Evaluate Alfalfa Fields for Harvest Timing

Using PEAQ method is recommended to help you make alfalfa harvest timing decision for first cutting.

Predictive Equations for Alfalfa Quality, or PEAQ, is a method you can use to predict the forage quality of standing alfalfa. "It predicts forage quality based on the height of the tallest stem and maturity stage of the alfalfa field," explains Brian Lang, an ISU Extension field agronomist at Decorah in northeast Iowa. PEAQ is pronounced "peak" and you can use a specially marked "PEAQ" stick - which resembles a yardstick--to measure the Relative Feed Value of a standing alfalfa crop in a field to help you make your harvest timing decision.

The PEAQ method has worked very well as a "ball park" indicator to estimate the best time to make the first cutting of alfalfa, he says. ISU has a PEAQ fact sheet you can use to interpret your field. You can find it at www.extension.iastate.edu/butler/ along with an update on PEAQ readings in fields that are being monitored each week by ISU Extension in northeast Iowa.

Alfalfa has been running a little behind average this year in terms of growth. "It is important that farmers measure their own crop to determine the PEAQ value," says Lang. "On average alfalfa quality will drop 3 to 5 points in Relative Feed Value per day in the spring. It is recommended that you produce alfalfa forage around 150 RFV for milking dairy herds, and 120 to 130 RFV for heifers, stocker cattle and lactating beef cattle.

Typically, 15% of forage dry matter is lost

Under typical harvest conditions, 15% of the forage dry matter will be lost, says Lang. Therefore, it is suggested that you cut the hay at PEAQ readings of 165 to 170 RFV (bud stage alfalfa about 27 inches tall) to end up with harvested forage of approximately 150 RFV.

"Once alfalfa reaches about 25 inches tall and is in the bud stage, and the weather pattern is favorable for harvest, it is time to start the first crop harvest for dairy quality hay," he adds.

What happens when hail hits alfalfa?

Some areas of northeast Iowa received hail on May 25. Alfalfa that is significantly "cut" by hail should be harvested as soon as is feasible for two reasons, says Lang. First, to salvage the forage cut by the hail. And second, to provide for even regrowth for the second crop.

An additional common problem that often follows hail damage to alfalfa is an increase in leaf disease problems. The accompanying rain in the hail storm splashes disease inoculum from leaf residue on the soil surface onto the freshly open wounds on the plants caused by the hail. "However, since this hail storm came before the first crop harvest, there is a good chance that the harvest process will remove most of the newly-infected plant tissue and greatly reduce this disease potential," says Lang.

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