Benefits and Impacts of Partial Season Irrigation on Alfalfa Production

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Year Published: 2018
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Author: Perry Cabot, Joe Brummer, Sumit Gautam, Lyndsay Jones and Neil Hansen
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Prolonged drought and increasing demand for water resources has caused growing concern over
Colorado’s ability to fulfill legal water obligations as identified in the Colorado River Compact.
A Western Slope Water Bank, which would entail agricultural water users entering into short-term
leases and temporarily withholding or reducing irrigation, could be a partial solution to free up
water to fulfill these obligations. Alfalfa (Medicago sativa L.) hay may be ideal for inclusion in a
water bank as it is one of the primary users of agricultural water in this region and may have a
greater ability to withstand water stress in comparison to other crops. This study was conducted to
determine effects of implementing partial season irrigation on lower elevation alfalfa hayfields on
forage yield, nutritional quality, and associated recovery. A total of 6 established alfalfa fields
were subjected to irrigation treatments including normal irrigation (REF), irrigation stopped later
(low-risk) in the growing season, and irrigation stopped early (high-risk) in the growing season for
2 consecutive years. All fields then received consistently full irrigation in the third and final year.
In the final study year of recovery evaluation, average 1st cutting yield on control, low-risk and
high-risk plots was 2279, 2524, and 2869 kg ha-1). Similarly, during the fully irrigated recovery
year, 2nd cutting yield on control, low-risk and high-risk plots was 2616, 2392, and 2794 kg ha-1.
Third cutting yields on control, low-risk and high-risk plots was 2298, 2392, and 2357 kg ha-1.
Total fiber concentrations (aNDF) were greatest in the control at 34.6% and lowest in SA1 plots
at 28.2%. By the 2nd cutting, SA1 plots had the highest digestibility (IVTD) at 80%, and by the
3rd cutting, SA2 and SA1 plots were equally greater than the control (80 vs. 75%). Effects on CP
content were inconsistent. These results suggest that reduced irrigation may improve forage quality
slightly, but will significantly reduce yields. When irrigation is returned the following year, alfalfa
yields may fully recover depending on length and severity of reduced irrigation. Due to its ability
to recover, using partial season irrigation treatments on alfalfa hayfields may be a practical
approach to make water available to a Western Slope Water Bank.

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Partial-season irrigation, water banking, alfalfa forage quality

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