Changes during 3 years in the size and composition of the seed bank beneath a long-term pasture as influenced by defoliation and fertilizer regime.
Abstract
Changes in the seed bank beneath an Agrostis/Festuca pasture following defoliation treatments and NPK application were studied during 1978-80. Over 12 000 seeds/m2 representing 33 spp. occurred in the top 15 cm of soil in April 1978; the main constituents were Juncus spp., Agrostis capillaris, Trifolium repens, Poa trivialis, Deschampsia caespitosa and Ranunculus repens. The spp. composition of the sward was only weakly correlated with that of the seed bank. 30-40% of grass seeds occurred in the top 2 cm of soil, compared with a smaller proportion of dicotyledonous spp. and Juncus spp.; occurrence of grass seeds declined with increasing soil depth. Without input of fresh seed, grasses declined at 27%/yr, compared with 16%/yr for dicotyledons. When plots were not cut until late June 1978 the seed bank was transiently doubled by a large shedding of Cerastium fontanum subp. glabrescens. It was concluded that in dense undisturbed swards the chances of seeds being incorporated into the seed bank were low. In disturbed swards the nature of the seed bank and the depth of soil disturbance would affect the botanical composition of the sward.