Spatial Variation of Soil Organic Carbon under the Linear Simultaneous Agroforestry System

Most research on spatial variability of soil organic carbon (SOC) has been conducted in forest and grassland soils, but no research has been conducted on agroforestry soils. Knowledge about the variability of SOC can assist in generating effective sampling designs and can help to scale-up carbon inventories. The aim of this study was to investigate the spatial variation of SOC concentrations in linear simultaneous agroforestry systems and recommend a suitable sampling design. The study was conducted at Kifu National Forestry Resources Research Institute (NaFORRI) in Mukono district, Central Uganda. The study was conducted within an existing experiment, established in 1995 as a randomised complete block design with a multifactor factorial treatment structure. Soil samples were collected at three depths; 0-25 cm, 25-50 cm, and 50-100 cm, twice; before clearing the site and planting the maize crop and after harvesting. Geostatistical tools were used to describe and predict spatial variation using semi-variograms, and to conduct spatial interpolation. Results indicate that spatial dependencies among neighbouring locations exist at all soil depths. However, results indicate a short distance of spatial continuity of SOC, varying from 3.4 to 13.8 m. Knowledge of spatial arrangement can be used to form strata and hence stratified random sampling design is recommended to be used in future data collection procedures. In order to improve the precision of the estimated SOC, a distance of less than 6.9 m between sampling pointswould be appropriate to capture the spatial autocorrelation in the linear simultaneous or similar agroforestry system.