Carbohydrates (CHOs) produced through photosynthesis are stored in alfalfa roots and crowns to help develop cold hardiness and survive winter temperatures. In the spring the stored energy is used to initiate growth after dormancy and continued growth after each cutting. The use of stored CHOs slows when plants reach 6 to 8 inches in height because the plants can produce CHOs during photosynthesis. At this stage, more energy is produced and stored in the roots and crowns than used for growth. Storing CHOs continues and reaches their highest level at about full flower (Figure 1).
Challenges may occur during the growing season that may cause the last cutting of the season to be late. When harvesting late, it is important to follow best management practices (BMPs) for the future success of the crop. The timing of a single cutting should not be made without considering the impact on future seasonal cuttings as several agronomic and marketing factors should be considered. The number of possible alfalfa cuttings varies by environmental conditions, field location, alfalfa product selection, and other management considerations. Key factors to also consider when determining harvest intervals include total seasonal tonnage potential, forage quality, the price spread between different quality categories, marketability of the crop, and the impact of cutting schedule on stand survival.
A late summer alfalfa cutting should be done early enough so plants can regrow, produce, and store adequate CHO reserves or be cut so late that plants do not regrow. This can help plants survive winter temperatures and use the stored CHO to regrow in the spring. Research has shown that a late fall cutting can be done if fewer than 200 Growing Degree Days (GDDs) occur after the cutting to prevent regrowth and depletion of stored CHOs. 1 If regrowth is desired prior to winter dormancy, about 500 GDDs are required to provide sufficient regrowth.
Deciding when to cut can be a difficult decision and no single cutting schedule can fit all situations. Alfalfa tonnage and quality potentials are almost always inversely related to a growth cycle.1 Shorter cutting intervals generally reduce tonnage potential and increase forage quality. Conversely, longer cutting intervals usually increase tonnage potential and reduce forage quality. As alfalfa matures, the quality decreases because the stem weight increases and lignin (tissue to help standability) becomes increasingly indigestible. Cutting alfalfa at immature growth stages can shorten the stand life, reduce plant health and population, and aid in the increase of weed populations.2
The need for quality versus tonnage depends on an operation's feed requirements or marketing if selling for revenue. Higher quality may add additional nutritional value while less cutting could increase tonnage. Seasonal or yearly alfalfa prices may support cutting more for tonnage over quality; however, the end user's needs should be considered. Therefore, cuttings should be flexible to market and user conditions.
Reducing the lignin content in alfalfa can increase the digestibility of alfalfa and allow for harvest to potentially occur up to 7 days after the plants are at their peak without a reduction in potential yield and quality.4 According to the USDA Forage Research Center, a 10% decrease in lignin could result in a milk production revenue increase of $350 million per year and a reduction in manure production of about 3 million tons per year.4
HarvXtra® Alfalfa with Roundup Ready® Technology (Figure 2) is a biotechnology-derived alfalfa product designed to ease the tonnage versus quality trade-off. Research conducted by Forage Genetics in 2015 demonstrated that HarvXtra Alfalfa with Roundup Ready Technology provided a marked, and statistically significant improvement over the commercial check products used in the test for acid detergent lignin (ADL) and percent of neutral detergent fiber digestibility (NDFD) at every sampling date in the experiment (p < 0.05).5 The lignin content in HarvXtra® Alfalfa with Roundup Ready® Technology was greater than two LSD units lower than the commercial checks at every sampling date and greater than 20% lower than any of the commercial check products at the last sampling date.5 The reduced lignin HarvXtra® Alfalfa with Roundup Ready® Technology product contains about 16 to 20% reduced lignin compared to related alfalfa lines without HarvXtra® Alfalfa with Roundup Ready® Technology.6
To realize the full potential of a HarvXtra® Alfalfa with Roundup Ready® Technology product, the first cutting should be harvested at the generally accepted time for conventional alfalfa products. The later cuttings can be delayed 7 to 8 days because the reduction in lignin allows for quality to be comparable to the first cutting and tonnage potentially higher because of taller plants (Figure 1).5
For the 2017 growing season, this product is available across the U.S. In the following states, purchase and use of HarvXtra® Alfalfa with Roundup Ready® Technology is subject to a Seed and Feed Use Agreement, requiring that products of this technology can only be used on farm or otherwise be used in the United States: Arizona, California, Colorado, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, Washington and Wyoming. In addition, due to the unique cropping practices do not plant HarvXtra® Alfalfa with Roundup Ready® Technology in Imperial County, California, pending import approval and until Forage Genetics International, LLC (FGI) grants express permission for such planting. As of June 2017, HarvXtra® Alfalfa with Roundup Ready®Technology has pending import approvals. GROWERS MUST DIRECT ANY PRODUCT PRODUCED FROM HARVXTRA® ALFALFA WITH ROUNDUP READY® TECHNOLOGY SEED OR CROPS (INCLUDING HAY AND HAY PRODUCTS) ONLY TO UNITED STATES DOMESTIC USE.
1 Undersander, D. and Bland, B. 2012. Late Summer Cutting Management of Alfalfa. University of Wisconsin. http://ipcm.wisc.edu/.
2 Orloff, S.B. and Putnam, D.H. 2007. Harvest strategies for alfalfa. Irrigated Alfalfa Management for Mediterranean and Desert Zones. University of California. Publication 8299.
3 Orloff, S. and Putnam, D. Balancing yield, quality and persistence. Proceedings, National Alfalfa Symposium, 13-15 December 2004 San Diego, CA, UC Cooperative Extension. University of California, Davis.
4 Laca, A. 2016. Low-lignin lowdown. AgWeb. Dairy Herd Management. www.dairyherd.com/magazine/low-lignin-lowdown.
5 Smith, R. Reduced or low lignin alfalfa: advantages for hay and grazing. University of Kentucky.
6 Forage Genetics International, LLC trials comparing HarvXtra® Alfalfa with Roundup Ready® Technology 2017 FD4 commercial varieties to commercial checks. Trials were seeded in 2013 and harvested in 2014 and 2015 in Nampa, ID; Touchet, WA; Boone, IA; West Salem, WI; and Mt. Joy, PA.
Combs, D. 2016. Low-lignin alfalfa varieties offer potential quality gains. Hay & Forage Grower®. hayandforage.com/article-490-low-lignin-alfalfa-varieties-offer-potential-quality-gains.html.
Web sources verified 07/12/2017.