FOLEY, Minn. — Despite some colder temperatures, alfalfa stands appear to be looking nice heading into May. However, there can be differences between nice-looking fields and fields that will produce decent yields. This is why all stands need to be assessed each spring for winter injury to make sure that winter injury issues aren’t going to surprise you. For stand assessments we need to focus on two-parts; stem counts and root and crown health.
With stem counts, we usually measure this as stems per square foot. The relationship between stem density and yield is constant, making this method reliable in estimating yield. The steps of the procedure are as follows:
1. Mark off a 2 square foot section in each area you take a count
2. Count only those stems that are 2 inches or taller
3. Divide your count by two and average across all section
This will get you to the necessary stems per square foot needed to check yields. Typically, stem counts over 55 stems/sq. ft indicates a good stand. In that condition we would expect you could lose some plants and still produce good yields. Whereas, with stem densities of 39 stems/sq. ft or less and we would expect yields in those stands to be low enough to consider replacing.
When it comes to assessing stands visually, typically we would start from the top down. Looking at the tops of alfalfa plants we look for symmetry of the buds coming from all sides of the crown. Asymmetrically plants indicate winter injury did occur and yield potential may be lower. At this point you will also want to check to see if the root system is up out of the ground. Alfalfa taproots that have been pushed out of the ground by over an inch will most likely be short lived during the spring provided they don’t break off. Next, dig up plants from three or four representative locations in the field including at least the top 6 inches of the taproot to examine. Cut the crown in half and examine the color and rigidity of the inside of the crown. You want to see a firm, off-white interior with little to no signs of rotting. Discolored and spongy crown interiors indicate rotting and a plant that may not live another year.
When making decisions on whether to keep or replace a stand keep in mind both steps in the assessment. This is especially important with marginal stands as stands with 40 stems/sq. ft may still yield provided plant health is good throughout the field. Whereas the same stand containing plants with discolored crowns and asymmetric bud growth would indicate a potential reduction in yield and may need to be replaced.
If you have questions on the above information, please feel free to email me at ndrewitz@umn.edu, or call at 608-515-4414. To receive future events, educational programming, and agronomic updates by email, signup at z.umn.edu/tricountysignup.
— Nathan Drewitz, University of Minnesota Extension
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