## LESSON 4. ANALYSIS OF SOIL-MACHINE DYNAMICS IN TILLAGE

4.1. Analysis of Soil-Machine Dynamics in Tillage

The analysis of soil dynamics in tillage mostly involve determination of cutting forces for tillage implements as a function of soil, over burden (surcharge) tool and soil-tool factors. Once the cutting force is determined, it can be used with velocity or tool speed to obtain power requirement and specific draught using appropriate equations. A number of approaches have been used in this analysis. These include:

1.  Universal Earthmoving Equation (UEE),

2.  Trial Wedge Approach,

3.  Stress Characteristics Approach,

4.  Finite Element Approach and

5.  Similitude (dimensional analysis) Technique.

4.2. APPLICATIONS OF SOIL DYNAMICS IN TILLAGE

For the analysis of soil-machine dynamics to be useful, it must be applied to solving real life problems. In other words, it must be able to contribute towards improving the processes and machinery required for providing a sustainable tillage system. In this case, such a system should modify the soil to provide optimal conditions necessary for crop growth and yield and at the same time ensuring sustainability in terms of conserving energy, soil and water and ensuring non-destruction of soil structure. Some of the applications of the practical applications include:

1.  design optimization of tillage tools and traction devices,

2.  development of new tillage implements and traction devices,

3. energy, soil and water conservation and,

4. providing technical and scientific basis for evolving a sound economics of tillage.

i. Optimization of tillage Tools

As already noted, there are many tillage implements from hand tools to animal drawn ploughs and different tractor mounted plough tillers, harrows, etc. Although these machines are already designed and in use, engineers continue to work on them especially with respect to modifying them to address conservation issues and other issues relating to soil structure destruction. These involve changes in the tool parameters (width, depth, sharpness, rake angle, smoothness etc) and the manner in which they engage and fail the soil depending on how the tool forces are applied to the soil. By studying and manipulating the tool and soil parameters, it is possible to optimize the design and operation of these tools.

ii.  Development of New Tillage Implements

In the development of any tillage implement or related machinery, there is need to understand soil failure pattern, soil movements, and interaction between these and the machine. These will enable the designer to determine the best way to fail the soil, the best way to make the soil move through the surface of the blade or indeed how to reduce the soil strength without necessarily inverting or pulverizing the soil. The analysis of soil dynamics also enables the designer to determine maximum tool forces, soil bearing capacity, etc which will enable him determine appropriate sizes of components of the machine.

iii.  Energy Conservation in Tillage

In modern day tillage, especially with new knowledge in precision agriculture, the conventional tillage system of plough, harrow, and ridge in separate operations is no more in vogue. In the classical conventional method, the concept is to apply a force much higher than the bearing capacity or strength of the soil such that the soil fails and shatters. It is also inverted, pulverized and so on. All these consume excessive energy in terms of tractor fuel consumption. In addition, it results in frequent wearing of the tillage tool, all resulting in high cost of tillage and hence crop production. With advance in soil dynamics, it is now possible to have on-board computers that can assess the soil condition, and apply just the minimum force required at a particular place and depth, thus achieving real time process control and energy conservation.

iv. Soil and Water Conservation in Tillage

Environmental concerns have made it mandatory that tillage must ensure soil and water conservation. Thus, new and existing tillage tools must be used in such a way as to conserve the soil in terms of maintaining a stable soil structure, ensuring a good balance of soil nutrients at all times and ensuring that soil water is not allowed to evaporate excessively.

The study of soil dynamics enables the engineers and indeed the tillage practitioner to understand how to appropriately combine the tool and soil factors in such a way that the balance of the soil ecosystem is not destroyed. This has led to the emergence of a number of conservation tillage practices with their associated tools and machinery.

v.  Economics of Tillage

The total understanding of soil-machine dynamics enables scientists and engineers to handle tillage as an economic venture which it is. In an attempt to develop a guide to selection of optimum tillage system for any particular soil, crop and environment, Anazodo et al, (1991) presented the optimization scheme shown in Fig. 2. To be able to apply this scheme to any situation, an in-depth understanding of soil dynamics is required.