Comparing rolling coulters based on soil disturbance
Rolling coulters are widely used as a leading element on modem conservation till planters. Few studies have predicted or measured how coulters interact with the soil and what soil conditions they create. This research was initiated to study and compare popular rolling coulter designs; bubble, plain, 8-wave and 25-wave, based on the soil disturbance they cause. Soil disturbance was measured in terms of surface disturbance using a photoscanning technique, surface roughness using soil profiles, and strength changes using cone index profiles. Testing was conducted in rototilled and no-till clay loam, and in compacted and loose clay and sandy soils. Soil disturbance was greater in firmer soil conditions. The bubble coulter did the least soil disturbance and left firmer conditions around its path. Plain coulter disturbance was greater than disturbance by bubble coulter. 8-wave and 25-wave coulters caused the greatest surface disturbance. 25-wave coulter caused wider band of loosened soil (150 mm), than by 8-wave and plain (75 mm).;Substantial soil sticking (300 g) was observed for 25-wave coulter. The wavy coulters encountered higher horizontal and vertical forces. 8-wave coulter disturbance was moderate, and its performance was less dependent on soil conditions, compared to other coulters. Based on field tests, 8-wave coulter caused desirable disturbance. Simulation experiments were conducted to obtain theoretical lateral displacements of soil particles caused by each coulter design in a plastic soil. The geometry of the slot created by a coulter pass was predicted. The simulation results were in agreement with the photoscanning and cone index results obtained in the bin and field tests respectively. The study also concluded that the lateral displacement of a soil particle depends on what portion of wave or bubble first contacts the soil particle, and the length that they are in contact, and not so much on width or number of waves or bubbles on a coulter. The disturbance parameters measured in field tests support this finding.