Estimating the First-Crop Alfalfa Harvest Using PEAQ

By Shelby Gruss

Alfalfa growth and development is influenced by several factors, including temperature, soil moisture, stand age, and variety. With a mild winter leading into spring this year, many areas are seeing earlier green-up and more rapid growth. As such, relying solely on the calendar to determine the timing of the first alfalfa cutting may not be the most accurate approach. The old rule of thumb cutting around Memorial Day weekend is becoming less reliable with increasingly warmer springs. To ensure high quality forage, producers should base harvest decisions on plant development, not just the calendar date.

To help producers better estimate the optimal harvest window, the University of Wisconsin developed the Predictive Equations for Alfalfa Quality (PEAQ) method. This method uses the height and maturity stage of the tallest alfalfa stem (vegetative, bud, or flower stage) to estimate relative feed value (RFV).

How to Use the PEAQ Method

1. Select a representative area (approximately 2 square feet) in your field.
2. Determine the stage of the most mature alfalfa stem vegetative, bud stage, or flower stage.
3. Measure the tallest stem from the soil surface to the tip of the stem (not the leaf tip), straighten the stem for accuracy.
4. Estimate the RFV using the PEAQ chart , based on the stem height and maturity stage.
5. Repeat in five areas of the field to get a reliable average.
6. Adjust for harvest losses, subtracting 15–25 points depending on whether you’re harvesting for haylage or hay.
7. Consider livestock needs, drying conditions, and forecasted weather to determine the best time to cut. Remember that RFV typically drops 3–5 points per day.

Using PEAQ to determine your first cutting date is very important to ensure you are meeting animal requirements; lactating dairy cattle need RFV of 140 or greater, while cow-calf needs ~ 125 RFV. Using the PEAQ method helps ensure harvesting at the correct time, particularly as the first harvest can be approximately 40% of the year’s total yield. 

Iowa State University Extension and Outreach maintains a PEAQ website that includes a fact sheet to explain how to use the PEAQ method to determine when to harvest first crop alfalfa. This website also includes postings of PEAQ values from alfalfa fields across Iowa that are monitored by Iowa State University Extension and Outreach staff. Following these reports is helpful in tracking alfalfa development but remember that crop conditions vary field-by-field. Therefore, it is recommended to take PEAQ measurements in your own field for the best assessment of when to harvest alfalfa for the optimum forage quality for your operation.