Decline of Arable Weed Seeds During 20 Years in Soil Under Grass and the Periodicity of Seedling Emergence After Cultivation

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Abstract
(1) The decline of seeds of a natural population of arable weeds under a grass sward was monitored by germination in the field. Plots of 0.9 m2 were dug out of the turf in the 1st, 2nd, 3rd, 19th and 20th years of the experiment. All seedlings were counted and removed and the plots recultivated to a depth of 0.2 m at the end of each month for 24 months. (2) Twenty-one species were recorded of which Matricaria recutita L. and Papaver rhoeas L. were the most abundant. Chrysanethemum segetum L. and Raphanus raphanistrum L. seeds declined most rapidly with mean annual declines of over 30% per year (half lives of 1.5 and 2 years respectively), while Fumaria officinalis L. and Aethusa cynapium L. declined least with means of < 1% per year (half lives > 20 years). Other species were intermediate. (3) The monthly emergence of nine species, which occurred in sufficient numbers, are presented. All the species germinated to some extent in spring and autumn, although seedlings of Fumaria officinali L. and Trifolium repens L. emerged mainly in spring. (4) The results indicate that, as a control measure, planting a weedy arable field to grass for 20 years will not eradicate the seeds of even the most rapidly declining species.