Sustainable Agriculture Literature Review - Boulder County

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Whether to reduce the number of irrigated acres or irrigate at a rate less than adequate
capacity can be a difficult decision when water is limited due to either supply constraints
or system capacities. A study conducted in Western Kansas found that net returns to
land and management are reduced when all acres are irrigated at less than adequate
capacities compared to reducing irrigated acres while maintaining adequate capacity. 239
When irrigation was reduced below optimum supply for all acres, overall corn yields
were reduced, compared to maintaining an adequate supply with fewer acres. 240
Crop rotation has been found to help increase yields in water-limited systems. A study
conducted by Schneekloth found that net returns were greater when a three-year
rotation of corn-soybean-wheat was irrigated compared to a continuous corn rotation.
The increase in yields was attributed to the increase in corn grain yields following wheat
and the inclusion of lower water use crops such as soybean and wheat, which had yields
that were closer to fully-irrigated grain yields when compared to the corn yields. 241
Changes in agronomic practices can increase the capture and utilization of precipitation
and reduce irrigation water needs. Changes include using no-till practices and cycling in
lower water requirement crops that have different critical times for water. Crop rotation
can extend the irrigation season and allow for longer operation of irrigation systems with
proper irrigation management. This allows for producers with low capacity systems to
effectively manage the irrigation. 242
Crop Water Use
Water requirements for crops depend mainly on environmental conditions, with the
prevailing weather conditions being the driving force. Different crops have different water
use requirements, even under the same weather conditions. For example, according to
CSU, “in the Greeley area, the seasonal water use of sugar beets is 30 inches while
corn for silage uses only 22 inches of water. That means sugar beets require 36 percent
more water than corn to fully irrigate.” These water requirements are the amount a crop
will use (not counting water losses such as deep percolation and runoff) in an average
year. Figure 15 shows the average water requirements for selected crops in Longmont,
CO. 243
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Figure 15: Estimated Seasonal Water Requirement (consumptive use) in
Longmont, CO (inches/season) 244
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