Every alfalfa grower's goal is to harvest and preserve high-quality alfalfa silage starting with the first cut of the season. The first cut of spring regrowth is one of the most important alfalfa cuttings of the year, because it represents the largest proportion of total seasonal production. Forage quality in spring tends to be lower and declines substantially during bud development and flowering.
Spring regrowth can be a slow process. In the upper Midwest, alfalfa usually breaks dormancy and develops new shoots in late March. Healthy alfalfa will reach bud stage around mid-May, in about 45 days or so, depending on weather. During this relatively cool, moist growth period, alfalfa produces a lot of dry matter. Total yield rises an average of 100 pounds per acre per day. During the late vegetative and flowering stages, leaf growth decreases as stem growth drives yield. This reduces the leaf-to-stem ratio of the plant, which contributes to the quality decline.
Quality is Key
Growers and dairymen require high-quality alfalfa forages for dairy animals, which makes the timing of the first cut critical. It's important to predict forage quality before harvest. Alfalfa and alfalfa-grass stands mature more quickly and lose nutritive quality faster during the spring growth cycle than during summer or fall growth.
University of Wisconsin data suggests the average decline in alfalfa's relative feed quality (RFQ) is 4-5 units per day during the late vegetative and flowering stages of growth. Even a three- or four-day delay in harvest can make the difference between high-quality and average-quality silage. Complications include weather and growth conditions affecting plant development and quality.
Several tools can help predict alfalfa forage quality prior to harvest. Two key tools are the Predictive Equation for Alfalfa Quality (PEAQ) and the scissor-clip programs.
In the PEAQ system, users measure plant height and evaluate the development stage (vegetative, bud, flower) of the most mature stem in a field sample. Putting this data into an equation determines the relative feed value (RFV) of the sample. To evaluate multiple samples quickly, researchers developed the PEAQ stick, with markings that show RFV for each stage and stem length measured.
PEAQ sticks are widely used. A side benefit is that the user must be in the field and therefore can observe other potential issues: insect pressure, disease, etc.
The PEAQ method has two drawbacks: First, sticks are less precise in fields suffering from lodging. Second, the PEAQ system measures neutral detergent fiber (NDF) and RFV. While RFV offers a good sense of forage quality, RFQ (which factors in NDF and fiber digestibility) has become the preferred method of prediction.
Scissor-clip programs also help identify changing forage quality across both geography and time during spring alfalfa growth. The University of Wisconsin publishes results of scissor-clip samples from around the state on its website. Growers can monitor alfalfa quality changes in nearby counties to help with harvest timing decisions.
Timing of Harvest
A key question is when to begin harvest. A good rule of thumb is to begin when readings are 15 to 20 points higher than your target RFV. If you target 175 to 180 RFV, begin harvesting when readings are 190 to 200. It is always best to run comparisons between PEAQ readings on your farm with final harvested samples to know how much adjustment is needed.
Weather delays and rain damage can reduce forage quality quickly and impact silage fermentation. Delayed harvest reduces quality because fiber increases as crude protein and energy density decrease. Rain on cut alfalfa may spur growers to adopt additional field practices to encourage drying. This can lead to leaf shatter issues. Rainfall on cut alfalfa also leaches away soluble sugars. Since sugars are a direct food source for lactic acid bacteria, their loss can impact the ability to lower pH levels in ensiled alfalfa silage.
Your best first-cut alfalfa crop starts with understanding the trade-offs between yield and quality. Plan for animal and operational needs based on inventory and quality needs. Once you set a quality target, use a predictive tool such as PEAQ or scissor-clip to help hit the target. Finally, prepare your equipment and crew to harvest and ensile alfalfa silage quickly to achieve the best possible fermentation
Consult with Professionals
To choose the measurement system that's right for you or for more information on alfalfa, consult your local DuPont Pioneer expert or authorized Pioneer sales representative.