Resumo

MANDOLESI, María Ester et al. Fracciones granulométricas y carbono orgánico oxidable en un suelo típico del centro sur bonaerense (ARGENTINA). Cienc. suelo [online]. 2014, vol.32, n.2, pp.159-170. ISSN 1850-2067.

Soil organic components reflect the changes due to land use and soil management. An experiment carried out in the south center of Buenos Aires province (Argentina) provided the range of conditions to pursue the following objectives: 1) to compare soil organic carbon (COS) in fractions separated by a physical method with variables related to oxidizable COS in soil samples, 2) to explore COS oxidability in particle-size fractions and determine soil organic nitrogen (NOS) and 3) to assess the effect of soil management, tillage system and sampling time and depth on the variables under study. In topsoil samples (0-20 cm) two soil fractions were separated by wet sieving: coarse (FG >100 µm) and fine (FF <100 µm). In the soil samples, in FF and FG we determined a) oxidizable COS by Walkley & Black method and at 12 and 18 Eq L^-1 H₂SO₄, b) total COS by dry combustion and c) NOS. Variables obtained through COS oxidation with 12 and 18 Eq L^-1 H₂SO₄ in the soil (COX₁₂ and COX₁₈) correlated significantly with COS in FG. COS oxidability in FF reflected heterogeneous quality of this fraction. COX₁₂ and COS oxidated with 12 Eq L^{-1 in FG (COP}₁₂) were sensitive to the tillage systems and the nature of crop residues and/ or cultural state at the time of sampling. Differences due to soil previous use were only detected through determinations in the FF. NOS in soil and FG were not significantly affected by the treatments in the experiment. COX₁₂ was more sensitive than particulate organic carbon to soil management and sampling depth. Determination of COX₁₂ is simple and could be easily adaptable by other laboratories.

Palavras-chave : Soil organic matter, physical fractionation, oxidability, soil management.

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