| Abstract: | Uprooting by weed harrowing and the potential of the uprooting process for selective weed control at early crop growth stages was studied. Effects of working depth, seed depth, soil moisture content and working speed on uprooting of Lolium perenne L., Lepidium sativum L. and Chenopodium quinoa Willd. were investigated in laboratory harrowing experiments on a sandy soil. Harrowing uprooted on average 51% of the emerging plants and 21% of the plants in the seedling stage. Seventy per cent of all uprooted plants were completely covered by soil. An increase in working depth from 10 mm to 30 mm doubled the average fraction of uprooted plants. Uprooting was also promoted by higher soil moisture contents and higher working speeds. Average uprooting selectivity (=fraction of uprooted emerging plants/fraction of uprooted seedlings of the same species) varied between 2.0 (deep tillage and high speed) and 5.6 (dry soil). If tines could keep a distance of more than 3 mm from the crop and weed plants, the average selectivity of all treatments would improve from 2.4 to 5.5 and the average fraction of uprooted seedlings would decrease from 21% to 8%. This study indicates that uprooting may be a more important weed control mechanism than commonly believed. If working depth and the path of the harrow tines in relation to crop rows could be accurately controlled, uprooting could be a relatively selective weed control mechanism at early crop growth stages. |
