When should you take the first cutting of alfalfa for high quality? Traditionally, the crop has been harvested at a certain stage of maturity or by a calendar date. Variations in weather and growth patterns from year to year cause these to be unreliable methods.
To help alfalfa producers in monitoring quality and plant growth, University of Illinois Extension again is conducting the Alfalfa Watch project across the state. Alfalfa plant development and nutrient quality indicators are being reported twice weekly and are provided to local Extension offices, through various media, and on the Web at http://peaq.outreach.uiuc.edu/.
What is Alfalfa Watch? The project uses a method of estimating preharvest quality in the field called PEAQ (Predictive Equations for Alfalfa Quality). PEAQ predicts fiber and relative feed value (RFV), based on the height of the tallest stem and stage of maturity within a sampling area. This method, developed by the University of Wisconsin at Madison, has been used in Illinois for many years and has been a reliable guide to help producers determine the optimal harvest date for the first cutting.
About 15% of the dry matter of alfalfa will be lost during harvesting, so to have harvested forage of 150 RFV, cut at 165 to 170 RFV, based on the in-field PEAQ estimate.
A change of 3 to 5 points of RFV per day in the standing forage has been noted, so adjustments need to be made for total harvesting time. This adjustment means that alfalfa may have to be harvested before the 165 to 170 RFV previously mentioned.
PEAQ is not designed to balance rations. It does not account for quality changes from wilting, harvesting, and storage. The procedure is most accurate for good stands of pure alfalfa in healthy condition. Subsequent cuttings for high quality can be made by either stage of maturity or harvest interval.
At the Web site, you can learn how to calculate PEAQ, view PEAQ values for Illinois by region and by county, enter and track your own PEAQ values, and so on. If you do not have access to the Internet to check the Web site, contact your Extension office.
Finally, many alfalfa seed companies have a PEAQ measuring stick that will indicate the RFV of standing alfalfa, based on the height and stage of maturity.--Jim Morrison