Heat Effects on Alfalfa

Heat Effects on Alfalfa

As we experience the extreme heat of summer, plants adjust in various ways. Alfalfa plants grow more slowly and moisture stress becomes common, even in moist soil.  Production of high-quality hay is nearly impossible due to high temperatures, especially at night.  High night-time temperatures cause rapid respiration rates in alfalfa, burning off valuable nutrients that plants accumulated during the day.  This often produces alfalfa hay with fine stems that contain high protein, as well as have high fiber and low relative feed value.  If your hay tests low, blame the heat.

Another problem is how fast alfalfa plants mature.  When it’s hot, alfalfa may begin to bloom in less than four weeks.  If you use blooming as a signal to harvest, this early bloom can be misleading.  Alfalfa plants need more time, not less time to rebuild nutrient reserves in its roots during hot weather because nutrients burn off rather than move to the roots. During these conditions watch the calendar and your plants to schedule the next cutting.

When you do cut during high heat periods, consider when you cut. Some research has shown that cutting in late afternoon produces higher quality hay than cutting in the morning.  But, on good drying days it still may be wiser to cut in the morning.  When cut hay stays above 50% moisture, plant cells continue to respire, burning away valuable nutrients.  Hay cut late in the day respires all night long, losing yield and quality.  On good drying days, plant cells can dry enough to be stabilized before nightfall, reducing respiration losses.

Getting high quality hay is challenging.  Both you and the weather must cooperate and even then there are no guarantees.


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