Nutrient Management Research Database

Irrigation with treated wastewater is expected to increase significantly in California during the coming decade as a way to reduce the impact of drought and mitigate water transfer issues. To ensure that such wastewater reuse does not result in unacceptable impacts on soil permeability, water quality guidelines must effectively address sodicity hazard. However, current guidelines are based on the sodium adsorption ratio (SAR) and thus assume that potassium (K) and magnesium (Mg), which often are at elevated concentrations in recycled wastewaters, pose no hazard, despite many past studies to the contrary. Recent research has established that the negative effects of high K and Mg concentrations on soil permeability are substantial and that they can be accounted for by a new irrigation water quality parameter, the cation ratio of structural stability (CROSS), a generalization of SAR. We show that CROSS, when suitably optimized, correlates strongly with a standard measure of soil permeability reduction for an agricultural soil leached with winery wastewater, and that it can be incorporated directly into existing irrigation water quality guidelines by replacing SAR.

Recycled wastewater from cities and farms are increasingly being utilized for irrigation water, especially during drought.

The statewide goal is to resuse 2.5 million ac-ft per year.

High salinity and [Na] pose management challenges

High [K] and [Mg] can cause issues with soil hydraulic properties, though are often not considered.

CROSS, new irrigation water parameter. Cation Ratio of Structural Stability accounts for relative flocculating/dispersal power of each cation.