The Influence of the Rotation Length of Eucalypt Plantations on Soil Organic Matter Dynamics in Southern Brazil

Abstract

The rotation length of forest plantations can influence soil organic matter (SOM) pools. However, this is not well documented in eucalypt systems in Brazil. Therefore, we assessed the total organic carbon (TOC), total nitrogen (TN), and SOM fractions with different turnover rates (i.e., light organic matter [LOM], alkali extractable [AE], and nonextractable [ANE]) in the top 1 m of soil of 10‐, 13‐, and 22‐yr eucalypt rotations, and compared them with those of a native grassland in southern Brazil. The 22‐yr rotation yielded greater TOC stocks in the 0‐ to 60‐cm soil depth (107.2 Mg ha−1) than the grassland (86.7 Mg ha−1). Total N stocks were lower in the upper soil layers (0‐ to 40‐cm depth interval) in the eucalypts than in the grassland, except for the 10‐yr rotation. The changes in TOC and TN resulted in wider soil C/N ratios in the soil (0‐ to 100‐cm depth interval) in longer rotations (13 and 22 yr). The LOM‐C and LOM‐N fractions were similar between the grassland and longer rotations but were reduced in the 10‐yr stand. Overall, afforestation increased AE‐C stocks; the 10‐ and 13‐yr stands yielded the greatest AE‐C stocks at the 0‐ to 60‐cm and 0‐ to 100‐cm soil depths, respectively. For ANE‐C, the 22‐yr stand yielded the greatest stock at the 0‐ to 100‐cm depth (88.8 Mg ha−1). Our study showed that longer eucalypt rotations promoted soil C accrual compared with the grassland and shorter rotations; however, TN stocks were less affected, resulting in wider soil C/N ratio as rotation length increased.