PRE-SEASON ALFALFA IRRIGATION

by Bruce Anderson, Extension Forage Specialist University of Nebraska-Lincoln

              

Attention growers of irrigated alfalfa.  Have you ever irrigated before first cutting?  If you’ve received little spring precipitation, now might be a good time to start.

 

               Seems silly to irrigate alfalfa before first cutting, doesn't it.  But look at your soil moisture profile.  If it's dry, as is common in some areas, you may need to.  In fact, early spring often is the best time to irrigate alfalfa.  After all, it's about the only time you can actually build a reserve water source for summer use.

               Alfalfa can develop roots more than eight feet deep.  But it will only do this when surface moisture does not meet crop needs and moisture is available all the way down to those depths.  Deep roots that have access to deep moisture will make your summer irrigating much easier by providing extra moisture when plants use as much as half an inch per day.  Unfortunately, typical shallow watering during summer encourages only shallow rooting.

               The biggest advantage of reserve deep water comes after each summer cutting.  Alfalfa roots need oxygen in the soil if plants are to regrow rapidly.  Irrigating right after cutting suffocates roots, slowing down regrowth.  Immediate watering also stimulates shallow rooted or sprouting weeds, especially at a time when alfalfa plants are not very competitive.  Both problems are reduced when water is available for deep alfalfa roots while the top several inches of soil remain dry.  After alfalfa regrows several inches it will out-compete most weeds so irrigation then can begin again.

               Improve your alfalfa irrigation by watering early, with a goal of having six to eight feet of soil at field capacity at first cutting.

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               Remember that pivot systems are often only designed to deliver water at the Evapotranspiration rate.  This means that when you system is down for cutting or for a mechanical failure, you will be "getting behind" without any good way to catch up.  Early season irrigation is often the only way build up a reserve of soil moisture for later in the season.

Chad Cheyney, Butte County Extension Educator

Glenn Shewmaker, Extension Forage Specialist, Idaho.