Calibration assesses nutrient profile of mixed forages

Calibration assesses nutrient profile of mixed forages

Cornell researchers fine-tune NIRS calibrations for mixed grass/legume forages grown in Northeast and think process may be used in other regions.

It is important for farmers to watch what their cows are eating to make sure the cows are getting the right amounts of grass and legumes. When the grass and legumes are grown together, however, it’s difficult to accurately measure how much of each is in the mixture.

Cornell University professor of agriculture Jerry Cherney said commercial laboratories can only tell if samples are “mostly grass” or “mostly legume.” This type of crude estimate just doesn’t cut it; farmers need to know what percentage of the mixture is legumes and what percentage is grass so they can make sure their cows are getting a healthy, balanced diet.

Cornell University researcher Ken Paddock assessing a mixed forage stand on Beck Farms LP in Freeville, NY. Credit: Seth Paddock.

To more accurately measure the composition of these forage mixtures, researchers have started using near-infrared reflectance spectroscopy (NIRS).

Legume and grass molecules vibrate at different frequencies, emitting invisible energy known as infrared. Scientists can use instruments to measure specific near-infrared wavelengths and then, based on those measurements, determine what percentage of a mixture is legumes and what percentage is grass.

Still, NIRS has its challenges. Mainly, in order to provide accurate measurements, the instruments need to be calibrated.

“In the past, NIRS calibrations were typically instrument-specific; they only worked with the instrument used to develop the calibration,” Cherney explained.

So, Cherney and his team of researchers worked to develop a single calibration that could be used with many different NIRS instruments.

The research team collected samples from mixed forage fields of alfalfa and grass at 91 sites throughout eight counties in New York. They collected three years of samples to develop their calibration and collected another year of samples to use later to verify their calibration. After collecting the samples, they separated the alfalfa from the grass. Then, they made more than 500 samples that were mixtures with known percentages of alfalfa and grass.

Next, Cherney worked with Dairy One, a commercial forage testing laboratory, to scan the samples. All of the samples were scanned twice, and then the researchers used three different instruments to analyze the scans. With the analyses from the three instruments, the researchers developed four calibrations: one for each instrument individually, and one for all three instruments combined. Finally, the team tested whether the calibrations worked.

They took the final year's samples and combined them into random known proportions. They scanned and analyzed these 98 samples to see if the calibration from the three instruments combined was still accurately measuring the amounts of alfalfa and grass.

Ultimately, Cherney was able to show that a single calibration can measure alfalfa and grass percentages across instruments. This is great news for farmers and their cows in the northeastern U.S., as farmers now have more accurate information about what’s in the feed their cows are eating.

“While we’re confident that the calibration should work for sites in the northeastern U.S., we are not sure if it works for midwestern-grown mixtures,” Cherney explained. Calibrations for other parts of the country, like the Midwest, can be developed using the same process Cherney followed in the Northeast.

Read more about Cherney’s work in Crop Science.

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