Predictive Equations of Alfalfa Quality (PEAQ) provides an estimate of the Relative Feed Value (RFV), for the first cutting alfalfa standing in the field. Climatic variations impact alfalfa growth and development making it impossible to use a calendar date each spring to best determine when to harvest the first crop. The PEAQ method uses alfalfa stand height and maturity stage to estimate the RFV. It is most appropriate for good stands of pure alfalfa with healthy growth.
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. Typically, the RFV of first crop alfalfa will decline three to five points per day as the crop matures. Under the best conditions, 10 to 20 percent of the forage dry matter will be lost at harvest. This amounts to approximately 15 RFV points for haylage and 25 RFV points for hay. Therefore, to end up with 150 RFV alfalfa, you should harvest the crop when PEAQ measurements predict a RFV of 165 to 175 for the standing forage.
Since the first cutting is usually has the highest yield with 35-40 percent of the year’s total crop, it is important that it is the quality forage your operation needs. Making the first cutting at an immature stage and it becomes difficult to feed because its fiber level is too low for most high producing cows plus it can lower the life of alfalfa stands. Timely cutting permits aftermath growth to begin at a time when temperature and soil moisture are favorable for plant growth and generally increases total yield per acre.
Each year I monitor alfalfa fields in Sioux and Plymouth counties and the information is posted on our ISUEO Dairy Team website, added to my Northwest Iowa Dairy Outlook blog and included in weekly news releases to local papers.
If you are interested in monitoring your own fields, here are the steps to make the evaluations yourself.
Step 1: Choose a representative area in the field and mark it so you can come back to it for each reading.
Step 2: Determine the most mature alfalfa stems in the area. Determine if the most mature stems are vegetative, bud or flower stage.
Step 3: Measure the tallest stems in the area. The tallest stems may not be the most mature stems. Measure from the soil surface to the tip of the stem. Straighten the stem for an accurate measure of height.
Step 4: Based on stem maturity and stem height, estimate the RFV of standing alfalfa crop using the PEAQ Fact Sheet at: http://www.extension.iastate.edu/dairyteam/files/page/files/PEAQ.pdf
Step 5: Subtract 15 to 25 RFV units to account for harvest losses during the haylage or hay harvest process, respectively to estimate harvested quality.
Step 6: Determine your optimum harvest time using the PEAQ estimate, your livestock forage quality needs, considerations of upcoming weather forecasts favorable for harvest or not, and the general assumption that RFV drops about four points per day.
For more information contact me at 712.737.4230.