Effect of soil sampling methods on physical soil parameters and carbon stock in Madagascar’s open ecosystems

Abstract

Soil organic carbon (SOC) storage is fundamental for climate change mitigation and food security and more precise and detailed SOC stock data are required to accurately assess the main ecological functions on climate regulation. However, soil sampling for SOC stock assessment is labor-intensive when conducted according to international standards using the cylinder method for measuring bulk density (BD) and coarse fragment (CF) which are key components of SOC stock. This study evaluated the performance of soil auger as a soil sampling tool, as a simplified and less destructive method, to assess the BD and CF for SOC stock calculation across the two main soil types in Madagascar. Soil samples from ferrallitic and ferruginous open ecosystem areas were collected at five layers: 0-10 cm, 10-20 cm, 20-30 cm, 50-60 cm and 80-90 cm, using both soil auger and cylinder, with volumes of 100 cm 3 and 502.65 cm 3 respectively. The BD, CF and SOC stocks derived from each soil sampling method were assessed and compared by soil types and depth. Results showed that no significant differences in BD values were observed between auger and cylinder methods regardless of soil layers (p>0.06) in both soil types. The comparative analysis of CF values indicated that the auger method could serve as an alternative to the cylinder method only in ferruginous soil (p>0.13) due to lower CF values in this soil type. For SOC stocks, non-significant differences were observed between the two methods in ferruginous soil and for topsoil (0-20 cm) in ferrallitic soils highlighting the potential applicability of the simplified method in SOC stock assessment.