DEVELOPMENT OF AN EQUIPMENT FOR SOIL TILLAGE DYNAMICS AND EVALUATION OF TILLAGE PARAMETERS

Abstract

An equipment was developed and used to evaluate tillage parameters. The equipment consist of a soil bin, soil processing trolley, tool carriage and tool carriage subframes (adjustable and fixed types). The soil processing trolley was essentially a rectangular framework with a levelling board and compaction roller. The tool carriage and soil processing trolley were designed to move steel railings with Teflon wheels. This equipment enabled studies to be carried out on the draught requirement of model tillage tools (tines mid blades) and the nature of soil disturbance as they were affected by tillage parameters, that is, soil implement and operational parameters. Also developed for this study was a soil-material friction measuring device (or apparatus). The apparatus enabled us to measure the angle of soil interface friction. The soils tested in this study were loamy sand, clay soil, sandy loam and sandy clay loam (bin soil). The physical properties of the soils showed that the mean bulk density of loamy sand was 1.56 Mg/m3 with a standard deviation of 0.1 Mg/m3. Its clay ratio and saturated hydraulic conductivity were 13.6 and 5.3 mm/min respectively. The bulk densities of the clay soils were not significantly different at 5% level of significance. Similarly, the bulk densities of the sandy loam soils were not significantly different at 5% level of significance. Neither were the bulk densities of the sandy clay loam soil (bin soil) significantly different at 5% level of significance. The mean saturated hydraulic conductivity of the sandy clay loam soils ranged from 0.85 to 1.22 mm/min. The cohesion of the soils ranged from 1.62 to 1.77 kPa jar loamy sand, 10.0 to 15.6 kPa for sandy loam, 230 to 30.6 kPa for sandy clay loam and 35.2 to 44.2 kPa for clay. Mean values of cone index for the experimental soil ranged from 120 to 130 kPa for loam sand, 870 to 1340 kPa for clay and 752 to 870 kPa for sandy loam. Effect of moisture content and applied pressure on the compaction of the soils showed that loamy sand soil achieved higher bulk densities when the soil is approaching saturation. Clay soil are highly susceptible to compaction especially when their consistency changed from moist to wet. Compaction of sandy loam showed that increase in compaction are less dependent on moisture content but rather almost entirely due to applied pressure though these were not high neither. The sandy clay loam soils were extremely sensitive to water content at the time of compaction. The percentage increase in soil compaction for the sandy clay loam is related more to changes in water content than to applied pressure. The effect of applied pressure on bulk density of sandy clay loam could be described by a number of compaction behaviour equations. The equations were those of power, logarithmic, exponential and linear functions with very good R2 value, while power fit seemed to be the best. The angle of internal friction of the soil ranged from 39.6 to 42.0 degrees for loamy sand; 25.3 to 30.1 degrees for clay; 29.6 to 32.9 degrees for sandy loam and 30.7 to 33.0 degrees for sandy clay loam. For the coefficient of soil-interface friction, it was highest for rubber followed by smooth steel and least with Teflon. Effect of variation in soil parameters on soil disturbance and draught showed that draught of implement increased at a decreasing rate as the soil moisture content increased from 11.0 to 22.5% (db) in sandy clay loam soil. Polynomial equations best described the relationship with very good R2 values. Also draught of implement increased at an increasing rate as the cone index increased by means of compaction. Effect of variation in implement parameters on soil disturbance and draught showed that draught increased at a decreasing rate with tine width. The draught of blades increased in the order of magnitude; VEE blade (BVE); triangular blade (BTR); convex blade (BCV); semi cicular blade (BSC); convare blade (BCC) and wide tine (TWT). In all the blades draught increased at an increasing rate. Draught was also found to be affected by surface finish. The draught force requirement was highest for rusted steel surface (SRS), followed by clean steel surface (SCS) while that of Teflon coated surface (STS) was least. Effect of cutting edge thickness showed that draught of implement increased at an increasing rate as the cutting edge thickness increased from 1 mm to 8 mm thickness. The increase in draught was typically 48 to 62%. Effect of variation in operational parameters showed that draught increased with depth of operation at an increasing rate. An exponential curve best described the relationship. Also draught increase with forward speed at an increasing rate. Quadratic equation best described the relationship. Similarly, draught increased quadratically with increase in rake angle with minimum draught occurring at about 45o rake angle. The parameters of soil disturbance are: ridge to ridge distance (RRD); width of crescent (WC); total disturbed width (TDW); after furrow depth (d;); height of ridge (h) and rupture distance (f). Generally, the parameters of soil disturbance increased as the tillage parameters increased. However, it was observed that rupture distance decreased as the rake angle increased.