The effects of rate and timing of application of fertilizer nitrogen in late summer on herbage mass and chemical composition of perennial ryegrass swards over the winter period in Northern Ireland

A small-plot experiment was carried out in Northern Ireland on a predominan tly perennial ryegrass sward over the period July 1993 to March 1994 to inv estigate the effect of timing and rate of fertilizer nitrogen (N) applicati on on herbage mass and its chemical composition over the winter period. Eig hty treatment combinations, involving four N fertilizer application dates ( 28 July, 9 and 30 August and 20 September 1993), four rates of N fertilizer (0, 30, 60 and 90 hg N ha(-1)) and five han est dates (1 October, 1 Novemb er, 1 December 1993, 1 February and 1 March 1994, were replicated three tim es in a randomized block design experiment. N application increased herbage mass at each of the harvest dates, but in g eneral there was a decrease in response to N with increasing rare of N and delay in time of application. Mean responses to N applications were 13.0, 1 1.5 and 9.5 kg DM kg(-1) N at 30, 60 and 90 kg N ha(-1) respectively. Delay ing N application, which also reduced the length of the period of growth, r educed the mean response to N fertilizer from 14.3 to 7.4 kg DM kg(-1) N fo r N applied on 28 July and 20 September respectively. Increasing rate of N application increased the N concentration and reduced the dry-matter (DM) content and water-soluble carbohydrate (WSC) concentrat ion of the herbage but had little effect on the acid-detergent fibre (ADF) concentration. Delaying N application increased N concentration and reduced DM content of the herbage. The effect of date of N application on WSC conc entration varied bt tween harvests. A decrease in herbage mass occurred from November onwards which was associa ted with a decrease in the proportion of live leaf and stem material and an increase in the proportion of dead material in the sward. It is concluded that there is considerable potential to increase the herbag e mass available for autumn/early winter grazing by applying up to 60 kg N ha(-1) in early September.