One of the first things to do in late summer or early fall is an assessment of your alfalfa stand. Start by evaluating overall stand quality. If the stand is more than two or three years old, count stems from healthy areas of the field to determine if you have adequate yield potential going into the winter (more than 55 stems per square foot). Look at the entire field to see what percentage is in good versus poor condition. Factor this into your decision. Finally, look at the field’s current season yield to determine whether or not it meets your production goals.
Fertilize for healthy plants
Fertilizing alfalfa with potash in late summer and fall can enhance the winter survival potential of a healthy stand. Alfalfa plants require potassium (K) for several important physiological processes, including the creation and storage of carbohydrates in the roots and crown. Harvesting alfalfa forage results in the removal of more K than any other soil nutrient (10 to 15 pounds per acre of K removed per ton of dry matter). Replacement of K is critical to maintaining good plant health and yield.
Applications of potash following a third or fourth cutting allow alfalfa plants to take up K during the fall period when they’re going dormant and storing carbohydrates. Alfalfa’s root system tends to absorb K most heavily from near the soil surface. As a result, alfalfa can quickly absorb K fertilizers from top-dressed applications. Finally, split applications during the season help prevent the loss of K through leaching. In addition to K fertility, continue to monitor the phosphorus (P) and sulfur (S) status of the soil so the levels don’t become yield limiting.
Manage fall harvest timing
Cold tolerance and winter survival – and the ability to initiate and sustain spring regrowth – is highly dependent on keeping root and crown carbohydrate (sugar) reserves high. During the late fall, alfalfa will begin going into a dormant state. Dormancy slows or stops top plant growth and forces the accumulation of sugars in the underground parts of the alfalfa plant.
One of the ways to increase alfalfa’s potential for winter damage is to cut it mid-fall during the critical period when the plants won’t have adequate time to regrow and store carbohydrates. It’s a matter of arithmetic: If a grower depletes the energy source prior to dormancy, the plant may not have adequate energy to initiate spring growth.
Initial spring growth comes from crown buds, which get their energy to grow from stored carbohydrates. Energy or carbohydrates are consumed from initial spring growth until the plant has 6 to 8 inches of growth. After this time, energy produced by photosynthesis fuels more rapid growth. In fact, excess energy is produced and stored in the plant until the plant fully flowers.
Ideally, allow six to eight weeks of growth to occur after the last summer cutting to ensure adequate growth and storage of carbohydrates for winter. For many parts of the Upper Midwest and the Northeast, this means avoiding alfalfa harvest during most of September and October. After mid to late October, plants can be harvested again to remove this fall regrowth. When cut in late October or November, alfalfa plants have become sufficiently dormant and will not attempt regrowth. Also, when a hard freeze occurs for two or more nights at temperatures of 24 to 26°F, alfalfa plants will not regrow and harvest can occur.
Challenge yourself to reduce risk
Alfalfa producers considering a late harvest should always evaluate the need for extra forage. Any fall harvest will increase the risk of damaging or losing a portion of the alfalfa stand over winter. Remember that the forage quality of alfalfa changes little during the fall growth period, so harvesting before dormancy versus delaying harvest by one to two weeks is not a decision based on quality, but rather on the likelihood of winter injury or survival.
Risk of alfalfa injury due to fall management ranges from low to high and is often an accumulation of multiple plant stressors. The risk of winter injury can be decreased when the following factors exist:
- Stand age (less than two to three years)
- Good field drainage
- Adequate to high levels of soil fertility
- Late summer K application
- Harvest timing that allows adequate fall accumulation of energy reserves
- Good plant and root health
The overwinter survival of alfalfa is best achieved when we pay attention to several key fall management strategies. Make and execute your fall plans now so you can enjoy the excitement of new regrowth in your alfalfa fields next spring. FG
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Daniel Wiersma
- Alfalfa Business Manager
- DuPont Pioneer
