Determinants of Flemingia congesta and Dactyladenia barteri mulch decomposition in alley-cropping systems in the humid tropics

Effects of soil macrofauna, micro-environment and mulch quantity were investigated on an acid Ultisol in a high-rainfall area in SE Nigeria, using litterbags or littertubes with leaves from the trees of an alley cropping system with Flemingia congesta or Dactyladenia barteri as hedgerow species. There was no effect of mulch quantity on the rate of decomposition. Soil macrofauna contributed to between 30 and 40% of mulch decomposition over the period of approximately 50% of disappearance of the original material. The faunal effect became apparent after a longer incubation period (>20 weeks) with the slower decomposing Dactyladenia than with the Flemingia mulch (immediate effect). This is presumably related to Dactyladenia's higher lignin content (40% compared to 22% for Flemingia). The Flemingia mulch decomposed faster in alley cropping with Dactyladenia hedgerow than with Flemingia hedgerow, irrespective of faunal access, suggesting a microclimate effect on decomposition. There were no marked changes in chemical composition of the mulches with decomposition period, except for a rapid decrease of K content in both mulches and a rapid increase in lignin content of the Flemingia mulch within the first 10 days of decomposition, which indicates that early decomposition affected the relatively easily degradable compounds.