Online Tool Helps Farmers Harvest Alfalfa at the Right Time

May 10, 2023
ICM News

Alfalfa growth has been slow this spring due to cooler than normal weather. This is a good reminder that using a calendar date to determine when to harvest the first crop of alfalfa may not be the best method. A better way to make harvest decisions is the PEAQ method (Predictive Equations for Alfalfa Quality) which takes several factors into account to roughly estimate the relative feed value (RFV) of standing alfalfa in the field.

Alfalfa measurement.
Caption: Measuring the tallest stem (16”) in the sample area. (Photo by Josh Michel)

PEAQ uses alfalfa height and maturity stage (vegetative, bud, or open flower) to estimate RFV. In general, it is recommended to harvest alfalfa at about 150 RFV for milking dairy herds and 125 RFV for heifers, stocker cattle and lactating beef cattle. The RFV of first crop alfalfa can drop three to five RFV points per day after it reaches peak value.

While PEAQ provides an estimate of RFV, adjustments also need to be made for harvest loss. Even under the best harvest conditions, 10-20% of the forage dry matter can be lost at harvest. This amounts to approximately 15 RFV points for haylage and 25 RFV points for dry hay. Therefore, to end up with 150 RFV alfalfa, harvest the crop when PEAQ measurements estimate a RFV of 165 for a haylage harvest and 175 for a hay harvest. Additionally, consider weather forecasts and allowing for proper drying time when deciding when to harvest alfalfa.

Steps for using PEAQ to determine when to harvest first crop alfalfa

Step 1. Choose a representative two square foot area in the field.

Step 2. Determine the stage of the most mature stem as defined in Table 1.

Step 3. Measure the tallest stem in the area. The tallest stem may not be the most mature stem. Measure the stem from the soil surface to the tip of the stem; not to the tip of the leaf. Straighten the stem for an accurate height measurement. Based on stem maturity and stem height, use Table 1 to estimate the RFV of standing alfalfa crop.

Step 4. Repeat steps 1-3 in five representative areas across the field.

Step 5. To estimate harvest quality, subtract 15-25 RFV units to account for harvest losses during the haylage or hay harvest process, respectively.

Step 6. Determine optimum harvest time using the PEAQ estimate, livestock forage quality needs, considerations of upcoming weather forecasts favorable for harvest and drying, and the general assumption that RFV drops three to five points per day.

Using the PEAQ method

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.

Table 1. Predictive equations for alfalfa quality (PEAQ).

Stage of the most mature stem
Height of the tallest stem
From soil surface to stemp tip.

Late vegetative stage
16 inches or more with no visible buds.

Bud stage
One or more nodes with visible buds.
No visible. flowers.

Flower stage
One or more nodes with an open flower.

Inches RFV
16 237 225 210
17 230 218 204
18 224 212 198
19 217 207 193
20 211 201 188
21 205 196 183
22 200 190 178
23 195 185 174
24 190 181 170
25 185 176 166
26 180 172 162
27 175 168 158
28 171 164 154
29 167 160 151
30 163 156 147
31 159 152 144
32 155 149


33 152 145 137
34 148 142 136
35 145 139 131
36 142 136 128
37 138 133 126
38 135 130 123
39 132 127 121
40 129 124 118



Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Integrated Crop Management News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on May 10, 2023. The information contained within may not be the most current and accurate depending on when it is accessed.


Joshua Michel Field Agronomist in NE Iowa

Joshua Michel joins ISU Extension and Outreach as a field agronomist after working at the Muscatine Island Research and Demonstration Farm. While at the farm he was responsible for coordinating corn and soybean field studies that included planting, harvesting, tillage and pest management. Mi...