For most of Kansas, alfalfa should be stopping growth after the hard freeze that occurred on October 15. The timing of the last cutting can impact the productivity of the stand in the following year. Thus, at this point in the year, the best approach is to cut right after the first killing freeze, before too many of the leaves have dropped. Producers should be prepared to enter the fields as soon as soil moisture conditions allow. 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.
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 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 based on expected crown regrowth rather than one-tenth bloom because of the decreasing photoperiod. The last cutting should be made so there will be 8 to 12 inches of foliage, or 4 to 6 weeks of growth time, before the first killing frost. This should allow adequate time for replenishment of root reserves.
Figure 1. Alfalfa stand with approximately 12 inches of top growth prior to winter dormancy. The last cut in this stand was performed early September, and this photo was taken late October. This stand will be hayed immediately following the first killing frost. Photo by Romulo Lollato, K-State Research and Extension.
For northern areas of the state, particularly northwest, late September is usually the target date for the final cutting before dormancy. The last week of September is usually the cutoff date for southwest Kansas. The first week of October is usually the cutoff for southeast Kansas. However, we are well past those dates for the current year, and a killing freeze already occurred. Thus, producers should be prepared to perform the last cut as soon as conditions allow for fieldwork.
Making a cutting now, after the killing freeze occurred, should prevent regrowth, avoiding reducing root reserves during this critical time. About the worst thing that could happen to an alfalfa stand that is cut in late-October would be for the plants to regrow about 3 to 6 inches and then get a killing frost, which should not occur this year due as the killing frost already occurred and regrowth is less likely. In that scenario, the root carbohydrate reserves would be at a low point. That could hamper green-up next spring.
Consider soil sampling alfalfa fields now
Late fall is 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. Key soil tests include pH, phosphorus, and potassium, and to a lesser extent, sulfur and boron. In particular, potassium is highly related to winter survival so it’s important to make sure to have optimum range of potassium in soil before entering winter. When sampling for immobile nutrients, sampling depth should be six inches, while mobile nutrients (sulfur) should be sampled to 24 inches.
Romulo Lollato, Wheat and Forages Specialist
lollato@ksu.edu
Doohong Min, Forages Specialist
dmin@ksu.edu