Litter and biomass production from planted and natural fallows on a degraded soil in southwestern Nigeria

To rehabilitate a degraded Alfisol at Ibadan, southwestern Nigeria, Senna s iamea (non-N-fixing legume tree), Leucaena leucocephala, and Acacia leptoca rpa (N-fixing legume trees) were planted in 1989, and Acacia auriculiformis (N-fixing legume tree) in 1990. Pueraria phaseoloides (a cover crop) and n atural fallow were included as treatments. Litterfall and climatic variable s were measured in 1992/1993 and 1996/1997 while biomass production and nut rient concentrations were measured in 1993 and 1995. Total litter productio n from the natural and planted fallows was similar, with means ranging from 10.0 (L. leucocephala) to 13.6 t ha(-1) y(-1) (natural fallow) during the 1996/1997 collection. Leaves constituted 73% (L. leucocephala) to 96% (A. a uriculiformis) of total litterfall. Acacia auriculiformis grew most quickly but S. siamea produced the highest aboveground biomass which was 127 t ha( -1) accumulated over four years, and 156 t ha(-1) accumulated over six year s of establishment. The aboveground biomass of P. phaseoloides and natural fallow was only 6 to 9 t ha(-1) at six years after planting. Nitrogen conce ntration in the leaves/twigs of was 2.5% for L. leucocephala, and 2% for ot her planted species and natural fallow. Pueraria phaseoloides had concentra tions of P, K, Ca and Mg comparable to levels in the leaves/twigs of the tr ee species. Through PATH analysis, it was found that maximum temperature an d minimum relative humidity had pronounced direct and indirect effects on l itterfall. The effects of these climatic variables in triggering litterfall were enhanced by other variables, such as evaporation, wind, radiation, an d minimum temperature. Improvement in chemical properties by fallows was ob served in the degraded soil.