Comparaçao de métodos de determinação do carbono orgânico em solos cultivados com eucalipto Comparison of methods for determination of organic carbon in soils under eucalypt plantations

A determinação de C orgânico do solo tem sido realizada, principalmente, por métodos baseados na oxidação química. Contudo, recentemente, o C tem sido determinado por métodos de combustão seca, como o CHNS/O. Este trabalho teve como objetivo comparar três métodos para determinação do C de solos cultivados com eucalipto em regiões com diferentes características edafoclimáticas. Foram comparados os métodos: Walkley-Black, Yeomans & Bremner e combustão seca (CHNS/O), utilizando amostras de diferentes classes de solos obtidas nas seguintes profundidades: 0-20, 20-80 e 80-130 cm nos Cambissolos; 0-25, 25-70 e 70-110 cm nos Latossolos; e 0-18, 18-50 e 50-110 cm nos Neossolos. Amostras de TFSA foram trituradas em almofariz, passadas em peneira de malha de 0,2 mm e submetidas aos três métodos de determinação de C. Os teores de C obtidos correlacionaram-se positiva e significativamente entre si. Os métodos Walkley-Black e Yeomans & Bremner tenderam a subestimar os teores de C em relação ao método de referência, CHNS/O, tanto no que se refere às camadas superficiais quanto àquelas mais profundas, com menores teores de C. Equações de regressão linear com elevados valores de R² permitiram transformar os teores de C obtidos por Walkley-Black e Yeomans & Bremner em C por combustão seca.<br>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.

Abstract licence: CC BY

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