USE OF THE AMAZONIAN TREE SPECIES INGA EDULIS FOR SOIL REGENERATION AND WEED CONTROL

Land for agriculture in the tropics is often cleared through slash and burn, which is a shifting cultivation system. however, shortening of fallow periods led to soil degradation, decreased yields and increased weed pressure. our objective was to evaluate the effects of short-term tree fallow of inga edulis on weeds and soil fertility. we compared four treatments, namely, (1) natural fallow, (2) planted fallow with i. edulis, (3) planted fallow with i. edulis + herbaceous cover crop kudzu (pueraria phaseoloides) and (4) continuous cropping of cassava (manihot esculenta). tree and weed biomass amount and composition were determined at 3, 6, 9, 13, 17, 20, 24, 28 and 33 months after establishment, while soil samples at 17 and 25 months. the growth rate of i. edulis was slow when compared with other studies. however, improved fallows were able to significantly decrease aboveground weed biomass. total biomass of improved fallows increased more rapidly than that of natural fallow and cassava cropping. there were no significant soil fertility differences between treatments and all fallows increased the organic matter in topsoil over time. available p declined in all treatments but stocks of aboveground n, p and k increased more rapidly under improved fallows. planted fallows using trees such as i. edulis have the potential to reduce growth of weed species and improve some soil fertility parameters but, on highly degraded soil, a longer time and possibly p fertilisation may be needed to achieve these increases.