The effect of crop rotation on weeds in organic arable fields.
Crop rotation is an essential element in organic farming weed management. The effect of five different crop rotation systems on the abundance of arable weeds was investigated. Therefore, a vegetation survey was carried out on the study plots from 2013 to 2016. 93 different weed species were recorded in 120 observations. Weed species number and composition in potatoes hardly differed between the crop rotation systems. Only crop cover was higher on plots with manuring and with a biennial grass-clover. In summer barley weed abundance was lower when there was grass-clover included in the crop rotation instead of field bean. Especially the dominance of the perennial Sonchus arvensis and of Avena fatua was reduced. Similar results were observed in the winter wheat. The crop rotation without potatoes and grass-clover was more susceptible both for annuals and perennials so that weed abundance in general was higher.