Expression of andic properties in soils from Galicia (NW Spain) under forest and agricultural use.

The organic matter (OM) of soils with andic properties has long been considered highly stable because of the presence of Al–humus complexes and sorption of organic ligands onto amorphous compounds. In this study, we characterized soils under different land use regimes located within an amphibolitic massif close to Santiago de Compostela (Spain), where soils with andic properties are present. Slash and burn agriculture was a common practice in the area until the second half of the 20th century. Thereafter, modern agriculture was progressively introduced into the area (AGR soils), and the rest of the land was either reforested or abandoned (FOR soils). We found that the mean organic C content of AGR soils (48.7 g kg−1) was∼ 50% that of FOR soils (94.2 g kg−1). Mean soil pH was significantly greater (P < 0.05) in the AGR than in the FOR soils (4.95 compared with 4.63), which is attributed to liming and Ca-phosphate fertilization of the former. Mean concentrations of the Al forms studied (extractable with CuCl2, sodium pyrophosphate, ammonium oxalate, or NaOH) were significantly smaller (P < 0.01) in AGR (1.4, 4.9, 9.3, 11.0 g kg−1, respectively) than in FOR soils (3.9, 10.2, 16.5, 17.9 g kg−1, respectively). The results show the vulnerability of the OM and Al–humus complexes in these soils to modern agricultural practices, which has led to the attenuation– and in some cases even the disappearance– of andic soil properties in a relatively short time (< 30 years) following changes in land use/management. We propose the inclusion of the formative element‘andic’ in the criteria for the definition of Umbrisol subunits; this would avoid the abrupt discontinuity observed in the current World Reference Base classification. [ABSTRACT FROM AUTHOR]