| With a high population in China,there is a great demand for increased food production for sustenance and stability of the nation.The Yangtze River Delta region in East China is one of the country’s major agro-ecological zones responsible for producing key staple cereal crops(i.e.,wheat and rice).The region’s farming system is defined by a double-crop rotation between wheat in winter and rice in summer.The two crops are grown in a sequence within a tight annual farming calendar.Productivity in the agroecological zone is however limited by climatic conditions which causes insufficient light and heat-resource that slows down the growth and delay the ripening of the crops.This leads to a shortened period between the harvesting of one crop and sowing of the next.Therefore,to facilitate immediate shift between the two crops and avoid the risk of the growing seasons overlapping and causing loss of yield,highly mechanized back-to-back field operations(i.e.,harvesting,clearing of the farms,and land preparations for sowing of the following crop)have to be undertaken.The intensive mechanization of the farming operations together with improved irrigation techniques,increased fertilization,and use of high-yielding cultivars have ensured consistently high yields from the rice-wheat rotation system.However,intensified mechanization has also been identified to cause complications in the farming system such as increased costs of production,a decline in soil productivity,and excessive generation of crop residues.The rigorous mechanical working of soil using heavy-duty conventional machinery leads to soil erosion and degradation,resulting in substantial decrease in soil organic matter,decline in soil fertility,poor soil physical structure,and shallow tilth layer with severe physical and chemical limitations for root growth,and consequently reduced yields.To minimize the high costs and avoid the negative impacts of conventional land preparation,conservation farming technologies have been proposed.Nonetheless,proper implementation of conservation tillage in the prevailing farming conditions of the rice-wheat systems is challenging.The degraded clayey paddy soils and excessive cropresidue conditions cause low efficiency and poor work quality during conservation tillage and direct sowing operations,causing operator frustration and reductions in field capacity.Farmers generally have resorted to burning the voluminous residues on the fields to get rid of them and to ensure timely sowing of the next crop.Burning of the crop residues causes environmental pollution,kills useful soil microorganisms,creates net negative nutrient balance,decreases organic matter levels and eventually results in the soil health deterioration.Practical implementation of conservation tillage in the challenging and pervasive conditions of the rice-wheat rotation demands high-efficiency and adaptable machinery that can achieve the diverse,interdependent,and yet conflicting agronomic requirements of conservation farming.The soil-engaging tools need to be optimized to improve soil infiltration,reduce soil resistance,reduce energy demands,improve straw cutting,and minimize soil disturbance.Even so,the unavailability of effective and adaptable tools and machines,appropriate to the intensive rice-wheat farming system have further confounded the adoption and implementation of the conservation technologies.Conventional and inappropriately designed tools have high-energy demands,low economic efficiency,poor straw handling performance,and achieve sub-optimal seedbed quality.These cause inefficient management of crop residues,cause poor seedbed quality,inhibit seed placement during sowing,weak crop-stand,delayed seed germination,clogging of seeding machines,hinder successive farm operations,and cause loss of yield.For proper implementation of conservation tillage in the intensive rice wheat rotation farming,there is thus a need to design and develop highefficiency soil-engaging tools that are adapted to the challenging working conditions.In the recent years,biomimetic engineering has been widely adopted to innovate the design of agricultural tools to meet the diverse requirements of modern agriculture.Biomimetic designs of soil engaging tools simulate the well-adapted morphological features and capabilities of living organisms into practical ideas,structures,and mechanisms that improve working performance.Biomimetic designs of cultivation tools are suggested to reduce cutting resistance,enhance the structural strength of tools,and improve working efficiency based on the bionics principles and prototypes developed by learning from soil burrowing animals.For instance,the mole rat(Scaptochirus moschatus)is an excellent digger and can dig up to 91m long tunnel in a single night.Their wide and shovel-like foreclaws are their principal digging tools.The well-formed and adapted claw features give them high working efficiency during digging.Through biomimetics the geometrical structure of the mole’ s claws and its movement during digging can provide good basis for optimizing the design and adaptability of tillage implements for improved performance during conservation tillage in the intensive rice-wheat farming system.One major challenge faced in the optimization design of modern soil engaging tools for adoption in the conservation farming systems is ensuring their adaptability to the dense straw cover on the soil surface during post-harvest tillage.The prominent tillage tools used for conservation tillage in commercial crop farming are mainly classified as narrow and very narrow tools,which include tines,discs,rotary blades,and strip-tillers;used as crop residue handling units and furrow openers in direct seeding machines.Narrow and very narrow tools are preferred in conservation agriculture due to their ability to perform minimal soil disturbance while eliminating the need for heavy machines.Furthermore,in the process of optimization design of soil engaging tools for conservation farming it is important to understand the working mechanics of the tools in the specified working environments.During conservation tillage,the tools’ working mechanism forms a soil-tool-residue interaction system with complex dynamics.Gaining understanding into the interaction behavior between soil,tool,and plant residue systems would be useful in defining fundamental adaptation features for optimization of tools for effective conservation tillage.However,conducting studies on these intricate dynamics are difficult due to the unpredictability of the anisotropic soil and plant materials together with the random deformation loads experienced during tillage.Research on these nonlinear soil mechanics in agricultural engineering applications have been inconclusively studied and are short of theoretical bases and guidelines.In view of the above-mentioned facts,this research was designed to explore the possibility of applying biomimetic design as a means to optimize the design of narrow soil-engaging tools for conservation farming in rice-wheat rotation systems.The main objective was to examine the performance of the biomimetic designs in improving tillage efficiency and straw management capabilities of the soil-engaging tools while minimizing soil disturbance during conservation tillage.Toothed discs and rotary tiller blades were modified to mimic the configurations of the cutting profiles of the mole rat’s(Scaptochirus moschatus)claw and their performance characteristics when working in densely straw-mulched soils were compared to those of conventional designs.Additionally,the nonlinear mechanics of soil-tool and plant residue interactions of the narrow tools are modeled in terms of tillage resistance forces,soil and straw cutting forces,stress distribution,straw-cutting efficiency,the rate of soil disturbance and uniformity of tillage depth when used to cut straws and open furrows in the context of no-till conservation farming.The research involved indoor and field experimental tests,theoretical analyses,and numerical simulations.Indoor experiments were conducted in the soil-bin laboratory of the department of agricultural mechanization,Nanjing Agricultural University.Field experimental tests were performed in the university’ s experimentation farm using a multi-functional in-situ test-rig facility.Theoretical analyses were made using the modified classical soil mechanics equations.Numerical finite element analyses(FEA)were performed using Abaqus/CAE 6.14 software.Theoretical analysis and mathematical modelling of soil-tool interactions took into account applied loads,soil cutting effects,induced stresses,soil reaction forces and underlying failure mechanisms.In FEM,soil and straw were treated as continuums while stresses and strains represent forces and displacements within particles.The choice of the constitutive laws governing stress-strain relationships were based on the non-linear elastic plastic behaviours of soil and straw determine from laboratory tests.The specific research items were as follows:1.A biomimetic tillage disc mimicking the structure of a mole rat’s claw was developed with the object of providing an adaptable and efficient soil-engaging tool for managing the dense straw-cover conditions in the high yielding farming systems.The tooth outline of the biomimetic disc was traced from an image of the mole’s claw using computer aided design(CAD)software and reverse-engineered into a disc with six identical soil-engaging teeth.The performance of the biomimetic disc was evaluated at 3 tillage depths(i.e.,40,70,and 100 mm)in an indoor soil-bin experiment,in comparison with traditional discs(i.e.,a plain and a notched disc).The soil bin measured 23.5 m long,2.4 m wide and 2.0 m deep,and was filled with clay-loam soil.It was equipped with an electronic trolley-carriage consisting of a traction motor with maximum power of 22 kW.The trolley carriage contained an inbuilt system of rotary tines,a levelling board and a roller for preparing the soil-bed.The hitching mechanism contained load cells for measuring tillage forces.The trolley-carriage was controlled at a constant speed of 1 km hr-1 in all the tests while SIMATIC WinCC,TIA Portal software was used for data acquisition.Results showed that tillage resistance of the biomimetic disc was reduced by up to 28.7%,as compared with the notched disc.The biomimetic disc also achieved 23.9%improvement in straw-cutting efficiency compared to the plain disc,and 11.7%improvement in cutting-efficiency compared to the notched disc.The biomimetic disc also had the least soil disturbance rates across all the 3 tillage depths.The improved performances of the biomimetic disc were due to its optimized soil-engaging profiles that mimic the smooth,continuous,and efficient working mechanism of the mole-rat’ s claw.The claw-shaped edges easily penetrate through densely mulched soil while avoiding tool-sliding over the straw,and achieves minimum soil disturbance.The biomimetic tool design thus presents a viable option for the diverse performance requirements by conservation tillage in intensive farming systems.2.The straw cutting performance of the toothed biomimetic disc was evaluated with soil bin test,which demonstrated its effectiveness for application in no-till conservation agriculture.Additionally,the toothed discs induced minimal soil disturbances when used as furrow openers.Based on this experimentally acquired results,the interactive mechanics of a toothed disc were studied with combined approaches,i.e.,theoretical model analysis,3D finite element analysis(FEA),and experimental evaluation in the field.Geometrically straight-edged teeth simplify theoretical analysis using classical soil-mechanics models and guarantees reliable cross-checking with the finite element method FEM and experimental outcomes.Classical theoretical models were modified by introducing the inertial effects of the toothed disc acting as a very-narrow tool under translational and rotational loads.FEA simulations were performed using Abaqus/CAE 6.14 software.FEA modelling assumed the tool to be a discrete part with a reference point at its geometric centre.The FEA soil model was considered a non-linear elastoplastic material that exhibits hardening regime during failure.Field experiments were conducted using an in-situ test rig platform while varying the tillage depth at 40-,70-,and 100-mm.Data acquisition of the resistance forces was done using LabVIEW2010 software,interfaced with Advantech portable module.Each test was replicated three times in a randomized block design.Results showed that both the modified analytical model and the FEA models had good agreements with experimental outcomes.The analytical model moderately over-predicted tillage forces,while furrow-width estimates increased relatively with depth.The FEA predictions were within a prediction error of 29.23%of mean forces and prediction error of 26.28%of furrow widths.There was a strong positive correlation between values of specific draughts(0.936)and disturbance indexes(0.920)derived from FEA simulations and field tests.These finding add new knowledge of soil-tool interaction dynamics of toothed discs;and show the reliability of the finite element method(FEM)in complementing analytical models and providing cost-effective,and timely analysis of unique tool geometries for conservation tillage.Nonetheless,there is a need for performing more studies to improve the prediction accuracy of the models.3.Toothed discs have shown better performance in minimizing tillage resistance and processing crop residues.Performance assessment on adaptability of soil-engaging tools for managing crop residues in conservation tillage scenarios require proper definition of their technical designs as well as the tool-induced soil-straw dynamic interactions.Few studies have characterized the performance of tillage tools based on their design considerations and mechanical responses.A study was therefore undertaken to evaluate tillage forces,structural strength,straw-cutting performance,and tillage-depth uniformity of a bionic curved-edged toothed disc in comparison to a straight-edged toothed disc,working at depths of 40,70,and 100 mm.The design of the curved toothed disc was inspired by the arc-shaped structure of the mole-rat’s claw.The curved claw profile of the mole rat’s second toe was traced from its image using computer aided design CAD software and the longer arc used for reverse-engineering the curved edge of the bionic curved-toothed-disc.3D finite element analysis(FEA)was used to simulate the discs’interactions with soil and straw.In FEA soil was modelled as an elastic-plastic material subjected to extended Drucker-Prager linear yield criterion with hardening during failure.Straw was modelled with an elastic-plastic failure behavior,having ductile damage and linear softening displacement.Field experiments were conducted to validate the FEA results.It was revealed that the curved disc minimized tillage forces by up to 22.8%,and significantly reduced stresses on the tool.The disc also achieved uniform tillage depths and improved straw-cutting efficacy by up to 26.31%.Bionic curved cutting-profiles on soil-engaging tools thus provide structurally enhanced,energy-efficient option for effectively managing crop residues and improving seeding performance in no-till conservation farming.4.Rotary tillage facilitates conservation agriculture in rice-based crop farming systems through minimal soil disturbance for seedbed preparation and crop residue management.The efficiency of rotary tiller blades used for reduced conservation tillage in rice-wheat cropping systems is however hampered by degraded clayey paddy soils and excessive crop residue conditions.Biomimetic designs present an edge in the optimization design of cultivation tools and can be employed to improve the efficiency of rotary tillage.In this work,biomimetic rotary tiller blades were developed by mimicking the geometrical structure of the toe claw of a mole rat(Scaptochirus moschatus).The arch-shape of the middle claw toe was replicated on the curved scooping edges of a conventional blade to form the biomimetic rotary tillage blade.Five concave arcs were created and equally arranged on the blade’ s curved cutting edges.Field experiments were designed to evaluate the performance of the biomimetic rotary tiller blades in terms of torque and power requirements,soil fragmentation ability,soil displacement characteristics,as well as the rate of straw incorporation.Results revealed that the biomimetic blades minimized torque by up to 21.05%,and produced finer tilth with granular and more even clod sizes compared to the conventional blades.It also achieved more redistribution of topsoil and improved straw burial rate.During soil engagement,the curves and crests on the biomimetic rotary tiller blades enhanced penetration and cutting into the soil with less resistance and optimized the blades’ soil and straw cutting as well as incorporation capability.The biomimetic rotary tiller blades are thus energy-efficient and can improve soil structure and the quality of seedbeds,besides managing crop residues through incorporation,and therefore advance conservation tillage in intensive farming systems.In summary,intensive mechanization of farming systems ensures maximum productivity in the face of the increased global competition with the free-trade markets of agricultural outputs.Nonetheless,agricultural development cannot be intensified at the expense of the bearing capacity of natural resources(i.e.,soil and the ecosystem).Intensification of the farming system must be executed in a judicious and sustainable way in order to maintain the function of the soil and the integrated farming ecosystems.This includes enhanced conservation of soil and proper processing of plant residues.Through design of well adapted and optimized tools and implements for preserving the soil and efficiently managing plant residues,the sustainability of the farming system can be assured.This will facilitate sustainable agricultural productivity,through adaptive mechanization and will fundamentally contribute to meeting food security challenges of the future.In this work,it has been demonstrated that biomimetic designs of soil-engaging tools are structurally enhanced,energy-efficient,can achieve better management of crop residues with minimum soil disturbance,and thus satisfy the requirements of conservation farming.biomimetic designs can therefore contribute to the implementation and promotion of conservation tillage while upholding sustainability of the intensive rice-wheat farming systems.In undertaking the study,classical soil mechanics equations were modified to account for translational and rotational kinematics of the toothed disc acting as a very-narrow rotary tool and used to predict the resistance forces and furrow widths of a toothed disc.The modification in passive earth prediction equations allowed for simplified prediction of the kinematics of the toothed disc,with an agreeable precision.In addition,the finite element method(FEM)has been shown to be a convenient and reliable numerical technique for modeling the soil-tool-residues interactions and crop residue cutting mechanism of tillage tools.FEM can therefore augment analytical models and provide understanding of the complex soil-tool-residues interaction mechanics.Nonetheless,these models can be improved using more robust theories and techniques to achieve better accuracy.Finding presented in the work can provide a guide for defining the performance parameters for optimal operations,and guide the design and development of adaptable high-efficiency tools for conservation farming. |
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