Competitive Agricultural Systems in a Global Economy
Soil Water Depletion Levels for Irrigating Wheat and Barley
Issue
The generally accepted soil water depletion level for irrigating wheat
and barley is when 50 pecent of the plant available water in the root
zone is depleted. This critical depletion level has not been verified
in Arizona. The optimum soil water depletion level should be derived
from grain yield, water cost, and associated production costs on a local
level.
What has been done?
University of Arizona researchers have studied the relationship between
soil water depletion and wheat and barley yield for two years at Maricopa
Agricultural Center and for one year for wheat at a commercial farm
near Stanfield, AZ. This research has been reported in several publications
and newsletters.
Impact
The highest grain yields were obtained at 35 percent depletion of plant
available water in the soil. However, this increased grain yield of
about 800 lbs/acre is produced with the cost of an additional two irrigations
compared to irrigating at 50 percent depletion and of an additional
35 lbs N/acre required in wheat to maintain equivalent grain protein
levels. Assuming current grain prices and water costs, irrigating at
35 percent depletion is economically advantageous only where water costs
are low, such as along the Colorado River. In the counties along the
Colorado River (ie., Yuma, La Paz, and Mohave) irrigating at 35 percent
rather than 50 percent depletion would generate about an additional
$2 million in income.
Funding
Arizona Grain Research and Promotion Council
Contact
Michael J. Ottman
Extension Agronomist
1140 E. South Campus Dr.
Plant Sciences Department
University of Arizona
Tucson, AZ 85721
Tel: 520-621-1583
FAX: 520-621-7186
Email: mottman@ag.arizona.edu
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