Response of higveld grass species to ammonium and nitrate nitrogen

Abstract

Forty-one populations in twenty-two species of highveld grasses were grown in pots of soil fertilized with solutions for comparing ammonium and nitrate nutrition. Cotton, tomato, cereal crops and pasture grasses were included for comparison. Roots and shoots were harvested separately, weighed and analysed for major and minor cations. Cotton, tomato, cereal crops and annual and pioneer species of grasses yielded nearly equally on either source of nitrogen. Climax perennial grasses from highveld soils yielded significantly more on ammonium nitrogen. Shoots of species yielding more from ammonium contained more aluminium, iron and manganese. Eighteen populations in eleven species were grown on limed or unlimed soil fertilized with the two nutrient solutions. Lime had no significant effect on yield or nitrogen content. All species yielded more and assimilated more nitrogen from the ammonium source, but the concentration of nitrogen, especially in water-soluble forms, was greater in plants fertilized with nitrate. It is suggested that native climax perennial grasses from sourveld are more calcifuge than annual species, pioneer species, or cultivated Gramineae. The suggestion is discussed in relation to published work on the effects of nitrogen fertilization on veld productivity and botanical composition.

Keywords: responses|highveld grasslands|grass species|ammonium|nitrate|nitrogen|plants|fertilisation|nutrition|cotton|tomatoes|cereal crops|pastures|comparisons|roots|shoots|cations|perennial grasses|soils|veld yields|botanical compositions