Study of finger-star disc working tools of an inter-row cultivator

Abstract

This study combines laboratory force-deflection characterization, tomato transplant pull-out measurements and a descriptive field verification of an inter-row cultivator equipped with polyurethane finger-star discs. The objective was to relate finger hardness to crop mechanical resistance and thereby define a practical screening criterion for reducing crop damage. Discs with hardness values of 73, 83 and 93 Shore A were loaded at finger deflections from 0 to 50 mm. Pull-out force was measured for individual established tomato transplants at MG-44 instrument-reported relative soil-moisture readings of 18% (n = 5) and 10% (n = 7) in the 0–100 mm layer. The force–deflection relationships were linear (R2 = 1.000), and transplant pull-out force increased linearly with stem diameter (R2 = 0.991–0.994). During field operation at a working width of 4.2 m, travel speed of 1.0–2.0 m s–1 and disc working depth of 1.5–5.0 cm, complete visible destruction was observed for weeds at the white-thread stage and no visible injury to established tomato plants was recorded. These field proportions were obtained in a non-randomized engineering verification and are therefore descriptive. Within the tested range, 73, 83 and 93 Shore A discs are provisionally recommended for crops with pull-out forces of at least 10, 15 and 25 N, respectively. An Euler–Bernoulli cantilever-beam analysis explains the observed linear response and identifies the contact conditions that favour finger sliding rather than crop displacement.