Sow and Grow with Sara:

I’ve received several questions about alfalfa winter injury predictions this year. Of course we cannot predict with certainty whether stands will experience injury, but there are a few factors that come into play when determining the likelihood of experiencing issues.

Although plant stress from drought conditions may weaken plant vigor, dry conditions can also have a positive effect on alfalfa winter hardiness. Alfalfa grown in well-drained areas tends to be less prone to winter injury, and low fall moisture levels can actually make winter kill less likely to occur. Dehydration of the plant is one of the primary factors required for alfalfa to tolerate winter temperatures. Stands that go into the winter months with lower soil moisture have less difficulty losing remaining plant moisture and are actually less likely to winter kill. In some areas, extreme drought may have caused more plant stress, but dry environmental conditions are also helpful for plant dehydration.

In addition, our giant blanket of snow this winter has helped insulate soils. Temperature fluctuations in the soil tend to be minimized under snow cover. In fact, a 4-inch blanket of snow can result in a 10°F difference in soil temperatures. Leaving more stubble (~6”) after the last fall cut can help to catch snow and provide more insulation as well. Winterkill usually occurs if soil temperatures (2-4” deep) reach 12-13°F or lower.

Other factors that can effect winterkill include:

Stand age- the older a stand gets, the more susceptible it tends to be to winter injury.

Soil fertility- stands with high fertility, especially adequate to high potassium levels, are less likely to experience winter injury than stands with inadequate fertility.

Cutting schedule- Harvest frequency and the timing of the last fall cutting are important factors in stand winter hardiness. Intense, frequent cutting schedules tend to experience higher levels of winter stress. In addition, if a cutting was taken between September 1 and mid-October, the stand is at higher risk for winter injury as plants may not have had enough time to replenish root carbohydrate reserves before a hard frost.

Variety- varieties with excellent winter-hardiness ratings and high disease resistance markers tend to experience less winter injury.

Soil pH- A soil pH of 6.6-7.5 is most ideal for alfalfa stands.

Ice sheeting- Refroze snow/rain or winter rains can result in ice sheets that prevent air exchange to alfalfa crown roots. A healthy alfalfa stand can tolerate up to ~3 weeks of being covered by ice before dying.

Heaving- repeating freeze/ thaw cycles may result in an alfalfa field pushing a portion of the plant roots out of the ground, causing a heaved appearance. This may cause the crown and root to have exposure above the soil surface. Often, these exposed roots are cut during harvest, resulting in plant death.

When the snow clears and temperatures rise, check for alfalfa winter injury. Should you have concerns, stem or plant counts should be taken across problem areas, and replant options can be considered based upon stem density threshold values. Search the SDSU Extension website for “Alfalfa Winter Kill” for more information on this topic.

Lastly, I wanted to remind you to check grain bins this spring. Spring is a busy time for many crop and livestock producers and it is easy to forget about your stored grains. As temperatures warm up, so does the bin. Grain bins experience more heating on the south wall of the bin on March 1 than they do midsummer. Dry grain should be kept at or below 40°F as long as possible. As summer temps hit, the goal is to keep bins at 60°F or below to limit insect activity and mold growth.

Here are a few tips to help keep your stored grain in condition if you plan to store it into the summer:

Cover bin aeration fans when not in use. Fans essentially go through the ‘chimney effect’ where wind moves wet, warm air into the fan, and it travels upwards, affecting the grain inside.

Provide an inlet for air near the roof eave and outlet exhaust near the roof peak to allow warm air to exit the bin (much like the principles of an attic). Several vents at the same elevation can still allow heat to remain at the top of the bin without exhaust at the peak or roof exhaust fans.

Add a temperature sensor near the south wall of the bin to collect readings, or be sure to take some grain samples from this area, which is likely the warmest part of the bin.

Periodically run bin fans throughout the spring to help keep grain cool and slow warm-up.

During summer months, choose cool mornings every two-to-three weeks to run the aeration fan to push cool air up through warm grain near the top of the bin.

Run the fan only long enough to cool the grain at the top of the bin; this may mean running fans for a couple hours on more than one cool, dry morning. Running fans more than necessary could result in grain warming near the bottom of the bin.

Unload some grain. By unloading grain in bins with center sumps, warm grain from the top of the bin is unloaded first, leaving a funnel shape in the center of the stored grain. This can help to reduce grain temperature near the top of the bin and eliminate cone-shaped peaks (which lead to excess grain warming).

Check your bin airflow rates. Visit the University of Minnesota Extension’s ‘online fan selection tool’ for more information on fan selection (bbefans.cfans.umn.edu).

Resources:

Cosgrove, D., and D. Undersander. Evaluating and Managing Alfalfa Stands for Winter Injury. Focus on Forage-Val. 5. No. 8 by UW Extension. 2003. fyi.extension.wisc.edu/forage/evaluating-and- managing-alfalfa-stands-for-winter-injury/#:~:text=Winter%20injury%20or%20death%20can,which%20kill%20the%20alfalfa%20plant.

Hellevang, K. Keep Stored Grain Cool During Spring and Summer. North Dakota State University Extension Service. 2018. www.ag.ndsu.edu/news/newsreleases/2018/feb-20-2018/keep-stored-grain-cool-during-spring-and-summer/

SDSU Extension is an equal opportunity provider and employer in accordance with the nondiscrimination policies of South Dakota State University, the South Dakota Board of Regents and the United States Department of Agriculture. Learn more at extension.sdstate.edu.