Litter Production and Soil Condition Under Agroforestry Trees in Two Agroecological Zones of Southern Nigeria

Abstract

ABSTRACT Tree species in agroforestry systems contribute to soil improvement through the litter produced on the soil surface and below-ground modification of soil structure by tree roots. Therefore, litter production and soil characteristics under 11 tree species were evaluated in the derived savanna (Ibadan) and humid tropical forest (Onne) zones of southern Nigeria between 1998 and 1999 in 7-year old arboreta. In Ibadan, the soil was a gravelly Alfisol, while in Onne it was an Ultisol. The trees were Alchornea cordifolia, Baphia pubescens, Calliandra calothyrsus, Dactyladenia barteri, Dialium guineense, Grewia pubescens, Inga edulis, Irvingia gabonensis, Nauclea diderrichii, Pterocarpus santalinoides and Treculia africana. Forest and natural regrowth (no-tree) plots were included as control. Litter-fall under the trees ranged from 5 to 14 t ha−1 y−1 compared to 15 t ha−1 y−1 for the forest at Ibadan, while it ranged from 7to16tha−1y−1 compared to 20t ha−1 y−1 for the forest at Onne. Litter production was high under D. barteri and I. edulis and relatively low under A. cordifolia, G. pubescens, I. gabonensis and P. santalinoides. There was a more drastic change in soil chemical properties in the Alfisol than the Ultisol, particularly with available P. Soil bulk density and penetrometer resistance were improved by A. cordifolia, C. calothyrsus, D. guineense, G. pubescens and T. africana. This study showed that ecological differences resulted in differences in annual litter production for only 33% of the species considered. However, the effects of the trees on soil properties were strongly linked to inherent soil properties.