Changes in the weed flora of an arable field cultivated for 20 years.
Changes in the weed flora of Boddington Barn field were monitored during 20 years of arable cropping after being ploughed out of grass in 1960. Seedlings were identified and counted in spring in a grid of 151 quadrats in 14 of the 20 years. Spp. number varied from 23 to 53, with max. numbers after 4 years of cultivation. Grassland weeds did not persist long under continuous arable cropping; Trifolium repens survived the whole 20 years, Ranunculus bulbosus survived 14 years, Rumex obtusifolus 12 years, Plantago lanceolata 8 years, and of the 13 other spp. recorded, 9 were extinct within 5 years. When the permanent pasture was ploughed in 1960, 2 overlapping areas of the field yielded contrasting arable weeds. One area, probably cultivated sometime between 1940 and 1945 was characterized by Fumaria officinalis, Aethusa cynapium and 4 other weeds; seeds of these spp. survived 15-20 years in the soil. The other area cultivated between 1949 and 1960 was characterized by Papaver rhoeas and 3 other weeds. Mean seedling density increased over the period from 29/m2 in the 1st arable crop to 196/m2 after 20 years. Composition of the weed flora in any year was determined primarily by the season of crop planting.