Making sense of irreversible soil salinization and sodification

Soil salinity and sodicity present serious risks to agriculture, in the face of dwindling freshwater resources and changing rainfall patterns. As a finite resource of crucial importance, soils must be protected from irreversible degradation. However, very little is known about how soils respond to adverse conditions in the long run, in particular regarding salinity and sodicity. As a proxy for soil stability and health, we will discuss what (little) is known about the irreversible deterioration of saturated hydraulic conductivity (Ks), subjected to water of varying levels of salinity and sodicity. We present novel soil column experiments measuring Ks hysteresis, for three soils of varying clay content. We then present a mathematical framework that allows us to make sense of the hysteresis in Ks, and that helps us understand the pivotal role of a soil's history of salinization and sodification in determining future Ks behavior. Most importantly, our model gives specific guidelines of what to measure in order to best characterize a soil's partial decline in Ks. We will focus on the role of reversal curves as the key to unlock a full characterization of the Ks hysteresis. With the help of weighting functions, we will show that our modeling framework is able to describe soils of any texture and clay mineralogy, making it both versatile and useful.