Speaker
Description
Reliable and affordable determination of soil organic carbon (SOC) is essential for evaluating carbon-farming practices and developing scalable soil-carbon monitoring systems. This study aimed to validate an effective analytical approach for routine SOC determination and demonstrate its applicability through multi-crop field monitoring under carbon-farming conditions in North Macedonia.
The classical Walkley-Black method and its spectrophotometric modification were evaluated through linearity, precision, accuracy, repeatability, reproducibility, and analysis of reference soil material. The titrimetric method demonstrated excellent linearity over 0.3-3.0% OC (R² = 0.999), while spectrophotometric determination of Cr³⁺ at 600 nm showed similarly strong linearity (R² = 0.9996). Validation using reference soil produced OC values of 1.75% by titrimetric WB and 1.78% by spectrophotometric determination, both within the accepted reference interval (1.72-2.14%), demonstrating good analytical agreement and supporting the applicability of the rapid spectrophotometric approach for routine monitoring.
The analytical approach was further applied to track soil-carbon dynamics under carbon-farming (CF) and conventional management systems (CMS) across corn, sunflower, barley, and chickpea. Under CF, soil C increased from 1.20 to 1.89% in corn, 1.19 to 1.42% in sunflower, 1.25 to 1.68% in barley, and 1.18 to 1.57% in chickpea. In contrast, CMS showed consistent depletion, reaching final values of 0.93, 0.76, 0.89, and 0.91%, respectively. Final carbon concentrations under CF were approximately 73.1-103% higher than under corresponding conventional systems.
The combination of analytical validation and field application demonstrates that validated, cost-effective carbon determination can provide sufficient analytical performance for repeated soil monitoring. Such approaches could substantially increase monitoring frequency and spatial coverage while supporting future measurement, reporting and verification (MRV) frameworks for carbon farming.
Keywords: soil organic carbon, method validation, Walkley-Black, spectrophotometry, carbon farming.