A comparison between reduced lignin and reference alfalfa varieties
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 structure 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 reduces the fiber digestibility of forages.
New alfalfa varieties with reduced lignin concentrations are now commercially available. 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 is best suited for high-producing livestock. This could allow for a wider optimal harvest window, making it possible for alfalfa growers to delay alfalfa harvest and achieve greater yields while still maintaining a high forage nutritive value.
Evaluating yield and forage quality
This study was designed to evaluate the yield and forage nutritive value of reduced lignin and reference alfalfa varieties when subject to diverse cutting treatments during the first production year. Alfalfa was planted at Becker, Rosemount, and St. Paul, MN in April 2015 and research was conducted during the 2016 growing season. Alfalfa varieties included the reference alfalfa varieties ‘54R02’, ‘DKA43-22RR’, and ‘WL355.RR’, as well as the reduced lignin variety ‘54HVX41’. Treatments included four cutting treatments with varying harvest frequencies ranging from 30- to 45-days. Forage yield, forage nutritive value, and plant maturity were measured.
Figure 1. Cumulative forage yield (tons per acre) by variety for alfalfa grown in Becker, Rosemount, and St. Paul, MN during the first production year (2016).
Cumulative forage yields for the first production year (2016) ranged from 6.6 to 9.8 tons per acre (T/A) (Figure 1). Yields were similar among alfalfa varieties at Rosemount and St. Paul. At Becker, yields for reduced lignin alfalfa (54HVX41) were less compared to reference varieties. As anticipated, yields were greater with a 40-day cutting schedule compared to a 30-day cutting schedule (average of 8.3 and 7.5 T/A across locations, respectively).
On average, reduced lignin alfalfa demonstrated an 8 percent reduction in acid detergent lignin (ADL) and a 10 percent increase in neutral detergent fiber digestibility (NDFD) compared to reference alfalfa varieties (average of 8.5% ADL and 30% NDFD; Table 1). Forage from reduced lignin alfalfa had similar crude protein (CP; 18%) and neutral detergent fiber (NDF; 42%) concentrations compared to reference alfalfa varieties (average of 18% CP and 43% NDF). As anticipated, cutting treatments with shorter harvest intervals generally resulted in higher forage nutritive values, including increased CP, decreased NDF and ADL, and increased NDFD compared to those with longer intervals between harvests.
Table 1. Average forage nutritive values for reduced lignin and reference alfalfa varieties grown in Becker, Rosemount and St. Paul, MN during the first production year (2016).
|Forage quality measures||Reduced lignin varieties||Reference varieties|
|Crude protein (%)||18.5||18.0|
|Neutral detergent fiber (NDF) (%)||42.0||42.9|
|Acid detergent lignin (ADL) (%)||7.9||8.5|
|Neutral detergent fiber digestibility (NDFD) (%)||33.5||29.7|
Forage quality over time
Figure 2. Predicted alfalfa relative forage quality averaged across locations for reduced lignin (54HVX41; y1) and reference alfalfa varieties (y2) in response to average cumulative growing degree days. Lines indicate predicted values, while the shaded areas indicate the 95% confidence interval for each line; non-overlapping confidence intervals indicate a significant difference between lines. Relative forage quality was increased for reduced lignin alfalfa from 772 to 1,248 GDD, which represents a range of cutting intervals between 28 and 40 days.
When relative forage quality (RFQ) was averaged over locations and expressed as a function of growing degree days (GDD), RFQ for reduced lignin alfalfa was greater from 772 to 1,248 GDD, which represents a range of cutting intervals between 28 and 40 days (Figure 2). The increase in RFQ observed for reduced lignin alfalfa across a wide range of GDD and cutting intervals demonstrates the potential of this new trait to provide increased flexibility for alfalfa growers.
Growers could choose to harvest reduced lignin alfalfa at the same time as reference varieties to obtain a more digestible forage, or could harvest reduced lignin alfalfa under a delayed cutting schedule and maintain forage quality across a lengthened harvest window. For example, reduced lignin alfalfa harvested on a 35-day cutting interval showed a 21 percent increase in yield and only a 3 percent reduction in RFQ compared to reference varieties harvested on a 30-day harvest interval (Figure 2). 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 high forage nutritive values.