Timing of your last cutting is one of the most important factors for maintaining alfalfa persistence over winter. The Ohio Agronomy Guide recommends that cutting finishes by Sept 7 for northern Ohio and Sept 15 for southern Ohio—these recommendations are based on the amount of time it typically takes for alfalfa to regrow to ~8 inches before a ‘killing’ frost occurs, stopping growth for the year.
What’s the value of fall regrowth?
Fall regrowth ensures the plant has sufficient sugars and carbohydrates in the root system, which is critical for winter survival. The biomass of plants above ground also helps protect the crown against harsh winter weather by helping to hold onto snow, which can help insulate plants from the drying effect of cold winds. Plant material also helps cover the soil surface, which can reduce the intensity of rapid freeze-thaw cycles that contribute to frost heave. Taking a fall harvest will provide feed this year, but often at the expense of next year's spring yield.
Why is timing fall harvest particularly important this year?
Even though the taproot of alfalfa can continue growth during short-term dry weather, its growth is reduced by longer-term dry conditions. The drought monitor for our region indicates that much of the state is currently classified as D0, and forecasts indicate that the dry weather will persist for at least another week. This will reduce the recovery growth of alfalfa going into winter, increasing the risk that late-cut alfalfa may not regrow sufficiently before hard frosts.
If you need more feed for the winter, when should you harvest?
The best harvest option for more feed is after the fall rest period, when the alfalfa has undergone winterization. Winterization correlates to cutting after a killing freeze (23-24°F for several hours), after which the plant is dormant. This is not as stressful to the plants as cutting during winterization and can be a viable option for those who need feed and do not want to risk next year’s stand. However, remember that you should leave 5-6” of stubble, which leaves some plant tissue and helps to reduce erosion and provide some insulation during freezing and thawing cycles. The freeze-thaw risk is most significant on poorly drained soil. As dry conditions persist, your best options if feed is needed will be to harvest corn as corn silage or consider alternative feeds such as corn grain and corn stalks.
How does soil fertility impact alfalfa fall management?
Potassium (K) is critical to alfalfa growth and enhances cold tolerance during winter . Physiologically, K is needed for plants to regulate water; if K levels are too low, plants will be at greater risk of winterkill and especially desiccation-related winterkill. In fields with low soil test K (STK below 120-170 ppm for agronomic crops in Ohio, when analyzed via Mehlich-3 extraction), applying potash a few weeks before growth stops for winter allows fertilizer to enter the soil profile and begin being taken up by plants.
Even in fields with high levels of soil test K (STK), potassium uptake may have been reduced this summer and fall due to low water availability. While low water availability impacts uptake of all nutrients, K uptake is particularly sensitive to dry conditions due to interactions between K and clay particles. Currently, we do not have evidence for management options that consistently improve K uptake during fall drought.
Further Reading:
Ohio Agronomy Guide, 16th Edition. https://extensionpubs.osu.edu/ohio-agronomy-guide-16th-edition/
Tri-State Fertilizer Recommendations for Corn, Soybean, Wheat, and Alfalfa. https://extensionpubs.osu.edu/tri-state-fertilizer-recommendations-for-corn-soybean-wheat-and-alfalfa-pdf/?searchid=0&search_query=974