TILLERING AND PARTITIONING OF DRY-MATTER AND NUTRIENTS IN LOLIUM-PERENNE GROWING WITH NEIGHBORS OF DIFFERENT SPECIES - EFFECTS OF NUTRIENT SUPPLY AND DEFOLIATION

The hypotheses that performance of Lolium perenne L. (ryegrass) differ s when plants grow with conspecific or heterospecific neighbours, and that nutrient supply and severity of defoliation modifies the effect, mere tested in a target:neighbour pot experiment. Target L. perenne pl ants were grown with neighbours of five grass species (L. perenne, Poa pratensis L., P. trivialis L., Festuca ovina L. and F. rubra L.) and Trifolium repens L. (white clover), at three nutrient levels (high, me dium and low) and three defoliation severities (no defoliation or cut every 2 wk to 4 cm or 8 cm) over a 12 wk experimental period. Performa nce of L. perenne plants differed depending on the species of neighbou r. Tiller numbers and dry weights of clippings of L. perenne, at both individual cuts and the total accumulated over all seven cuts, were gr eater with P. pratensis, F. ovina or T. repens as neighbours than in a monoculture. The differences were generally confined to medium and hi gh nutrient lev els. The pattern of clippings depended on species asso ciation; clippings were similar at successive cuts except in mixtures with P. pratensis, F. ovina and T. repens, where they increased until the 4-5th cuts. The total accumulated dry matter (DM) and nutrients of L. perenne and the percentage contribution of DM to the pot total wer e also greater in these mixtures. Individual linear regressions of til ler numbers and accumulated N for each species combination best descri bed the relationships between L. perenne and its neighbour. Neighbouri ng species had no significant effect on the relative losses of dry wei ght or nutrients in clippings of L. perenne when expressed as a propor tion of the total accumulated, but partitioning of DM to L. perenne ro ots (root weight ratio) was greater in associations with Poa species t han in a monoculture. It was concluded that the species of neighbour a ffected the accumulation and partitioning of dry matter and nutrients in L. perenne and that nutrient supply, but not defoliation, modified the responses. The results are discussed in relation to species intera ctions in grazed swards.