EFFECT OF QUACKGRASS ON THE PRODUCTIVITY OF BARLEY SEEDED AT DIFFERENT SEEDING RATES AND ROW SPACINGS

A 4-yr study was conducted to evaluate the effect of two row spacings (10 and 20 cm) and five seeding rates of the cereal (100, 200, 300, 40 0 and 500 viable seeds m(-2)) on the interference between quackgrass [ Elymus repens (L.) Nevski] and barley (Hordeum vulgare L. 'Cadette'). Narrow row spacings had no effect on the yield of barley in presence o r absence of quackgrass. However, seeding rates influenced the product ivity and development of barley when quackgrass was present. At a seed ing rate of 100 seeds m(-2), the yield reduction caused by the presenc e of quackgrass was 41%. When barley was seeded at 500 seeds m(-2), th e yield reduction was 19%. These yield reductions were mainly attribut ed to a decrease of spike density. In presence of quackgrass, the spec ific weight, number of kernels per spike, number of spikes per plant, 1000-kernel weight, harvest index and N concentration of grain were re duced. In contrast to a decrease of the row spacing, increasing seedin g rate can be used to reduce interference between quackgrass and barle y.