SOIL PROPERTIES AFFECTING WEED DISTRIBUTION IN SPRING CEREAL AND VEGETABLE FIELDS

The incidence of weed species in 482 cereal and 224 vegetable field pl ots in southern and central Finland was investigated. The occurrence o f the 16 most common weed species was related to soil properties. Chen opodium album L., Lamium spp. L. and Fallopia convolvulus (L.) Love we re more abundant in clay than in coarse mineral or organic soils. Elym us repens (L.) Gould, Erysimum cheiranthoides L., Lapsana communis L., Myosotis arvensis (L.) Hill and Poa annua L. thrived better in coarse than in clay soils. Polygonum lapathifolium L. and Rumex spp. L. were more abundant in organic than in mineral soils, and Lamium spp. was n ot found at all in organic soils. Rumex spp., Poa annua and Polygonum lapathifolium had higher densities at the lowest pH level, < 5.2. Lami um spp. and Myosotis spp. thrived at the highest pH levels. Poa annua and Spergula arvensis were most common in soils where the extractable calcium concentration was below 1000 mg l-1 soil.