No. 6 Article 1/May 5, 2006

Alfalfa Watch

Alfalfa producers and dealers in the northern half of Illinois can still benefit from the Alfalfa Watch project, which provides assistance for monitoring plant quality and growth and for timing the first cutting. Alfalfa Watch estimates preharvest quality in the field using the Predictive Equations of Alfalfa Quality (PEAQ) technique. 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 specialists at the University of Wisconsin, has been used in Illinois for many years, and it is a reliable guide to determine the optimum harvest date for first cutting.

Alfalfa plant development and nutrient quality indicators are reported twice weekly on the Illinois Predictive Equations for Alfalfa Quality Web site (peaq.traill.uiuc.edu), where you can calculate PEAQ, enter and track your own PEAQ values, and view PEAQ values by county and region in Illinois.

Because approximately 15 RFV units are lost during harvest, alfalfa needs to be cut at 165 to 170 RFV, as determined by PEAQ, to have 150 RFV of harvested forage. 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 165 to 170 RFV.

PEAQ is not designed to balance rations and does not account for quality changes due to wilting, harvesting, or storage. The procedure is most accurate for good, healthy stands of pure alfalfa. Subsequent cuttings for high quality can be made by either stage of maturity or harvest interval.

Many alfalfa seed companies have PEAQ measuring sticks that indicate the RFV of standing alfalfa based on the height and stage of maturity.

Lastly, producers need to balance the PEAQ technique with short-time weather forecasts.--Jim Morrison

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