UC Davis

Clearly, there is a growing demand for freshwater. The agricultural sector accounts for the largest share of freshwater usage, with 70 percent of the total worldwide freshwater. Recycled water reuse for irrigation purposes can serve as an alternative water supply to sustain agricultural production for the growing population. However, the utilization of recycled water can potentially lead to increased land salinity, specific ion toxicity and sodicity where sodicity is directly linked to infiltration issues. In the context of irrigation practices, the assessment of infiltration rates typically relies on both the sodium adsorption ratio (SAR) standard and the salinity of the irrigation water. SAR is commonly employed to estimate changes in infiltration rates when the water is primarily dominated by sodium cations. Nonetheless, recent research findings have indicated that the cation ratio of soil structural stability (CROSSf) provides better predictive capabilities for both soil structure and threshold electrolyte concentration compared to SAR especially when the water contains a mixture of both potassium and sodium cations. Accurate assessment of the potential soil infiltration rate changes and possible soil structure stability alteration is vital to ensuring the sustainable use of recycled water, treated wastewater and low-quality water use in irrigation. In this study, synthetic recycled water was prepared using sodium chloride, potassium chloride, calcium chloride, calcium sulfate (gypsum) and magnesium chloride to prepare treatments with 1.5 dS/m electrical conductivity. Then, SAR and CROSS were evaluated using soil columns and a greenhouse experiment using clay loam soil for both experiments. For the soil column experiment, 30-columns were conducted. The columns were subjected to evaluation for soil structure and saturated hydraulic conductivity. The irrigation process involved applying water to soil columns under a continuous 1 cm water head following pre-saturation. The salinity level of the applied solution was consistently maintained at 1.5 dS/m. The results demonstrated a strong correlation between CROSSf and both saturated hydraulic conductivity and soil aggregate stability (measured as clay dispersion) in comparison to SAR. The coefficient of determination (R2) for hydraulic conductivity and soil aggregate stability was recorded 0.90 and 0.94 for CROSSf, whereas for SAR, these values were 0.75 and 0.78, respectively. Additionally, clay dispersion was evaluated over the depths of the soil column. We found that the treatments that have 0-SAR values but contain potassium in their solutions have significantly more dispersible clay than the calcium chloride treatments for the entire soil column. For the greenhouse experiment, a total of 11 solution treatments with EC of 1.5 dS/m were prepared. The SAR treatments included 0, 4.9, 9.8 and infinity. The same treatments had CROSSf values ranging from 0 to 12.6 and one infinity CROSSf. The analyses of the results were divided into two sections. For the first part, the soil structure degradation was evaluated by a permeability test, an infiltration test using Wooding Infiltrometer, soil moisture content using a TDR sensor and clay dispersion using Spontaneous Dispersible Clay Method. The results of the average infiltration relative rates showed an R2 of 0.20 and 0.60 with respect to SAR and CROSSf, respectively. The infinity SAR treatment had the lowest average infiltration rate. The infiltration rate decreased with increasing SAR and CROSSf, however, CROSSf predicted infiltration reduction better than SAR. Moreover, the average moisture content measured after 7 days of terminating the irrigation slightly increased with increasing CROSSf and SAR with R2 of 0.63 and 0.44 respectively. The infinity SAR or CROSSf treatments had the highest soil moisture content. The moisture content analysis indicates that degraded soil held water for longer periods than aggregated soils. Strawberry growth and development under recycled water irrigation was evaluated in a greenhouse experiment. The objective was to evaluate the correlation between plant growth and development to SAR and CROSSf. The cationic composition in the plant and the sugar content of the fruit were also measured. CROSSf had better correlation with both average plant fresh- and dry-biomass with R2 of 0.6 and 0.5 compared to SAR with R2 of 0.3 and 0.2, respectively. Additionally, CROSSf exhibited a stronger correlation with fruit yield, displaying an R2 of 0.56 in contrast to SAR's R2 value of 0.29. Another important finding was that the maximum Na, K, Mg, Ca and Cl that strawberry plants can uptake were determined to be 21, 40, 7.7, 24 and 29 parts per thousand, respectively. Uptake of Na, K, Mg, Ca and Cl from the Osmocote-slow-release fertilizer was 0 (because the fertilizer does not contain sodium), 14, 5.3, 9.1 and 0 parts per thousand, respectively, based on the plant content at the end of the experiment. It was observed that the plant content of magnesium and calcium slightly decreased as the potassium in the irrigation water increased. Additionally, all salts added to the solution was observed in the plant tissue and it was consistent with the respective treatment content. In both experiments, it was concluded that CROSSf could offer enhanced accuracy and insight into the effect of recycled water reuse for irrigation on soil infiltration rate and soil aggregate stability. Therefore, it could be an appropriate standard for predicting sodicity impacts than SAR. For future work, it was recommended that treatments be designed such that the values of CROSSf have more spread at a given SAR. This could improve the statistical analysis. Additionally, it is worth comparing the two models in different soils that have clay mineralogy other than montmorillonite which was the case of the soil used in this study.