Growers know that alfalfa yields taper off after first cutting, a fact borne out in 25 years of forage yield research by University of Wisconsin.
This year, however, ample moisture and cooler weather are setting the stage for an excellent hay crop. “It’s going to be cool and there may be problems with harvest, but there is potential for very high yields and good quality yields,” said Dr. Dan Undersander, UW Extension professor of agronomist, during “Quality and Quantity: Reap the Most All Summer Long”.
The July 2 on-line presentation was the second of a three-part World Class Webinar, “Fantastic Forage: Step-by-Step Through This Year’s Crop Season” being presented by Professional Dairy Producers of Wisconsin.
According to Undersander, the total yield for a three cutting system breaks down to 45 percent at first cutting, 25 percent at second and 30 percent at third. A four-cutting system is typically 35 percent, 25 percent, 20 percent and 20 percent. The question is how to raise yields in later cuttings.
Alfalfa growers need to recognize that there are particulars they cannot control, starting with the temperature. Top growth initiates at 46-50 degrees and stops at 95 degrees, while the optimum temperature for root growth is 69 -76 degrees. The optimum is 80 degree days and 70 degrees night.
Growth tapers off to zero on really hot days, Undersander noted. That change in yields is even more dramatic for grasses, which have an optimum temperature of 75 degrees.
Soil moisture is another uncontrollable issue. Grasses and, particularly, alfalfa need moisture as they begin to regrow. According to Undersander, good soil moisture the first two weeks after cutting promotes root growth and high yield potential. “The good news, for the most part, we will be at a good soil moisture level this year,” he said. “We’ve also been on the cool side this year, where in previous years, we were into the 90s and 100s.”
Among the things alfalfa growers can control is how often and when the plants get run over. Pay attention to wheel traffic, Undersander advised, since studies show traffic each day after mowing breaks stems and reduced yield of the next cutting by 6 percent a day.
“That’s why haylage fields yield more than hay fields”, he noted. “Haylage-making is a good way to increase our yields.”
It appears contract harvesting is beneficial on many farms for that reason. One of the largest selling mowers in Wisconsin was a 10 foot model, likely pulled by a tractor with 18 inch tires. “The point as the field is getting covered 80-90 percent with wheel traffic per cutting,” Undersander said. With a custom harvester’s 36-foot-wide mower, wheel traffic is vastly reduced.
When round balers are used, consider a bale accumulator to eliminate the need to drive separately over the field to collect the bales, which causes compaction and, more importantly, breaks off alfalfa stems.
Another controllable issue is insects which, left to themselves, can eat into yields. Although potato leaf hopper can be a problem in Wisconsin, rain tends to wash them off the crops. “There is little leaf hopper issues this year,” Undersander observed.
This year, aphids are making an appearance, which is a little unusual. “The damage they do is not as visible, so you need to walk the fields,” Undersander said.
There is an ongoing discussion concerning the ability of fungicidal applications to increase yields. There’s been a lot of interest in Headliner, Undersander noted. With fungicide costs of $35 an acre and hay running between $100-$200 a ton, he now considers it an economical consideration.
Fungicides do provide some control of diseases like anthracnose, rust, leaf spot and powdery mildew. “We have seen fungicides most beneficial on first cutting, which tends to be a cool and wet crop,” Undersander said. “This year, it probably would have been beneficial on second crop.”
The problem is fungicides have to be applied before the grower knows he has a disease problem. Some premium varieties of alfalfa have good disease resistance, he added, which means they will have less response to fungicide treatments, particularly after first cutting.
Tests show a mixed bag of results and the need for more data. “I will say, frankly, that the majority of the time, we have not seen an economic response,” Undersander said, noting tests were conducted in drier years. “However, a lot of farmers along the eastern coast of Wisconsin, where it’s cooler and wetter, tell me they’ve seen really significant response.”
With first cutting, another important issue is fungicides are only effective for two or three weeks. “So if you put it on and disease occurs at four weeks, it still doesn’t help you,” he observed.
In cool, wet years, Undersander thinks fungicides are probably a good idea. Application of a fungicide is economical if disease occurs, he pointed out, with yield responses up to half and three-quarters of a ton per acre possible.
Fertilizing for high yields
Alfalfa growers can also control soil nutrients and soil pH, “I am surprised at how many people are not really fertilizing as well as they should. You need to feed the forage, just like you do the cattle on your farm,” Undersander stressed.
Everyone, in this day and age, should be sending in samples for tissue tests prior to harvest for mineral analysis, he said. Fertilize to replace what the alfalfa plants are removing. For high yields, the important nutrients include phosphorus (which is often a limitation), potassium, sulfur and boron.
Soil pH is important for nutrient availability and optimum alfalfa growth, and should run about 6.8 for good yield and regrowth. If it doesn’t, alfalfa plants will be more susceptible to disease, not as thrifty and nodules won’t function as well as they could. Bear in mind that lime needs to be put on a year ahead of time.
The amount of nutrients removed per ton of alfalfa is 14 pounds of phosphate and 50-55 pounds of potassium, as well as sulfur, boron, calcium and magnesium. The latter two are seldom issues in Wisconsin soils, although sulfur levels are an emerging issue. “We used to get 15 to 20 pounds of sulfur in acid rain. Now it’s one or two pounds, and we need to make that up,” Undersander explained.
In addition, while corn grain removes little sulfur, corn silage removes sulfur at the same rate as alfalfa. A deficiency in alfalfa shows in the leaves turning yellow, although the yield reduction usually occurs first.
Although a lot of soil tests provide a sulfur analysis, Undersander said it is basically not worth the paper it’s written on. “The only way to tell if your crops need sulfur is to do a tissue test,” he said.
He recommends split applications for sulfur, based on yields, and applying one or 2 pounds of boron annually.
When manure is applied to the fields, most of the potassium can be recycled on the farm. “The real issue is: are we getting it back on the fields and are we letting it be reused?” Undersander asked. Most of the potassium is in the urine, he explained. “We need to pay more attention to this, getting that liquid back on the fields.”
Phosphate is generally adequate through manure, while potash should be applied in split applications according to yield. Apply one portion after first cutting and another after cutting around the first of September. If the entire amount is put on after the first cutting, the alfalfa will take up more off than it needs and run out by the end of the year.
For the same reasons, sulfur should be applied in split applications, while boron should be applied at the rate of one or two pounds annually.