The effect of fertilizer nitrogen rate white clover variety and closeness of cutting on herbage productivity from perennial ryegrass white clover swards
Frame, J.; Boyd, A.G.
Grass and Forage Science 42(1): 85-96
ISSN/ISBN: 0142-5242 DOI: 10.1111/j.1365-2494.1987.tb02094.x
Four varieties of white clover (small-leaved cv. Aberystwyth S184, medium-leaved cv. Grasslands Huia and large-leaved cvs Linda and Olwen) were sown at 3 kg ha-1 together with 10 kg ha-1 perennial ryegrass cv. Talbot. Herbage productivity was measured for three harvest years, 1979-81, over four annual rates of fertilizer N(0, 120, 240 and 360 kg ha-1) and two closeness of cutting treatments (80 and 40 mm from ground level). A simulated grazing regime of six cuts per year at 3- to 6-week intervals was used. Production of total herbage DM was increased by increasing N rate; mean annual DM production ranged from 7.83 t ha-1 with no N to 11.70 t ha-1 at 360 kg ha-1 N. Mean herbage response to N (kg DM per kg N applied) was 7.3, 9.0 and 10.8 for the three successive N increments relative to no N. Mean white clover DM production was reduced from 4.14 t ha-1 with no N to 0.51 t ha-1 at 360 kg ha-1 N. The large-leaved clover varieties were more productive than the small- or medium-leaved varieties at all N rates. Close cutting increased total herbage and white clover by a mean annual 16% and 31%, respectively. White clover varieties did not interact with either N rate or closeness of cutting. It is concluded that repetitive N application over the growing season is incompatible with white clover persistence and production, even with large-leaved clover varieties or with close cutting, two factors which improved clover performance in the experimental swards.