Soil nutrient stocks are maintained over multiple rotations in Brazilian Eucalyptus plantations

Abstract

Intensive management in tropical plantation forestry has increased global wood production per unit of time and land. Eucalyptus trees in southeastern Brazil grow exceptionally fast, even on the highly weathered and nutrient-poor soils of the Atlantic Forest and Cerrado biomes. By remeasuring plantation soils after twelve years and 1–2 rotations, we investigated how established plantations alter soil stocks of carbon, nitrogen, calcium, potassium, and phosphorus, and whether any changes might limit future plantation productivity. We hypothesized that each harvest cycle would deplete soil stocks of nitrogen, because less nitrogen is often added in fertilizer than is removed in wood, and that the balance between harvest and fertilizer would also dictate changes in stocks of other nutrients. In 2004 and 2016, we sampled soils to a depth of 100 cm in plantations and adjacent pastures and native vegetation reserves, and compared total nutrient stocks across time and vegetation type. We found that nutrients were not significantly depleted over time, and that soil stocks of carbon and nutrients in the plantations all tended to increase, with significant increases in the top 20 cm of 20% for potassium in the Atlantic Forest biome, and 23% for carbon and more than 500% for calcium in the Cerrado. Changes in soil nutrient stocks can be attributed in part to both fertilizer inputs and redistribution from changing stocks of biomass. We also observed changes over time and substantial spatial heterogeneity in nutrient stocks under non-plantation vegetation, highlighting the difficulties of using other vegetation types as static “controls” to assess the effects of plantations on soils. Overall, soil nutrient depletion does not appear to threaten sustainability in these intensive plantation forests over the time period studied.