WSP04560

• File Number: 8271.300
• Description: Colorado River Basin Salinity Control Program - General Information and Publications - Reports
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 2/9/1994
• Author: John Hedlund
• Title: Salt Primer - Water and Salt Budgets
• Water Supply Pro - Doc Type: Report/Study

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1

SALINITY PRIMER
WATER AND SALT BUDGETS 1/

February 9, 1994

N Introduction
~
1-' Salinity in soil and water has been a major concern throughout
~! history to irrigators in most of the arid and semi-arid portions
of the world. Until the early 1970's almost all research and
technical assistance had addressed the issue of sustaining crop
production by maintaining a salt balance in the root zone with
leaching.

In 1972 a new US focus was added - - a concerted effort was made
to address the salinity damages to the economy created by
drainage return flow to downstream water users on the Colorado
River. Since then, salinity and toxic minerals in our water
supplies have become a major focus of the environmental community
in many areas where water quality adversely affects downstream
crop yields, wildlife, livestock, industry, and public health.

Awareness of downstream salinity damages provides a new direction
to water conservationists who have been advocates of improved
irrigation efficiency. It changes the scope and focus of
recommendations by irrigation and drainage specialists. In the
past, excess leaching was not discouraged, but frequently
recommended.

Leaching was sometimes practiced by farmers in irrigation
districts using good quality ~ater of less than 400 mg/L salinity
concentration. In one area farmers were encouraged to over
irrigate with 200 mg/L water and "blacken" the soil across the
furrow beds in the spring. It was not unusual to get 2 to 3 feet
of deep percolation with early irrigations; over ten feet of deep
percolation per season has been monitored on both a sprinkler and
surface system in this area. Based on the quality of water
applied and the crops grown the leaching requirement for salt
balance is 5 to 10 percent or 2 to 3 inches.

Leaching requirements determined by using the USDA Salinity
Handbook 60 can be excessive due to mis-interpretation.
Secondly, current research has demonstrated ways to reduce the
leaching requirement. The third important change in scope of
consideration is that returning subsurface irrigation return flow
in some areas picks up large amounts of salt and toxic minerals.
In some areas an acre-foot of deep percolating water can pick up
an additional five tons of salt. Two or three acre-feet of deep
percolation and salt added is 10 or 15 tons per irrigated acre.

1/ This salinity primer is a record of procedural concepts used
to plan and implement the Colorado River Basin Salinity Control
Program between 1972 and 1994. Prepared by John D. Hedlund,
Salinity Coordinator at the WNTC, SCS, Portland, Oregon.