Study On The Effects Of Tillage Measures On The Physical Properties Of Cultivated-layer And Regulation Of Red Soil Sloping Farmland

Red soil slope farmland is an important type of farmland resources in the southern hillyregion of China.Due to the influences of rainfall,unreasonable tillage,soil management for a long time,the soil and water losed seriously of the slope farmland,and the cultivated-layer quality and physical properties obviously degenerate.Moreover,the soil productivity drops sharply,as well as the crop yields are low and unstable.These seriously restrict the sustainable development of agriculture in the hilly area with red soil.Therefore,it is beneficial to the sustainable utilization of slope farmland resources in red-soil hilly area by analyzing the cultivated-layer quality change characteristics and their obstacle types of red soil slope farmland as well as studying the influence of physical properties of cultivated-layer of slope farmland.This is also the premise and foundation to achieve the quantity,quality and ecology"trinity"protection of red soil slope farmland.This study takes the cultivated-layer of red soil slope farmland as the research object.Firstly,some comprehensive research methods are adopted,such as field investigation for the cultivated-layer of slope farmland in a small watershed scale,location experiment of tillage measures for the slope farmland in a patch scale,the compaction simulation experiment of indoor tillage,etc.Then,the minimum data set of cultivated-layer quality diagnosis of red soil slope farmland is built,and the obstacle types of cultivated-layer of red soil slope farmland is divided.Simultaneously,the influences of different tillage measures and tillage compaction on the physical properties of cultivated-layer of red soil slope farmland are contrastively analyzed.Next,from the perspectives of water retention and drought resistance,soil reinforcement and erosion resistance as well as soil fertility improvement,this study proposes three kinds of regulation measures and modes of reasonable cultivated-layer of slope farmland.The results can provide theoretical support and technological parameters for the cultivated-layer quality restoration of red soil slope farmland in southern hilly area,construction of reasonable cultivated-layer,suitability regulation of crop production,as well as water and soil loss control.Finally,the main research conclusions are as follows.1.Quality characteristics and obstacle types of cultivated-layer of red soil slope farmlandThe minimum data set for the cultivated-layer quality evaluation is composed of cultivated-layer thickness,saturated hydraulic conductivity of soil,clay particle of soil,the shear strength of soil,organic matter and available phosphorus.There is a significant difference in the suitability level of the quality evaluation index of the cultivated-layer of slope farmland.The average thickness(18.83±4.9cm)of the cultivated-layer is close to the optimum thickness for crop growth.The average mass fraction of clay particle is(12.28±6.72)%,and the average shear strength of soil is(3.78±1.01)kg/cm~2.Then,the soil structure damage is caused by unreasonable tillage ways as well as the water and soil loss.The organic matter(15.46±4.58cm)of soil and the total nitrogen(1.09±0.22cm)are at a moderate impoverishment level.The red soil slope farmland can be divided into six types,that is,the sticky heavy board type of obstacle cultivated-layer,erosion and degradation type of obstacle cultivated-layer,water restriction type of obstacle cultivated-layer,soil acidification type of obstacle cultivated-layer,thinning type of obstacle cultivated-layer and obstacle-free type.The main obstacle factors of cultivated-layer of the slope farmland are high content of clay particle in soil,low pH value,small thickness of cultivated-layer,and small shear strength of soil.On the basis of the nonlinear relationship between the cultivated-layer quality with anthropogenic and natural factors such as agricultural production,rainfall,etc.,the DPSIR concept model is built from five aspects of driving factor of cultivated-layer degradation(D),environment pressure of reasonable cultivated-layer construction(P),cultivated-layer state show(S),cultivated-layer problem influence(I),and regulation response countermeasures(R).There exists significantly same or opposite path relationship among all the impact factors of cultivated-layer quality of red soil slope farmland of DPSIR.The change rate of R with I in the opposite direction is11%,as well as the change rates of P and I with R in the opposite direction are 3%and 39%,respectively.Hence,it is helpful to take positive response measures to inhibit the cultivated-layer quality degradation and improve cultivated-layer quality.2.Influence of tillage measure on the stability change of cultivated-layer of red soil slope farmlandUnder various measures,the soil aggregates compositions of cultivated-layer of slope farmland present a negatively skewed distribution,the soil structure stability of cultivated-layer in the NT slope farmland is the strongest,and their soil aggregation degree is significantly higher than those of other measures.The content of aggregates more than 10mm from large to small is 36.15%(NT),30.74%(C),29.28%(CS),25.13%(CK)and 17.33%(S),which is similar to the change rule of the contents of aggregates with the sizes of 10~7cm and 7~5cm.The effects of NT and C on the water stability improvement in the cultivated-layer soil of slope farmland are significantly superior to those of other measures.The content of water stability aggregate with a size more than 5mm is the lowest with a value of 4.67%(CK),however,the largest contents are 12.43%(NT)and 13.65%(CS).Retention probability and water stability index of aggregates with a size more than 0.25mm are 1.8,2.64,respectively,both the largest ones with C,while the smallest values are 1.3,2.27,respectively,with CK.This suggests that C improves the compactness of particles in soil,and the NT has a small disturbance,so the structure is relatively stable.The enhancement effects of NT and C on soil force stability of cultivated-layer of slope farmland are higher than those of other measures.As the NT depth is 20~30cm,the shear strength(6.13kg/cm~2)of soil in the cultivated-layer is the largest,however,as the S depth is 0~10cm,the shear strength(1.87kg/cm~2)of soil in the cultivated-layer is the smallest.The smallest mean of soil compactness is 232.01 N/cm~2(S),and the largest mean of soil compactness is 319.72 N/cm~2(C).The K value of NT soil erodibility is 0.26,which has the most significant role in improving the erosion resistance of soil in the cultivated-layer of slope farmland.The K values of soil erodibility with other measures are 0.386(CS),0.426(S),0.436(C)and 0.472(CK),respectively.Therefore,some factors,such as tillage depth,tillage manner and so on,would affect the soil erosion resistance of slope farmland.3.Effects of tillage measures on soil infiltration and retention performance of cultivated-layer of red soil slope farmlandThe sub-soiling(S)is obviously superior to other measures in improvement of soil aeration porosity,enhancement effect of water conductivity porosity and soil infiltration performance for the cultivated-layer of slope farmland,while the compaction process(C)has a certain lag in soil infiltration.Soil aeration porosity mainly distributes in the 0~20cm cultivated-layer.The largest value is 66.16%with S,while the smallest values of soil aeration porosity are 40.52%and 39.52%,respectively,corresponding to the measures of the conventional tillage(CK)and C.The water conductivity porosities of soil are 7.39%,6.4%,6.13%,4.36%,and 2.51%from large to small,corresponding to the five measures of S,no-tillage(NT),S+C(CS),CK and C,respectively.Compared with other measures,the preferential flow path of soil in the cultivated-layer of S slope farmland is significant.Dyeing area of S is the largest at grade 5(5.58%),grade 7(7.48%)and grade9(6.67%),and the dyeing area of NT is the largest at grade 2(3.82%)and grade 3(3.95%).The enhancement effect of S on water retention performance of cultivated-layer soil in the slope farmland is significantly better than those of other measures.The largest total storage capacity of soil is 42.48t/hm~2 with S,and the smallest value is 39.47t/hm~2 with C.For the five measures,their actual storage capacity of soil from the large to the small is 342.67t/hm~2(S),316.07t/hm~2(C),315.1t/hm~2(CK),305.35t/hm~2(CS)and 304.61t/hm~2(NT),similar to the variation rule of the water retention efficiency of soil.The drought-resistant performance(4.342)of the soil in the cultivated-layer of S slope farmland are obviously better than those of other measures.And it has a significant effect on the seasonal drought resistance.However,C(-3.191)has a poor drought-resistant performance due to the insufficient water retention space.4.Influence of tillage compaction on the physical properties of cultivated-layer of red soil slope farmlandTillage compaction has an important impact on the pore structure and retention performance of cultivated-layer of red soil slope farmland.From the perspectives of soil retention performance of cultivated-layer,the times of tillage compaction both for loose slope farmland(1.1g/cm~3)and normal cultivated-layer(1.3g/cm~3)should not be more than twice.Moreover,the soil porosity,stable infiltration rate and maximum effective storage capacity of cultivated-layer gradually decrease with the compaction times increasing.As the compaction times change from the one to two,three and four,the soil porosities of the normal cultivated-layer in the growing season(moisture content of20%)are 41.78%,38.81%,35.56%and 33.57%,respectively.Under the interaction between compaction times and volume-weight,the porosity of the loose cultivated-layer is obviously larger than those of normal and compact(volume-weight is 1.5g/cm~3)cultivated-layers.Likewise,under the interaction of compaction times and moisture content,the soil porosities tend to be stable after cultivated-layer compaction for three times in rainy season(25%moisture content),growing season and dry season(15%moisture content).After compaction for two times,the stable infiltration of the soil in cultivated-layer tends to 0,and the maximum effective storage capacity of the soil becomes stable,which would accelerate the formation of plow pan.In addition,the tillage compaction has a significant effect on the erosion resistance of red soil slope farmland.From the perspective of soil erosion resistance performance enhancement,the twice tillage compactions of slope farmland is appropriate.The cohesive force of cultivated-layer soil increases with the increase of compaction times,soil volume-weight and moisture content.Furthermore,the internal friction angle of the soil increases with the compaction times and soil volume-weight increasing but decreases with the increase of moisture content.Under the interaction of compaction times and volume-weight,there is no obvious change in the cohesive force of soil after the loose cultivated-layer compaction for four times,the normal cultivated-layer compaction for three times,and the dense cultivated-layer compaction for one time.In addition,under the interaction of compaction times and moisture content,the cohesive forces of soil become stable after twice soil compaction in dry season,growing season and rainy season.For various volume-weight and moisture contents,the internal friction angle of the soil in the cultivated-layer tends to be stable after tillage compaction for three times,thus the compaction times is the main factor to affect the internal friction angle of soil in the cultivated-layer.Tillage compaction significantly affects the stability of cultivated-layer of red soil slope farmland.In consideration of the stability maintenance and the suitability of crop growth,the cultivated-layer compaction should not be more than 3 times.Soil compactness increases with the increase of compaction times and volume-weight but decreases with the increase of moisture content.Under the interaction between compaction times and volume-weight,the change amplitude of soil compactness after cultivated-layer compaction for two times is still larger.Moreover,under the interaction between compaction times and moisture content,the soil compactness become stable after cultivated-layer compaction for three times in the dry season.Under the interaction of compaction times and volume-weight,the cultivated-layer thickness tends to be stable after compaction for three times.Likewise,under the interaction of compaction times and moisture content,the cultivated-layer thickness tends to be stable after compaction for three times.Moreover,the compacted cultivated-layer obviously thins in the rainy season and thins less in the dry season.5.Regulation effects of different tillage measures on the cultivated-layer of red soil slope farmlandFrom the perspectives of water conservation,soil conservation,fertilizer conservation and yield increase potential,the suitability thresholds of the reasonable cultivated-layer diagnosis index are as follows.The cultivated-layer thickness is more than 20.39cm.The saturated hydraulic conductivity of soil is more than 6.24mm/min.The content of soil clay particle is between 10 and 71.93%.The shear strength of soil is more than 3.16kg/cm~2,the organic matter content of soil is more than15.23g/kg,and the available phosphorus content is more than 58.48mg/kg.Different tillage measures have different regulation effects on the physical properties of the cultivated-layer obstacle type in the slope farmland.Simultaneously,the improvement effects of S on the cultivated-layer thickening and moisture retention performance of soil are significant.Compared with K,S and CS can increase the cultivated-layer thickness by 45.45%and 13.64%,respectively.Furthermore,there is no obvious effect on cultivated-layer thickness with other measures.The shear strength of cultivated-layer soil by compaction is the largest with a value of 5.81kg/cm~2,while the shear strength of cultivated-layer soil by S decreases by 39.91%than by CK.The improvement effects of NT and S on cultivated-layer nutrient obviously precede those of other measures.The regulation effects of S on the moisture restriction type of and cultivated-layer thinning type of obstacle cultivated-layers are significant.In addition,NT and C have an optimal regulation effects on the erosion degradation type of obstacle cultivated-layer,simultaneously,the CS has a moderate comprehensive regulation effect on various obstacle cultivated-layers.Obviously,S and NT are superior to other measures in the cultivated-layer quality improvement effect of slope farmland.The cultivated-layer quality indexes with CK,C,S,NT and CS are 0.45,0.37,0.58,0.53 and 0.50,respectively.The regulation measures of reasonable cultivated-layer of red soil slope farmland include water conservation and drought resistance type of S measure,soil consolidation and erosion resistance type of soil and water conservation measure,as well as soil fertility improvement type of green manure intercropping measures.Therefore,from the perspectives of water conservation and drought resistance,soil consolidation and erosion resistance,and soil fertility improvement,the recommended technological mode for the construction of reasonable cultivated-layer in red soil slope farmland is"S+green manure+hedgerow".