CENTRAL PLAINS: This time of year, alfalfa growers are often tempted to try and capture one last alfalfa cutting. With adequate moisture, this last cutting usually results in very high feed value for hay; however, it is important to understand the tradeoff that could be involved with taking this last cutting too late in the season.
During the season, managing alfalfa cuttings based on regrowth or a percentage of bloom is simply a visual way of assessing the status of root carbohydrates. This root carbohydrate reserve is also the dynamic that comes into play when assessing whether that one last cutting is really worth it.
Carb levels in the root will fluctuate with the cutting interval. When we take a cutting off, we remove almost all of the leaf surface area from the plants, so plants must use their stores of root carbohydrates to supply energy to the plant for regeneration. A cutting reduces the root carbohydrates until the plant reaches about 6 to 8 inches. At this height, the plants will again have enough leaf surface area to provide for regeneration and to start building root reserves in advancement of the next cutting – or killing freeze.
Therefore, when considering whether to try taking one last cutting, think about what is going on inside the plants. Once a killing freeze hits, the plants will lose their leaf surface and their ability to produce carbohydrates. However, these plants are still alive! Although the plants are dormant during the winter, respiration still takes place and that requires an energy supply be available during the winter. Without an adequate carbohydrate supply, the plants undergo stress and will be slow to generate new growth in the spring.
As a rule, we will want to shoot for a minimum of 8 inches of regrowth prior to a killing freeze. Remember, the days are getting shorter. So, with adequate moisture, we are typically only going to get 2 to 3 inches of new growth per week this time of year, meaning it likely will take at least four weeks to obtain 8 inches of regrowth. This amount of regrowth is generally what you’ll want to sustain the crop through the winter and get the field off to a quick start next spring.
So, for a quick rundown:
- Make sure the plants are showing regrowth before even considering cutting. If not, the field is not ready to cut anyway and will recover slowly.
- Estimate if the field will have a minimum of four weeks (ideally six weeks) to recover prior to the first killing freeze (26 degrees).
- If it’s a close call and you decide to cut, raise the cutterbar height as high as is reasonable, ideally leaving at least 4 inches of stubble and as much regrowth as possible for regeneration.
- Following a killing freeze, the field can be cut for hay without affecting the carbohydrate supply to the roots.
Reporting from Whitewater, KS
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