The effect of low soil temperature and fertiliser N rate on perennial ryegrass (Lolium perenne) and white clover (Trifolium repens) grown under controlled conditions
The response of perennial ryegrass and white clover to soil temperatures of 6, 12 and 18°C, and to nitrogen applications equivalent to 0, 50, 100 and 150 kg N ha-1, were investigated under controlled conditions. Ryegrass primary dry matter production (PDM) at the end of the first regrowth cycle (31 days) increased as fertiliser N rate was increased from 0 to 100 kg N ha-1. Residual dry matter production (RDM) at the end of the second regrowth cycle (60 days) and total dry matter production (TDM) over the two regrowth cycles were increased by all N application rates tested. Although yield responses were less at 6°C compared to 12 and 180°C, results clearly showed that N applications could be used to stimulate dry matter production of ryegrass during the cool season. White clover PDM, RDM and TDM were significantly influenced (P0.05) by soil temperature resulting in lower yields at 6°C. None of the fertiliser N treatments tested resulted in significant reductions in clover PDM, RDM and TDM. Increasing fertiliser N rates increased (P0.05) the number of ryegrass tillers, but stolon growing points of white clover were not affected. Leaf nitrogen content at the end of the first regrowth cycle was higher than levels regarded as adequate for optimum perennial ryegrass and white clover dry matter production. Results suggest that fertiliser N rates as high as 150 kg N ha-1 applied at low temperatures will stimulate perennial ryegrass dry matter production without any direct negative effect on white clover productivity.