Response of grass swards to fertilizer N under cutting or grazing

SUMMARY An experiment was conducted at six widely separated centres in England and Wales for 4 years to compare the response of a perennial ryegrass (cv. S. 23) sward to fertilizer N at input rates of 200, 400 and 600 kg N/ha under cutting-only or grazing-only management systems. Under both managements the yield response to N varied substantially and was always greater under cutting than grazing and the response was greater in the first than in subsequent years. Under cutting, significant responses were obtained from 200 to 400 kg N/ha at all sites and in all years but very few sites responded significantly from 400 to 600 kg N/ha after the first year. Under grazing there was on average of all sites (but not at every site) a significant response from 200 to 400 kg N/ha only in the first year. In subsequent years no single site gave a worthwhile response in each year. Under grazing no site showed a significant response from 400 to 600 kg N/ha. At the lowest application of nitrogen, 200 kg N/ha, dry-matter yields under grazing were greater than those under cutting on eight of the possible 24 centre-year occasions. At the two higher rates of applied nitrogen dry-matter yields under cutting were consistently greater than those under grazing. With smaller responses to applied nitrogen on grazed than on cut swards maximum yields were achieved under grazing with an input of about 200 kg N/ha less than under cutting management. The results suggest that cutting experiments cannot be used to predict herbage yields and responses to fertilizer nitrogen under grazing conditions.