The osmotic potential of soil solutions in salt tolerance studies: Following M. Th. van Genuchten's innovation

The osmotic potential in soil solutions decreases as salinity increases, and plants cannot take up enough soil water. Therefore, the osmotic potential of soil solutions can serve as an important metric of plant growth conditions in regions affected by soil salinization. Measurements of osmotic potential are labor and time consuming. This work aimed to determine more readily available soil salinity metrics to estimate the osmotic potential in soil solutions. A model to compute the osmotic potential from soil solution composition was developed and validated with data from the U.S. states of Washington, Oregon, Colorado, and Idaho. The mean relative error was 7%. Then, this model was applied to 230 datasets on soil solutions from various salinity-affected regions of Eurasia. The correlation coefficient between logarithms of concentration of highly soluble (not including carbonates and sulfates of calcium and magnesium) in soil solutions at saturation and logarithms of osmotic potential values was above 0.99. The concentration of highly soluble salts in soil solution at saturation was chosen as the predictor of the osmotic potential. It was used to develop nomograms for evaluating the salinity-related yield loss for major field crops, vegetables, and fruits. This work is a part of the Vadose Zone Journal tribute to the scientific legacy of Martinus van Genuchten, who championed the use of the osmotic potential for better quantification of crop salt tolerance at the macroscale and provided invaluable contributions to modeling soil salinity development and mitigation as a part of the global struggle for food security.