Choice of Cultivars in Organic Farming: New Criteria for Winter Wheat ldeotypes : II. Weed Competitiveness of Morphologically Different Cultivars

The effect of differing ground shading resulting from cultivar selection on natural weed cover and defined seeded model weeds was tested in field trials in 1989, 1990 and 1995 at the organically managed experimental farm Wiesengut near Bonn, Germany. Cultivars with planophile leaf inclination could reduce weed growth significantly, especially at wide row spacings and north-south direction of the drilling row. Morphology and seed production of weeds were also influenced by shading ability of the selected winter wheat cultivars. The effect of morphological features of different cultivars on ground shading exceeded the effect of increased N-fertilization of 40, 120 or 160 kg N ha-1 , given as farmyard manure to the precrop potato. By optimizing and combining cultivar selection, row spacing and direction of rows, the competitiveness of a winter wheat stand in Organic Farming might be so much enhanced, that hoeing is not necessary in stands of relatively low weed density.