No. 7 Article 1/May 9, 2008

Time for Alfalfa Watch

Alfalfa producers, consultants, and dealers across Illinois can benefit now from the Alfalfa Watch project, which provides information about plant development and quality and helps with timing the first cutting. Alfalfa plant growth and nutrient quality indicators are reported twice weekly at the Illinois Predictive Equations for Alfalfa Quality (PEAQ) Web site.

People involved with the Alfalfa Watch project estimate preharvest quality in the field using the PEAQ technique, which involves predicting fiber and relative feed value (RFV) based on the height of the tallest stem and the stage of plant maturity in a sampling area. The method, developed at the University of Wisconsin, has been used in Illinois for 12 consecutive years; it is a reliable guide for determining the optimal harvest date for the first cutting. At the Web site you can calculate PEAQ, enter and track your own PEAQ values, and view PEAQ values by Illinois county and region.

To obtain 150 RFV of harvested forage, you need to cut alfalfa at 165 to 170 RFV (predicted using PEAQ), because about 15 to 20 RFV units are lost during harvest and storage. Some fields in southern Illinois are at this point or rapidly approaching it. 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. The adjustment means that alfalfa may have to be harvested prior to 165 to 170 RFV as indicated by PEAQ.

PEAQ is not designed to balance rations, nor does it account for quality changes due to wilting, harvesting, or storage. The procedure is most accurate for good, healthy stands of pure alfalfa. Many alfalfa seed companies have PEAQ measuring sticks that indicate the RFV of standing alfalfa based on height and stage of maturity.

Lastly, producers need to balance the PEAQ technique with short-term weather forecasts. Timely harvest of alfalfa is one of the best approaches for obtaining high-quality forage.--Jim Morrison

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