This post contains affiliate links. As an Amazon Associate I earn from qualifying purchases. If you click a link and make a purchase, I may receive a small commission at no extra cost to you.
The fertilizer you use for alfalfa depends heavily on your soil test results, but a balanced approach with phosphorus, potassium, and sulfur is almost always essential.
You can’t just pick any bag off the shelf and expect great results, because alfalfa is a heavy feeder with very specific nutrient demands.
In this post, we’ll break down what fertilizer you need for alfalfa, how to read soil tests, and the best application strategies to boost your yield.
Let’s dig into the details so your alfalfa stands tall and productive.
What Fertilizer Do You Use for Alfalfa: The Core Nutrients
When you ask what fertilizer you use for alfalfa, the answer always starts with understanding the big three macronutrients plus a few micronutrients that alfalfa absolutely craves.
Alfalfa doesn’t need nitrogen fertilizer because it fixes its own nitrogen through bacteria in its root nodules.
So, what fertilizer do you use for alfalfa? You focus on phosphorus (P), potassium (K), sulfur (S), and sometimes boron (B).
1. Phosphorus for Root and Stand Establishment
Phosphorus is arguably the most critical nutrient when deciding what fertilizer you use for alfalfa, especially in the establishment year.
It promotes vigorous root development, which helps young alfalfa plants survive winter and drought.
A common phosphorus fertilizer choice is 0-46-0 (triple superphosphate) or 11-52-0 (monoammonium phosphate).
If your soil test shows phosphorus levels below 15 ppm, you’ll want to apply 60 to 100 pounds of P2O5 per acre before seeding.
For established stands, topdressing with phosphorus in early spring or after each cutting keeps roots strong and regrowth fast.
2. Potassium for Winter Hardiness and Yield
Potassium is another key part of what fertilizer you use for alfalfa, because it boosts winter survival and disease resistance.
Alfalfa removes a ton of potassium from the soil with every cutting, so you must replenish it regularly.
Typical potassium sources include 0-0-60 (muriate of potash) or 0-0-50 (sulfate of potash).
Soil test levels below 100 ppm K mean you should apply 150 to 250 pounds of K2O per acre split across the season.
Don’t skip potassium, because low K leads to thin stands, weak crowns, and lower protein content in your forage.
3. Sulfur for Protein Synthesis
Sulfur is often overlooked when people ask what fertilizer you use for alfalfa, but it’s vital for amino acid and protein production.
Alfalfa with sulfur deficiency looks pale and stunted, with yellowing on younger leaves first.
You can use elemental sulfur, ammonium sulfate, or gypsum (calcium sulfate) to correct this.
If your soil test shows sulfate-sulfur below 10 ppm, apply 20 to 40 pounds of sulfur per acre.
Sandy soils and high-rainfall areas are especially prone to sulfur leaching, so annual applications make sense there.
4. Boron: The Micronutrient Alfalfa Loves
Boron is the micronutrient that often makes the difference between good and great alfalfa yields.
Boron helps with cell wall formation, pollen germination, and seed production, so it’s essential.
What fertilizer do you use for alfalfa that includes boron? Look for borated fertilizers like 0-0-60 with 1% B, or apply solubor directly.
Apply 1 to 3 pounds of actual boron per acre, but be careful because boron toxicity is a real risk on sandy soils.
A soil test for boron will tell you exactly how much you need, so never guess on this one.
How to Choose the Right Fertilizer Blend for Alfalfa
Now that you know the nutrients, how do you pick the exact fertilizer blend?
The only correct way is to pull a soil sample and get it tested by a reputable lab.
What fertilizer you use for alfalfa should always be tailored to your specific field, not a generic recommendation.
1. Soil Test First, Then Fertilize
Take soil samples from 0 to 6 inches deep, and ideally from 6 to 24 inches for sulfur and nitrate.
Send samples to your local extension office or a commercial lab that gives recommendations for alfalfa.
The lab report will tell you your phosphorus, potassium, sulfur, boron, and pH levels.
If your pH is below 6.5, you should add lime first, since alfalfa hates acidic soils.
Once you correct pH, then you can decide what fertilizer you use for alfalfa based on the numbers.
2. Calculating Application Rates
Let’s say your soil test recommends 80 pounds of P2O5 and 200 pounds of K2O per acre.
If you’re using 0-46-0 for phosphorus, you’d apply about 174 pounds of that product per acre.
For potassium with 0-0-60, you’d apply roughly 333 pounds of that product per acre.
You can also use a pre-mixed blend like 5-20-20 or 10-20-20 that already contains balanced ratios.
Just remember that blends rarely match your exact soil needs, so individual sources often work better.
3. Organic and Natural Options
If you grow organic alfalfa, you might wonder what fertilizer you use for alfalfa that’s natural.
Composted manure is a great source of phosphorus and potassium, but its nitrogen content is wasted on alfalfa.
Rock phosphate provides slow-release phosphorus, and greensand adds potassium along with trace minerals.
Kelp meal and soybean meal offer small amounts of nutrients and help build soil biology.
However, organic sources often have lower nutrient concentrations, so you’ll need larger application volumes.
When and How to Apply Fertilizer for Alfalfa
Timing matters just as much as the fertilizer blend you choose for alfalfa.
1. Pre-Seeding Application
For new seedings, apply phosphorus and potassium right before planting and work them into the top 4 to 6 inches.
This places the fertilizer in the root zone where young alfalfa can reach it easily.
Sulfur can also be applied pre-plant, especially in sulfate form so it’s immediately available.
Boron should be mixed thoroughly or banded to avoid seed damage from close contact.
2. Topdressing Established Stands
For established alfalfa, split your potassium applications into two or three doses per year.
Apply the first dose in early spring before growth starts, then again after the first and third cuttings.
Phosphorus is less mobile, so you can topdress it annually without worrying about it moving too deep.
Sulfur is highly leachable, so apply it in split doses too, especially on sandy soils.
Broadcast the fertilizer evenly using a spinner spreader, and consider incorporating it lightly with irrigation if possible.
3. Foliar Feeding as a Supplement
Foliar feeding can be a quick fix if you notice micronutrient deficiencies mid-season.
Spray soluble boron, zinc, and manganese directly on the leaves in the early morning or late evening.
This isn’t a substitute for soil-applied fertilizer, but it helps correct issues fast.
What fertilizer you use for alfalfa via foliar should be low-concentration and chelated for better absorption.
Avoid foliar feeding during hot, sunny days to prevent leaf burn.
So, What Fertilizer Do You Use for Alfalfa?
What fertilizer you use for alfalfa ultimately comes down to your soil test results.
You can’t rely on one universal product, because every field has different nutrient levels.
However, in most cases, you’ll be applying phosphorus and potassium as the backbone, with sulfur and boron as regular additives.
Nitrogen fertilizers are unnecessary because alfalfa fixes its own nitrogen.
So the best practice is to test your soil, follow the recommendations, and split your applications to match the crop’s growth stages.
Doing this will keep your alfalfa healthy, productive, and profitable season after season.
Hope this clears up what fertilizer you use for alfalfa, and now you’re ready to make smarter decisions in the field.