No. 4 Article 8/April 29, 2010

Predicting Optimum Dates for Alfalfa Harvest

In many areas alfalfa growth is ahead of normal, and some southern Illinois fields have already been harvested. Alfalfa producers, consultants, and dealers are encouraged to follow the "predictive equations for alfalfa quality" (PEAQ) technique, which predicts optimum dates for first cuttings by monitoring plant development and quality.

PEAQ consists of 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 by the University of Wisconsin, has been used in Illinois for many years and is a reliable guide. The Illini PEAQ website provides an overview of the technique and helps you calculate and track your own PEAQ values.

Since approximately 15 to 20 RFV units are lost during harvest and storage, alfalfa needs to be cut at 165 to 170 RFV calculated using PEAQ to have 150 RFV of harvested forage, which is recognized as high quality alfalfa. RFV of 172 infield equates to alfalfa 26 inches tall and in the bud stage.

A change in RFV of 3 to 5 points per day in the standing forage has been noted, so adjustments are needed for total harvesting time, meaning that alfalfa may have to be harvested prior to a PEAQ value of 165 to 170. Producers need to balance decisions based on the PEAQ technique with short-term weather forecasts and field conditions.

PEAQ predictions are most accurate for good, healthy stands of pure alfalfa. The method is not designed to balance rations, and it does not account for quality changes due to wilting, harvesting, and storage. Nutrient analysis will be needed to properly balance rations.

Many alfalfa seed companies have PEAQ measuring sticks that indicate the RFV of standing alfalfa based on height and stage of maturity. A PEAQ stick is also available through membership in the Illinois Forage and Grassland Council (618-664-3590, ext. 3).--Jim Morrison

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