Eucalyptus grandis plantations: effects of management on soil carbon, nutrient contents and yields

The expansion of fast-growing tree plantations is a worldwide process, with consequences on soil fertility and soil carbon storage. Disparate results were found on the effects of afforestation with Eucalyptus on soil carbon and other nutrient contents. These discrepancies are usually caused by differences in climate, land use history, soil texture as well as by management related factors such as plantation age, number of rotations, method of establishment (plantation or coppice), harvest residue management and soil preparation. We studied the effect of plantation age, number of rotations, and method of establishment on soils and plant nutrient concentrations in Eucalyptus grandis plantations in NE Argentina on different textured soils. We also determined if yields changed with nutrient variations in soils, and compared soils under plantations to soils under grasslands they replaced. Thirty-one E. grandis stands of different ages, number of rotations and method of establishment were evaluated as well as eight grassland sites. Levels of carbon, nitrogen, phosphorus, potassium, calcium and magnesium were determined for soils and plants. Soil carbon and nitrogen decreased over the number of rotations and were more pronounced in soils with 50-60% sand than soils with > 75% sand. Coppice stands showed higher soil carbon and nitrogen levels than plantations, suggesting a negative effect of site preparation before planting on soil nutrient conservation, especially in fine-textured soils. Foliar nutrient concentrations did not follow the trends observed for soil nutrients nor did they reflect nutrient limitations. There was no evidence of decreased yields over successive rotations. Soil carbon and nitrogen contents decrease when grasslands are replaced by E. grandis plantations, and therefore a yield limitation may occur in a medium to long-term frame, especially in stands re-established for short-rotation management. Harvest residue management and site preparation must be specifically designed for improving soil nutrient management.