Influence of fertiliser nitrogen on herbage dry matter and nitrogen yields, and botanical composition of a grazed grass-clover pasture

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Abstract
The response of a ryegrass-white clover pasture, grazed by sheep, to lime-ammonium nitrate was studied. A dry matter (DM) yield response to annual inputs of 112 and 448 kg N/ha was clearly established. The heavier rate gave diminishing returns, but resulted in a 20% increase in total yield over the 18 t DM/ha recorded in the absence of applied nitrogen. Ryegrass responded and clover was suppressed with nitrogen use. The reduction in clover yield was small (15%) and unrelated to nitrogen rate. Herbage nitrogen yields are reported, Annual turnover of nitrogen through herbage ranged from 720 kg/ha for the control (no nitrogen) to 920 kg/ha with the heavier nitrogen input. Apparent recoveries of nitrogen for the year, 38% and 46% respectively, and are considered in relation to nitrogen rate, seasonal influences, and effects of nitrogen on clover performance.