Allelopathy in a Grass‐Legume Association: I. Effects of Hemarthria altissima (Poir.) Stapf. and Hubb. Root Residues on the Growth of Desmodium intortum (Mill.) Urb. and Hemarthria altissima in a Tropical Soil.1

Abstract

In Hawaii, Desmodium intortum (Mill.) Urb. ‘Greenleaf’ could not be established in a pasture of the tetraploid Hemarthria altissima (Poir.) Stapf. and Hubb. ‘Bigalta,’ while good survival of ‘Greenleaf’ seedlings was obtained in a sward of the diploid H. altissima ‘Greenalta.’ To help characterize the association further, Greenleaf seeds were planted alone and in mixtures with cuttings of Bigalta or Greenalta in pots with soil containing root residues of Greenleaf and the two grasses. The effects of these residues on the growth and mineral nutrient content of the three species were measured.Growth of Greenleaf was very poor in soil containing root residue of Bigalta. Plant fresh weights were only about one‐fourth of those obtained in the presence of Greenleaf and Greenalta residues. Levels of N, K, Mg, and Ca in the tops of Greenleaf were unaffected by residue source. However, the level of P in Greenleaf tops grown in Bigalta residue was 0.15% on a dry weight basis compared to 0.20% or greater for plants grown in the other two residues. The inhibition of Greenleaf growth in soil in which Bigalta had been grown previously was likely due to allelopathic substances in the Bigalta root residues rather than to competition for environmental factors.