Potassium is an important nutrient for alfalfa, but high potassium concentrations can be especially concerning when fed to lactating dairy cows, according to an announcement from the American Society of Agronomy.
With an annual economic value of $9 billion in the U.S., alfalfa is the most valuable crop behind corn and soybeans. Because of its high nutritional content, alfalfa is a common feed source for farm animals like cattle, horses, sheep and goats. So, understanding this relationship between alfalfa and potassium is a worthwhile goal, the announcement said.
"Potassium plays a role in many processes within an alfalfa plant," University of Minnesota researcher Jacob Jungers said. "For example, it's important for converting sunlight to energy, transporting molecules and growing new cells."
However, too much potassium can be a problem. "When alfalfa plants are given more potassium than they need, the concentration of potassium in the tissues increases," Jungers said. "This is called luxury consumption."
This increased concentration of potassium affects the nutritional balance of alfalfa as a feed source for livestock.
"In addition to being costly for growers, over-fertilization can put dairy cows at risk of milk fever," Jungers said. Milk fever is a metabolic disease cows can get around the time of calving that causes weakness and sometimes even death.
So, Jungers and his team wanted to identify potassium fertilization rates that increase yield and nutritive value while reducing the potassium concentration in the plant tissue.
The University of Minnesota researchers experimented with five different rates of potassium fertilizer on alfalfa fields. Throughout the four-year study, they took measurements of the yield, nutritive value and potassium concentrations in the plant tissue. Soil samples were also taken to track the potassium levels in the soil, the announcement said.
"Potassium fertilization increased alfalfa yield but decreased forage quality," Jungers said. "This trade-off was consistent among all alfalfa cultivars in the study." Intensively harvested alfalfa did differ in overall yield, but it did not differ in its yield response to potassium fertilization, he added.
When applied at recommended levels, potassium fertilization is important for high alfalfa yields. However, potassium fertilization will not prolong alfalfa stand life or productivity beyond the third production year.
"Many soil types are abundant in potassium, but relatively little is available to crops at any given time," he said. "The amount of potassium that might someday be available to crops is largely dependent on soil texture, moisture and other environmental factors."
Potassium fertilizer rates for alfalfa should be determined based on expected yield, soil test levels and whether the crop will be fed to cows, Jungers said.
More about this research can be found in the Agronomy Journal. This work was funded by the Minnesota Department of Agriculture Fertilizer Research & Education Council and the Midwest Forage Assn.