Dan Martens, University of Minnesota Extension, reports that Extension is working with Central Minnesota Forage Council, agribusinesses and farmers on the Alfalfa Harvest Alert Project again this year.
The project helps growers with determining first-crop alfalfa quality and feed value. Accordingly, quality at cutting impacts feed and nutrition management.
Martens says cooperator sites have been arranged in Stearns, Benton, Morrison and Wright counties. Information will be shared from McLeod, Meeker and Carver counties, too.
Martens says when alfalfa is around 24 inches tall, growers can expect to see buds.
“At this time, forage tests could be in a range where harvesting for better-quality dairy hay makes sense if the weather looks favorable,” he says. “We normally anticipate harvesting alfalfa for milk-cow-quality hay during the last 10 days of May, but that can vary quite a bit with how spring unfolds. Last year, some alfalfa was cut prior to May 20. We are likely to see some variability this year because of winter conditions, and variability with spring weather.”
Project cooperators will sample fields on Monday and Thursday mornings starting when the crop is 14 to 16 inches tall to establish a trend line. Some project cooperators might start taking their first samples during the second week of May, he says.
Clipped samples are tested to determine relative feed value (RFV), neutral detergent fiber (NDF) and other alfalfa quality factors related to harvest decisions.
“We note the stage of maturity and the height of the tallest stems to estimate quality and maturity,” Martens says. “This is based on a predictive equation for alfalfa quality — known a PEAQ or ‘peek.'”
To take a PEAQ reading, use a specific PEAQ yardstick in a 2-foot-square area at several locations in the field. You measure the height of the tallest stem and the growth stage of the most mature stem to read the PEAQ charts (see tables).
The RFV numbers shown in the first table correspond to what you could expect from a fresh-cut sample lab test, Martens says. Because of harvest and storage losses, there could be a 15- to 25-point drop from what the PEAQ chart or a fresh-cut sample test indicates.
The Relative Feed Value Index estimates digestible dry matter of alfalfa from acid detergent fiber, and calculates the dry matter intake potential from neutral detergent fiber. The bottom line: Higher RFV values indicate higher forage quality.
“To get hay in the feed manager at 160 RFV, we might aim to start harvesting when the PEAQ chart or fresh-cut test shows 180 or 185,” he says. “Consider your own nutrition goals and past experience.”
Martens says growers also can use NDF as the gauge for harvest decisions.
“The goal might be to have hay in the manger with NDF less than 40, for example,” he says. “An NDF of 40 typically correlates with hay at about 150 RFV. NDF might increase 3 to 6 points from field samples' results to what will be in the manger.”
To have hay at less than 40 NDF, aim to harvest when PEAQ charts or fresh-cut tests are around 35, he says.
“Some farmers want to be closer to 35 NDF in the bunk,” he adds. See the second table for numbers from the PEAQ NDF chart.
Neutral detergent fiber consists of the slowly digested fibrous portions of the plant: hemicellulose, cellulose and lignin. NDF is a predictor of voluntary intake because it provides bulk or fill. In general, low NDF values are desired because NDF increases as forages mature.
Martens says Alfalfa Harvest Alert Project information will be shared with KASM 1150-AM and KLTF 960-AM radio in the Stearns-Benton-Morrison County area. Internet users can search for “Minnesota Extension crop news” for posted information.
You can check for messages on a voicemail box by calling 800-964-4929, and entering "5081" when it answers. Call 320-968-5077 if a local call to Foley. Other counties might be working with other radio stations and information access points, he adds.
For more information or if you have questions, contact Martens at 800-964-4929 or 320-968-5077 if a local call to Foley.
Source: U-M Extension