Be water wise when you irrigate alfalfa
For Melvin Kruse of Bow Valley, irrigation provides insurance that he will always have alfalfa hay to harvest. This spring, Kruse planted another field of new-seeding alfalfa under a center pivot.
His irrigation plan is simple. “As soon as I get a cutting of hay baled and hauled off, I give the field a good soaking right away,” says the Cedar County farmer. “If you can get it soaked right away, the alfalfa will grow back, and it really takes off. Then, a week and a half later, I’ll give it another inch and a half if we need it.”
At a glance
• Bow Valley producer irrigates alfalfa after each cutting is harvested.
• Overwatering can injure plants and cause compaction problems.
• Alfalfa’s water needs peak during the hot days of July and August.
When it comes to irrigated alfalfa, Nebraska is unique. Unlike most Western states where irrigation provides the majority of water, it only supplements rainfall in Nebraska.
Most of the questions farmers have about irrigating alfalfa center around when to start irrigating, how much water should be distributed and the best way to monitor conditions.
In 2008-2010 irrigated alfalfa studies conducted in Butler County, University of Nebraska Extension Educator Michael Rethwisch says, “Differences became greater as the season progressed, with the lowest yields and greatest differences from irrigated alfalfa [compared to dryland fields] on the side hills with the most slope.”
Irrigating alfalfa is different
Irrigating alfalfa is much different than irrigating corn and soybeans, because it is a perennial crop with a deep root system that can pull water from deep within the soil profile. Because alfalfa is harvested several times during a growing season, there are at least seven to 10 days in each growth cycle when irrigation is not possible. There are also issues with compaction from repeated traffic from haying equipment, and the potential for over-watering, which can injure alfalfa plants.
“My recommendation is to have the top 6 feet of the soil profile near field capacity at first cutting,” says Bruce Anderson, UNL Extension forage specialist. “The ability of alfalfa to yield and respond to water declines through the season, so the worst time to be short is during the first two cuttings,” he says. “Late-season irrigation can be very efficient, however, in producing extra yield of high-quality forage, but care must be exercised to avoid overwatering and its resulting cost.”
Peak water use for alfalfa in Nebraska will normally range from 0.3 to 0.35 inch per day in July and August, but it may rise to 0.5 inch on hot, windy days. It takes around 5 or 6 inches of water from irrigation or rainfall to produce a ton of dry hay.
Using a soil moisture monitor helps producers decide when to irrigate. In Butler County studies where soil moisture monitors were placed at 6-, 12- and 24-inch depths in each field, it appeared that monitors placed at 6 inches were more accurate than at 12 inches, Rethwisch says.
“Splitting the difference at 9 inches may be best for the silt loam soil types involved,” he says. Differing soil types require different depth placement due to varied water-holding capacities.
Farmers normally try to irrigate alfalfa as close to harvest as they can, without causing overly wet harvest conditions and interfering with the drying process. “Soil type has a big effect,” says Anderson. Sandy soil may only need one day to dry, while clay loam may take several days.
“Your fertilizer program is just as important,” says Kruse. If producers are going to invest in irrigating alfalfa, they need to have nutrients available to produce as much as possible with the extra water.
Fall irrigation is an important management tool in drier parts of the state. “As alfalfa plants near the end of their winterizing period, though, it is better for them to experience slowly drying conditions to strengthen their wintering ability,” Anderson says. “Soil moisture is critical over winter to prevent desiccation from killing plants.”
For more information on irrigating alfalfa, contact Michael Rethwisch at 402-367-7410 or Bruce Anderson at 402-472-6237. Learn more at water.unl.edu/web/cropswater/home.
SOAK IT UP: Melvin Kruse of Bow Valley irrigates immediately after each cutting of alfalfa has been baled and the bales have been removed, to boost regrowth potential for the next cutting.
This article published in the May, 2011 edition of NEBRASKA FARMER.
All rights reserved. Copyright Farm Progress Cos. 2011.