Studies on the weeds of vegetable crops. 6. Seed populations of soil under commercial cropping.
The weed seed populations built up in the top 6 in. of soil in land on which vegetable crops have been grown for long periods, was estimated from soil samples obtained during the winters of 1958-62, from 58 fields distributed in 23 English counties. The numbers of seeds found ranged from 6.6 to 348 millions/ac and half the fields had seed populations within the range 25-90 million Fewer than 20 million seedswere found in only 10 of the 58 fields sampled. Although seeds of more than 70 species were encountered, 7 species, Poa annua, Urtica urens, Senecio vulgaris, Stellaria media, Capsella bursa-pastoris, Chenopodium album and Veronica persica together accounted for approximately 80% of all the seeds recorded. The prevalence of these species appears to be associated with the frequent cultivations involved in the production of vegetable crops.-M.Y.