Resumo

BONEL, Beatriz A.; MORRAS, Héctor José María  e  BISARO, Vilma. Microstructure and organic matter modifications in an Agiudoll under different conditions of cultivation and conservation. Cienc. suelo [online]. 2005, vol.23, n.1, pp.1-12. ISSN 1850-2067.

The microstructure and the organic matter of the upper part of the A horizon of a silty-loamy Typic Argiudoll in two non cultivated situations (NLp: park in an Experimental Station; NLv: preserved area close to a railroad) and under two agricultural management systems (SD: no-till; LR:disk ploughing), are compared. In all cases micromorphological analyses revealed a marked vertical anisotropy constituted by at least three microstructural levels in the first 10 cm of the soil, though the characteristics of those layers differ among the studied situations. Synthetically, NL situations showed a predominance of packing voids and biological features; the SD treatment is characterized by a subsurface layer with laminar aggregates and a predominance of horizontal planar voids; the LR treatment shows a crust development at the surface, low porosity determined by horizontal planar voids and vesicles, together with a lower content of organic residues. There were no significative differences in the quantity and quality of organic matter in the soil comparing SD and LR systems. In this context, it is considered that the long lasting laminar structure developed in the SD system and the temporary surface crust in the LR system are acting in a converging way, both restricting the mixing of organic and mineral phases of the soil. In SD a high accumulation and conservation of the organic compounds occur at the surface, but the biological activity after 10 years of cultivation was not strong enough to incorporate it at more than a few mm of depth. In LR, after ploughing, there is a deeper incorporation of OM, but collaterally a higher degradation occurs. In this way the final balance of the OM in the A horizon appears to be similar in both systems. The similarity in the organic pool between both situations seems to be reflected also by a similar aggregate stability obtained with the Henin method.

Palavras-chave : Micromorphology; Organic carbon; Aggregates stability.

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