May 31, 2012

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Hot, windy days can quickly dry up alfalfa fields.  Irrigation helps, but it can stimulate weeds and actually weaken alfa

lfa stands if not done properly. 

Alfalfa uses a lot of water — up to 40 inches a year and sometimes over 0.4 inch in one day.  No wonder irrigators find it difficult to keep up with these water demands.  As a result, we often irrigate as soon as hay is removed from the field until we start the next cutting.

Constant watering has its costs besides fuel, labor, and depreciation.  It encourages grassy weeds like foxtail and perennial grasses like bluegrass to invade alfalfa.  Constant watering also can weaken alfalfa plants by encouraging root diseases and reducing the oxygen content of the soil.

How can you avoid weakening your alfalfa and strengthening weeds with irrigation?  You do it by modifying irrigation management to encourage deep rooting of alfalfa and dry surface soils during harvest.

Stop irrigating a couple days before harvest so the soil surface will dry out and become firm.  Then, don’t irrigate after harvest until regrowth is three to four inches tall.  Shallow rooted weeds like foxtail and bluegrass won’t be able to grow until alfalfa has a head start.  Alfalfa will regrow more rapidly because the roots will find more of the oxygen they need in soil that has not been saturated with water.  Of course, this assumes you have been deep watering when you do irrigate so there is water deep in the profile that alfalfa roots can reach, but not weeds.

By putting on a little more water a little less frequently, your alfalfa can be cleaner, healthier, and more productive.

Bruce Anderson
Extension Forage Specialist