Die Bodenkultur - Journal for Land Management, Food and Environment

K.-U. HEYLAND and H. MERKELBACH:

Undersowing Used for Weed Suppression and Competitive Effects Between Weeds and Undersown Grass or Clover on the Yield Formation of Winter Wheat

Summary

The aim of the experiment was to examine the competition effects of weeds and undersown crops in winter wheat at various methods of cultivation. Additionally, it was evaluated, whether it is possible to alternatively control weeds by undersowing clover or grass. Also the influence of the sowing date of undersown on the competition effects between weeds, undersown and crop was examined. These subjects were tested during 1985 and 1986 in field trials at the experimental farm "Dikoshof" and "Klein-Altendorf" of the University of Bonn. The comparison of weedy plots to those with undersown clover or grass showed that the biomass of all non wheat plants in the clover plots was the smallest. Plots with early undersown grass on the other hand showed a higher biomass production of non wheat plants than weedy plots. The winter wheat during the early stages of development was not affected by the companion plants. Its biomass after stem extension was influenced by the development of the companion plants and mainly local conditions. High competition by companion plants in late winter wheat development stages caused yield losses by a reduced number of ears/m2 and kernels/ear. The experiments showed, that a plant community including winter wheat, weed and undersown is a stabile, self regulating system. The dominant species in this system was the winter wheat. The influence of the companion plants on the crop yield was depending on the competitive power of the winter wheat and thus on the crop management. The competition intensity of the companion plants is bound to the local conditions. In practice it could be concluded that it is possible to develop a low competitive companion plant community by undersowing suitable crops. Combining this with an adapted crop management (variety, sowing, fertilizer) which improves the competition power of winter wheat, it should be possible to minimize the risk of yield damage. Key words: wheat; winter wheat; weed competition; weeds; undersowing; herbicides; crop rotation; yield formation.