Wood annual average increment and K, Ca and Mg mineral compartments in soils cultivated with eucalypt

Forestry continuously grows in Brazil and it increases the concerns among planted forest companies regarding sustainable production. Knowledge about soil mineral reserves and nutrient release kinetics may introduce an opportunity to optimize fertility management, improving production. The objectives of this study were to evaluate the contents of K, Ca and Mg in the reserve, non-exchangeable, exchangeable and available soil compartments and the nutrient release speed, as well as their correlations and effects on eucalypt productivity. Soil samples were collected from eucalypt plantation sites at the state of Rio Grande do Sul, Brazil, comprising seven soil classes. The contents of K, Ca and Mg were determined in sulfuric digestion extract, boiling nitric acid, ammonium chloride, Mehlich-1 and potassium chloride. Nutrient release kinetics were evaluated per Sparks (1989), while CMPC Celulose Riograndense provided the wood volumetric annual average increment (AAI) from the eucalypt plantations. The contents of K, Ca and Mg varied between compartments and depths and were concentrated in the reserve compartment, indicating the importance of this compartment for midand long-term nutrient supply. Most compartments of K, Ca and Mg showed significant correlation; and eucalypt wood productivity (AAI) correlated significantly with the different compartments in both depths, mainly with the reserve compartment and release kinetics expressing their relevance for productivity; in particular for the case of long-cycle plant species, where nutrient release at intermediate and long terms is important.