Determining Harvest Based on PEAQ
Dave Fischer
Dairy Extension Educator
Producing high quality alfalfa is essential to a profitable forage enterprise. Alfalfa producers face several challenges in deciding when is the optimum time to begin harvesting the first cutting. It is well documented that alfalfa nutrient quality decreases as the plant matures from the bud stage to full flower. At the same time, the pounds of plant material harvested per acre increases as the plant mature. Thus, the optimum harvest date is the compromise between the feed quality and the feed quantity produced.
University of Illinois Extension is in its 10th consecutive year of conducting the annual Illini PEAQ study at various locations around the state to assist Illinois alfalfa producers in monitoring plant growth and quality. Progress reports on the plant development and nutrient quality will be reported twice weekly for approximately four-six weeks at each location. The PEAQ monitoring results will be available on the PEAQ web site http://peaq.traill.uiuc.edu/, local radio or television stations, and print media sources.
Alfalfa producers will be encouraged to harvest the first cutting based on the relative feed value (RFV) of standing alfalfa. Keep in mind that the nutrient analysis in the field does not include harvesting and storing losses. Various research trials have shown that field and storage losses account for 15 to 20 points of RFV. Therefore, in order to strive for premium quality alfalfa, it would be necessary to harvest the crop when the field tests around 170 RFV.
First cutting alfalfa needs to be harvested as soon as the RFV in the field reaches 170 in order to achieve high quality and to set-up the cutting schedule for the rest of the growing season. Subsequent cuttings should be taken every 26 to 30 days. The first cutting must be taken in the bud stage since quality reduces rapidly as the plant matures. It may be difficult to make top quality first cutting alfalfa due to weather factors, coarse plant material, and possible weed and insect infestations. However, by prioritizing hay harvesting over all other cropping chores, many dairy and hay producers are able to make satisfactory first crop alfalfa. In addition, dairy producers may be forced to feed the first crop alfalfa to the milking herd because their past winter hay supply is exhausted, so it makes it even more critical to harvest hay that will be high enough in RFV.
The relative feed value is a measure of the fiber fractions, which dictate the digestibility and feed intake potential. The higher RFV, the higher quality feed value is obtained from the alfalfa. Relative feed value is a way to compare two or more similar forages for energy intake. Dairy producers with high producing cows often look for alfalfa with a RFV of 150 to 160 and higher. The crude protein content is not taken into account in the RFV calculation and needs to be evaluated separately. A common goal for dairy producers is to raise or buy alfalfa that has 20% or higher CP, 30% or lower ADF, and 40% or lower NDF which will equate to a RFV of near 150.
