The soil C content has been determined most frequently by wet combustion methods. More recently, however, the dry combustion method has been used as the reference method for soil C determination. The main purpose of this study was to compare three C determination methods for soils under eucalypt plantations in southeastern Brazil. Samples of different soil types and located under distinct climate conditions were collected. Soil C contents were determined by two wet (Walkley-Black and Yeomans & Bremner) and one dry combustion method (CHNS/O Analyzer) in samples from six soil classes and different horizons: 0-20, 20-80 and 80-130 cm in Inceptsols; 0-25, 25-70 and 70-110 cm in Oxisols; and 0-18, 18-50 and 50-110 cm in Entisols. The soil samples were ground and sieved (0.2 mm) and the C concentration was determined by the three methods. The soil C contents determined by the three methods were positively correlated. However, the C content tended to be underestimated by the Walkley-Black and Yeomans & Bremner methods as compared to the reference dry combustion method, for surface as well as for the deeper soil layers with lower C contents. Linear regression equations with high R² values were adequate to transform C contents determined by the wet combustion methods into C contents equivalent to that determined by the dry combustion method.
dry combustion; wet combustion; correction factor
