Analyses Of Tillage Resistance And Soil Profile In Deep Tillage Based On Discrete Element Method

Deep tillage is the key field operation involving strong implements that penetrate the soil layers and mechanically break up and shatter the soil for sustainable agriculture.Farmers tend to use implements to till the land deep to obtain the required depth for plant growth.However,without proper knowledge of the specific type of implement,farmers ended up improperly turning agricultural soils,which became the major challenge in tillage or seedbed preparation.In addition,most deep tillage machines/implements consume high energy due to soil resistance and destructing soil structure,which is very important for crop growth.This study investigated tillage resistance and the soil profile that induces changes after deep tillage operation.This study provides the base for improving the tillage performance,structure,and working parameters of the subsoiler,mouldboard plough,and subsoiler cum rotary tiller in cohesive soils.To archive,the objective,analytical and Discrete Element Method approaches were used to model the prediction of formed soil structure and tillage resistance for tillage tools.Then,the models were used to evaluate the effect of deep ploughing,subsoiling and rotary mixing on the soil structure and the tillage resistance.The field experiments were conducted at Babaiqiao,Nanjing,Jiangsu Province,China,during the turn-round period from rice to wheat.The Soil Mechanics Laboratory,Department of Agricultural Mechanization Engineering,College of Engineering,Nanjing Agricultural University in China was used to carry out laboratory experiments.The selected soil was clay loam which is cohesive.The significance of this research is to study and assess the importance of minimizing the tillage resistance and the formed soil profile after tillage operation.Tillage resistance of tillage tools relies on machine parameters,shape,geometry,material and speed.These are reasonably straightforward to model soil mechanical properties,modes of failure,and displacement,which are far more complex.Agricultural soils are dynamic,structured porous materials with mechanical properties ranging from viscous liquid to cemented solid.Hence,three deep tillage implements,i.e.,subsoiler(subsoiling),mouldboard plough(deep ploughing),and subsoiler cum rotary tiller(deep mixing),were used to study their interaction with soil at the field,soil bin,and discrete element simulation experiments.The performance of the three implements was assessed in terms of soil tillage resistance and soil profile formation at different operating conditions.Using different techniques and methods allowed us to understand better the tillage resistance and potential effects of tillage on soil structures.Sensors,tracers,and DEM were used in this study.However,DEM was found to provide a better vision for the study of soil-tillage interactions,pointing toward a future direction for this area of work.The research methods used to make this study possible were the experimental tests in the field,soil bin and computer simulation.The ball tracers labeled with numbers were used to measure soil movement from the bottom to the top layer.A soil bin trolley and in-situ testing rig with sensors were used to obtain data in the soil bin and field,respectively.The analytical equations and MATLAB were used to obtain output parameters:tillage resistance and soil profiles.Also,the Taguchi method was used to optimize the entire parameter space with a lesser number of experiments.Further,the DEM model was developed by adding the different values of normal cohesion force in the default Hertz-Mindlin to change Hertz-Mindlin from non-cohesion contact to cohesion contact model.After developing the DEM model,the model was calibrated using an angle of repose method and then verified by comparing simulation results with experimental and analytical methods results.The results are generalized as follows:1.Prediction of tillage resistance and soil behavior with discrete element simulationUnderstanding tillage resistance and the soil profile induced changes before deep tillage operation is the major challenges faced during seedbed preparation.A Discrete Element Method(DEM),a computerized testing rig and a soil bin were used to investigate the tillage resistance and the soil profile induced changes by a mouldboard plough.Different methods have been used to study deep tillage,but there are still cases of excessive use of energy and soil profile destruction.Therefore,this study aimed to provide a clear understanding of the deep tillage using the prediction model.Experimental data obtained in the soil bin trolley and a computerized testing rig with sensors were used to verify the model.By using DEM,the motion of particles is given by collisions between particles.Soil-tillage tool interaction simulation was established by a 3D geometry of a mouldboard plough created using PTC Creo Parametric 3D Modeling software and seedbed modelled by discrete element particles using EDEM software.A bond element was introduced between particles and soil cohesion was formed to create a simulation of the actual cohesive soil.The horizontal and vertical resistance and soil disturbance in terms of bulk density at different speeds and depths were investigated.However,the simulation experiments followed the field experiments conducted using a computerized testing rig.Further,the soil resistance on the plough and the resulting bulk densities were estimated from the simulated results and compared with the actual results from the field.Also,the accuracy of the developed model to predict soil displacement was measured and compared with the soil bin data with an average relative error of 1.317%.The simulated horizontal,vertical resistance and bulk density results matched well with the results obtained in the field experiment with the relative error of 4.435,3.029 and 3.119%,respectively.The vertical resistance provided the best regression results of 0.9948 R2 with RMSE of 0.5964,followed by 0.9884 R2 with RMSE of 0.4089 and 0.8391 R2 with RMSE of 0.5441 for horizontal resistance and bulk density,respectively.All regression results were obtained at(p<0.05).The ANOVA test showed that the p-values for the horizontal resistance,vertical resistance and bulk density were 0.753,0.695 and 0.025,respectively.There was no significant difference between the simulation and experiment results for tillage resistance,while there was a significant difference for the bulk density at(p<0.05).This model can be applied as an accurate,consistent and fast method of effectively predicting the final soil condition and tillage resistance.2.Prediction of precise subsoiling based on analytical method,discrete element simulation and experimental data from soil binPrediction of a precise subsoiling using an analytical model(AM)and Discrete Element Method(DEM)was conducted to explain tillage resistance and the soil profile induced changes by a subsoiler.Although sensors,analytical models,and Discrete Element models exist,there are still cases of soil structure deformation during deep tillage.Therefore,this study aimed to provide a clear understanding of the deep tillage using prediction models.Experimental data obtained in the soil bin trolley with sensors were used to verify the models.Experiments were designed using the Taguchi method.In the AM,the modified-McKyes and Willat&Willis equations were used to determine tillage resistance and soil furrow profile,respectively.Calculations were done using MATLAB software.The elastoplastic behavior of soil was incorporated into the DEM.The DEM predicted results with the best regression of 0.984 R2 at a NRMSE of 1.936,while the AM had the lowest R2 of 0.957,at a NRMSE of 6.008.All regression results were obtained at p<0.05.The ANOVA test showed that the p-values for the horizontal and vertical resistance were 0.9396 and 0.9696,respectively.The DEM predicted better than the AM.DEM is easy to use and effectively develops models for precision subsoiling.3.Evaluation of rotary mixing in the soil structure and the tillage resistance using discrete element methodThis part aimed to evaluate the effect of deep tillage on soil structure and the measured and simulated tillage resistance of subsoiler cum rotary mixing implement.Soil bin measurements were collected using a motorized trolley with sensors and a soil profilometer.A 3D geometry of the implement was created using PTC Creo Parametric 3D Modeling software and seedbed modelled by discrete element(DE)particles using EDEM software.Accurate calibration of DE model parameters was done based on the reproduction of the soil bin.The cohesion between the particles was created by adding a cohesion force to the normal contact forces to create a simulation of the actual cohesive soil.It was found that the shape of the rotary blades has a significant impact on the tillage resistance and the formed soil profile.The precision of the model with a relative error of 0.430,4.928 and 4.27 was obtained for horizontal resistance,vertical resistance and soil profile,respectively.The horizontal resistance showed the best regression results of 0.9997 R2 at a NRMSE of 0.04,followed by the soil furrow with 0.9936 R2 and NRMSE of 0.23 and vertical resistance with 0.9 R2 and a NRMSE of 0.27.The unpaired T-Test showed no statistically significant difference(p<0.05)between simulation and experimental results.Regardless of the tillage depth,soil layers cannot be destroyed using the proper blades of rotary tillers.DEM can be applied as an accurate,consistent and fast method of effectively predicting the final soil condition and soil tillage resistance.