Nitrogen response of seedlings of Aristida ramosa R.Br. and Danthonia DC. Spp

Abstract

Aristida ramosa R.Br., Danthonia linkii Kunth, and D. richardsonii Cashmore, common components of the native pastures on the North-western Slopes of New South Wales, differed markedly in their responses to applied nitrogen in the seedling stage in pot trials. Growth of A. ramosa was depressed and at higher levels seedlings were killed by nitrogen applied as a variety of sources, viz, ammonium nitrate, sodium nitrate, ammonium chloride and urea, especially when application occurred immediately prior to, or soon after seedling emergence. A significant nitrogen-phosphorus interaction was recorded, the negative effect of nitrogen being greatest at low soil phosphorus levels. Applied nitrogen enhanced growth of Danthonia seedlings. A dosage-mortality relationship was calculated with an application of 200 ppm nitrogen resulting in kills of 100 and 87% of A. ramosa seedlings at phosphorus levels of 0 and 50 ppm respectively; at the same nitrogen level the growth of D. linkii was enhanced at the higher phosphorus level and not affected at the lower level. An increase in the soil nitrogen level in a pasture containing these species could markedly affect the botanical composition.