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Agronomic Crops Network

Ohio State University Extension


Alfalfa Risks from the Wild Weather Ride This Winter

As farmers call in to discuss this strange winter and its risks to their alfalfa stand, concerns continue to grow as the green color has started to come back to alfalfa fields. Actually predicting what this weather is going to do to our alfalfa crop is impossible but scouting this spring will be imperative to determining how your alfalfa crop might do this year.

As temperatures rose into the 60’s or even set records in the 70’s recently it has awakened at least some of the alfalfa plants from their winter dormancy. Once dormancy is broke, the plants start using the nutrients that were stored in the roots and crowns to start spring growth. The early start to regrowth is not the problem, the challenge is going to be how many times winter temperatures returned to average and force plants back into dormancy. Then when another round of warm weather comes through, the plants will break dormancy again utilizing more of their root reserves. Alfalfa is a strong deep-rooted crop and can handle this cycle a couple times but eventually it can run out of root and crown reserves.

The other risk factor we are concerned about is ice formation on the soil surface each time we get a rain shower and it drops below freezing. The ice stops the exchange of gasses between the air and soil, if the exchange stops for a prolonged period of time toxins can build up in the soil, causing the roots to run out of oxygen that damages the roots, weakening the plant reserves to break dormancy. The other risk of wet soils and freezing and thawing is crown heaving. This usually snaps the taproot and raises the risk of crown damage during harvest. When the taproot snaps secondary roots can form that keep the plant alive but its nutrient uptake and ability to survive drought conditions decreases. 

The next step is going to be an intensified scouting program this spring paying special attention to low areas and soils that warm up and cool faster which could have broken dormancy more times than other areas of the field. While scouting look for areas that are greening up slower or have uneven regrowth. In these areas root digs will be beneficial. Healthy roots are going to be white and firm while injured roots are spongy, yellowish grey, dehydrated, or even worse, they can be brown with a rotting slim feel.

When doing your scouting after dormancy breaks you will want to take stem counts per square foot to get an idea of how the stand will perform this year. If stem counts are greater than 55 stems per square foot, stand density will not be a limiting factor. When densities decrease to 55-40 stems, there will be some yield reductions but, yields will still be adequate in years of low inventory or high hay values. When stem counts fall below 40, the stand is poor and termination options need evaluated. If damage is spotty across the field and a mixed stand of grass and alfalfa could work for your operation, you could consider inter-seeding annual or perennial grasses to improve yield.

Crop Observation and Recommendation Network

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.