Soil quality indicator selection in Chilean volcanic soils formed under temperate and humid conditions

Volcanic soils are extremely productive thanks to their particular characteristics. Therefore, even though they represent < 1% of the soils worldwide, they are very important for global and local agriculture, as they account for > 60% of the arable land of Chile. However, studies evaluating their soil quality are still scarce. Subsequently, soil quality indicators have not yet been established for Chilean volcanic soils. Hence, the aim of this study was to select a set of soil quality indicators to evaluate changes in Chilean volcanic soils, mainly due to land use, but also considering seasonal changes. Thus, three soils derived from volcanic materials were sampled (with different intrinsic properties), on five sampling dates, under three land uses (intensities): native forest (NF), prairie (P) and crops (C). Soil samples were taken to evaluate both chemical (disturbed samples) and physical (undisturbed cylinders and soil blocks) properties. A total of 27 soil properties were measured and/or calculated, among these are: penetration resistance, saturated hydraulic conductivity, air conductivity, bulk density, total porosity pore size distribution, aggregate stability, pH, nutrient contents, Al saturation, effective cation exchange capacity, soil organic carbon and extractable Al. To effectively select the indicators a multivariate analysis (PCA) was performed. The proposed set of indicators for soils derived from volcanic materials include: i) bulk density, ii) plant available water pores in volcanic soils, iii) wide coarse pores, iv) air conductivity at 6 kPa, v) soil organic carbon, vi) extractable Al with ammonium acetate, vii) pH in water, viii) P-Olsen and ix) base sum. Main difference in soil quality indicators chosen in this study, compared to previous studies of this type, was the inclusion of extractable Al with ammonium acetate indicator, which is strongly related to the inherent soil properties of these volcanic soils.