Alfalfa rotation – base your decision to reseed on yield potential of stand
To decide when to rotate from alfalfa, you need to evaluate stand-density and yield relative to your needs. You’ll want to factor in rotation requirements, farm plan, total acreage of forage needed and your ability to reseed. Most of these factors are farm specific.
Alfalfa has a tremendous ability to produce maximum yield over a wide range of stand densities. New seedings should have at least 25 to 30 plants per square foot the seeding year. Stands will gradually thin, and weeds may invade. Stands with weeds force the choice between using an herbicide (which increases cost) or harvesting lower-quality forage.
The decision to reseed new fields of alfalfa should be based on the yield potential of the stand, ideally using actual yields from the field. The next best method is to count stems when the alfalfa is 4 to 6 inches tall and use the data from the chart below to estimate yield potential.
In many areas, yield often begins to decline in the third year of production. Fields with reduced yields still cost the same as high-yielding fields. This is because high-yielding fields require less herbicide to produce high-quality forage. Plowing down more dense stands will produce nitrogen credits. There is also a rotational benefit to corn following alfalfa: It yields 10 percent to 15 percent more than corn following corn.
The best time to make stand decisions is in the fall. During the last growth period, record stem density. Then dig a random sampling of plants and assess root health. Typically, stands that fall below 40 stems per square foot (or three to four healthy plants per square foot) are no longer profitable, although the critical yield range will vary among individual operations. Marginal stands that are healthy may be kept, while fields with high levels of crown rot will decline rapidly and should be considered for rotation along with low yield potential fields.
Source: The “Alfalfa Management Guide,” published by the American Society of Agronomy, the Crop Science Society of America and the Soil Science Society of America.