Data were tested for homogeneity of variance using the Levene's test and log-transformed (log10) when required. Plant biomass and yield, chlorophyll content and earthworm abundance were evaluated using two-way ANOVA with repeated measures. Time was the repeated measure and treatments were within-subject factors. Soil chemical properties and the abundance of earthworm casts at the end of the one-year experiment were tested with a two-way ANOVA. Comparisons between means were tested with an LSD test. A principal component analysis (PCA) was also carried out on the soil chemical properties. All statistical calculations were carried out using R software (R Development Core Team, 2008). Differences among treatments were declared significant at the