Research update: Alfalfa cutting management

Figure 1. Project management dilemma of picking two priorities (left),
and alfalfa tradeoff priorities (right). Adapted from the Developer
Society (April 5, 2018)

M. Scott Wells – Extension forage and cropping system agronomist

Balancing alfalfa tradeoffs between yield, quality and persistence reminds me of the "Good, Fast, and Cheap" paradigm where only two can be selected (Figure 1; Dev. 2018).

Cheap and fast typically corresponds to lower quality work whereas fast and good tends to be expensive. But wait, what about good and cheap? From my experiences, good and cheap are seldom in alignment. Now substitute good, fast and cheap with alfalfa yield, quality, and persistence (Figure 1). It is easy to see that alfalfa management priorities also fit the project management paradigm with a few caveats.

Optimizing alfalfa production

Optimizing alfalfa tradeoffs is a bit more challenging than picking project management priorities. In the management paradigm, we are assured that any two priorities are selectable; however; in alfalfa, there may be a way to pick all three pairs. Before we explore the “pick-three” option, let’s discuss the “pick-two” options.

Pick two options

Alfalfa yield and persistence are a logical pairing, since delaying harvest does increase forage yields. It also potentially lessens year-to-year stress, so persistence increases.

Figure 2. Tradeoffs between alfalfa yield and quality as impacted by
alfalfa maturity stage. Adapted from the Alfalfa Management Guide.

Yield and quality, another pick-two pairing, are related, where both must be fully optimized (Figure 2). Historically, the last pairing, quality, and persistence are contradictory much like the good and cheap.

For example, let's assume an alfalfa farmer needs high-quality alfalfa and plans to reseed the alfalfa after four production years. This means that the farmer needs the alfalfa stand to deliver high-quality alfalfa each year for the four-year duration consistently. Here is the dilemma: When the farmer increases the cutting frequency to harvest less mature plants, they are lower in lignin and quality is improved. However, the alfalfa stands are less able to build up root reserves and are at a higher risk of reduced persistence (Brink and Marten, 1989). On the surface, the pick-three option isn’t apparent.

The pick three option

Recent advances in alfalfa breeding suggest emerging opportunities to attenuate these tradeoffs, potentially allowing for simultaneous improvements to quality, yield, and persistence (i.e., the pick-three). Modern alfalfa cultivars' regrowth potential (i.e., Fall Dormancy rating) has been primarily decoupled from winter hardiness, which may allow for both higher yields and persistence. Also, new alfalfa traits have directly improved alfalfa forage quality through the reduction of lignin which may accumulate greater yield while limiting reductions in relative feed value (Lamb et al., 2012; Grev et al., 2017).

Can modern alfalfa cultivars along with intensive management provide farmers with a pick-three solution? To address the question, a recent study evaluated eight modern cultivars with a range of fall dormancies (only two shown for brevity) for forage yield, quality, and persistence across four, five and six- annual harvest corresponding to 21, 28 and 45-day cutting intervals in Minnesota.

Study details

In the spring of 2014, the experiment was initiated at the Minnesota Research and Outreach centers located at Becker and St. Paul Minnesota. The project continued until spring 2017 at both locations.

• Alfalfa cultivars with Fall Dormancy (FD) ratings 2.1 (FD_2.1 - very dormant) and 5.0 (FD_5.0 - moderately dormant) were established into prepared seedbeds at 13 lb-live seed per acre. Lower dormancy ratings exhibit less fall growth.
• Weed control - Raptor and Poast were applied for broadleaf and grass control respectively.
• Insect pest control - Arctic 3.2 EC was applied when potato leafhoppers exceeded thresholds.
• Harvest - Alfalfa cultivars were harvested via a Carter forage harvester. Bulk yield samples were weighed fresh and subsampled for quality. Forage quality was determined using under near infrared reflectance spectroscopy.
• Stand assessment- In the spring of each year, plant densities were measured in two locations within each plot using a frequency grid.

Trial results

Yield

Figure 3. Total season alfalfa forage yield as influenced
 by alfalfa fall dormancy (FD) rating and harvest intervals.

Alfalfa total season-long yields were impacted by cultivar and harvest intervals. On average, the FD_5.0 cultivar produced 9 percent more biomass dry matter than the FD_2.1, and increasing harvest intervals increased alfalfa dry matter yield (Figure 3).

The 21-day harvest interval (5.0 ± 0.82 tons/acre ) produced less alfalfa dry matter than both the 28 and 45-day treatment (6.3 and 6.2 ± 0.82 tons/acre) respectively.

Both the cultivar and harvest interval impacts on alfalfa dry matter yield production are not surprising. The FD_5.0 has a fall dormancy rating 5, which may have contributed to greater regrowth potential when compared to the FD_2.1.

Forage quality

Figure 4. Relative Forage Quality as impacted  by
 alfalfa fall dormancy (FD) rating and harvest interval

Unlike forage dry matter yield, alfalfa Relative Forage Quality (RFQ) was not impacted by alfalfa cultivar with the average RFQ of 167.3 ± 7.6 for FD_5.0 and FD_2.1.

Although cultivars did not differ, RFQ was inversely proportional to harvest intervals (Figure 4). For each day increase in harvest interval, there was a -2.9 point decrease in RFQ.

Although increasing the harvest intervals (e.g., 21 to 45-day harvest intervals) did improve alfalfa dry matter yield (Figure 3), the delay in harvest negatively impacted RFQ with nearly a 40 percent reduction in RFQ between the 21 and the 45-day harvest intervals (Figure 4).

Milk production

Figure 5. Milk production (pounds milk per ton of alfalfa)
 as determined by alfalfa fall dormancy (FD) rating and
harvest intervals. 

The decrease in RFQ associated with harvesting older plants was no surprise, nor was the impact of higher quality alfalfa on milk production (Figure 5).

Both alfalfa cultivar and harvest interval impacted milk production where the FD_2.1 cultivar produced slightly more (approx. 1.6%) milk per ton of alfalfa than the FD_5.0 cultivar (Figure 5).

The forage quality reductions as a consequence of delaying harvest or increasing the interval between harvest did impact milk production at every level with nearly a 17% reduction in milk production between the 21 and 45-day harvest intervals (Figure 5).

Cutting alfalfa more frequently may reduce yield, but it does improve forage quality which can directly result in more milk production. But what about the pick-three option?

Alfalfa persistence

Figure 6. Alfalfa persistence in the third production year
 as impacted by alfalfa fall dormancy (FD) rating and
harvest intervals. 

Recall the third "pick-two" option was persistence and quality. Fortunately, neither alfalfa fall dormancy rating nor alfalfa harvest interval influenced the alfalfa persistence in the third production year.

There was a visible trend of increasing persistence with an a widening of the harvest intervals; however, the variation across the treatments was relatively high preventing detection of differences (Figure 6).

Picking all three

Based on this snapshot, picking all three is possible in alfalfa production. Predicting alfalfa persistence is not easy. There are many factors (e.g., management and weather) that impact the life and productivity of an alfalfa stand.

We have little control of the weather; however, management can play an essential role in maintaining highly productive stands that persist year after year. Even with the best management, Mother Nature has the final word, and alfalfa stands should be assessed every year.

When evaluating an alfalfa stand, ask yourself, do I have enough alfalfa in this field to meet my forage demands? There are several resources to help decided if there is sufficient high-quality alfalfa to met production goals.

Please visit Extension's forage production  website for more information. You might also be interested in Alfalfa winter injury assessment and management.

Additional contributors

James Eckberg, Jake Jungers, and Craig Sheaffer.

References

Grev, A.M., M. Scott Wells, D.A. Samac, K.L. Martinson, and C.C. Sheaffer. 2017. Forage accumulation and nutritive value of reduced lignin and reference alfalfa cultivars. Agron. J. 109(6): 2749–2761. doi: 10.2134/agronj2017.04.0237.

Lamb, J.A.F.S., H.J.G. Jung, and H. Riday. 2012. Harvest impacts on alfalfa stem neutral detergent fiber concentration and digestibility and cell wall concentration and composition. Crop Sci. 52(5): 2402–2412. doi: 10.2135/cropsci2012.01.0027.

Brink, G., and G. Marten. 1989. Harvest management of alfalfa-nutrient yield vs. forage quality, and relationship to persistence. J. Prod. Agric. 2: 32–36.