Resumen

TABOADA-CASTRO, M. M.; RODRIGUEZ-BLANCO, M. L.; TABOADA-CASTRO, M. T.  y  OROPEZA-MOTA, J. L.. Structural vulnerability on coarse texture soils under crop and orchard. Terra Latinoam [online]. 2011, vol.29, n.1, pp.11-21. ISSN 2395-8030.

Soil disaggregation by the effect of water is a consequence of various physical and physical-chemical mechanisms influenced by soil type, texture, organic matter and water content, among other factors. In an agricultural district of La Coruña province (northwestern Spain), whose soil is sandy loam, plots with three soil uses (winter wheat, maize and orchard) were selected. We analyzed the structural stability of the surface layer in order to (i) identify the mechanisms that cause aggregate breakdown under the three soil uses, (ii) assess the ability of stability test for predicting crusting and erosion susceptibility in these plots, and (iii) characterize a crust developed on a seedbed (winter wheat) from a micromorphological perspective. The aggregates were subjected simultaneously to three treatments: fast wetting (T1); mechanical breakdown by stirring after pre-rewetting in ethanol (T2) and slow wetting by capillarity (T3). The effect of each process was evaluated by mean weight diameter (MWD). The values resulting from MWDT1, MWDT2 and MWDT3 indicate that mechanical breakdown due to rainfall impact was the main aggregate-breakdown mechanism, followed by slaking due to compression of entrapped air during wetting. The sandy loam texture induces important macroporosity, which could contribute to reduce slaking. Even so, these soils are susceptible to crusting, a phenomenon affected by conventional tillage and by the action of accumulated rainfall on bare soil or with low vegetation cover. Micromorphological studies of a sedimentary crust developed on these soils reveal that this crust consists of a dense layer less than 1 cm thick.

Palabras llave : aggregate-breakdown mechanism; sandy-loam soils; cultivated soils; surface crusting.

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