Alfalfa fertility needs

By Brooks Warner, Ohio State University Extension Ag and Natural Resources Educator, Scioto County

Alfalfa is known as the queen of forages for its ability to produce incredible amounts of high-protein forage in an array of different environments. Proper management of alfalfa stands can help producers maintain the highest quality and yielding alfalfa for their livestock enterprises. In Ohio, alfalfa thrives in our growing conditions and producers can potentially harvest five times in a growing season. For maximum yield and a healthy alfalfa stand, proper soil fertility is crucial. Soil tests are crucial in understanding which nutrients we are deficient in, and with the price of fertilizer and high-quality alfalfa, it is important to know if we are applying too much or not enough fertilizer.

Soil pH

Highest yielding alfalfa is grown in soil with a pH of 6.7 (Mclean and Brown, 1984). In southeastern Ohio we tend to have low pH soil, so applications of lime are regularly needed.

Soil pH plays a large role in alfalfa stand longevity and plant density. Low pH can have a negative effect on yield, as acidic soil reduces the effectiveness of Rhizobia bacteria to create nitrogen for the plant, whereas higher pH does not affect yields in alfalfa. If soil pH is below 6.7 lime should be applied to raise pH.

In addition to low pH decreasing yield, low pH also reduces crude protein and increases fiber content. This adds to an overall decrease in alfalfa hay quality.


Alfalfa is a nitrogen fixing legume, meaning that through nodulation in the roots from Rhizobia bacteria, N is produced naturally for the plant to utilize. An application of N is not recommended in alfalfa production. Seeds will be inoculated with the N fixing bacteria before planting.


Phosphorus is the most yield limiting nutrient in alfalfa, meaning that yield is in direct correlation with P availability to the plant. Desired P levels should be at least 15 parts per million before alfalfa is seeded. Each ton of alfalfa harvested can remove 14 pounds of phosphate P205 from the soil, so soil samples should be taken annually to know if a P2O5 application is needed.

P deficiency can simply look like reduced yields, as well as stunted plants and chlorosis. P2O5 can be broadcasted and incorporated before seeding, or as a topdressing on established stands.


K is the most important nutrient for alfalfa’s ability to overwinter without experiencing plant death. K deficiencies can look like winterkill, as well as yellowing on the outside of leaves towards the top of the plant. Each ton of alfalfa removed can take 60 pounds of K2O with it, so annual soil samples should be taken to know if a potash application is needed. K2O, like our P2O5 application can be broadcasted and incorporated before seeding or top-dressed to established stands.

Fertilizer application timing

Fertilizer applications in alfalfa should be made twice annually. A split application of P and K should be made in fall after the last harvest, and again in late spring or early summer after the first cutting. This ensures that growers do not run low on nutrients for the third or fourth cutting of alfalfa. The fall application allows K to be taken into the root system during the winter months and P will become available in the spring. The application after first cutting will provide the alfalfa plants with sufficient nutrients for third and fourth cutting.

With the cost of inputs this year it can be daunting to look at the fertility needs of alfalfa to ensure a good harvest and maintain alfalfa stand health. For this reason, I urge producers to focus primarily on soil pH and utilization of lime if you have low pH issues in your soil. With a low pH, a fertilizer application may not be utilized fully and will not be beneficial in your alfalfa crop or for your billfold this year. Looking at correcting soil pH before a fertilizer application does not just apply to years when fertilizer prices are high, but this year there should be a clear emphasis made on pH before money is spent on fertilizer if your soil test comes back and you are not deficient in P or K.

Lime applications do not amend soil pH immediately, producers that apply lime this year will see improvement in pH in the following year. With this being said, fertilizer prices will most likely remain high next year.

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