NEWS for North Dakotans
Agriculture Communication, North Dakota State
University
7 Morrill Hall, Fargo, ND 58105-5665
May 21, 1998
North Dakota’s first alfalfa harvest will be earlier this year than it’s been in more than a quarter century—in some places as early as May 26, according Dwain Meyer, forage management specialist at North Dakota State University.
That’s why producers need to start watching their fields right now to be sure they catch their crop at the optimum harvest stage.
"People who normally harvest about the 10th to the 15th of June will probably be harvesting alfalfa in the last days of May to the first days of June this year," says Meyer. "That’s the time the crop will reach the mid-to late-bud stage, the stage many dairy producers like to shoot for."
The unusually early crop is the result of three weeks of unusually warm April temperatures combined with the right moisture.
How to evaluate the optimum stage for harvesting alfalfa?
"In the past the recommended stage was the late-bud to the 10-percent-blooming stage," says Meyer. "But today there’s a much more accurate system available to measure the feed quality of alfalfa standing in the field. It’s called the PEAQ system—which stands for Prediction Equation for Alfalfa Quality."
Here’s how to use it.
In a 30-acre alfalfa field go into five different areas. Select the most mature stem in each area and determine its maturity index using the following:
n Maturity index 2, the late vegetative stage—Stem is more than 12 inches tall, no visible buds or flowers.
n Maturity index 3, early bud stage—1 to 2 nodes with visible buds, no open flowers.
n Maturity index 4, late bud stage—More than 2 nodes with visible buds, no open flowers.
n Maturity index 5, early flower stage—1 node with at least one open flower
n Maturity index 6, late flower stage—2 or more nodes with open flowers.
In each of the areas also measure the height of the tallest stem, from the soil surface to the tip of the stem—not to the tip of the highest leaf. You can pick the same stem that you’ve already selected as the most mature, or a different one. Just so it’s the tallest.
Next, take the two numbers you’ve determined in one of the areas—the maturity index number and the height of the tallest stem in inches—and use them to solve the following two equations (the first equation gives the alfalfa’s NDF, or neutral detergent fiber, while the second gives the ADF, or acid detergent fiber):
NDF=15.86 + (0.69 x height) + (0.81 x maturity index)
ADF=10.78 + (0.53 x height) + (0.79 x maturity index)
Do this same thing for the other four representative areas you’ve selected, and then average the five NDF numbers and the five ADF numbers so you end up with an average NDF and an average ADF for the entire field.
Now convert these two averages to the average relative feed value for the field of alfalfa. To do this you’ll first need to find the percentage of digestible dry matter (DDM), then the percentage of dry matter intake (DMI). Using these two numbers you can find the relative feed value, or RFV.
Like this:
DDM= 88.9-(0.779 x ADF)
DMI= 120/NDF
RFV= (DDM x DMI)/1.29
"Producers should shoot for a relative feed value of 150 to 160 in the bale," says Meyer. "But whatever the relative feed value of alfalfa standing in the field, it will be less in the bale since there will be harvesting losses. The average producer will lose about 25 units of RFV in the harvesting procedure. That means if you want to harvest prime hay at 151, you’ve got to start harvesting when the RFV of alfalfa standing in the field is 175 or greater."
Many people will find it easier to determine NDF, ADF and RFV by using tables rather than equations. Tables are available from any county office of the North Dakota State University Extension Service, or may be found at http://www.ext.nodak.edu/aginfo/dairyext/alfalfa.htm on the World Wide Web.
Meyer notes that recent rains have caused some lodging in alfalfa fields. He warns that if alfalfa is lodged extensively, producers should consider harvesting it immediately since at that point the alfalfa won’t improve. "You’ll start to lose dry matter on the lower leaves of the canopy, and overall dry matter may actually start to decrease rather than increase in the field," he says.
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Source: Dwain Meyer (701) 231-8154
Editor: Barry Brissman (701) 231-7866