NITRIFICATION AND SOIL QUALITY UNDER EUCALYPTUS STANDS AT DIFFERENT AGES

Abstract

This study was conducted using soil samples randomly collected in commercial plantations of Eucalyptus grandis and of E. grandis x E. urophylla hybrids, at six different ages (3 to 84 months), in a 180-month-old seed orchard, and in a secondary forest of native vegetation, all areas belonging to CENIBRA Celulose Nipo-Brasileira S.A., MG. The objective of this work was to study the effects of tree harvest on soil nitrification and on other biochemical and microbiological processes. The activity of-glucosidase, phosphomonoesterases, ammonium content, and net ammonification and nitrification rates increased with vegetation age. The highest values were recorded for the native vegetation area and for a 3-year-old no-till eucalyptus stand. Nitrate content, on the other hand, showed an inverse relationship to stand age, as well as potential nitrification. Thirty-five physical, chemical, biochemical, and microbiological variables were analyzed by multivariate analysis for grouping the areas under study. The areas with younger trees were positioned farther away from the area with native vegetation, used as reference, and from a seven-year-old eucalyptus stand. Tree harvest and the subsequent planting of a new eucalyptus stand greatly disturbed the soil microbial community. The increase in stand age and the adoption of a more conservative soil management system, i.e., no-till, contributed to the reestablishment of the biochemical and microbiological conditions found in the area with native vegetation.