Tractability Conditions for Disc Ploughing on a Loamy Sand Soil in the Ilorin Agro-Ecological Zone
For agricultural field operations such as tillage and planting, an agricultural soil is considered tractable if it can develop adequate shear resistance to minimize tyre slip and soil damage and can produce required soil tilth without undue soil pulverization or the formation of large clods. Furthermore, the soil must be devoid of physical obstructions like stones, stumps, ant-hills, etc and be of a light vegetative cover. Tractability conditions for disc ploughing on a loamy sand soil based on soil moisture have been determined for Ilorin agro-ecological zone, which fall within the Guinea Savannah zone of Nigeria. This was achieved by carrying out disc ploughing on an experimental plot at thirteen different soil moisture levels ranging from 8.90 to 91.74% of field capacity. The tyre slip and wheel sinkage measured at each soil moisture level, were used to judge whether the soil was tractable or not. Soil is adjudged tractable if the observed tyre slip is either 15% or less. The corresponding soil moisture range was selected as the soil moisture condition at which the soil is tractable. It was found that the loamy sand soil of Ilorin agro- ecological zone was tractable between soil moisture levels of 8.90 and 60.08% of field capacity. Results showed that differences in soil moisture distribution along the slope of the land had no significant (P< 0.05) effect on the towing force and the drawbar pull of the tractor. However, differences in soil moisture levels had significant effect on them. Furthermore, data such as towing force, drawbar pull, soil cone index and tyre slip generated and analyzed using regression analysis, were used to establish empirical trafficability prediction equations; which are useful in studies of soil-machine interactions.