Abstract

VIDELA, Lina Sonia; ROSTAGNO, César Mario  and  TOYOS, María Alicia. Particulate organic-matter: a comparison of methods for its determination and its role as an indicator of soil quality for some soils in the province of Chubut. Cienc. suelo [online]. 2008, vol.26, n.2, pp.219-227. ISSN 1850-2067.

Particulate organic-matter (MOP) is a dynamic soil component that quickly and selectively responds to management changes and to different disturbance regimes. We compared two techniques to determine the MOP content in different soils and assessed the potential of this variable as an indicator of soil quality. We studied the soils of three ecological sites located in the province of Chubut under different management schemes or affected by different disturbance regimes: Media Luna exclosure (ML_C), Media Luna-grazing (ML_P), Puerto Madryn bioturbed (PM_B), Puerto Madryn nonbioturbed (PM_NB), Punta Ninfas uneroded (PN_NE) and Punta Ninfas eroded (PN_E). We collected soil samples from the 0 to 5 cm (PM and PN) or 0 to 10 cm (ML) depths to determine total soil organic-matter (MOT) and MOP using wet combustion MOPh (Walkley and Black method) and weight loss-on-ignition in a high temperature oven set at 430° C (MOPi). In the Mollisols and the Aridisols from Puerto Madryn, MOPi was higher than MOPh; in the Aridisols from Punta Ninfas, however, the differences between MOPi and MOPh were not significant. In soils with high calcium carbonate (PM_B and PM_NB) or allophane (ML_C and ML_P) contents, the loss-on-ignition method overestimated MOP contents. The MOT contents were highly correlated to both MOPh and MOPi for all soils (r²= 0.89 and r² = 0.73, respectively). Both MOT and MOP were sensitive to land management and soil erosion. The soil that displayed the greatest MOP/ MOT ratio was the PN_NE. On the contrary, the PN_E site showed the lowest values for this ratio, which would indicate that the low MOT content of this soil is predominantly associated to the < 0.053 mm fraction, and that the erosion process decreased the MOP reserves more than the MOT. For the Puerto Madryn soils, the MOPi / MOT ratio was greater than 1. This seems to be mainly due to the overestimation of the loss-on-ignition method in soils with abundant carbonates. Both MOT and MOP, determined by the two methods, can be used to detect differences in management or the state of soil degradation. However, MOP seemed to be more affected by soil erosion and sheep grazing compared to MOT. These results would allow us to consider MOP as a good indicator of changes in soil quality by either soil erosion or sheep grazing.

Keywords : Disturbance; Management; Erosion; Bioturbation.

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