Forage Facts

Survival and high production of an alfalfa stand begins with an understanding of root reserves.
Forage Facts - Articles

Updated: July 28, 2016

Forage Facts

Alfalfa is a perennial forage crop. Alfalfa leaves use sunlight to produce sugars and starches.

The fall of 2015 will be remembered for some different weather patterns. First will be the unusually warm and sunny conditions that lead to excellent growth of fall seeded oat crops and regrowth of alfalfa. Then the heavy rains immediately after Thanksgiving and the sudden drop in temperatures from the 50's to the low teens. The question has already been raised on what affect these sudden change in conditions will have on alfalfa winter survival.

Survival and high production of an alfalfa stand begins with an understanding of root reserves. Alfalfa is a perennial forage crop. Alfalfa leaves use sunlight to produce sugars and starches. These carbohydrates are used by the plant to support new growth. When levels of carbohydrates exceed the need for regrowth the excess amounts are transported to the tap root and stored for future regrowth. This regrowth may come during the growing season following mowing or in the spring. During winter alfalfa plants may be in "hibernation" but they still carry on basic plant functions at a slower level. These stored carbohydrates are necessary for winter survival as well as regrowth. Management that maximizes root reserve levels at the onset of cooler temperatures and shorter days in the fall sets the stage for optimizing alfalfa stand survival in the spring.

Winter survivability is influenced by many factors:

  • Stand Age. Younger stands are more stress tolerant. Younger stands have lower levels of disease incidence and less physical damage.
  • Soil Fertility. Stands with high levels of potassium (K) are less likely to experience winter injury than stands grown on low fertility. K is vital for carbohydrate movement to the tap root. K levels must be present before the fall rest period. Topdressing in October/November is too late for optimum conditions. Soil pH above 6.5 is preferred.
  • Soil Moisture. Most winter injury is actually caused by the plant drying out. High soil moisture levels increase freezing and thawing cycles which "heave" the crowns out of the soil. This heaving tears roots off and exposes the crown to cold drying winds.
  • Cutting Management. The shorter the interval between cuttings during the growing season, the greater the risk of winter injury. This is related to the total amount of excess carbohydrates that are translocated to the roots. Similarly a fall harvest forces the plant to use stored reserves to initiate new growth. If growing conditions following this harvest do not allow reserves to be replenished the plant enters the long winter period at a more at risk stage.

This March -- Check Your Fields

  • Check all alfalfa fields when temperatures begin to warm up and legumes and grasses begin to regrow.
  • Look over the entire stand to get a feeling of uniformity or unevenness.
  • Look closely at several sites in each field.
  • Observe buds, shoots, crows and roots. Look for bright green shoots and healthy buds and firm white roots.
  • Check stands more than once. Plants may green up, then die off later. Other stands may develop more slowly.

Stem counts are used to evaluate yield potentials of alfalfa stands. Make a frame of wire one foot square. Toss the frame into a stand and then count the number of stems within this square foot area. Stands with greater than 55 stems/ft² will have highest yield potential. Stands with 40 to 55 stems/ft² will have a yield loss and stands with less than 40 stems/ft² should be considered for rotation.

Authors

Paul Craig