Soil Organic Carbon Stocks as Influenced by Topography and Vegetation Cover Types at Different Soil Depths

Abstract:

Data on soil organic carbon stock in wooded grassland is important for assessing its contribution towards offsetting greenhouse gas emissions through carbon sequestration. Understanding the effect of topography and vegetation cover types on soil organic carbon stocks is therefore essential for adopting suitable strategies for reducing greenhouse gases emissions but little has been done to ascertain this. This study was conducted during the long (LRS) and short rainy seasons (SRS) of 2016 in Ilmotiok to determine the effects of topography and vegetation cover at different depths in the wooded grasslands of Laikipia County, Kenya. Randomized completely block design was used; the main plot was topographical zones (TZ); mid slopes (MS), foot slope (FS), toe slope (TS) and subplots vegetation cover (VC); tree (T), grass (G), bare (B). Soil samples were collected to a depth of 50 cm at an interval of 10 cm using soil auger. The samples were analyzed for texture, bulk density (BD) and soil organic carbon. The bulk density was highest under FS*B at 0-10 cm with a mean of (0.88gcm^-3 and 0.97 gcm^-3) for LRS and SRS respectively as compared to other TZ. The lowest bulk density was observed for MS*GR at 0-10 cm (0.78 gcm^-3 SRS and 0.86 gcm^-3 LRS) in comparison to the other VC. Highest SOC concentration (1.21 MgHa^-1 and 1.10 MgHa^-1) was recorded under TS*G at 0-10 as compared to 40-50 (0.52 MgHa^-1 and 0.40 MgHa^-1) whereas the lowest (0.92 MgHa^-1 and 0.91 MgHa^-1) was recorded on MS*B at 0-10 cm and 0.39 MgHa^-1 and 0.28 MgHa^-1 and at 40-50 for the LRS and SRS respectively. The same trend was observed for SOCs highest (9.72 MgHa^-1 and 9.90 MgHa^-1) for TS*G at 0-10 cm and (5.11 MgHa^-1 and 5.66 MgHa^-1) at 40-50 cm and lowest under SU*B at 0-10 (7.66 and 7.11 MgHa^-1.) and (3.19 and 2.60) MgHa^-1 LRS and SRS respectively. The results from this study indicates that topography and vegetation cover of the wooded grassland has an influence on soil organic carbon stocks. Grass vegetation act as a sink to carbon stock therefore revegetation using grass is highly recommended.