Soil Degradation Risks Assessed by the SOTE Model for Salinity and Sodicity

Abstract

Soil salinity and sodicity are serious environmental hazards, with the potential to limit agricultural production and cause destructive soil degradation. These concerns are especially high in dry areas, which often rely on saline and sodic irrigation water to support agriculture. To assess long-term soil degradation risk, we introduce the Salt of the Earth (SOTE) model, which describes the dynamics of soil water content, salinity, and sodicity, as driven by irrigation and rainfall. The SOTE model incorporates how changes in salinity and sodicity affect saturated soil hydraulic conductivity, K s , on a soil-specific basis. The model was successfully validated against results from a multiyear lysimeter experiment involving different irrigation water qualities and precipitation. We evaluated the impact of shorter rainy seasons on the dynamics of soil degradation in a Mediterranean climate. Critical degradation risk, indicated by reductions in K s greater than 20%, increased from 0% to 3% when the rainy season was shortened from 130 to 80 days. Alarmingly, when irreversible degradation is allowed for, overall risk increases to 68%. Assessing the effect of irrigation water on different soils textures, we found that while greater clay fractions are usually more susceptible to dispersion, accurate risk assessment hinges on soil water dynamics. SOTE is amenable to large-ensemble simulations of stochastic climatic conditions, for which trends in the statistics of salinization and soil degradation can be identified. As such, SOTE can be a useful land management tool, allowing planners to understand the risk of long-term soil degradation given irrigation practices, soil qualities, and climate conditions.

Hysteresis in soil hydraulic conductivity as driven by salinity and sodicity – a modeling framework

“…The reversibility index is a convenient quantitative measure; however, it does not determine the risk of irreversible degradation given a particular climate and irrigation regime (Kramer and Mau, 2020). This risk depends on the specific history a soil has been through, and further research is required to unravel the interplay between soil characteristics, environmental drivers, and the actual dynamics of water and solutes in the soil.…”

“…We will briefly present this framework and then apply it to model K s . We highly encourage the reader to use the interactive widgets found in the GitHub repository for this paper (Kramer et al, 2020), as they greatly enhance the explanatory power of the figures in the following sections.…”

“…Kramer et al: Hysteresis in soil hydraulic conductivity as driven by salinity and sodicity 2007Code availability. All code described in the paper is available in our Zenodo repository at https://doi.org/10.5281/zenodo.4013423 (Kramer et al, 2020). This repository also includes interactive widgets designed to supplement the theoretical overview of the model.…”

“…Failure to account for hysteresis limits the ability to forecast whether a particular climate and irrigation regime will lead to long-term land degradation (Kramer and Mau, 2020). When even a crude hysteresis mechanism is considered, it has been shown that changes in K s may be compounded, such that initially small declines in K s may lead to serious degradation (Kramer and Mau, 2020). Considering the limited nature of land and fresh water resources, maximizing land production through the use of saline and sodic water is likely to prove essential for maintaining food security.…”

Assessing the potential of exogenous caffeic acid application in boosting wheat (Triticum aestivum L.) crop productivity under salt stress

“…Soil salinity is a major abiotic constraint that disturbs the major cellular functions, affecting plant productivity and survival all over the world. Soil degradation due to water scarcity, diminishing natural resources and global warming negatively impacts agricultural production and food security [ 1 ]. Soil salinity is major abiotic stress in many regions and an estimated 9–34% of the world’s cultivated land is severely affected by soil secondary salinization [ 2 ].…”