Abstract

VIDELA, Cecilia  and  TRIVELIN, Paulo C.O.. Influence of soil dispersion method on organic matter quality separated by particle-size fractionation. Cienc. suelo [online]. 2008, vol.26, n.1, pp.97-103. ISSN 1850-2067.

Particle-size fractionation is supported by the concept that soil organic matter (SOM) fractions associated with different mineral particle sizes have different structure and functions, and play different functions in SOM turnover. The objective of this work was to verify the quality of the organic matter fractionation of a Molisol dispersed with water or Na-hexametaphosphate (HMP) and to analyze the C and N distribution and δ¹³C values of the separated fractions. We compared the mineral fraction distribution of the soil by completely oxidizing SOM through heating with hydrogen peroxide (AGUAOX) versus water dispersion and HMP dispersion. The soil suspension was wet-sieved with 200, 50 and 20 μm-sieves. The >200 μm fraction was suspended in water in order to separate the floating material (light, L) from the heavy one (H) which settles. The accumulated soil mass (98.4- 99.7%), N (87.4-99.4%) and C (91.4- 96.2%) recoveries were high, but water dispersion presented the higher values. HMP presented more variability than water dispersion; but it dispersed the >200 μm aggregates, allowing the recovery of the high amount of N and C accumulated in the smaller fractions, whereas the use of water did not disperse those aggregates appropriately. High N quantity was recovered in <20 μm fraction, while the C was mainly accumulated in the 200-50 μm fraction. The δ¹³C values in the smallest fraction were near to the original ones for soils developed under C3 and C4 plants mixture (-21.7‰) whereas the coarse light fraction ones were similar to those of C3 plants (-27.7 ‰). Considering these results, we conclude that the HMP dispersion method is suitable for the particle-size fractionation of the analyzed soil.

Keywords : Mollisol; Organic matter; Particle-size fractionation.

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