No. 7 Article 1/May 7, 2004

Time for Alfalfa Watch

To help alfalfa producers monitor quality and plant growth and decide the date of first cutting, 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 made available at 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 consists of predicting fiber and relative feed value (RFV) based on the height of the tallest stem and stage of maturity in a sampling area. The method, developed by researchers at the University of Wisconsin at Madison, has been used in Illinois for many years and is a reliable guide for determining the optimum harvest date for the first cutting. Many alfalfa seed companies have a PEAQ measuring stick that indicates the RFV of standing alfalfa based on the height and stage of maturity.

About 15% of the dry matter is lost during harvesting, so to obtain harvested forage of 150 RFV, a producer should 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 prior to the 165 to 170 RFV mentioned previously. Also, producers should balance the PEAQ technique with short-term weather forecasts.

PEAQ is not designed to balance rations. It does not account for quality changes due to 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 either by stage of maturity or by harvest interval.

At the PEAQ 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 more. If you do not have access to the Internet to check the Web site, you can contact your local Extension office.--Jim Morrison

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