Irrigating Alfalfa May 9, 2018
With low soil moisture levels in many areas, now might be a good time to start to start irrigating alfalfa.
It may seem silly to irrigate alfalfa before first cutting, but check your soil moisture profile. If it's dry, especially in the subsoil, irrigation may be warranted now. In fact, early spring often is the best time to irrigate alfalfa. It's about the only time you can actually build a reserve water source for summer use.
The biggest advantage of reserve water comes after each mid-summer cutting. Alfalfa can develop roots that will use water more than eight feet deep, but it will only do this when surface moisture does not meet crop needs and moisture is available at deeper depths. If you have deep roots and deep reserve moisture, though, it will make your summer irrigating much easier by providing extra moisture when plants use as much as one-half inch per day.
Unfortunately, typical shallow watering during summer encourages shallow rooting. Shallow summer watering causes other problems. Alfalfa roots need oxygen in the soil if plants are to regrow rapidly. Watering right after cutting suffocates roots, slowing 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 reserve water is available for use by deep alfalfa roots. Then the top several inches of soil can remain dry for a couple days until alfalfa regrowth is well underway.
Take Home Point
Improve your alfalfa irrigation by watering early, with a goal of having at least the top six feet of soil at field capacity at first cutting.