VEGETATION ESTABLISHMENT ON CHALK MARL SPOIL - THE ROLE OF NURSE GRASS SPECIES AND FERTILIZER APPLICATION

The Channel Tunnel workings on the UK side have yielded nearly 4 milli on m(3) of chalk-marl spoil which now forms a 36 ha landscaped reclama tion platform. To establish vegetation of amenity and conservation int erest on the spoil, seed mixtures of native wild flowers and grasses w ere sown with Lolium perenne (perennial rye grass) as a nurse species. Potentially, L. perenne is a suitable nurse species for grassland cre ation on infertile substrates as it provides rapid initial cover and s tability, but it is non-persistent and declines in vigour with time, a llowing wild flower species sown alongside to expand their cover and s pread in the longer term. On very low fertility substrates like chalk marl, an initial application of fertilizer is needed to encourage plan t growth. Results are reported of a fertilizer experiment on Channel T unnel spoil to determine appropriate levels of fertilizer for establis hment of species-rich grassland vegetation. An area hydroseeded with L . perenne and wild flowers in autumn 1992 was subjected to factorial t reatment of four levels each of N and P in spring 1993. The results th e following summer showed significant positive effects of nitrogen and phosphorus on L. perenne biomass and a negative impact of nitrogen on densities of wild flower species, especially legumes, establishing in the L. perenne sward. In general, low fertilizer applications encoura ged low productivity and maximal species richness in the vegetation. C onversely high applications encouraged high productivity and competiti ve exclusion of sown wild flower species. Fertilizer applications must therefore balance encouragement of the stabilising nurse grass sward, while preventing competitive exclusion of wild flowers by the nurse g rass.