|
|
Fall dormancy, winter- survival and stand longevity
Fall dormancy in perennial plants is a measure of
winter-hardiness. This is due to a hardening off process in which fall
growth slows.
There are 10 dormancy classes in alfalfa; the 1 through 4 classes, and sometimes 5 the dormancy class are grown in the northern U.S. Recently industry, together with some public research has come up with a winter hardy index. This index is obtained by rating vigor and uniformity of spaced out plants at two locations. Since this is done on unnatural conditions of spaced plants and winter conditions in a given year, this rating is of questionable or limited value. In addition, as with the disease index, companies are supplying their own, even more questionable data. All 1 through 4 dormancy varieties, survive the first winter, the exception being lack of oxygen for winter respiration, which can occur under water saturated soils or ice. After the second hay year root and crown rots become an important factor in winter survival. Extremely cold temperatures without snow cover occasionally causes some damage the first winter. Another factor as important as cold injury is the breaking of spring dormancy in March or early April followed by a 15 degree cold snap. More dormant varieties are slower to break dormancy.
Solution: Losing stands from winter-kill can be extremely costly, especially for small dairy farmers. For long rotations, and especially if concerned about winter-kill, plant 2 or 3 dormancy alfalfa varieties and give some value to MN-WI winter survival data, if available. Varieties with a 2 or 3 dormancy will also better recover from winter damage and compensate for stand loss by developing a larger crown. I compared company winter-survival data with the WI-MN winter-survival data. Over half did not agree. Put more faith on stand survival ratings after the 3rd or 4th year, if available. |
|