Effects of eucalyptus thinning on soil chemical attributes in an unfertilized silvopastoral system 6 years after thinning

Abstract Tree thinning is a common practice in silvopastoral systems, but there is no standard percentage of thinning used by farmers. Moreover, it is unclear how the percentage of thinning affects soil chemical attributes throughout the soil profile and throughout the transect between eucalyptus lines. To address this gap, this study evaluated the effects of three percentages of eucalyptus thinning—0%, 50%, and 100%—on soil chemical attributes in a silvopastoral system in Brazil. The experimental design was a randomized block with a 3 × 4 factorial design comprising three treatments (thinning of 0%, 50%, or 100% of the eucalyptus trees) and four sampling positions relative to the eucalyptus line (0, 2.0, 4.0, and 6.0 m). Six years after eucalyptus thinning, soil samples were taken for chemical analysis and determination of fertility. Soil pH; total acidity pH 7.0 (H + + Al 3+ ); S‐SO 4 , P, K + , Ca 2+ , and Mg 2+ contents; base saturation (BS); and cation exchange capacity were determined. Soil acidification was observed at depths of up to 0.2 m in the 0% thinning treatment, accompanied by a decrease in Al 3+ content in the 0.6–1.0 m layer at 0 and 2.0 m from the line and an increase in S content in the 0.2–1.0 m layer at 4.0 and 6.0 m from the line. Under 50% thinning, BS and K + and P contents increased, while 100% thinning increased pH and Mg 2+ and K + contents and decreased total acidity and P, S, and Ca 2+ contents. The decomposition of accumulated plant material and of eucalyptus roots acidified the soil at 0 and 2.0 m from the line compared with 4.0 and 6.0 m from the line, decreasing pH and K + , Ca 2+ , and Mg 2+ contents and increasing total acidity and Al 3+ content. The decreases in K + , Ca 2+ , and Mg 2+ contents also reflect the uptake of these nutrients by eucalyptus. These results can be used to guide improved practices for managing soil chemical fertility and the most appropriate thinning percentage in silvopastoral systems.