Manage alfalfa quality losses with LEAF

Dr. David Weakley, Forage Genetics International director of forage nutrition research
One of the major factors negatively impacting harvested alfalfa forage quality is leaf loss. Leaf percentage accounts for 71% of variation in forage quality because leaves have a Relative Forage Quality (RFQ) of about 550 while stems have an RFQ of 70 to 80. Therefore, growers must know the percentage of leaves in their alfalfa to better manage quality losses while growing and harvesting their alfalfa.

Prediction equation development and accuracy
The Calibrate^® predicted alfalfa leaf percent equation was developed from work conducted at the FGI Gray Summit In Vitro Digestibility Lab from 2019 to 2020. This equation explained 84% of the variation in leaf percentage in the calibration sample set. When the equation was tested against an independent set of 40 samples, it showed the standard error of the prediction was extremely low across a wide range of 35% to 64% leaves across the samples. The standard error of the prediction tells you how “off” the regression prediction equation is on average. These 40 samples were added to the original 160 samples in the calibration sample set and a new prediction equation, LEAF™ (Leaves Enhance Alfalfa Forage), was developed that predicts percent leaves in alfalfa from NDF, protein and NDFd28 measured in the sample.

What Is a typical leaf percentage in alfalfa?
The LEAF equation was used to predict the leaf percentage of 360 samples of alfalfa that were collected during 2019 from across the U.S. and analyzed at the FGI Gray Summit In Vitro Digestibility Lab. The samples represented a wide range in quality, ranging in NDF from 16% to 67%, crude protein from 8% to 30%, and NDFd from 34% to 62%. The leaf percentages predicted ranged from 10% to 77%, with an average of 48% (standard deviation of 12.6%). When these sample data were combined with the calibration sample data, the average leaf percentage in alfalfa was approximately 50%, with a standard deviation close to 10%. Therefore, two-thirds of the sample population had a leaf percentage between 40% and 60%, which could be considered a “typical” range.

What causes leaf loss in alfalfa?

• Fungal and other diseases
• Mower/conditioner type and settings
• Rake type, excessive raking or raking when the alfalfa is less than 40% moisture
• Baler type and settings
• Grinding or excessive mixing of hay before feeding

How should I use the Calibrate predicted alfalfa leaf percent value?

If the LEAF percentage is less than 45%, evaluate areas for alfalfa management improvement. Consider options such as fungicide application, using more disease or pest resistant alfalfa varieties and don’t forget the many harvest management improvements that can be put into action.

How can I get this test?
The LEAF test has not been validated with alfalfa/grass mixed forages and is currently intended only for pure stands of alfalfa. Furthermore, the LEAF test has only been validated against nutrient inputs from the Calibrate High Quality Forage Analysis Test. Lab variation in these nutrient input measurements from other forage tests could likely affect the accuracy of the percent leaf predictions if they were used as replacement values in the LEAF test. Currently, the LEAF test is available as part of the Calibrate High Quality Forage Analysis results provided by SureTech^® Laboratories, Dairyland Laboratories, Inc., Cumberland Valley Analytical Services, Rock River Laboratory, Inc. and Dairy One.

Click here for more information about the development of the LEAF test.