Physical properties of “sorriba”-cultivated volcanic soils from Tenerife in relation to andic diagnostic parameters

In volcanic regions, soils containing both noncrystalline materials and layer silicates are widespread. Although the respective contribution of these components to soil physical behaviours is difficult to quantify, it is an important issue in the Canary Islands, where Andisols and andic soils are transported to the low lands for cultivation (“sorriba”). In this new soil environment, salinisation and sodification processes, induced by irrigation and heavy fertilisation, are potential threats to soil degradation. The purpose of this work was to evaluate some relevant physical properties of the sorriba-cultivated volcanic soils from Tenerife in order to relate them to salinity and sodicity soil conditions, amounts of layer silicates and remaining andic properties, characterised by: bulk density (ρb), Al and Fe extracted with ammonium oxalate (Alo, Feo) and P retention. An Andisol under forest was included in the study as a representative natural reference. Clay dispersion, water release curves and saturated hydraulic conductivity, Ks, were the selected physical properties. Four distinctive types of water release curves were identified, showing sandy behaviour at low suctions while retaining large water holding capacity at large suctions. The van Genuchten parameters helped to differentiate these curves and identify the main pore-size ranges. Under certain combinations of exchangeable cations distribution, salinity and clay mineralogy, very low Ks values were observed for Alo contents lower than 3%. The results suggest that the aggregating effect of Alo (allophanes) could not counterbalance soil structure deterioration. Furthermore, only a multivariable analysis carried out on chemistry, mineralogy and physical data had the merit to classify the studied sorriba-cultivated volcanic soils in terms of soil quality and soil functioning.