Composition and decomposition of roots of ryegrass and red clover

Abstract

Red clover roots contained much more lignin and pectin, slightly more cellulose, and less hemicellulose than roots of perennial ryegrass, when these components were expressed as a proportion of organic matter. Much smaller amounts of p-hydroxybenzoic, p-coumaric and ferulic acids were released from the roots of red clover by NaOH, than from perennial ryegrass. Roots of both species were incubated with soil for up to 33 weeks, under both well-aerated and waterlogged conditions, and changes in the composition of the organic matter of the light fraction were examined. In general, the proportions of lignin increased and pectin decreased, and there was some tendency for hemicellulose to increase and cellulose to decrease. N, S and P in the organic matter of the light fraction decreased initially and then increased to reach, after 33 weeks, values greater than those in the roots. Whether the soil was well-aerated or waterlogged had little effect on these changes. Incubation with red clover roots increased considerably the amounts of p-hydroxybenzaldehyde, p-hydroxybenzoic acid, vanillin and syringic acid extracted from the soil (after removal of the light fraction) by a buffer solution of pH 8.4. Incubation with ryegrass roots increased the amounts of p-hydroxybenzaldehyde, p-hydroxybenzoic acid and syringic acid extracted by the buffer solution. The effects of incubation with roots on the amounts of phenolic compounds extracted by NaOH were particularly marked with ryegrass: p-hydroxybenzaldehyde, p-hydroxybenzoic acid and ferulic acid were greatly increased, and p-coumaric acid was increased to a smaller extent.