Applying manure to alfalfa may be an economical way to supply the potassium (K) the crop needs, says Jonathan Rotz, Penn State University Extension educator in Franklin County, PA.
“Obviously, we cannot limit nutrients to crops but sometimes simply changing where those nutrients come from may be of economic benefit,” says Rotz.
He notes that manure is typically high in K, but it’s usually applied to corn ground and commercial fertilizer is used to supply alfalfa’s nutrient needs. Corn can make better use of the other nutrients in manure, especially nitrogen (N). If the amount of manure is limited, “you need to push the pencil to see if it is more economical to buy N for the corn or K for the alfalfa,” says Rotz.
Excess N in alfalfa fields can lead to increased competition from grasses and other weeds. Because of that, the typical recommendation is to not use manure on newly established stands. Older stands will likely be rotated sooner and may also have a competitive advantage against weeds.
Stay away from manure that may clump or get picked up with future alfalfa harvests, such as dairy pack manure. Dry poultry manure is suitable, but liquid manure is the best option.
Apply the manure immediately after a cutting. “Make sure you have a current soil test as well as a manure test and apply to potassium levels to get a lower rate of application,” Rotz advises. “This lower rate will allow less traffic across the field and can limit the negative impact on the alfalfa stand that may be seen from the heavy loads.”