PH‐dependent extraction of soil and soil amendments to understand the factors controlling element mobility

Abstract

SummaryA combination of the pH‐dependent leaching test CEN/TS 14429 and geochemical modelling (LeachXS©‐ORCHESTRA) was used to evaluate the partitioning of major, minor and trace elements in relation to their phosphorus retention capability, the release of non‐nutrient constituents, their reduction of soil acidity and their organic matter retention. One Australian soil sample and two different soil amendments (Red Lime and Alkaloam) were studied. The pH‐dependent leaching test showed that the acid neutralization capacity and the phosphorus retention of the soil were improved, respectively, by a factor of two to five and by a factor of two to ten after addition of these amendments. The amendments improved retention of dissolved organic matter (by a factor of 3–10) and did not increase leachability of undesired contaminants. The partitioning as obtained from modelling between free and dissolved organic‐carbon‐bound metals provides insight into the potential for uptake (bioavailability). This partitioning is very pH‐dependent and therefore testing and associated chemical speciation modelling provide valuable information for judging traditional soil improvers and soil amendments, including the waste‐derived soil amendments Alkaloam and Red Lime.