EFFECTS OF WEED-CONTROL ON THE EARLY GROWTH OF BETULA-PENDULA SEEDLINGS ESTABLISHED ON AN AGRICULTURAL FIELD

Various herbicides (glyphosate, sethoxydim, pendimethalin, chlorthiami d, dichlobenil, terbuthylazine) as well as particle board mulch and a cover crop (clover, Trifolium repens) were compared during the first t wo post-planting years as weed control means in a silver birch (Betula pendula) plantation established on agricultural soil in southern Finl and. Chlorthiamid, dichlobenil and terbuthylazine exhibited good weed control for two years and also increased the height growth of the seed lings by 40-50 cm and much greater relative increase in leaf area and volume as compared to untreated control plots. Weed control had a sign ificant effect on the foliar nutrient concentrations of birch, particu larly that of N. As the amount of weed vegetation increased, foliar N, P (second year), K, Cu and B decreased and, respectively, foliar P (f irst year), Ca and Mg increased. Vegetation control also had a great i ndirect influence on the state of health of the seedlings. Incidences of vole damage and bark necrosis disease were associated with a high c over-percentage of weeds, particularly of clover which is much favoure d by voles. Particle board mulch seemed to increase vole damage by pro viding shelter for the voles. The competition by weeds for nutrients, and probably also for water, was much more important than their compet ition for light. Use of mulch and a cover crop did not reduce root com petition as effectively as did the best herbicides.