| The rice-wheat rotation is one of the important cropping systems in Chinese Yangtze valley,However,the production of wheat following rice is restricted because of shallow rotary tillage or flood and drought in recent years.The depth of paddy soils plough horizon becomes shallow gradually,soil structure is getting worse.All of this are disadvantage to root system growth of wheat and result in lower soil integrated quality.Subsoiling can improve the soil condition effectively,promote the growth of root system,increase crop yield and water use efficiency by breaking subsurface,deepening topsoil,improving air and water permeability of soil.Nowadays,research results of subsoiling are mostly about dry farming region in northern China,but relatively few in number about subsoiling perturbations and effects in south.In this article,using colligation test-bed in situ to study the subsoiling resistance and disturbance of soil structure during the operations process of paddy soils by combing video-test and discrete element simulation under the different penetrating angle a and tillage depth D.1.Video-assisted quantification on disturbance behavior of subsoilingIn order to quantitatively describe the disturbance behavior of paddy soil in the process of subsoiling,soil in-situ tillage comprehensive test platform was used to carry out subsoiling experiments with different rake angles and depth of tillage.video-recording method provided forward soil rupture distance R,soil disturbance width W and lifting height H,all of which were significantly correlated with both a and D.This indicated that both design parameters of the subsoiler and the working parameters can have their influence on soil lifting.R was linearly correlated with forward protruding length of the bent leg beneath soil surface,while W increased with α.The results proved that video-assisted multi-indice measurement is an important means for optimized subsoiler design for paddy soil.2.DEM analysis of subsoiling process in paddy soilThe dynamic disturbance behavior of soil in the process of subsoiling is a complex process.in this paper,the discrete element simulation model of wet clay paddy soil is used to study the movement and compressive force of soil particles in the process of subsoiling with soil particles as the research unit.It provides a theoretical support for the soil depth disturbance recorded by in-situ video recording in the field.The velocity field of soil particles shows that the crescent-shaped failure of the soil above the critical depth occurs in the tillage layer,The disturbance boundary is formed mainly in the upward and bilateral movements,and the lateral extrusion failure occurs in the bottom soil below the critical depth,and the deep grooves are formed mainly in the bilateral movement.In addition,a new soil compaction zone was formed by the downward movement of the soil directly below the subsoiler.The lateral soil disturbance process shows that the soil shear failure occurs on both sides of the subsoiler.The distribution of soil particle field indicates that the stress concentration of the soil moves from around the tip of the spade to the rake edge of the subsoiler and then down to the vicinity of the tip of the spade during a complete subsoiling process.The periodic fluctuation of the stress field in front of the contact surface is helpful to improve the mechanical properties and tillage effect of the tillage tools,and also to provide theoretical support for the energy saving and resistance reduction of the vibration subsoiling.3.Paddy soil subsoiling tillage draughtBecause of the high moisture content of paddy soil in rice-wheat rotation area in the middle and lower reaches of the Yangtze River,the high soil moisture content,and the excessive resistance in the process of subsoiling,it is always the technical bottleneck to popularize the subsoiling in the south of the Yangtze River.Therefore,effects of angle a and depth D of subsoiling on tillage draught and disturbed area with subsoiler were studied using a comprehensive test platform for in-situ soil tillage.The results showed that the soil angle a and tillage depth D had significant effects on the tillage draught F,and the tillage draught F increased linearly with the soil angle α,and increased exponentially with the tillage depth D.Soil angle a and tillage depth D have significant effects on the disturbed area.The disturbed area increases with the increase of soil angle α,then decreases with the tillage depth D,and reaches the maximum at 20 cm.subsoiling angle a had no significant effect on tillage specific drgught,while tillage depth D had significant effect on tillage specific drgught,and after tillage depth reached 20 cm,it showed a sharp increase in step form,considering comprehensively the soil entry performance of subsoiler.When the input of energy and soil disturbance is 22.5° and the depth of tillage is 20 cm,the best subsoiling effect can be obtained in the rotation area of rice and wheat in southern China.4.Study on the quality of subsoiling in paddy soilThe soil micro-topography damage after subsoiling directly determines the sowing quality of the follow-up machines,and the soil cone index after tillage also has a significant effect on the root growth and distribution of crops.Therefore,in this paper,the soil surface roughness and soil cone index distribution of subsoiling trench after tillage were selected,and the soil tillage quality of subsoiling rake angle a and tillage depth D was systematically evaluated.The results showed that there was no significant effect on surface roughness by subsoiling rake angle α,but the influence of tillage depth D on surface roughness was significant.After D at 20 cm depth,the surface roughness was significantly greater than 10 cm and 30 cm;Considering the agronomic requirements of reducing the damage of micro-landform after tillage and improving the quality of subsequent sowing,the effect of 30 cm tillage depth is better than that of other agronomic requirements,such as promote crop roots growth and enhancement of field irrigation and drainage capacity.The contour distribution map of soil cone index in the section of subsoiling trench shows that the subsoiling angle a has no significant effect on the distribution of soil cone index,but the depth of tillage D has a significant effect on the distribution of soil cone index.In 0～10 cm soil layer,the depth of 20 cm tillage can not show the effect of subsoiling,and in 10～20 cm soil layer,20 cm tillage depth could provide the maximum soil loosening effect.In the 20～30 cm soil layer,after 30 cm tillage tillage depth,the soil cone index contours appear narrow "grooves",which not only indicates that the disturbance ability of the subsoiler to the soil layer here is sharply reduced.It also reflects the mechanical characteristics of deep subsoiling of paddy soil.The dense distribution of soil cone index contours under all treatments indicated that the soil compactness changed violently and resulted in soil compaction.5.Effect of different tillage methods on physical properties of paddy soilReasonable tillage methods create good soil environment and conditions for crop growth.In this paper,the effects of subsoiling,no tillage and conventional rotary tillage on soil bulk density,moisture content and water holding capacity in wheat growing period were compared and analyzed.The results showed that the subsoiling can break the ploughing pan layer by breaking the soil bulk density,moisture content and water holding capacity.Compared with no-tillage and conventional rotary tillage,the average soil bulk density of 0-30 cm soil decreased by 5.2%in comparison with no-tillage and conventional rotary tillage,and the soil bulk density was decreased by 5.2%and 2.5%in comparison with that of no-tillage and conventional rotary tillage;The moisture content increased 7.4%and 10.4%respectively.The water holding capacity was increased by 10.7%and 6.8%respectively.Among them,the improvement effect of subsoil ing on the bottom soil(15-30 cm)was more significant,and the average soil bulk density was decreased by 5.5%and 5.2%,respectively,and the average soil bulk density was decreased by 5.5%and 5.2%respectively.The water content increased by 11.7%and 14.3%respectively,and the water holding capacity increased by 12.6%and 13.8%respectively,which provided good soil conditions for the growth and development of crop roots.6.Effects of different tillage methods on root,yield and water use efficiency of wheatSoil is the basis of crop growth,and the changes of soil physical properties by different tillage methods directly affect the growth and development of crops.In this paper,the effects of three treatments,subsoiling,no-tillage and conventional rotary tillage,were compared and analyzed.The effects of yield and water use efficiency on wheat growth were evaluated systematically.The results showed that the subsoiling treatment could promote the root growth and the whole down-pruning degree of wheat,improve the root growth space and increase the total root quantity.No-tillage,conventional rotary tillage was distributed in 0～25 cm soil layer,while subsoiling was distributed in 0～35 cm soil layer.Two-year field experiment data showed that,compared with no-tillage and conventional rotary tillage,the average root quantity of subsoiling increased by 25.0%and 27.4%respectively,and the percentage of root number distribution below tillage layer was increased as a whole.The average yield of wheat increased 6.6%and 14.9%respectively,and the water use efficiency increased 5.3%and 14.0%respectively. |
PDF Full Text Request