Study On Maize Sowing Quality Evaluation And Soil Covering-compacting Device

The sowing quality is directly related to crop yield.Soil nutrient content,working mode,machine performance and seed distribution uniformity are the main factors affecting the sowing quality.Based on the above factors,the relationship between soil physicochemical properties and soil respiration in long-term maize stalk retention during seedtime wasn't totally understood yet,the traditional seed distribution uniformity evaluation methods were limited to the one-dimensional and vertical seeding planes,the traditional soil covering device and soil compacting device have poor working stability,the adjustment accuracy of the opening-angle and inclination-angle adjustment mechanism of traditional double-disc soil covering device was difficult to control.Through theoretical analysis,mathematical modeling,simulation analysis,experimental design and other methods.In this paper,the relationship between soil physicochemical properties and soil respiration in long-term maize stalk retention during seedtime was studied,the seed distribution uniformity evaluation method was studied,the mechanism and device of conical soil covering-compacting were studied,the opening-angle and inclination-angle quantitative adjustment mechanism design method of double-disc soil covering device was studied.?1?The soil physicochemical properties and soil respiration during seedtime can be used to characterize soil nutrient content.Therefore,two experimental zones with same management history were chosen to conduct the comparative study.Monoculture rain-fed maize was the sole crop that cultivated in the study site.One zone was covered by 5639 kg/ha^-1 maize stalk residue after harvesting,and the other zone was left bare since the autumn of 2000.The soil temperature,soil water content,soil organic carbon composition,soil microbial communities and their microbial abundances and soil respiration rate during seedtime of 2015,2016 and2017 were measured and analyzed.The test results showed that the maize stalk returning mode can change the soil properties?such as lowering soil temperature,increasing soil moisture,increasing soil nitrogen and organic carbon content?due to long-term return of maize stalks,thereby reducing the soil respiration during seedtime.And the maize stalk retention may contribute to soil carbon sequestration.In addition,the difference in soil respiration during seedtime also makes soil microbial abundances and carbon composition differences in the two experimental zones.Therefore,the maize stalk retention mode can be beneficial to the corn spring sowing by increasing the soil nutrient content during seedtime.?2?The seed distribution uniformity in soil after sowing can be used to evaluate the sowing quality.A new index for evaluating the seed longitudinal distribution uniformity,that is,the deviation between theoretical sowing point and actual sowing point was proposed in this paper.Three types of furrow openers?double disc,sliding cutting and single disc?were test on a soybean sowing machines at two working speeds?1.4 m/s and 2.2 m/s?.And the seeding space,sowing depth and deviation of the seed from the row center were measured.The test results showed that the index of seed longitudinal distribution uniformity proposed in this paper is more accurate than the traditional ones,and the evaluation method is also superior.The seed distribution areas on the horizontal and vertical planes were calculated by the ellipse and integral criteria,the seed distribution volumes were calculated by the ellipse criteria,and the two-dimensional and three-dimensional scatter plots of the seeds distributed in the soil were plotted by the orthogonal projection onto the two intersected planes that were perpendicular to the row and parallel to the soil surface.The results showed that under the same working conditions,with increasing work speed,the seeds distribution uniformity in two-dimensional planes and three-dimensional space became bad based on seed distribution areas and seed distribution volumes.The seed distribution areas and the two-dimensional scatter plots showed,under the two working speed,the minimum seeds distribution area on the horizontal plane was double-disc furrow opener,and the minimum seeds distribution area on the vertical plane was sliding-cutting furrow opener.The seed distribution volumes and the three-dimensional scatter plots of seeds showed,when the working speed was 1.4 m/s,the double-disc furrow opener and the sliding-cutting furrow opener were better in the three-dimensional spatial distribution uniformity.When the working speed was 2.2 m/s,the best seed distribution uniformity in three dimensions was double-disc furrow opener.?3?The stability of soil covering and soil compaction operations directly affects the seed distribution uniformity in the sowing depth direction and sowing quality.Based on the basic parameters of the conical soil covering-compacting wheels,combined with seed furrow shape,the external load and analyzing the soil stress and movement process of soil covering-compacting.The soil-covering and soil-compacting mechanisms was clarified,and the theoretical models of the conical soil covering-compacting wheels were proposed.The main structural parameters of the conical soil covering-compacting wheels and the range of operation parameters were determined.At the same time,three main influencing factors?load,spacing between left and right conical wheels and inclined angle?were determined.To validate the feasibility of the theoretical models,we simulated the conical soil covering-compacting wheels on finite element software of ABAQUS under different structural parameters and loading conditions?load=500,700,900 N;spacing=0,15,30 mm;inclined angle=10,15,20°?and established 27 models.Finite element simulation results proved that the horizontal stress S₁₁ and vertical stress S₂₂ of the contact zone between the conical wheels and soil can better reflect the soil-covering theoretical model and soil-compaction theoretical model,and the finite element simulation results also proved that the theoretical models were feasible.?4?In order to further verify the performance of the conical soil covering-compacting wheels designed according to the theoretical models,the 3 indices as the experimental factors using Design-Expert software were take,the Box-Benhnken experiments of 3 factors and 3levels were conducted,and the results showed that the order of the influence of the factors on the soil compactness in the top 5 cm soil layer of the seed from high to low was the load,the spacing between left and right conical wheels and the inclined angle.The order of the influence of the factors on thickness of covering soil was the inclined angle,the load and the spacing between left and right conical wheels.The optimal parameter combination of the device was the external load of 900 N,the spacing between left and right wheels of 13 mm and the inclined angle of 16°.Verification testing indicated that the soil compactness in the top 5 cm soil layer of the seed was?43.8±1.9?kPa with the coefficient of variation of 4.3%,and the thickness of covering soil was?32.9±2.3?mm with the coefficient of variation of 6.9%.The soil-covering and soil-compacting device designed in this paper has good performance of soil-covering,soil-compacting and working stability,and seeds has a better distributed in the sowing depth direction.?5?The soil covering thickness is one of the indicators for evaluating the quality of soil-covering operating.The structural parameters of the soil-covering device directly affect the soil covering thickness.Based on the coordinate three-dimensional transformation criterion,an opening-angle and inclination-angle quantitative adjustment mechanism design method of double-disc soil covering device was built by determining the adjust axis coordinate position and rotation angle.Based on the design method proposed in this paper,the design of quantitative adjustment mechanism was proposed.The mechanism is mainly composed of left and right soil-covering disc assemblies,left and right adjustment shafts,left and right adjust bolts and frame.Through adjustment card fixed on the adjustment shaft by adjusting bolt to achieve quantitative adjustment of the opening angle and the inclination angle.Through the modeling results of the designed adjustment mechanism in software of CATIA,the relative errors after the adjustment of the opening angle and the inclination angle were 0.065%and0.01%,respectively.The measurement results showed that the adjustment mechanism design method proposed in this paper has certain feasibility.The above research work can provide theoretical basis and technical means for improving the sowing quality,optimizing the sowing mode and the evaluating sowing quality.