Spatial distribution assessment of extractable Al, (NaF) pH and phosphate retention as tests to differentiate among volcanic soils

• Three soil chemical tests used in soil classification were evaluated in six Andisols.
• Extractable Al (Alex), (NaF) pH and P retention were determined to differentiate among Andisols.
• Soil chemical tests were able to differentiate among Andisols.
• When spatially analyzed, the chemical tests were useful to determine differences within each Andisol.

The unique features of Andisols differentiate them from other soils and influence their management and use, which should be specific for each soil within the general concept of Andisols. Since it is difficult to determine the type and amount of clay in these soils, validating simple, cheap, fast methods capable of differentiating among volcanic soils is essential for site-specific management. Thus, the aims of this study were to assess the spatial variability of extractable Al by ammonium acetate (Alex), (NaF) pH and P retention in order to determine if these chemical tests are useful to categorize volcanic soils developed under different conditions. Therefore, we sampled 6 soil series, all classified as Andisols, under pasture management, between 38° 53′S, 72° 23′W and 40° 44′S, 72° 26′W. The soil series chosen were as follows: Pemehue-PEH, Los Prados-LOP, Los Lagos-LLO, Malihue-MAL, Osorno-OSR and Puerto Fonk-PFO. Alex, (NaF) pH and P retention were evaluated in all of the soil series using descriptive statistics in addition to a geostatistical analysis to differentiate among soil series and varieties of soils within a series. Three of the proposed chemical tests were useful to differentiate among Andisols. The clearest differences among and within each series (see spatial analysis figures and equation parameters) were shown by (NaF) pH and Alex, while differences were less clear when analyzing P retention. In addition, we found consistent associations among the variables studied. The most solid relationship was between (NaF) pH and Alex, indicating that both of these chemical tests should be used when differentiating among Andisols and when looking for differences within the same soil series. This was confirmed by the geostatistical analyses within each soil. In addition, we found that Alex was a better indicator of soil reactivity in Andisols than the clay content.