Effects of spring-tine settings and operational conditions on the mechanical performance of a weed harrow tine

Understanding the mechanical actions of weeding with a spring-tine harrow at different tine settings is necessary to achieve optimal weed control. The mechanical actions of a tine harrow in two different soils at two different locations on the harrow were investigated, pointing out the effects of varied implement settings and operational conditions on the tine weeding performance. A commercially available flexible harrow tine was investigated in sandy and sandy clay loam soils. The tine was pulled in soil bins without plants in order to avoid biological variances. Tine movements and forces acting on the tine were measured with strain gauges and analysed as the mean backward and upward tine torsion, the variation of the tine location around the mean position in sideward and upward direction and the properties of the vibrational frequency in sideward and upward direction during working. In addition, a high-speed camera was used to provide visible description of tine mechanical actions. Results showed that different tine settings and operational conditions and their interaction with soil type and tine location have different responses on certain weeding and tine parameters. High selectivity requires minimising the tine upward and lateral movements, preserving a constant penetration depth and a constant distance from crops. This could be ensured by a low speed, a thin tine and a trailing or vertical tine orientation for a constant depth and trailing or leading tine orientation for constant distance from crops. However, effective weed uprooting would require a high speed, a deep penetration, standard thick tine and a leading tine orientation. As the high selectivity and high effectivity requirement need different tine settings, optimisation of the weed harrow depends on intended effects. (c) 2005 Silsoe Research Institute. All rights reserved Published by Elsevier Ltd.