Effect of calcium, pH and nitrogen on the growth and chemical composition of some tropical and temperate pasture legumes. II.* Chemical composition (calcium, nitrogen, potassium, magnesium, sodium and phosphorus)

Abstract

The chemical composition of tops and roots of nodulated and non-nodulated plants of some tropical and temperate pasture legumes grown in sand culture is reported and discussed in relation to nodulation efficiency and dry matter production, and nutrient interaction.

In most species, increasing pH raised the nitrogen concentrations in the tops of nodulated plants; calcium treatment had little effect.

Increasing the calcium concentration of the nutrient solution from 0.125 to 2.0 mM markedly increased the calcium~ concentration in the tops of all species, but in the roots to only a minor extent. Concentrations in tops differed between species. Concentrations in the tops of modulated plants were increased as a result of increasing pH, particularly at the low calcium treatment and for those species sensitive to low pH (Glycine wightii, Medicago species). Increasing the calcium concentration lowered the magnesium concentration, but the total cation content was not significantly affected.

In the tropical species, phosphorus concentrations in the tops were increased by reducing pH at both calcium treatments; values were higher at the low calcium treatment than at the high calcium treatment. Roots accumulated inore phosphorus than the tops.

Differences in the response of the species cannot be directly related to their mineral composition. With respect to nodulation and dry matter production, it is considered that the pH is the dominant factor and operates in the nodule initiation phase and in subsequent nitrogen production.

_______________ *Part I, Aust. J. Agric. Res., 27: 611 (1976).