Effects of slash and litter management practices on soil chemical properties and growth of second rotation eucalyptus in the Congo

Effects of slash and litter management practices on soil fertility and eucalypt growth were studied over a full rotation. Soil properties were compared to a depth of 1 m before harvesting the previous stand and at 1, 3 and 8 years after harvest management treatments. Stand overbark volume ranged from 84 m3 ha-1 to 161 m3 ha-1 seven years after planting depending on slash and litter management treatments. Burning increased stand growth in the first year after planting, but reduced the mean annual increment by 13% at seven years of age compared to harvesting only stemwood. There was a significant decrease in exchangeable Ca and Mg concentrations in the 0-10 cm soil layer one year after establishment in all treatments, and concentrations then remained about the same until the end of the rotation. There were no significant effects of slash and litter management treatments on organic carbon content, total N and exchangeable cation concentrations in soil below 10 cm. In the surface layer (0-10 cm), organic carbon content, total N, exchangeable Mg and Na concentrations were significantly lower under the residue-removed treatment compared to the treatment with the highest amount of slash and litter one year after treatment establishment but differences between these treatments were no longer significant at three years of age. Highest concentrations of exchangeable Ca and Mg were in the burning treatment at eight years of age. Stand volume at the end of the rotation was not significantly correlated with soil C and nutrient concentrations in any soil layer at any time after treatment establishment. By contrast, the volume of the 7-yearold stands was highly correlated with the mass and the nutrient contents of litter and slash above the mineral soil at planting. The study highlights the crucial role of organic matter management in the sustainability of fast-growing plantations in this tropical sandy soil and the need to take into account the amount of slash and litter from the previous rotation when determining site-specific fertiliser inputs. (Résumé d'auteur