ABUNDANCE, CASTING ACTIVITY, AND CAST QUALITY OF EARTHWORMS IN AN ACID ULTISOL UNDER ALLEY-CROPPING IN THE HUMID TROPICS

The density of earthworms, their surface cast production and the compo sition of surface casts were studied on an acid Ultisol in S.E. Nigeri a. Maize and cassava were grown as food crops, continuously or every o ther year in a maize/fallow rotation, in alley-cropping systems with F lemingia congesta or Dactyladenia barteri as hedgerow trees. Except in the unproductive Flemingia continuous cropping system, > 60 earthworm s per square metre were recorded in spite of the low soil pH(H2O) of 4 .1, but biomass was low (approximately 2 g m(-2)). Surface casts consi sted of tubular, up to 3 cm high casts of Pontoscolex corethrurus and some other large earthworm species and small granular casts of Eudrili dae earthworms. The standing mass of casts after 5 months of activity (May-September) ranged between 260 and 570 kg ha(-1). Tubular cast pro duction between September and December dropped from 97-18 g m(-2) day( -1). In spite of the lower biomass than reported in literature for les s acid soils, and in light of the low nutrient status of the soil, the estimated amounts of C and nutrients returned to the surface in casts were considerable: 750 kg C, 51 kg N, 16 kg Ca, 2.5 kg Mg and 2 kg K per hectare per year on average. (C) 1997 Elsevier Science B.V.