Potassium Application and Cutting Schedules Can Improve Alfalfa Productivity – Part I

By Anowar Islam

Published on Jan. 4, 2020

            A few years back, I wrote an article about the importance of potassium and phosphorus on alfalfa productivity, especially in a mixed cropping system. Low levels of potassium and phosphorus in the soil are among the major causes of the poor persistence of alfalfa in mixed stands. 

Therefore, fertilizing soils, especially soils low in potassium, has the potential to increase not only the productivity but also the longevity of alfalfa.

            Forage yield of alfalfa is the most important factor determining profitability in alfalfa production systems. An efficient forage system requires an understanding of how management practices influence growth and development of plant. A perception of potassium usage by alfalfa can help us comprehend yield response of alfalfa to potassium application and cutting schedules.

Requirement of potassium in alfalfa

            Alfalfa requires large amounts of potassium for its maximum growth potential. Alfalfa absorbs potassium more than any other nutrient from the soil for producing healthy stand and optimum hay yield. Often, alfalfa is considered as a luxury consumer of potassium. 

            It takes up more potassium than needed when potassium is available at the root zone. However, there are feedback mechanisms which maintain a balance between demand and uptake. During the growing season, about 100 percent of the aboveground portion of alfalfa is cut and baled several times. 

            This results in the removal of substantial amounts of potassium from the soil each year. For example, cutting one ton of alfalfa removes about 65 pounds potassium per acre from the soil, which implies that in a single growing season, a fairly obtainable three tons of alfalfa removes about 195 pounds potassium per acre. 

            This may lead to potassium depletion in soils. Therefore, when soil potassium levels are limiting, the potential of alfalfa to maximize growth and yield decreases long before any visual symptoms of potassium deficiency, such as stunted growth, white spots on leaf margins and defoliation, are observed in the plant.

Utilization of potassium in alfalfa for its growth and yield

            In general, alfalfa seeds germinate in two to three days after planting. A germinating alfalfa seed gets its nutrients from the carbohydrates, proteins and fats stored in the cotyledons until the true leaves start to photosynthesize. 

            The young roots of emerged alfalfa plants penetrate the surrounding soil to search for nutrients and water. As the roots move through the soil, nutrients adjacent to the roots are absorbed for plant growth. Potassium absorption by roots of alfalfa occurs from the soil solution as an ion (K⁺) and the rate of uptake is closely related to the concentration of the soil solution.

             Consequently, the roots tend to grow and space themselves uniformly in the soil allowing potassium to diffuse through the soil to the roots and then transport to the tissues of the growing plant. This helps to strengthen the photosynthetic system of the plant to boost its physiological and biochemical processes for increasing growth and development. 

As a result of growth increase, forage yield of alfalfa increases. Since alfalfa roots penetrate deep in the soil, it is important to meet the moisture requirement of soils to increase mobility of potassium.

            I will continue discussion on potassium application and cutting schedules in my future extension columns – please keep an eye on the future writings.

            Anowar Islam is a professor and the University of Wyoming Extension forage specialist in the Department of Plant Sciences in the College of Agriculture and Natural Resources. He can be reached at 307-766-4151 or mislam@uwyo.edu.