Resumen

LA MANNA, Ludmila et al. Comparison of analytical methods for determining soil organic matter in Patagonian Andean Region: effects of vegetation and soil types. Cienc. suelo [online]. 2007, vol.25, n.2, pp.179-188. ISSN 1850-2067.

The determination of organic matter (OM) content is key for the knowledge of agricultural and forestry soil productivity. This study evaluated the relationship between OM content determined by weight loss-on ignition (OM_WLOI) and Walkley-Black wet oxidation method (OM_WO) in soils of the Patagonian Andean Region. The relation was evaluated for volcanic soils with and without amorphous components and with different vegetation types: Pinus ponderosa plantations, herbaceous steppe, shrubly steppe, shrubs and Austrocedrus chilensis forests. One hundred sampling sites were selected and composed samples were obtained from horizon A. Data were analyzed by means of analysis of variance and simple regressions. OM_WO was always lower than OM_WLOI. This is expectable since OM_WLOI includes the total OM, whereas MO_WO discriminates the strongly condensed carbon forms. Although differences in the relationship between the analytical methods for soils with and without amorphous components were not detected, a great relationship between these components and organic matter content was found. The relationship between the analytical methods varied according to the vegetation type. Soils with herbaceous steppe and pine plantations presented the greatest differences between the analytical methods. OM_WO was in average 37% lower than OM_WLOI for these types of vegetation, being significantly greater than soils with srhubs (26%). Soils with Austrocedrus chilensis forests and shrubly steppe presented intermediate values (30% and 35% respectively). Pinus ponderosa plantations (first rotation, average age 21 years) were located in areas with herbaceous steppe. The similarities found between both soils could be associated to the characteristics of OM in the herbaceous steppe environment and soil type, which did not change because of the little time passed since the implantation. Two linear regression models were generated that show the relationship between OM_WO and OM_WLOI for different vegetation types: Pinus ponderosa plantation and herbaceous steppe OM_WLOI (%) = 1.37 x OM_WO (%) + 0.81 (R² = 0.86; n = 40) Shrubs, shrubly steppe and Austrocedrus chilensis forest OM_WLOI (%) = 1.19 x OM_WO (%) + 1.58 (R² = 0.93; n = 60) These equations allow the comparison of MO content data generated by different analytical methods.

Palabras clave : Allophane; Shrubs; Austrocedrus chilensis; Herbs; Ponderosa pine.

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