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Heat affects alfalfa
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Forage Minute

Heat affects alfalfa

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Alfalfa trial

An alfalfa test plot.

As we move in to the “dog days of summer,” also known as the extreme heat period, keep in mind that forage plants also must adjust to these temperatures.

When it gets hot, alfalfa plants grow more slowly and moisture stress becomes common, even in moist soil.  Production of high-quality hay is nearly impossible due to the high temperatures, especially when the heat does not subside 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, but they also have high fiber and low relative feed value.  So, if your hay tests low, blame the heat.

Another problem with heat, is how fast alfalfa plants mature.  When it is 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.  During hot weather alfalfa plants need more time, not less time to rebuild nutrient reserves in their roots because they burn off nutrients instead of moving them to the roots when it is hot.  So, watch the calendar as well as your plants to determine when to cut your alfalfa fields.

You might also adjust the time of day when you cut hay.  Some research has shown that cutting in late afternoon produces higher quality hay than cutting in the morning.  However, on good drying days it may still be wiser to cut in the morning.  When hay in the windrow stays above fifty percent moisture, plant cells continue to respire, burning away 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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