Accounting for organic carbon and total nitrogen stock variability on a stony soil slope under a seasonally dry tropical forest

Stony soils are typical of the Brazilian semi-arid region and display specific traits that lead to substantial pedological variability. This hinders the effective quantification of stocks of soil organic carbon (SOC) and total soil nitrogen (TSN). The current study aimed to assess the variability of SOC and TSN stocks in a stony soil under Caatinga. In the topsoil, the SOC and TSN stocks were affected by rock fragments and clay contents. In the subsurface (>20 cm) layer, these stocks were influenced by P, SOC, and TSN content. These results confirm that SOC and TSN stocks are controlled by physical and chemical protection in topsoil and subsoil, respectively. The nugget/sill effect ratios indicated moderate carbon and nitrogen stock spatial dependence in the 0-10 and 10-20 cm layers, besides a strong dependence in the others. Consequently, a minimum distance of 73-m between sampling points is recommended to ensure sampling independence aiming for assessing SOC and TSN stocks in stony soil layers. This important difference between depths in local-scale can help to improve the accuracy of numerical models of carbon cycling in tropical dry forests.