SOIL PROPERTIES AFFECTING WEED DISTRIBUTION IN SPRING CEREAL AND VEGETABLE FIELDS

The incidence of weed species in 482 cereal and 224 vegetable field plots in southern and central Finland was investigated. The occurrence of the 16 most common weed species was related to soil properties. Chenopodium album L., Lamium spp. L. and Fallopia convolvulus (L.) Love were more abundant in clay than in coarse mineral or organic soils. Elymus 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 not found at all in organic soils. Rumex spp., Poa annua and Polygonum lapathifolium had higher densities at the lowest pH level, < 5.2. Lamium 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.