Evaluation of bentleg and straight narrow point openers in cohesive soil

The bentleg opener was developed to overcome the high soil disturbance caused by straight narrow point openers, with the original evaluation conducted on sandy soils. A bentleg furrow opener was compared to narrow point openers with varying rake angles (45 degrees and 90 degrees) and cutting edge cross-sections (blunt, and single- and double-side chamfers) for soil disturbance, tillage forces, and soil aggregate break down in Black Vertosol (Vertisol in the USDA Soil Taxonomy), a highly cohesive soil relative to sandy soils used previously. Whereas the 45 degrees rake angle caused greater soil disturbance, produced larger soil aggregates, and reduced draught and vertical force requirements, all openers with 90 degrees rake angle (blunt and chamfered openers) had a shallow critical depth (44-46 mm) and caused smearing. Contrary to previous findings in sandy soil, both single and double side chamfering of opener cutting edge had no significant effect on soil movement, furrow width, and furrow crosssectional area. However, greater soil movement was observed on the chamfered side of the single-side chamfered opener than the non-chamfered side. The chamfers significantly reduced draught and vertical forces and produced smaller soil aggregates. The bentleg opener loosened soil to the furrow bottom but caused the least soil movement out of the furrow and formed a ridge in the middle of the furrow, which resulted in the highest furrow backfill. It also encountered a downward vertical force which assisted penetration and had a greater proportion of aggregates within the optimum range (1.18 and 9.5 mm). The bentleg opener, thus, shows potential for improved seed covering and satisfactory performance at operating speeds above 8 km h-1.