ASA Paper

November/December 2005

Evaluating Alfalfa Stands

by Dean Slates

As winter approaches, there is always a question as to whether an alfalfa meadow is worth keeping over for another year or which meadows should be rotated to corn next spring. While there are no absolute answers to the questions, research has given some benchmarks to assess the productivity of questionable alfalfa stands.

Traditionally it has been noted that a meadow with less than 4-5 alfalfa plants per square foot will not be worth saving. However, depending on fertility and weed encroachment, research shows that five plants per square foot can yield as much as a stand with 10 to 15 plants. The correlation between plants and yield has been shown to be very low since alfalfa plants respond to decreasing stand by producing more stems per plant. Those increased stems compensate for the fewer plants and maintains the yield.

A better indicator of alfalfa stand production potential is the number of stems per square foot. Research shows that fields with 55 or more alfalfa stems per square foot, produce maximum yields. Once the stem count falls below 40 per square foot, profitability is doubtful and those fields should be rotated out of alfalfa.

Traditionally, the decisions about keeping alfalfa meadows has been made in the early spring, but (depending on how early you do the examination) you may not have the opportunity to count alfalfa plant stems at that time. The best time to do those alfalfa meadow evaluations is in October and November, before the onset of severe winter weather conditions.

It is possible that a severe winter with lots of freezing and thawing will damage some of the alfalfa plants, but it is assured that a field with less than 40 stems per square foot in the fall will have less than that in the spring. Fields that are in the 40 to 50 range this fall may merit a reexamination in the early spring.

A final idea for those fields that are judged to be not productive this fall and will definitely need to go to corn next spring relates to weed control herbicides. The application of a glyphosate herbicide before the ground freezes this fall will kill off the alfalfa and grasses (including quackgrass) and make planting and subsequent weed control in next year’s corn crop go a lot easier.

If you have dandelions or curly dock in the field, it is helpful if 2,4-D is included in the herbicide mixture with the glyphosate.

Whether you are in a no-till or conventional tillage program, that fall herbicide application will make next season’s corn weed control program easier and less expensive. Late fall is the ideal time to evaluate your alfalfa meadows as to their future productivity, and

depending on the decisions you make, it may be a great time to get some of your most troublesome weeds under control as well.