The effects of nitrogen nutrition of plants on the development of acidity in Western Australian soils. II. Effects of differences in cation/anion balance between plant species grown under non-leaching conditions

Abstract

The effects of supplying different forms of nitrogen on the cation/anion balance and associated changes in soil pH of four agricultural species (wheat, perennial ryegrass, subterranean clover and white clover) were examined. Plants were grown in unleached pots in an acidic, poorly buffered, sandy soil from Western Australia. Acidity was increased by over 1.0 pH unit when plants took up NH+4 and by up to 0.6 pH units when legumes were dependent upon symbiotically fixed N. In contrast to the previous studies with leached soil, acidity was decreased when plants took up NO-3. The relationship between the excess cation content (or ash alkalinity) and the final soil pH differed amongst the four species. Although lower ash alkalinity was always associated with higher acidity, much smaller changes in ash alkalinity in wheat and ryegrass were associated with bigger changes in pH than was the case with the legumes. The relationship between soil pH and ash alkalinity of subterranean clover shoots was markedly different from that for the other three species. Both extractable aluminium levels in the soil and manganese concentration in the plant shoots increased with decreasing ash alkalinity in the shoots through the effect on soil pH.