Reaction forces of lightweight mouldboard ploughs at slow speeds of tillage in Nitosol, Vertisol and Ferralsol soils under two moisture conditions

The mouldboard plough is the standard tillage implement used with animal power in Kenya. Various designs are currently used indiscriminately in varied soil types and conditions of operation. Their draught characteristics and comparative ability to achieve or maintain desired depths of operation under inherent edaphic conditions are unknown. The significance of variation in working speeds, when different species of draught animals are used, is also unknown. This study was therefore aimed at rating the performance of some common ploughs in order to advise farmers on optimisation of their use. Draught and vertical reaction (suction) on a per-tool basis were measured for four ploughs commonly used in the region; the Victory®, the Rumpstad winding-body® and two types of Rumpstad cylindrical-body® ploughs, using an instrumented rig. The experiments were in Pellic Vertisol, Ferralsol and Nitosol soils under two soil moisture conditions. Draught increased significantly with depth for all four ploughs, hence, regulation of tillage depth is paramount to avoidance of drastic fluctuations. Similarly, vertical reaction increased with depth of ploughing, which implies a more stable operation, hence, when draught can be sustained over an acceptable work duration, it is desirable to set the ploughs to work deeply. Significant speed-depth interactions were also recorded, and these imply that speed is important when operating depth is stochastic as is the case in the dynamics of these ploughs. Overall, the Victory plough had the lowest draught requirement (0.32-1.02 kN) under dry and moist soil conditions, hence, was the best option for use in areas represented by the three soil types in Kenya. Soil-type had a significant effect on mean draught and vertical reaction in the order (Draught, Vertical reaction); Vertisol (1.65 kN, 0.70 kN) > Ferralsol (0.66 kN, 0.44 kN) > Nitosol (0.64 kN, 0.01 kN), and Ferralsol (1.17 kN, 0.71) > Vertisol (1.09 kN, 0.23 kN) > Nitosol (0.49 kN, 0.11 kN) under moist and dry conditions, respectively. These results suggest that the duration of continuous work periods with draught animals should be based on soil-type.