Relationships between soil organic carbon and siteproperties in volcanic ash soils, southwestern Neuquén (Argentina)

An investigation was conducted to study the relationships between soil organic carbon and thoseproperties that may influence carbon accumulation in soils derived from volcanic ash through a rangeof bio-climatic conditions at the Andinopatagonian region in SW Neuquén, Argentina. Pedon andclimatic data of nineteen plots were used and grouped, through principal component analysis, by soilhydric regime –udic group (U) and xeric group (X)-. Within each group, a simple and a multipleregression analysis was carried out between organic C -content (t ha-1) or concentration (g kg-1)- andmean annual precipitation, bulk density, pH(H2O) and pH(NaF), oxalate extractable Al (Alo), pyro-phosphate-extractable Al (Alp), Alp/Alo, and Alo-Alp –the last four so as content or as concentra-tion. Mean annual precipitation, explained little variation in soil organic carbon in both groups (R2 =20), and bulk density was unrelated to soil organic carbon. Alp correlated strongly with organic Ccontent in both groups (U: R2 = 0.67, p<0.00001; X: R2 = 0.90, p<0.00001), but when expressed asconcentration Alp explanation was considerably lower (U: R2 = 0.10, p<0.02; X: R2 = 0.46, p<0.0006).When all factors were combined in a multiple regression analysis, the combination of Alp contents andmean annual precipitation, explained the greatest amount of variation in soil organic C content withinU group (R2U = 0.69, p