Sward structure and biological nitrogen fixation potential of perennial ryegrass-white clover swards

摘要

Sward composition and canopy structure can alter grazing dynamics. The objective of this study was to investigate the effect of perennial ryegrass {Lolium perenne L.) ploidy and white clover {Trifolium repens L.) inclusion on sward structure and biological nitrogen (N) fixation (BNF) throughout the grazing season under a high N fertiliser regime (250 kg N ha~(-1)) and a high stocking rate (2.75 livestock units ha~(-1)). The study was a 2 x 2 factorial design, consisting of two perennial ryegrass ploidies (diploid, tetraploid) and two white clover treatments (grass-clover, grass-only). Four sward treatments (diploid only, tetraploid only, diploid + clover, tetraploid + clover) were compared over a full grazing season. Perennial ryegrass ploidy had asignificant effect on leaf proportion, tiller density, sward white clover content, tiller weight and leaf area. Diploid swards had lighter tillers (-0.07 g), smaller leaves (-0.78 cm2), lower leaf proportion (-7%), greater tiller density (+1,225 tillersm"2) and higher white clover content (+8%) than tetraploid swards. White clover inclusion had a significant effect on leaf (-7%) and stem (+5% pseudostem, +4% true-stem) proportions, tiller density (-1,649 tillers m~(-2)) and BNF (+151 kgN ha~(-1)). Altering sward composition using ploidy and white clover can affect sward canopy structure and grazing dynamics.