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Did the alfalfa survive the winter?

Glenn Shewmaker for Progressive Forage Published on 30 March 2017
Winter kill

Freezing temperatures since November, an ice layer for weeks and several days under water – will there be any alfalfa stands remaining in the Northwest?

Record cold and wet weather in many parts of the country may have taken a toll on alfalfa stands. It is time to assess stands and plan for remedies or rotations.

Most high-elevation mountain valleys have adequate snow depth to moderate-extreme cold air temperatures. Many valleys still had 2 to 3 feet of snow into the first week of March and these stands are likely in good shape. This year, the mid- to lower-elevation alfalfa may be hardest hit.

Significant areas of fields had snow for several weeks, then an ice layer for 2 to 3 weeks and then were under water for several days. No one knows for sure how much damage there will be, but it is likely that large areas within fields may have significant stand loss.

We know ice sheets and standing water are a problem for alfalfa and other plants. In the case of an ice sheet, if you have old stubble still poking up through the ice – and depending upon how much – it may allow some plants to survive. In 1943, researchers found that dormant, cold-hardened plants, frozen and maintained in blocks of ice, were weakened after 12 days and all were dead within 20 to 26 days of such storage.

Winter flooding and ice and cause winter kill

Contacting ice was the most injurious of all the storage treatments employed. Experiments by researchers in 1967 concluded that carbon dioxide buildup was the primary cause of root death under ice. The other variables are the time of oxygen limitation and the environmental variables, such as air and soil temperature.

Flooding causes root growth to stop, even with warm temperatures. Research has shown that the higher the temperature when alfalfa is under water, the more damage occurs.

This is because plant roots need oxygen to continue respiration even while dormant. Aerobic soil microbes also require oxygen to respire and cycle through their life.

There is not much research on anaerobic conditions with cold soil temperatures for extended time periods. Some research was cited by Montana Agronomy Notes in 1997 (Table 1).

alfalfa response to flooding at various temperatures and times

Evaluating stand survival

Step 1: Monitor the stand. Get on your knees and poke around the crown to examine the presence of new buds and firmness of the crown. Use a shovel to dig some roots and look for proportions of healthy, whitish roots that are turgid or firm. Slice the roots at a diagonal to observe color and disease.

Weak or dead roots will be brown and spongy. The Wisconsin Extension Forage website has an excellent score sheet to evaluate winter damage in the A3620 bulletin. It can be found at (Alfalfa stand assessment: Is this stand good enough to keep)

Step 2: Estimate stems per square foot in several problem areas. Alfalfa breaking dormancy is a gradual process. Stressed plants are slower to develop elevated shoots, so estimating viable shoots per square foot is not easily done early in the season.

Fall-formed buds will be much further ahead than spring-formed buds. The research for predicting yield as a function of number of stems per square foot is based on counting stems that are several inches tall, so caution should be used when extrapolating the yield estimates.

If there are 55 stems per square foot or greater, you probably won’t see a significant yield reduction. If you have less than 39 stems per square foot, yield will be reduced and you should probably rotate out of alfalfa in that field.

Step 3: Estimate the area of the field affected. This is where a drone photo or video would be useful because your perspective at near-ground level is difficult to translate into acreage.

Step 4: Review cutting history, yield records and stress from pests or the environment. Stress tends to stack up and accumulate. If your field is stressed and you have doubts about its viability, then you probably need to rotate.

Step 5: There are three choices: 1) rotate out of alfalfa; 2) overseed Italian ryegrass or cereal such as a hay barley or forage oat to get a temporary yield rejuvenation; 3) wait a week and re-evaluate the stand.

A survey conducted at the recent Idaho Hay and Forage Conference showed 48 percent of 36 respondents estimated 0 to 10 percent alfalfa stand loss, 30 percent of respondents estimated from 10 to 20 percent stand loss and 11 percent of respondents estimated a 20 to 50 percent stand loss due to ice sheets and flooding.  end mark

PHOTOS: The brown spots throughout the field are mostly dead due to late winter flooding and winter kill on a field in southern Idaho. Photos provided by Glenn Shewmaker.

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