Abstract Accurate quantification of soil organic carbon (SOC) is essential for assessing agricultural sustainability and greenhouse gas (GHG) mitigation. However, determining the number of samples needed to capture SOC variability in tropical sugarcane systems is challenging due to soil texture and stratification from controlled traffic farming (CTF). This study estimated the minimum sample size required to assess bulk density (BD), carbon (C) concentration, and SOC stocks (0–100 cm) across three texture classes (55% clay + silt), assuming a maximum error of 20% and α = 0.10. Soils were collected from 67 commercial sugarcane fields in south-central Brazil, totaling 2,412 samples at six depths (0–10, 10–20, 20–30, 30–50, 50–70, and 70–100 cm). Variance estimators and bootstrap resampling (10,000 iterations) were used to evaluate spatial variability and sampling requirements. Significant differences between rows and inter-rows were observed in the top 0–30 cm: inter-rows showed 10–20% higher BD, 15–25% lower C concentration, and 10–30% lower SOC stocks. Soil texture strongly influenced variability and sample size. Fine-textured soils (>55% clay + silt) required fewer samples (BD: 3; C: 14; SOC: 14), whereas sandy soils (<20%) required up to 4, 27, and 26 samples, respectively. Variability and sampling needs declined with depth, reflecting localized effects of compaction and residue management. These results provide texture-based guidelines to optimize SOC sampling in sugarcane systems, reducing costs by 30–50% and supporting integration with MRV and certification frameworks, thereby strengthening sustainable production and climate commitments.
Popin et al. (Thu,) studied this question.