Abstract
ABSTRACT Harvesting and reform in eucalyptus can lead to changes in soil organic matter (SOM). The objective of this work was to evaluate the changes in total organic C (TOC) and N (NT), C and N in humic acid (HA), fulvic acid (FH), light organic matter (LOM) and microbial biomass (MB), in Ultisol of eucalypt stands over one, two and four years of renovated areas in Rio Grande do Sul state. After the first year of eucalyptus reform, there were 78% of increases in TOC (0.0-1.0-m soil layer). After two years, there was an increase in TN and an average reduction of 52% in LOM-C (0.0-0.1-m soil layer). FA-C, HA-C, and HU-C presented mean reductions of 43 Mg ha–1 (0.0-1.0-m soil layer) after four years of reform. The litter contribution of previous crop and the crop residues from the harvest resulted in increments of the SOM fractions. However, there is a negative effect in later years.
Highlights
In the last decades, the global growing demand for forest products (FAO, 2010) has promoted the expansion of cultivated areas with eucalypt
After 2 years of the reform management, it was observed that the total organic C (TOC) stock returned to the stock level observed in eucalypt plantation with 13-years-old of first rotation
Total nitrogen (TN) stocks did not change after 1 year of reform management in the 0.0-0.1-m and 0.0-0.4-m soil layers
Summary
The global growing demand for forest products (FAO, 2010) has promoted the expansion of cultivated areas with eucalypt. In Brazil, the total area of planted forests in 2015 reached 7.8 million hectares, in which 5.6 million hectares are eucalypts mainly distributed in the states of Minas Gerais (24%), São Paulo (17%), and Mato Grosso do Sul (15%) (IBÁ, 2016). Exposure of the soil to the sun and rain causes alterations in the humidity and temperature, besides lower water infiltration rate and a greater predisposition to erosion (Dias et al, 2007; Oliveira et al, 2013) These abiotic factors combination alters the biological activity and soil structure (Ndaw et al, 2009), with potential effects on soil organic matter (SOM) dynamics and sequestration. Negative effects seem to be minimized when only the wood is removed from the area (Strömgren et al, 2013; Versini et al, 2013)
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