland has two states:coordinated development and dysfunctional decline,and there are four kinds of states:synchronous type,lag type,profit and loss type and total loss type.Purple soil slope arable land can be divided into three types of plough layer.The dominant factors affecting crop yield are field slope,effective soil thickness,soil acidification and cation exchange capacity.Under the same ground conditions,the decline in crop yields is more pronounced,and the deterioration of the quality of the plough layer is lagging.The crop-plough layer coupling degree?Cd?showed that the I type of plough layer?0.4820?and the type II plough layer?0.5207?were the basic coordinated development crops,the plough layer was synchronous,the crop growth was barely suitable,and the type III?0.3343?was on the verge of dysfunctional decline.It is not suitable for the loss-yielding type of crops and the moderate growth of crops.The soil regulation of purple soil slope arable land is mainly as follows:soil thickness regulation can be realized by measures such as no-tillage,no-till,deep-slung,and bio-tanning;soil nutrient regulation can be applied with appropriate application of biochar+fertilization,straw Field+fertilization and other measures to achieve. |
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