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Phosphorus and Potassium Fertilization for Alfalfa Persistence

by Wyoming Livestock Roundup

Livestock production in Wyoming typically depends on quality of forage and hay. According to the recent report of Wyoming Agricultural Statistics, 1.3 million tons of alfalfa hay was produced in Wyoming in 2012. Its value is about $2.7 million, which far exceeds corn, grain, dry beans, barley and winter wheat. 

Although alfalfa is an important crop in Wyoming, the bloat potential associated with alfalfa when grazed by livestock is a major concern to producers. One of the best practices to reduce this issue is to mix alfalfa with grass species.

Grass-legume mixtures produce a high quantity of, and reduce the need for, commercial nitrogen fertilization associated with monoculture grass stands. This is because alfalfa is able to fix atmospheric nitrogen into forms easily available to plants. Successful establishment grass-legume mixtures, therefore, has the potential of increasing farm profits. 

However, alfalfa may disappear from the stands in many instances.

Further, loss of alfalfa in grass-legume mixtures can increase weed infestations, which reduces forage yield and quality and increases production costs. Carbohydrate content in roots is critical for winter survival and persistence of alfalfa.

Low levels of phosphorus and potassium in the soil are among the major causes of the poor persistence of alfalfa in mixed stands. 

Grasses are able to absorb much phosphorus and potassium even when these nutrients are available in small amounts in the soil. This is because grasses have a fibrous and extensive root system. Thus, grasses deprive alfalfa of soil phosphorus and potassium when they are inadequate. 

Fertilizing a soil low in phosphorus and potassium, therefore, has the potential of increasing the longevity of alfalfa in mixed stands.

Applying phosphorus and potassium can promote growth, yield, quality and increase root carbohydrate content. 

An increase in root carbohydrate due to phosphorus and potassium fertilization means persistence of alfalfa can be enhanced by applying phosphorus and potassium. Therefore, it is important to identify the appropriate rates of phosphorus and potassium to improve alfalfa persistence, especially in the mixed stands.

For the persistence of alfalfa in the grass-legume mixtures, it is recommended to check phosphorus and potassium status in the soils. A routine soil test is thus advisable.

Anowar Islam is an associate professor and the University of Wyoming Extension Forage Agroecologist in the Department of Plant Sciences in the College of Agriculture and Natural Resources. He can be reached at 307-766-4151 or

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