Evaluation of Leaching Requirements and Salt Balance in the Arkansas River Valley of Colorado
The Arkansas River contains increasing amounts of salts (dissolved solids) as it flows from Pueblo, Colorado, to the Kansas border. Data reports from April 1990 through March 1993 show 300 milligrams per liter (mg/L) at Pueblo to over 4,000 mg/L at the Colorado/Kansas border with an accrual rate of 30 mg/L per mile of river between John Martin Reservoir and Coolidge, Kansas. This same Arkansas River water is being used to irrigate crops and has caused increases in soil salinity and reductions in crop production. The objective of this continued research is to provide assessments of soil/salt relationships and determine the proper amount of irrigation deep percolation needed to maintain or restore crop production.
Need and Benefit
Variations in leaching requirement equations have an impact on the amount of a water supply needed to maintain the soil salt balance. Depending upon what methodology and equations are used, the amount of water supply required could be reduced or increased. If the computed leaching requirement is too small, the soil salinity can continue to buildup, resulting in poor crop productivity and poor soil health. Conversely, if the computed leaching requirement is too large, water-logging, salinity, and the need for expensive drainage systems can be the result. Additionally, use of salinity meters, such as the EM38 and EM31, can be calibrated and verified with actual field soil samples to provide accurate and more reliable results for growers and producers to track their own soil health and then adjust the irrigation management practices to either increase or decrease the amount of deep percolation required for the soil salt balance. The use of these meters now can provide a more real-time snapshot of the soil salinity and allow the grower to adjust his use of the water supply to maintain the soil salt balance. This periodic adjustment in the water supply would be for the single purpose of adjusting the leaching requirement to maintain the healthy soil salt balance. Hopefully, this leaching adjustment is in line with the computed leaching fraction, based on an accepted mathematical leaching equation. Reclamations initial goal of helping with irrigation development was to insure the long-term sustainable use of the soil and water supplies. Using the proper leaching requirement is a key to the long-term sustainable crop production, which is a part of the economic returns (repayment) of the project.
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