Has this ever happened to you? You finish harvesting a beautiful field of alfalfa, only to find out later the lab results showed the stand was only average. You wonder, what happened?

According to David Weakly, director of dairy forage nutrition for Forage Genetics International in West Salem, Wis., the cause is likely due to alfalfa leaf loss.

Quality alfalfa

“One of the major factors negatively impacting harvested alfalfa quality is leaf loss,” Weakly said during a forage seminar held at World Dairy Expo in Madison, Wis.

He said if you have ever wondered, while looking at lab test results, why relative forage quality (RFQ) is so low when neutral detergent fiber (NDF) is so high, then leaf loss likely is the culprit.

“University of Wisconsin research has shown that leaf percentage accounts for 71% of the variation in forage quality,” Weakly said. “Leaves have an RFQ of approximately 550, while stems have an RFQ of only 70 to 80.”

Standard alfalfa should have 50% leaves.

In 2019, Weakly and his associates at Forage Genetics International separated the leaves and stems from 160 alfalfa samples to measure the percentage of leaves. A total of 43 varieties of alfalfa were harvested using a variety of cutting schedules — 28, 33, 35 or 38 days — across a range of cuttings (first through third). In 2020, 40 new whole-plant samples were collected using similar methods to the previous year.

“Those samples were run through the same protocols to be used to validate the accuracy of the percent leaf prediction equation developed in 2019,” Weakly explained.

The findings from the 2020 validation set of 40 samples showed that the standard error of the prediction was very low (2.86 percentage units of leaves) across a wide range of 35% to 64% leaves in the samples.

“The samples were dried and weighed, and we then compared the nutrient content with the percentage of leaves to develop a prediction equation,” Weakly said. “This indicated the leaf prediction equation can be off by an average of only 2.86% of leaves on a sample.”

These 40 samples were added to the original 160 samples, and a new prediction equation called LEAF (leaves enhance alfalfa forage) was developed that predicts percent leaves in alfalfa from NDF and protein and other nutrients measured in the sample.

Weakly said a 1% unit loss in leaves translates into a $7-per-ton loss in the value of alfalfa.

Factors affecting leaf loss in alfalfa include:

What to do

Weakly said if the LEAF percentage is greater than 45%, then your goal is achieved and no action needs to be taken.

If the LEAF percentage loss is 40% to 45%, then be cautious — there is room for improvement.

“If the LEAF percentage loss is greater than 45%, then significant leaf loss has occurred, and you should contact your agronomist to evaluate areas of alfalfa management improvement,” he said. Weakly said growers should consider using more disease- or pest-resistant alfalfa varieties, applying fungicide, and improving harvest management.

How can growers get the LEAF test? Submit your alfalfa sample to a licensed lab for the Calibrate HQ analysis available at SureTech Labs, Dairyland Labs, Rock River Labs, Cumberland Valley and Dairy One.

More information about the LEAF test and Calibrate is available by contacting the labs listed here or emailing [email protected].