Adaptation of tropical forage species to acid soils: the influence of varying phosphorus supply and soil type on plant growth

Abstract

The present work compared the plant growth response of one tropical grass and three tropical legumes. The forages were grown in monoculture or in grass + legume associations at different levels of soil phosphorus (P). Two acid soils, both Oxisols, were used: one sandy and one clay loam. They were amended with soluble P at rates ranging from 0 to 50 kg ha-1. The forages, Brachiaria dictyoneura (grass), Arachis pintoi, Stylosanthes capitata and Centrosema acutifolium (legumes), were grown in the glasshouse. After 80 days of growth, biomass production, dry matter distribution, leaf area production, root length density, specific root length, and proportion of legume roots in an association were determined. The grass, grown either in monoculture or in association, responded more to applied P than did the three legumes in terms of both shoot and root production. At 50 kg P ha-1, the grass yield plant-1 in association with the three legumes was greatly enhanced, compared with that of grass in monoculture. The increase in size of grass plants in association, compared with that in monoculture, may have been caused by reduced competition from the legumes.