Irrigating Alfalfa

Summer is here, and with it the always present risk of drought. While the precipitation received so far is appreciated, much of our corner of Nebraska is looking pretty dry. When we consider forage options for dry times, alfalfa may come to mind.

While it is a relatively drought-tolerant forage, alfalfa does not have specific growth stages when it is less sensitive to water stress. If water is not available, the plant will slow or stop growing and go dormant. Then, when water becomes available, growth resumes. Dormant plants can be harvested or grazed with relative safety, but many not be worth the time or cost.

Still growing drought stressed alfalfa will mature faster than normal, with quality peaking sooner and quickly degrading.  Water stress can be seen by keeping an eye on plant color.  Alfalfa with adequate moisture will be a light green color and darken as water stress develops. 

When irrigation is possible, water should be applied when the plant is a dark green color, but before wilting occurs to prevent yield loss due to water stress.  Let’s take a look at some other irrigation pointers that can help improve your alfalfa crop this summer.

While alfalfa’s long growing season means it uses more water annually than other crops, it can be over-watered resulting in alfalfa plant injury and possibly weed invasion. Maintaining water use efficiency can be complicated due to multiple harvests preventing irrigation for about 7 to 10 days per growth cycle and frequent heavy equipment traffic compacting soils. To reduce compaction, stop irrigating 2-3 days before cutting the alfalfa and begin irrigating again after hay has been removed and plants have initiated regrowth.  We’ll talk about this more in just a bit.

Generally, the most yield impacting irrigation occurs just before the second cutting followed by the third and fourth growth periods.  Typically the plant will require 5-6 inches of water during these times for each ton of forage produced.  Peak water needs are typically in July and August at 1/3 inch per day. However, hot, windy and dry days can move the maximum water demand up to ½ inch per day.  While recent rains have improved soil moisture, producers who really want to capitalize on their irrigation scheduling should consider using an ET gauge to plan watering events. 

With deep roots and able to withstand multiple cuttings a year, a healthy alfalfa stand is able to outcompete most weedy species that might try to invade, especially after a good canopy has formed. One plant that seems to be a persistent nuisance however is bluegrass. 

High-density alfalfa stands can be effective in competing with bluegrass for sunlight, moisture and nutrients.  While alfalfa roots go deep, the plant will get 75-90% of its water needs from the top 4 ft. of soil.  We can use this to our advantage to control unwanted plants like bluegrass.

To do this, time irrigation so the upper several inches of fields are dry at harvest. Then, delay irrigation until significant alfalfa regrowth is initiated. Unlike alfalfa that has a deep root system, bluegrass is shallow rooted and will not compete well with the alfalfa if the topsoil is dry. Once up and growing, alfalfa will be able to compete with the bluegrass for top soil moisture. Conversely, early irrigation following harvest, may allow bluegrass to out compete the alfalfa for available surface moisture after cutting, since bluegrass basal leaves help it grow more rapidly after alfalfa is cut. 

Herbicide options can help get out of control bluegrass infestations back to a manageable state, but utilizing irrigation scheduling can keep it and other weeds out.   

Alfalfa is a fairly drought tolerant crop, but does respond well to properly timed irrigation. Schedule watering by using plant characteristics or ET measurements for efficiency and time events to provide weed control and prevent soil compaction.

-Ben Beckman is a beef systems Extension Educator serving the counties of Antelope, Cedar, Knox, Madison and Pierce.  He is based out of the Cedar County Extension office in Hartington.  You can reach him by phone: (402) 254-6821 or email: