Plant growth on a low calcium status solodic soil in a subtropical environment. II. Soil cation anisotrophy and plant cation balance

Abstract

Pot and field experiments were carried out on solodic soils from southern Queensland showing marked soil cation anisotropy and increasing sodium absorption ratio with depth. The growth and cation composition of Phaseolus lathyroides and Cenchrus ciliaris were compared in a pot experiment with the surface and subsurface horizons of a solodic soil from site 1. Significant yield responses were obtained on the subsurface soil to each of five different calcium compounds. Applied calcium was associated with decreased plant sodium percentages. Effects were small on the surface soil. The effects of cation pair and cation ratio and various rates of calcium carbonate and magnesium carbonate on the yield and cation content of P. lathyroides were also measured for the surface soil. The calcium content was greatly reduced by high levels of applied magnesium. Under these conditions the relative constancy of the total plant cation content was disturbed. Field data on the chemical composition of grasses and legumes grown on solodic soils showed species differences in relation to cation content. Chloris gayana and Avena sativa contained high percentages of sodium. Panicum coloraturn contained moderate sodium percentages but levels in C, cdiaris were low. Temperate legumes, particularly annual Medicago spp., contained moderate sodium percentages. Sodium levels of all tropicaLlegumes grown were low but magnesium percentages were high. The experimental results suggest that the low calcium level and relatively high sodium and magnesium levels may affect the growth of certain species on solodic soils in southern Queensland. The cation status of these soils may influence ion selectivity mechanisms, cation balance, and root integrity. In some aspects of plant nutrition these solodic soils are analogous to serpentine soils.