Jerry Ackermann, Lakefield, MN, has always wanted to monitor his alfalfa yields — just as he does for corn and soybeans.

This coming season he'll get to, now that the first yield monitor for big square balers is on the market.

From Harvest Tec, Hudson, WI, the monitor records tonnage, field position and moisture, says Jeff Roberts, company president. “I think 30-40% of combines have yield monitors on them. We're trying to give people with haying operations the same kind of tracking information,” he says.

“It will really be useful on alfalfa, especially on rolling ground,” enthuses Ackermann. He and his wife, Nancy, who grow 350 acres of alfalfa and 300 each of corn and soybeans, field-tested the yield monitor. They want to use its yield data to generate maps for variable-rate fertilizer application.

Actually, the Ackermanns worked with Roberts a few years ago, testing preservative applicators. That's when they urged him to create the yield monitor.

“Variable-rate applicators tell you how many tons per hour you're baling, what the moisture is and so forth,” Jerry Ackermann says. “I thought there should be a way to put that information on a map, take it to my fertilizer dealer and say, ‘Here's what we took off for yield and where it came off. Spread accordingly.’”

The yield monitor's baler-mounted sensors are two star wheels that measure crop flow and moisture. A GPS satellite receiver records field position. The information, stored to a data card, can then be transferred to a computer. Most field-mapping software can generate the yield maps.

The unit the Ackermanns tried last fall, on a 20-acre field, worked “flawlessly” and tested accurately, Jerry Ackermann says.

Roberts estimates that it's accurate plus or minus 2-4% of total yield based on the operator's accuracy in estimating bale weight. Since the system does not have a scale, a grower enters an average bale weight into the monitor, then must adjust that weight as bale density varies.

Ackermann bought an inexpensive hydraulic scale from Weigh-All Inc., Fort Gibson, OK, that he uses on his front-end loader to weigh bales. He calibrates it to a more accurate scale in town.

“If we start baling at 21% using preservative and the moisture comes down to 17%, we know the bales are going to be a little bit lighter. Then we have to adjust our inputs into the monitor. Once you calculate your scale on the loader, it doesn't take more than 30 seconds,” to estimate those new inputs.

The Ackermanns sell 3 × 3 bales to dairy, beef, sheep and goat producers and horse owners. They also custom bale and combine.

Nancy Ackermann says they'll probably offer yield maps to custom baling clients, but don't expect they'll be paid more for them.

Her husband says he's been telling others, at winter meetings, of how well the monitor tested. “A couple of people gave me their names and said to have Jeff get in touch with them, because they're definitely interested in it.”

To contact Harvest Tec, call 800-635-7468 or visit

For information on weighing with a front-end loader, visit: