FERTILIZER NITROGEN RESPONSES ON 2 HILL PASTURES OF DIFFERENT PHOSPHATE FERTILIZER HISTORY

Fertilizer N responses with and without applied phosphate were measured over spring on slopes and flat areas within 2 sheep-grazed hill pastures of different P status. One pasture had received little phosphate in recent years and contained low levels of legume (9.2%) and ryegrass (6.3%), whereas the other had received large P inputs and contained substantially more legume (14.9%) and ryegrass (13.9%). Pasture N responses on both pastures were large in spite of differences in species composition. Application of phosphate along with the N fertilizer did not affect total pasture production or grass species yields on either pasture. Legume production was little affected by fertilizer N, but was substantially greater with P on lower P status soils. Increases in pasture production with N were similar on flat (0-10.degree.) and steep (10-25.degree.) sites, despite different productivity and species composition. N deficiency over spring is apparently general in these soils and essentially independent of pasture types.