When checking spring growth to decide whether or not to keep an alfalfa stand for another year or harvest early and rotate to corn, growers should count stems per square foot, not plants, reminds Marvin Hall, Penn State University forage specialist. With established stands, the magic number of plants that traditionally indicated when it’s time to rotate out is four to five per square foot, says Hall. However, depending on fertility and weed invasion, alfalfa stands with that few plants can yield as well as much thicker stands. The correlation between plant counts and yield is very low since alfalfa plants respond to decreasing stand density by producing more stems.
Hall tells growers the number of stems per square foot is a better indicator of productivity. Fields with 55 or more stems per square foot produce maximum yields. As the stem number declines below 55/sq ft, yields begin to decline. Once they fall below 40/sq ft, alfalfa fields begin to lose profitability and should be rotated out of alfalfa.
There should be a plant density of at least 15 plants/sq ft in new alfalfa seedings made last fall or this spring. This greater density is needed because the plants have not developed large crowns yet and will consequently have fewer stems per plant than older plants, which is directly related to yield, says Hall.