CHANGES IN THE SOIL SEED BANK OF FOUR LONG-TERM CROP/HERBICIDE EXPERIMENTS.

(1) Numbers of viable weed seeds in the top 15 cm of the soil were determined over a 16-yr period for four adjacent monocrop/herbicide combinations in which both herbicide-treated and untreated plots were hoed and hand-weeded. (2) On all plots there was a progressive decline in the numbers of viable seeds of Aphanes arvensis, Raphanus raphanistrum, Chrysanthemum segetum, Arabidopsis thaliana, Papaver rhoeas, Viola arvensis and Trifolium repens. (3) Changes in the other species reflected opportunities for seed production. After 16 yr the main species in spring cereal (&plusmntri-allate;±MCPA) were Polygonum aviculare, Stellaria media and Poa annua; in maize(± simazine). Solanum nigrum and Urtica urens: in carrots(± linuron), Poa annua and Capsella bursa-pastoris. (4) Herbicides had little qualitative effect on species composition, but in maize and carrots the final populations where herbicides had been used were much lower than on the untreated plots. [ABSTRACT FROM AUTHOR]