Effect of applied potassium concentration on clay dispersion, hydraulic conductivity, pore structure and mineralogy of two contrasting Australian soils

Abstract

Re-use of industrial and agricultural wastewater for irrigation can increase the concentration of potassium ions in soil solution and affect soil structural stability. However, investigations of clay dispersion have traditionally focused on soils with high exchangeable sodium. The objective of this study was to quantify the effects of potassium application on physical, chemical and mineralogical properties of two contrasting soils from South Australia. This work combines traditional soil and clay analysis methods with a range of additional techniques, including, scanning electron microscopy, transmission electron microscopy, X-ray diffraction and modeling for characterizing and quantifying the movement of different forms of potassium in soil. In laboratory studies, soils were treated with varying amounts of potassium and the measurements were made on the range of soil/clay properties before and after treatments. The results show that applied potassium can cause dispersion of soil but to a lesser extent than sodium. Potassium cations also could increase soil hydraulic conductivity (HC) to some extent when applied to a soil with high sodium content by substituting the Na+ on exchange sites. Potassium could be fixed by clay minerals, changing their composition, decreasing cation exchange capacity and increasing mineral potassium content. This increase was confirmed by the decomposition of XRD diagrams and chemical analysis, consistently showing the increases in amount of mica/illite clay minerals in soils treated with potassium rich solutions. The dynamic of “illitisation” can be monitored by XRD analysis both qualitatively and quantitatively. X-ray computed tomography (CT) scanning of the soil columns has allowed visualization and quantification of the changes in pore system occurred due to the application of potassium.