A quantitative analysis of inter-specific competition in crops with a row structure

Competition with weeds can cause high yield losses, especially in crops with incomplete canopy closure. This thesis reports on studies carried out to quantitatively explain the effects of spatial arrangements, emergence dates, plant densities, and physiological and morphological characteristics of competing species in a canopy with a row structure, on the growth of those species. A model for inter-specific competition (interrow), that explicitly takes into account the row structure of a crop, is described. The main "model system" was a witloof chicory ( Cichorium intybus L.) crop grown for its storage roots, in competition with the weeds Senecio vulgaris L., Solanum nigrum L., or Chenopodium album L. Weed competition caused high reduction in storage root dry weight, which was primarily caused by early weed emergence, and to a lesser extent by weed density and weed position. Weed competition increased the percentage of storage roots with a diameter smaller than 32.5 mm, which have very little economic value, because they do not contain sufficient redistributable carbohydrates to produce a chicon of good quality. The model interrow correctly simulated light interception inside a canopy consisting of witloof chicory and S. vulgaris . White cabbage ( Brassica oleracea var. capitata), in which Trifolium repens L. or Trifolium subterraneum L. was grown as a cover crop, was selected as a second "model system", to evaluate the ability of the model interrow to simulate effects of competition in other multi-species associations. This thesis shows that the model interrow was able to accurately explain competition between witloof chicory and weeds, and between white cabbage and clover species sown as cover crop. Model analyses helped to explain experimental results and were used to generate recommendations about growing crops in such a way that yield losses due to weeds or cover crop are minimised. This thesis elaborated robust linear relationships between vegetative plant weight and reproductive plant weight of weed species, and showed a strong allometric relationship between the average storage root diameter and the average storage root dry weight of witloof chicory. These relationships can be included in the model interrow and enable the analysis of the effects of crop-weed competition on the population dynamics of weeds and the marketable yield of witloof chicory crops. The recommendations based on feasibility studies may help to prevent yield reduction due to weeds, by using appropriate crop husbandry procedures.