Effects of tree density and crop management upon earthworm cast productionin a young timber plantation after introducing understory crops

The effects of two timber stand densities and four low-input crop managemen t systems upon surface cast production by earthwonns were assessed in a six year old I: ivorensis timber plantation in the humid forest zone of Camero on. Cast production was also monitored in undisturbed control timber planta tion plots. Crop management treatments were sole plantain, sole tannia and a plantain-tannia intercrop, all mulched, and also sole plantain, where the slashed material was burned before planting. Casts were collected from fra mes for 27 weeks until the beginning of the dry season when casting ceased. There was significantly greater cast production in the undisturbed control (59.0 Mg ha(-1) dry weight) than in the cropped plots (27.8 ME ha(-1)). In the cropped treatments, on average 98.8 kg total N, 1078.2 kg organic C, an d 6.6 kg exchangeable Mg were deposited in surface casts, significantly les s than in the control plots. There were no differences in cast production o r amounts of nutrients in casts between timber stand density or crop manage ment treatments, however casts derived from high timber stand density treat ments had significantly higher concentrations of total N and exchangeable C a than those from low timber stand density treatments. Casts in the control plots had significantly lower concentrations of exchangeable: cations than those from cropped plots. Cast production in control plots was positively correlated with soil exchangeable Ca concentration. Cast production and nut rient concentrations in low timber stand density, mulched plots were strong ly correlated with weed biomass and initial soil properties. Thus weeds app eared to act as a substitute shade provider. in high timber stand density p lots, there were strong correlations between mulch, nutrient concentrations and cast production and nutrient concentrations. It is thus hypothesised t hat retaining trees and providing a nutrient input through mulch permits an increase in activity of litter-feeding species and thus higher quality but lower quantities of casts. If trees are removed, the less favourable physi cal conditions may reduce the activity of litter-feeders so cast production is predominantly by endogeics, leading to lower quality casts.