Availability of Micronutrients in Soils and Its Correlation with Foliar Contents in Young Plantations of Eucalyptus.

Eucalyptus is the most widely planted (3.4 million ha) forest species in Brazil. The use of highly productive clones and long-term periods of multiple harvests can result in the occurrence of micronutrient (Cu, Mn, Fe, and Zn) deficiencies. The objectives of this work were: 1) to identify the most appropriate extractant to evaluate the availability of micronutrients to eucalypt; 2) and to evaluate the influence of soil properties on predicting foliar micronutrients contents. Eucalypt plantations from six regions of the State of Minas Gerais, Brazil, were sampled for micronutrient availability. Samples were collected from the 0-20 cm soil layer, and leaf samples from two positions of the tree canopy: 1) the upper third, or 2) the bottom third. From each crown portion, completely expanded leaves from proximal and distal positions of the branch were collected. Total Cu, Mn, Fe, and Zn contents were determined in the leaf samples. Soil samples were analyzed for total organic carbon and clay contents, and pH. Micronutrient (Cu, Mn, Fe and Zn) contents were extracted by Mehlich-1, Mehlich-3 and DTPA procedures. Mehlich-1 gave the best correlation between extractable soil micronutrients and micronutrients contents in leaves. Soil total organic carbon and clay contents and pH, along with extractable soil nutrient content, improved significantly the power of the regression models in estimating the respective leaf nutrient content. As an example, the r² of the models between extractable Cu by Mehlich-1, Mehlich-3 and DTPA and leaf Cu contents (leaves from the proximal position of branch from the bottom third) were improved from 0.59, 0.33 and 0.27 to 0.69, 0.60 and 0.50, respectively, by adding clay content in the models. This data indicate that Mehlich-1 extractable Cu, Mn, Fe and Zn, combined with soil properties, will provide the best estimate of Eucalyptus leaf contents of these micronutrients.