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

Abstract

Summary 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.

Nature, properties and function of aluminum–humus complexes in volcanic soils

“…(Takahashi et al, 2006a), as was later verified in a laboratory incubation (Miyazawa et al, 2013). These results are consistent with field studies that demonstrated a marked decrease in Al p and SOM contents of Ap horizons in Andosols following cultivation and liming (Saigusa et al, 1988;Verde et al, 2005).…”

Modelling and mapping organic carbon content of topsoils in an Atlantic area of southwestern Europe (Galicia, NW-Spain)

“…This leads to the formation of stable organo-mineral complexes and to the sorption of organic ligands onto these amorphous compounds increasing the stability and accumulation of SOC. The formation of mineral-associated SOC complexes by aluminosiallitisation is an important geochemical mechanism for the stabilization of organic matter in soils developed on granites and quartz-rich metamorphic rocks (gneiss, schist and slate) and on soils with andic properties derived from mafic rocks (Macías et al, 1978;García-Rodeja et al, 1987Verde et al, 2005). The negative correlation coefficients observed in the remaining geologic classes is probably derived to their lower abundance of weatherable minerals and thus a lower supply of reactive metal forms which stabilize soil organic matter.…”

“…For peat soils, we used the mean bulk density value reported in previous studies for peatlands of the studied area (Pontevedra-Pombal et al, 2004). The resulting map of BD was validated using an external dataset of BD measurements in epipedons of 62 soils from NW Spain obtained from references (Álvarez-Olleros, 2001;Brañas et al, 2000;García-Rodeja et al, 1987;Garea, 1983;Veiga et al, 2001;Verde et al, 2005). The validation of the BD map shows a high correlation between BD and organic matter content (R-squared = 0.79; RMSE = 0.16, MAE = 0.13, ME = 0.07), which indicates that BD is highly influenced by the organic matter content.…”

“…They usually present a high content of organic matter in an umbric epipedon rich in organo-aluminium complexes, which is followed by a B cambic (Humic Cambisols) horizon, while Leptosols and/or Umbric Regosols are found in areas prone to erosion. Soils developed from mafic rocks and their transformations (amphibolites, gabbros, eclogites) often present andic properties and high amounts of reactive-Al and short-range ordered compounds, which form Alhumus complexes that stabilize organic compounds (Verde et al, 2005). In stable areas and on easily weatherable materials the soils present ferralic properties (Macías et al, 1982).…”

“…The nature of the mineral fraction also plays an important role in the storage capacity of organic carbon. Soils with andic properties, derived from the weathering of metamorphic and igneous basic rocks, have abundant active-Al forms, which can bind and stabilize organic compounds and have a high sorption capacity of organic ligands onto short-range ordered compounds that form stable Al-OM complexes (Alvarez et al, 1992;Carballas et al, 1979;García-Rodeja et al, 1987;Verde et al, 2005). The interaction of organic matter with soil minerals can be also an important mechanism for the stabilization of SOC.…”