Determinants of t Flemingia congesta and t 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 S.E. Nigeria, using litterbags or littertubes with leaves from the trees of an alley cropping system with t Flemingia congesta or t 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 t Dactyladenia than with the t Flemingia mulch (immediate effect). This is presumably related to t Dactyladenia's higher lignin content (40% compared to 22% for t Flemingia). The t Flemingia mulch decomposed faster in alley cropping with t Dactyladenia hedgerow than with t Flemingia hedgerow, irrespective of faunal access, suggesting a microclimate efffect 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 t Flemingia mulch within the first 10 days of decomposition, which indicates that early decomposition affected the relatively easily degradable compounds.