The utilization of N fertilizer, applied to perennial ryegrass/white clover pasture growing on a humus iron podzol in N.E. Scotland

Applications of N fertilizer (0.40, 80, 120 and 240 kg N ha−1 year−1 in dressings of 40 or 80 kg N ha−1) were made to a perennial ryegrass/white clover (Lolium perenne L. Trifolium repens L.) pasture growing on a humus iron podzol reclaimed from heather (Calluna vulgaris L.) moor in 1982 and 1983. Where no N was applied, estimates of Ni fixation and mineralization were almost equal, being approximately 50 kg N ha−1 year−1 from each source. Apparent efficiencies of fertilizer use were generally low; for each dressing they ranged between –0·7 and 25·5 kg dry matter (DM)kgN−1. Also, responses to N fertilizer were affected by previous dressings. The net N recovery in harvested herbage from application of 120 kg N ha−1 year−1 was 30 kg N ha−1 year−1.