No. 7 Article 4/May 11, 2007

Determine Optimum First-Cutting Date with Alfalfa Watch

Alfalfa producers and dealers in the northern half of Illinois can benefit now from the Alfalfa Watch project, which monitors plant development and quality and helps time the first cutting. Alfalfa plant growth and nutrient quality indicators are reported twice weekly. The project is not being conducted in the southern third of Illinois because of cold weather damage to alfalfa there. (See comments below regarding impact of cold temperatures on PEAQ.)

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 plant maturity within a sampling area. The method, developed by the University of Wisconsin, has been used in Illinois for many years, and it's a reliable guide to determining the optimum harvest date for first cutting. At the Web site you can calculate PEAQ, enter and track your own PEAQ values, and view PEAQ values by county and region in Illinois.

Since approximately 15 RFV units are lost during harvest, alfalfa needs to be cut at 165 to 170 RFV using 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 prior to 165 to 170 RFV as indicated by PEAQ.

This year, cutting based on PEAQ may need to be modified to reflect plant damage from the cold temperatures the first week in April. The general recommendation is to allow injured alfalfa to mature longer before cutting. This will help build up carbohydrates for subsequent production. If the stand was severely injured, first cutting should be delayed till bloom stage. With limited injury, allow the alfalfa to be perhaps 10% bloom, at the second or third cutting.

PEAQ is not designed to balance rations, and it does not account for quality changes due to wilting, harvesting, and 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 the height and stage of maturity.

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

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