Soil Carbon Inventory by Wet Oxidation and Dry Combustion Methods: Effects of Land Use, Soil Texture Gradients, and Sampling Depth on the Linear Model of C‐Equivalent Correction Factor

Abstract

Monitoring C content is essential for carrying out surveys and inventories on C storage in soils under different land uses (LUs). The objectives of the present study, which was conducted in five agro‐ecoregions in Brazil with contrasting climates, LU managements, soil texture gradients, and soil depths, were to: (i) develop a C‐equivalent correction factor (CF) between total organic carbon determined by dry combustion (TOC DC ) and organic carbon by wet oxidation recorded by the Walkley–Black (OC WB ) method, and (ii) assess the influence of LU, soil texture gradients, and sampling depth on a C‐equivalent CF based on a linear model adjusted for each experimental location. The results indicated an effect of LU at almost all sites, except for one subtropical location where clay content and sampling depth were the most important factors. Additionally, there were LU × clay and LU × sampling depth interactions on the C‐equivalent CF. The linear models computed to estimate the CF from this set of qualitative (LU) and quantitative variables (soil texture gradient and soil depth) differed among and within the agro‐ecoregions and LU managements. The C‐equivalent CF in subtropical sites ranged from 1.37 to 1.55, while for tropical sites ranged from 1.13 to 1.60. These models are site specific, and the results demonstrate the need to develop models calibrated for each site before extrapolating to other agro‐ecoregions to recalculate past soil C inventories and to evaluate temporal changes of SOC stocks.