Predicting First-Cut Alfalfa Yields from Preceding Winter Weather

"How's the alfalfa going to look next spring?" This question is currently being batted around the coffee shop as the winter of 1996-97 has already thrown at us double digit sub-zero temperatures and several days of near spring-like stuff. I learned the hard way a long time ago never to predict alfalfa survival and grain prices ----- but they're both still both fun to talk about. Let's dwell on alfalfa here.

Injury to alfalfa over winter can be caused by temperature fluctuations, lack of snow cover, and persistent ice sheeting. Weather conditions during the fall hardening period and during early spring can also impact alfalfa survivability.

Fluctuating temperatures with highs in 40 to 60 degree F range during winter can cause plants to break dormancy and initiate growth too early for normal spring development. Snow cover is usually beneficial from the stand point of temperature moderation at the crown and root zone and protecting the plant from extremely low temperatures. A rapid meltdown of snow followed by cold temperatures can result in long term ice sheeting. This may cause plants to smother in metabolic byproducts of respiration or result in injury from low temperatures because of the poor insulating value of ice.

Weather conditions during the fall hardening period have been implicated in the alfalfa plant's ability to overwinter. Long fall periods with sunny but cool conditions favor plant winter hardening whereas short fall periods with cloudy and warm weather tend to decrease plant hardening. In the early spring, extreme temperature fluctuations without the benefit of snow cover often contribute to plant injury or death.

Michigan State Study

With the large number of variables impacting plant survival over winter, it becomes very difficult to predict first-cut forage yield potential prior to the fact. Recently, researchers at Michigan State University studied long term first-cut alfalfa yields as they related to twelve weather variables. The researchers used data from moderately winterhardy alfalfa varieties managed in a four-cut system (last cut taken after October 15) to develop yield-weather relationships and predictive models. Yields were used from alfalfa variety trial field plots in their second and third production years. Weather variables included precipitation, temperature (both average and fluctuations), and growing degree days for various time periods.

What weather variables were most important?

Of all variables tested, winter temperature fluctuations (i.e., the number of times the mean daily air temperature rose above and fell below 31 degrees F on days with less than 6 inches of snow cover) and spring growing degree accumulation (base 38.5) were the most important weather variables affecting variability of first-cut alfalfa yields. A higher than average number of fluctuations in winter temperature resulted in lower yields and increased spring growing degree days improved yields. Interestingly, minimum daily winter temperature did not reduce first-cut yields.