Root and shoot competition between established grass species and newly sown seedlings during spring growth

Competition between established Dactylis glomerata or Festuca pratensis/Tar axacum officinale swards and seedlings of Trifolium pratense was studied un der field conditions in Norway. Root competition from the Festuca pratensis /Taraxacum officinale sward was significantly greater than that from a Dact ylis glomerata sward. The balance in root and shoot competition varied betw een experimental years because of variation in environmental conditions. In the first experimental year, root competition had a greater effect on seed ling dry weight than shoot competition, whereas the opposite was found in t he second year. However, both root and shoot competition (full competition) in comparison with no competition gave proportionally the same effects in both years, indicating that an alleviation in root competition will be foll owed by intensified shoot competition. An increasing effect of shoot compet ition with time on plant dry weight was found. In a second experiment, seed lings of Lolium perenne and Trifolium pratense produced the highest plant d ry weights in competition with an established Phleum pratense sward, follow ed by seedlings of Poa pratensis, Phleum pratense and Trifolium repens in d ecreasing order. However, no interactions between seedling species and comp etition treatments were found, indicating no differences in sensitivity bet ween seedling species to competition from the established grass sward. The results are discussed in the context of renovating grassland by direct dril ling.