The effect of fertilizer nitrogen rate, white clover variety and closeness of cutting on herbage productivity from perennial ryegrass/white clover swards

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 783 1 ha^‐1 with no N to 11701 ha^‐1 at 360 kg ha^‐1 N. Mean herbage response to N (kg DM per kg N applied) was 73,90 and 108 for the three successive N increments relative to no N. Mean white clover DM production was reduced from 4 14t ha^‐1 with no N to 051 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.