Efecto de las prácticas agrícolas sobre la estabilidad de los complejos organoalumínicos en suelos ándicos de Galicia

Abstract

The high degree of organic matter (OM) accumulation that takes place in soils with andicproperties is attributed to the physicochemical protection against degradation caused by the combination ofOM and ionic Al compounds of short-range order which gives rise to the formation of metastable organo-mineral associations of slow mineralization. Andic soil properties are associated with the incipient stages ofpedogenesis, but they tend to disappear as the soil develops. However, the intensity and speed at which theproperties disappear can be accelerated by changes in the pedoclimatic and physicochemical conditions ofthe soil induced by agricultural practices. The objective of this research was to evaluate the effect of the con-version from forest (FOR) to agricultural (AGR) use on the stability of Al-humus complexes of andic soilsdeveloped from amphibolites, located in a massif close to Santiago de Compostela (NW Spain) where theannual precipitation is 1624 mm and the mean annual temperature is 12.3ºC. The results indicated that theconversion from FOR to AGR use (carried out in recent decades) caused a decrease in the organic C con-tent of more than 40%. Parallel to this, decreases were observed in values of Al extractable with CuCl2, so-dium pyrophosphate, and ammonium oxalate with the mean values being significatively lower (at eitherP<0.05 and/or 0.01) in AGR than in FOR soils. The results obtained therefore indicated that the transfor-mation of FOR soils with andic properties, to AGR soils, caused important variations in their characteris-tics, leading to a sharp decrease in Al-humus complexes, and therefore, to the attenuation of the andic soilproperties. These results demonstrate the vulnerability of these soils, in spite of the well-known high stabi-lity of their OM, which lowers their C sequestration capacity.