Managing risk at the first alfalfa harvest

Craig Sheaffer, Extension forage specialist,  Nathan Drewitz and Jared Goplen, Extension educators

Alfalfa harvest is risky business! Within a growing season, 3 or 4 harvests are usually taken, but the first harvest has the greatest opportunity for profit or loss. The first alfalfa crop is the biggest of the year comprising about 40% of the total season dry matter production. The forage quality potential is the also the highest, but declines most rapidly with maturity. We propose use of seasonal harvest schedules that vary the timing/maturity of each cutting to achieve, yield, quality, and stand persistence goals. Here are some factors to consider.

Spring weather

A delayed first harvest

 Low air temperatures and cloudiness in April and early May this year have delayed alfalfa growth; temperature patterns in late May will affect growth prior to typical first harvest times in Minnesota. We will need significantly warmer temperatures for the remainder of May to achieve adequate growing degree days for maturation. Using a potential growing degree requirement for alfalfa harvest of 700, it appears that even with above normal air temperatures, it will be challenging for the crop to reach bud stage in central and southern Minnesota by June 1. For more information, see Using growing degree days to plan early-season alfalfa harvests.

Poor drying

In late May and June, it is challenging to get a 2-3 day period with good drying weather and no rainfall.

• June is the rainiest month of the year (averaging about 4 inches), resulting in soils that are wetter than later in the summer. Moist soils increase drying times of cut forage.
• The chance of receiving at least a small amount of rainfall (>0.04”) on any given day is about 40% (i.e., 60% chance of no rain), so there is a narrow window for drying; the probability of 2 and 3 days of dry weather in a row in June is 36 and 22%, respectively.

Rainfall at any time after cutting of hay can result in significant losses of dry matter and nutrients. These losses are greatest for partially dried forage due to leaf shattering, leaching, and prolonged respiration. Total dry matter losses are possible, but often range from 20 to 30%. Nutrients in forage are especially affected by rainfall and can be as high as 25% per inch of rain. To reduce risks of rain damage:

• Carefully monitor weather patterns to identify favorable weather for alfalfa drying. It may be necessary to compromise on forage yield, quality, and persistence objectives (see below) in order to harvest a crop with minimal loss of dry matter yields and nutrients due to rainfall.
• Harvest forage as haylage or baleage at the first harvest to reduce field exposure times. In the spring when soils are moist, it can take 1-2 days to reach a forage moisture content of 60% but 3-5 days for forage to reach 20%. To read more, see Wrapping hay
• Use a mower conditioner to crush stems, and then spread the cut forage over about 70% of the cut sward to maximize capture of solar energy.
• Consider tedding of forage to speed up drying. See How does tedding affect alfalfa silage production?

A side bar: Make hay while the sun shines.

The sun’s energy is critical for drying cut alfalfa forage to moisture levels that are safe for hay storage (<20%), or haylage (65%). Standing alfalfa contains about 80% moisture and to achieve a forage moisture content of 20%, about 144 gallons of water/acre to be lost per ton of forage harvested.

Yield, quality, and persistent tradeoffs

Figure 1. The relationship between alfalfa maturity stage and
total forage, stem, and leaf yield and forage digestibility.
Source: C. Sheaffer in Undersander et al., 2014. Alfalfa
Management Guide

Forage yield and forage quality are affected by alfalfa maturity at harvest. Harvest timing recommendations are often based on a target maturity stage (Figure 1). With good haymaking weather, harvest schedule decisions need to be guided by the intended use of the forage. For example, the stage to cut alfalfa for dairy cattle ranges from the vegetative to early bud stage. Later stages may be harvested for animals with lower nutritional requirements. A review of alfalfa growth and development:

• Alfalfa maturity and harvest recommendations are described in terms of floral development. Alfalfa is a long-day plant (flowers when days are long( ~12-15 hour), but flowering can be delayed by cool spring weather. So to remain on a seasonal schedule, alfalfa is sometimes cut by canopy height or calendar date. In the central Minnesota harvest alert program, a first harvest alfalfa height of 30 inches results in an RFV of about 180 (Figure 2).
• Hay or haylage in the feed bunk usually has an RFV 15 to 25 points lower than the fresh cut sample test or PEAQ RFV chart indicates.
• Alfalfa forage dry matter yield increases with height of the crop and maturity. Dry matter accumulates at an average rate of about 100 lb/day/acre from late vegetative to flowering stages. The rate of change declines with increased maturity.
• Increases in yield with maturity are largely due to the increase in the lower quality stem fraction. With maturity, the leaf proportion of the forage decreases. Leaf loss can be dramatic in tall and lodged canopies that create moist conditions conducive to leaf diseases.
• Alfalfa forage quality declines rapidly as the crop matures from vegetative to flowering largely due to changes in leaf/stem ratios. For example, in the MN harvest alert program in Central Minnesota, the relative feed value decreased 4.2 units per day from vegetative to early flowering stages (Figure 3).
• Persistence will be greatest if harvest occurs at flowering stages because root reserves are maximized at full flowering. Spring regrowth is intitially largely depenedent on carbohydrate reserves stored the previous fall. After plants are about 6 inches tall, they will start to recharge root and crown carbohydrates reserves for the next regrowth cycle. Season-long harvests at bud stages will reduce stand persistence.

Figure 2. The relationship between alfalfa height and alfalfa forage RFV. Alfalfa that is about 30 inches tall has an average RFV of about 180. Data from 2016-2021 from the alfalfa harvest alert program for Stearns, Benton and Morrison county.

Figure 3. The relationship between days after 1 May and alfalfa forage RFV. Data from 2016-2021 from the Alfalfa harvest alert ptrogram for Stearns, Benton and Morrison county. Alfalfa bud stage usually occurs at about 24 days.

Adjusting Seasonal Harvest schedules

Reaching all goals of forage yield, forage quality, and stand persistence at the first harvest is challenging. Here is an optional total season schedule for consideration that can minimize weather risks to forage yield and quality at the first harvest while allowing good stand persistence.

A “multiple goal” harvest schedule

• A flexible first harvest at the first weather opportunity at the end of May when alfalfa is from late vegetative to bud stage. Flowering can be delayed by low spring temperatures so the first harvest can be by calendar date or canopy height. This strategy for the first harvest will provide high quality forage but potentially result in less yield and stand persistence.
• Cut subsequent harvests at more mature stages to achieve forage yield and quality goals with at least one harvest going to the flowering stage. Risk of rain damage is less during harvests later in the season and forage quality changes less with maturity. A final harvest may be delayed until late October after considering strategies to reduce winter injury.

High yield and persistence schedule

• Cutting at first flower or later stages at the initial or subsequent harvests (three harvests before September 1) will provide for high yields but lower forage quality. Forage quality will be lower do to stemminess of forage.
• A late fall cutting can provide addition forage.

References

Brink, G.E. et al. 2010. Changes in alfalfa yield and nutritive value within individual harvest periods. Agronomy Journal 102(4) DOI:10.2134/agronj2010.0080

Digman, M., et al. 2011. Best practices to hasten field drying of grasses and alfalfa. https://learningstore.extension.wisc.edu/products/best-practices-to-hasten-field-drying-of-grasses-and-alfalfa-p1485

Drewitz, N.  Harvest alert program. https://extension.umn.edu/news/alfalfa-harvest-alert-program-2022

Rotz, C.A., and R.E. Muck. 1994. Changes in forage quality during harvest and storage. P. 828. In Forage quality, evaluation and utilization.

Undersander, D., et al. 2015. Alfalfa management guide. ASA, SSSA, CSSA, Madison Wisconsin.