Late-season management decisions for alfalfa

KSU Extension Agronomy eUpdate: In northern and western areas of Kansas, some fields of alfalfa may have already had a freeze. After a killing freeze, the remaining forage (if any) can be hayed safely. However, the producer should act quickly because the leaves will soon drop off.

On fields that have not yet been hit by a freeze, it’s time now to start planning to make the last cutting of alfalfa for the year. Producers may be tempted to wait a few more weeks before making the last cutting in the fall, especially if the crop is still growing. But that’s not a good idea. The timing of the last cutting can have a long-lasting impact on the productivity of the stand.

At this stage of the growing season, alfalfa plants need to store enough carbohydrates to survive the winter. If root reserves are not replenished adequately before the first killing freeze (24 to 26 degrees) in the fall, the stand is more susceptible to winter damage than it would be normally. That could result in slower greenup and early growth next spring.

The last cutting, prior to fall dormancy, should be made so there are 8 to 12 inches of foliage, or 4 to 6 weeks of growth time, before the average killing freeze date. This should allow adequate time for replenishment of root reserves.

For northern areas of the state, particularly northwest, late September should be the target date for the last cutting before dormancy. The last week of September should be the cutoff date for southwest Kansas. The first week of October is the cutoff for southeast Kansas.

Making one last cutting in mid-October, if significant growth has occurred, could reduce root reserves during a critical time. About the worst thing that could happen to an alfalfa stand that is cut in mid-October would be for the plants to regrow about 3 to 6 inches and then get a killing frost. In that scenario, the root carbohydrate reserves would be at a low point. That could hamper greenup next spring.

Late fall is also a great time of the year to soil sample alfalfa ground. This timing allows for an accurate assessment of available soil nutrients and provides enough time to make nutrient management decisions before the crop starts growing in the spring. Soil tests of most interest include pH, phosphorus, and potassium, and to a lesser extent sulfur and boron. When sampling for immobile nutrients, sampling depth should be six inches, while mobile nutrients (sulfur) should be sampled to 24 inches.

KSU Extension Agronomy eUpdate

Jim Shroyer, Crop Production Specialist Emeritus
jshroyer@ksu.edu

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