Soil Structure And Its Assessment For Soil Tillage Research

The key focus of soil tillage research is on the mediation of the biological environment ofagricultural soils. Thus it is required to apply engineering theories and methodologies toidentify and describe soil biological environment based on soil structures, so that therelationships among mechanics, machinery, soil management and soil structure can berealized. The ultimate goal for these efforts is to provide the optimum condition of seedbedthrough appropriate tillage operations.Soil tillage mechanics is based on the extended definition of soil structure. As soilstructure is directly related to infiltration, water storage and mass transportation propertiesof soils, as well as to gas transport, it thus determines the quality of the habitates for boththe plants and soil biological communities. Therefore, the study on soil tillage is animportant way for the improvement of soil biological environment.The research of soil tillage mechanics aimed at soil biological environment has to stresson the application of both laborotary and field methodologies. The indoor methodologiesinclude the search of the methods for the reconstruction of artificial soil structures, theformation of soil structure and its dynamic processes under simulated environmentalconditions, so that a reference for the soil structural behavior in field condition is possiblebased on the quantitative description of controllable state of artificial soil structures. Theoutdoor research on soil structures include field investigation and controlled tillage researchin agricultural soils, thereby providing the modelling of soil structure and its dynamicsunder real environmental conditions.Field investigation was firstly conducted in Nanjing regions which shown that soil typicalstructural properties happened under specific field conditions, such properties born clearstamp from tillage operations for Shuiba soil, while in Linchang soil a clear biologicalfootprint was exposed.The machine tillage in Shuiba resulted into dense clods which can be well preservedduring a whole crop season. The dense clods impeded crop rooting System from penetrating,and meanwhile, resulted into negative effects on the transportation and distribution of waterand nutrients within till-layer soils, the result of which also affected the development of soil biological communities. The negative effects of machine till on the soil biologicalcommunities can be qualitatively identified from the structural properties of root-region soiland the mophological state of crop rooting-systems. Contrary with this, well soil structuralstate was observed in Linchang field where a benigh cycling of soil biological environmentwas identified.The qualitative study on field investigation led to the definition on soil macro-structure.Soil macro-structure is composed of soil fragments encompassing all scales, which includessoil primary particles, compound particles, soil aggregates and tillage-induced soil clods, itis the topological relations among the constituent soil fragments. The topological relationsamong soil fragments governs the stabilities of soil structural dynamics and the spacialformation of pore networks within soil particles, thereby determines water, solute and gasmovement, as well as the condition of soil biological environment.To deal with the key focus of soil tillage research—soil fragmentation, a new mehtod,stress wavelets, was proposed for multi-scale and multi-resolution assessment on soilstructure. The proposed method bears physical identities with wavelets theory. Stresswavelets inherited from wavelets theory and considered two inherent properties of soilfragmentation process: scale and energy distributiion. And a combinative use of the twobears the benefit of multi-scale and multi-resolution assessment and therefore brings a newconcept forward. The indoor experiment shown a stable characteristics of the stresswavelets method.In addition to the indoor experiment of simulation aiming at testing the theory ofstress-wavelets, a field experiment was also carried out with the same objective. The resultsshown that fragmentation-related indices can be grouped in two classes: statistical indicesand mechanical indices. In comparing with fractals, stress wavelets expressed differentproperties of soil structure: Fractals indicated statistical properties of soil structure, whilestress wavelets uncovered mechanical properties of soil structure. When considering otherfragmentaton-related indices, it was shown that fragment fractal dimensions and perfragment fragmentation energy are easy to be derived and more sensitive in comparing withothers. Thus a combinative use of the two may serve well to soil tillage research.Both the two mehtods of quantification indicated that the winter soil dynamic processsignificantly improved soil structures. Autumn-tilled soil has a higher extent of breakage ascompared with spring-tilled soil, and in additon to this, its surface contacting energy wasmuch lower than that of the spring-tilled soil. All this proved that soil tillage is not a sole way for the improvement of soil structures. When coming to the structural state ofagricultural soils we have to consider environmental as well as weather factors.Both the two mehtods of quantification indicated that the winter soil dynamic processsignificantly improved soil structures. Autumn-tilled soil has a higher extent of breakage ascompared with spring-tilled soil, and in additon to this, its surface contacting energy wasmuch lower than that of the spring-tilled soil. All this proved that soil tillage is not a soleway for the improvement of soil structures. When coming to the structural state ofagricultural soils we have to consider environmental as well as weather factors.