Soil Organic Matter Fractions Under Eucalypt Plantation in Reform Management

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.

摘要 桉树（Eucalyptus）的采伐与更新作业会引发土壤有机质（SOM）的改变。本研究旨在评估巴西南里奥格兰德州桉树人工林更新后1年、2年及4年的老成土（Ultisol）中，总有机碳（TOC）、总氮（NT），腐殖酸（HA）、富里酸（FH）、轻组有机质（LOM）与微生物生物量（MB）中的碳、氮含量变化。桉树更新1年后，0~1.0 m土层的总有机碳（TOC）升高78%。更新2年后，0~0.1 m土层的总氮（NT）含量上升，而轻组有机质碳（LOM-C）平均降低52%。更新4年后，0~1.0 m土层的富里酸碳（FA-C）、腐殖酸碳（HA-C）及胡敏素碳（HU-C）平均降低43 Mg·ha⁻¹。前茬作物枯落物及采伐产生的作物残体可提升土壤有机质各组分的含量，但在更新后期会产生负面效应。