Did alfalfa stands survive the polar vortex this winter?

When it comes to the "queen of forages," a common question flying around at this time of year is whether or not the crop survived the winter. And for good reason. The sooner winter damage to alfalfa can be determined, the sooner producers can decide which option for replacing that lost forage will be best for them. 

Dr. David Combs with the Department of Dairy Science at the University of Wisconsin-Madison, has been getting a lot of questions about how the polar vortex has affected alfalfa crops. In an April 17 webinar presented by the Professional Dairy Producers of Wisconsin (PDPW), Combs discussed how to assess winter damage to alfalfa, what to do about the crop based off that assessment and ration adjustments for lactating cows if alfalfa is replaced by a different forage. 

Based off information from Dr. Dan Undersander, there are four issues that "tend to take alfalfa," Combs said — lack of insulation, frost heaving, ice sheeting and breaking dormancy repeatedly during the winter. 

Winter kill risk

About 4 inches of snow cover over a crop is needed to protect the alfalfa crown and tap root from being killed by low temperatures. Alfalfa can be killed if it is exposed to temperatures below 12 degrees Fahrenheit for long periods.

"In southern Wisconsin, we didn’t have a lot of snow in December or January, so there is a lot of concern about loss of stands because of lack of snow early in the winter," said Combs. "Repeated freezing and thawing is another factor that takes out stands."

Ice sheeting in southern Wisconsin this year may also have caused damage. With rain later in the winter and ponds forming in fields, "if those freeze over, it can actually suffocate alfalfa in the fields," Combs said. 

A mild, quick warm up around February or so would break dormancy and "going from freezing to thawing would essentially starve the plant to death," added Combs. 

"Where we’re at right now, it’s like a card game. It’s when to hold 'em and when to fold 'em," said Combs. "Ideally, within the next week or so we would like to know so we can make some decisions. Obviously it costs money to reestablish a crop. If we can hold it, we kind of would like to know the impacts — what damage might be on some stands."

Assessing a stand

Fields are starting to green up in the Madison area and Combs said calls have come in from producers saying their fields don't appear to be greening up as fast. 

"That's a bit of over anticipation, but slow green up is a sign of winter injury," Combs said. "Usually though, this is not a reason to take a crop out."

Alfalfa can be slow to green up because the fall buds on the plant were killed, which slows the spring growth, Combs explained.This causes a reduction in first crop yields, which happened last year in southern Wisconsin. Combs said it wouldn't be a surprise if that happened again this year. 

With older stands more prone to winter kill than new seedlings, it's important to take assessment of existing stands by first looking at the number of plants per square foot and then digging up the tap root to see if its healthy. 

In a stand that is two to three years old, Combs said you would ideally like to see five to six plants per square foot. 

"At that point, start digging up tap roots and taking a look at the tap roots and try to assess damage," said Combs. 

If the crown is brown and dehydrated, "that's a sign that there's severe winter damage and that tap root is probably dead," Combs described. A healthy tap root should look white like a potato. 

Since yield highly relates to the number of stems per foot, about 50 - 65 stems per square foot is about optimum for maximum yields, according to Combs. When there are about 40 stems per square foot, there is about a 25 percent yield reduction. 

"That's kind of the cut point. That's when we start talking if we should take the stand out and grow something else," said Combs. "If we're over 40 stems, we're probably going to leave that stand alone and look at taking yield reductions rather than invest in alternative forage."

Alfalfa replacement options

So what are the options for replacing that lost feed? If looking to buy hay on the market, the news isn't good. In February, dairy quality hay was high priced and "word on the street is it's probably higher now," said Combs. "So buying hay is probably not the option I would recommend."

A more realistic option would be to take a forage inventory to determine how much forage is on hand and what's needed to get through the summer. If inventory is low, producers will want options for feeding cows as soon as possible. If there is enough alfalfa to get through the summer, producers might consider replacing winter damaged stands with either corn silage or sorghum, for high total season yield, Combs said. 

If there is some damage, but producers decide to keep the stands, there is the option to take some ground that becomes available maybe after a winter wheat harvest and plant a forage in August or September for a high quality forage added for the upcoming year. 

If there is enough feed to get through the winter, another option would be to plant a spring forage like rye, triticale or winter wheat, that can be harvested next spring to add to the forage inventory for next year. 

When it comes to cost, replacing damaged alfalfa with corn silage is the most expensive, at about $760 per acre, but provides the highest tonnage. 

Italian ryegrass, though a one-year option, is a high quality grass that can be used to replace alfalfa in dairy diets. If planted early, the cost is less than half that of establishing a new stand, about $75 per acre, and it will get close to the same yield as an alfalfa stand, about 3 - 4 ton per acre, according to Combs.  

Sorghum-sudangrass could also be an option for planting by July or August, but costs almost as much per acre as corn silage, about $600 per acre, and requires high temperatures. 

An early option Combs said is small grain silage planted in early spring and harvested in early or mid July, which would provide about 2-3 tons of dairy quality feed per acre for establishment costs of about $65 per acre. 

Direct seeding alfalfa in spring on a new stand would yield about 2 ton per acre compared to 5-6 tons per acre from an existing stand and would include establishment costs of $160 per acre. 

Combs cautions when seeding alfalfa into corn or soybean stands that haven't been planned until this year due to winter kill, "make sure you go back and check the herbicide application on that ground.

"There are many different herbicides that are used on corn and soybeans that have residual effects for up to two years and inhibit seedling establishment of alfalfa," said Combs."So watch out for herbicide carryover."

Interseeding

Combs said producers ask about thickening up an existing alfalfa stand with grass.

"We usually don’t recommend that. The reason for that is because we don’t increase the yield," said Combs. "We can improve alfalfa fields killed by ice sheeting by seeding those dead spots with something like ryegrass."

Ryegrass is a good crop for replacing lost alfalfa stands due to ice sheeting or flooding because it grows the fastest and those spots are usually low and damp and ryegrass needs moisture. However, it doesn't work well for hay production since it doesn't dry at the same rate as alfalfa. Ryegrass is a better option for silage. 

Small grain forages, such as oats, peas or barley is another option. Combs said planting the small grains early and taking it off as it comes into boot stage yields almost as much as alfalfa. If planting is delayed until June or July, yields drop substantially. 

Adding peas has the additional benefit of a better quality feed for dairy cattle by reducing fiber and raising crude protein a little. 

"The key part of this is to try and get those plantings in early so that’s why this early assessment is really important," said Combs. "If you need a forage early this is a good option."

Nutrition

Whatever option producers choose in making up for lost alfalfa acres, Combs said diets have to be adjusted since taking out 6 pounds of fiber of alfalfa in a ration doesn't require the same amount of grass - probably closer to 3 pounds. 

"You will be feeding less grass than you would of the alfalfa because of the higher fiber content," said Combs. 

Grasses on a per pound basis are a little lower in energy and higher in fiber while corn silage is higher in energy.

"From a nutrition standpoint the advantage [of corn] is, it's a high energy feed and supports high levels of intake," Combs explained. "The downside is, a lot of that energy is coming from starch, so you're going to be pushing the starch levels in these diets higher if we take the alfalfa out pound for pound and replace it with corn."

Combs recommends formulating diets for cows to adjust the starch and reduce the risk of ruminal acidosis or other issues. Additionally, as corn silage in diets increases, crude protein and calcium decrease, which has to be brought in through supplements. 

"There's nothing wrong with adjusting alfalfa and corn silage ratios just make sure that you change grain and other things to try and hold those diets consistent and you should be alright," Combs added. 

Carol Spaeth-Bauer at 262-875-9490 or carol.spaeth-bauer@jrn.com. Follow her on Twitter at cspaethbauer or Facebook at https://www.facebook.com/carol.spaethbauer.