Research update: Performance of reduced lignin alfalfa
Alfalfa is widely used as forage for livestock due to its high nutrient content. However, the digestibility and utilization of alfalfa by these animals is hampered by its lignin content. Lignin is a complex structural polymer that makes up part of the fibrous portion of plants. While it provides the strength and rigidity necessary for a plant to stand upright, lignin is an indigestible component of plants and therefore reduces the fiber digestibility of forages such as alfalfa. In recent years, researchers have developed new alfalfa varieties with reduced lignin concentrations. These varieties have potential to increase the feeding value of alfalfa through increased forage digestibility. In addition, improvements in forage nutritive value may lengthen the time period when alfalfa has a forage nutritive value suitable for high-producing cows. This could allow for a wider optimal harvest window, making it possible for alfalfa growers to achieve greater yields by delaying alfalfa harvest while still maintaining acceptable forage nutritive value.
We conducted a study to evaluate forage yield and nutritive values for reduced lignin and reference alfalfa varieties when subject to diverse cutting treatments during the establishment and first production year. Research was completed at the University of Minnesota Agricultural Experiment Stations at St. Paul, Becker, Rosemount, and Rochester during the 2015 and 2016 growing seasons. All sites were planted the last week of April in 2015. Treatments included four cutting treatments with varying harvest frequencies. Four alfalfa varieties, three reference cultivars, and one reduced lignin variety. Prior to harvest, hand samples were taken to determine plant maturity and forage nutritive value. Alfalfa yields were then determined by mechanically harvesting plots using a flail harvester.
Cumulative forage yields ranged from 2.6 to 4.4 tons per acre during the seeding year (2015) and from 6.6 to 9.8 tons per acre during the first production year (2016). Yield differences among varieties were minimal, although yields for reduced lignin cultivar were reduced compared to reference cultivars at some locations. During the seeding year, yields were improved with the addition of a fall cut. During the first production year, yields were greater under wider harvest intervals compared to the 30-day cutting treatment.
Compared to the reference alfalfa cultivars, the reduced lignin alfalfa cultivar generally had reduced acid detergent lignin (ADL) concentrations, increased neutral detergent fiber digestibility (NDFD) predictions, and similar crude protein (CP) and neutral detergent fiber (NDF) concentrations. On average, the reduced lignin alfalfa cultivar demonstrated an 8% reduction in ADL and a 10% increase in NDFD. Cutting treatments with shorter harvest intervals generally resulted in higher forage nutritive values, including increased CP concentrations, decreased NDF and ADL concentrations, and increased NDFD predictions.
While these results are promising, much of the variability in the digestibility and intake of alfalfa can be associated with variations in cell wall concentrations. To assess this, the University of Minnesota is conducting additional research designed to further characterize changes in morphological development and to compare the forage nutritive value of stem and leaf fractions for reduced lignin and reference alfalfa varieties.