Soil workability as a basis for advice on tillage activities

In the tropical area of Mexico, when and how to carry out tillage is a qualitative decision. There is no quantified information about the interaction between a chosen process of cultivation, soil type and weather, which dictate the tool and power requirements. Waste of energy and soil degradation by erosion and compaction, and lack of timeliness are recognized problems caused by inadequate tillage management in the tropical area of Mexico.In this thesis, the workable range of soils was quantified in the field, and the limits of that range, represented in the laboratory by tests to soil samples. This information is the basic part of a soil workability based procedure which is developed as a decision support tool for selecting specific tillage practices. The methodology was conceived for application in the tropical area of Mexico. For this reason a description of the area under study in relation to the present agricultural production system, including tillage related problems, was presented in Chapter 2 .In Chapter 3, The field and the laboratory studies to quantify the workable range of soils in the area, were treated. The methodology and results from those studies were presented and discussed, considering the technological result of the tillage operation and the input of energy at a range of soil moisture contents. Empirical relationships between initial moisture content and the technological result of tillage showed that results from Loam and Clay soils changed from optimum to sub-optimum at soil water potentials that rather coincide with the plastic limit in relatively moist soil. As soil was drying out , the implement result changed from optimum to sub-optimum at soil water potentials well below to that for the shrinkage limit, so the actual field work was smaller than the theoretical friable range of the soils. The minimum input of specific energy to obtain optimum results was close to the soil water potential, where results changed to sub-optimum as the soils w