Weed vegetation on vegetable allotments E16
University of Helsinki, Lahti Research and Training Centre, FIN-15140 Lahti
|Weed occurrence and associations were studied on
16 vegetable-potato allotments in Lahti in southern Finland. The fields were cultivated
without herbicides. The weed vegetation was studied from 159 releves and was analysed with
DCA-ordination and PCA- and Twinspan-analysis. As environmental parameters, were studied
soil types as well as soil water content and acidity. Weed groups discovered with DCA were
also compared with Continental-European weed associations.
Although 83 weed species were found, generally only 16-32 species were found per one field. On sandy soils Galeopsietum-association and on peaty soils Polygono-Matricarietum matricarioides-association dominated. On loamy and clay soils Thlaspio-Fumarietum officinalis-association dominated. On an old-culture field with much humus Chenopodietum polyspermi-association was found.
In the DCA-ordination the first axis represented the moisture gradient, which was reflected also in the total coverage of weeds. The second axis represented the change from sandy soils towards loamy soils and clay soils. DCA-ordinated weed groups corresponded to the Continental-European weed associations previously found. PCA arranged the weeds in two main groups, those growing mainly in humus soils and those growing in mineral soils. There was, however, a continuum between these two groups according to individual releves. The most rare weeds found in this study were Erodium cicutarium, Anchusa arvensis, Chenopodium polyspermum, Sonchus asper, Vicia hirsuta, Vicia sativa subsp. nigra (angustifolia) and Euphorbia helioscopia. In Finland these weeds grow usually only in the southern coastal area.
According to this study the soil moisture and the soil type have the greatest effect on weed growth and on the formation of weed associations. The soil pH and nutrient contents seemed to be much less important in this respect.