ABSTRACT

Understanding soil organic carbon (SOC) dynamics is crucial for evaluating forest ecosystems' carbon sequestration potential and overall soil health. This study focuses on the Sirsi forest division, comprising three forest types: evergreen, semi-evergreen and moist deciduous forests. It aims to assess the SOC content, bulk density and SOC stock and to geospatially map SOC stock at three soil depths (0-30, 30-60 and 0-60 cm). Ten replicated composite soil samples were collected from each forest type in two depths to provide a comprehensive analysis.
Results revealed that Evergreen forests recorded the highest SOC content (2.273 %), whereas moist deciduous forests exhibited the lowest SOC (1.87 %). The top soil (0-30 cm) showed the highest SOC (2.23 %) compared 30-60 cm soil depth. It also revealed substantial differences in bulk density among forest types and soil depths. Evergreen forests had the lowest bulk density (1.005 Mg m-3), whereas moist deciduous forests showed the highest bulk density (1.093 Mg m-3). In terms of soil depth, the 0-30 cm had a significantly lower bulk density (1.007 Mg m-3) than the 30-60 cm. Similarly, SOC stock was found to vary significantly among forest types and soil depths. Evergreen forests recorded the highest SOC stock (68.03 Mg ha-1), while moist deciduous forests had the lowest (60.824 Mg ha-1). Among soil depths, the 0-30 cm showed a significantly higher SOC stock (67.15 Mg ha-1) compared to the 30-60 cm depth. The study used Random Forest (RF) model to predict soil organic carbon (SOC) stock across different soil depths. For the 0-30 cm soil depth, the predicted SOC stock ranging from 59.45 to 76.59 Mg ha-1, with an average of 68.02 Mg ha-1. At the 30-60 cm soil depth, SOC stock ranged from 53.4 to 71.87 Mg ha-1, averaging 62.63 Mg ha-1. For combined 0-60 cm, the total SOC stock ranged from 114.75 to 145.89 Mg ha-1, with a mean of 130.3 Mg ha-1. The SOC stock prediction maps demonstrate a notable trend of higher SOC content in the western parts of the study area compared to the eastern parts.