Boost Yields with Smart Soybean Fertilizer Timing and Rates

A well-designed nutrient management program is crucial for maximizing soybean yields. But what nutrients do you need to apply before planting to ensure your soybeans get the best start? Soybeans may fix their own nitrogen, but they still need balanced fertility, especially phosphorus, potassium and sulfur, to reach their full potential. Getting the timing and rates right can make the difference between average yields and a bumper harvest.

Soybean fertilizer recommendations

Primary Nutrients (N, P and K)

Phosphorus (P) and Potassium (K)

Both phosphorus and potassium are often recommended for soybean preplant applications, but exact soybean fertilizer requirements depend heavily on soil test results. Phosphorus is critical for root development, nodulation and seed formation. A deficiency often causes stunted growth, necrotic spots and purpling of older leaves. Potassium supports water regulation, stalk strength and disease tolerance. Deficiency symptoms typically appear as yellowing or scorching along leaf edges and between veins.¹

Nitrogen (N)

Preplant applications of nitrogen may give your soybean yields a slight boost, but they are not often recommended.³ The soybean’s ability to fix nitrogen accounts for 55% to 75% of its nitrogen needs, and the remaining percentage is taken from the soil.

Secondary nutrients (S, Ca and Mg)

• Sulfur (S)

  Sulfur has become increasingly important for soybean production, especially in fields with low organic matter or coarse soils where it leaches easily. It plays a key role in nitrogen fixation, protein synthesis and chlorophyll formation, directly impacting yield and seed quality. When deficient, soybeans may show uniform yellowing of younger leaves, often mistaken for nitrogen deficiency.

  However, sulfur leaches slowly in the soil, and residual amounts of sulfur may carry over from year to year. Your soil test is the best indicator of whether you should apply sulfur to your soybeans.²
  

• Calcium (Ca) and magnesium (Mg)

  Calcium and magnesium play vital roles in soybean plant metabolism. Calcium is used in cell walls and cell division, supporting plant structure and root development. Since calcium is immobile in the plant, soybeans require appropriate levels present in the soil throughout the season to support the plant.

  Magnesium is critical in chlorophyll production. Appropriate magnesium levels help soybeans efficiently produce energy for growth and pod development. Soybeans deficient in magnesium can experience reduce yields and decreased overall plant health.

  While calcium and magnesium deficiencies are rare, it is worthwhile to test your soils if you know they are acidic or sandy and assess your secondary nutrient levels.³

Micronutrients (B, Cu, Fe, Mn, Zn, Mo)

Micronutrients are just as important as the primary and secondary macronutrients but are needed in far less amounts.
Micronutrients like iron, zinc and manganese can become limiting in certain soils. Iron deficiency chlorosis is a common issue in high-pH soils where sufficient iron is present, but not available for root uptake due to the high pH. Symptoms will appear as yellowing between the veins of young leaves. In these cases, an iron chelate at planting may be beneficial. Soil pH itself is also critical for optimizing yields. Liming is recommended for acidic soils to keep pH in the optimal range and support nutrient availability.⁴

Soybean fertilizer application timing and field conditions

Phosphorus and potassium

Soybean fertilizer recommendations include phosphorus and potassium applied before planting, as foliar supplements don’t tend to give any benefits to soybean plants.⁵ Spring applications are especially valuable in soils with low fertility indices, since nutrients are more immediately available to seedlings.

Sulfur

Sulfur availability needs to extend throughout the season. Research from the University of Illinois shows that soybeans have the greatest sulfur demand around seed filling, with uptake rates of more than 0.25 pounds of sulfur per acre per day.⁶
However, not all regions see a clear response to sulfur applications. Research in Arkansas has shown little consistent benefit in soybean yield from added sulfur. However, on deep sandy soils, applying 10 to 20 pounds of sulfate-S per acre may still be worthwhile.⁷

Nitrogen

If you plan on applying nitrogen fertilizer or manure, make sure you don’t apply too close to planting. Small, targeted applications early in the season can support nodulation if soils are especially low in organic matter. Some research suggests late-season applications under specific conditions may help boost yield, but blanket nitrogen applications are rarely justified.⁸

Micro nutrients

Iron chelate is most effective when applied at planting in high-pH soils to minimize iron deficiency chlorosis. For acidic soils, lime applications should be made well before planting to give time for pH to stabilize, ensuring other nutrients remain available throughout the growing season.

Recommended soybean fertilizer rates

The best course of action to take when deciding your application rates is to use your most recent soil test as a guide for your soybean fertilizer recommendations.

Phosphorus and Potassium

The right amount of phosphorus and potassium depends upon your yield goals and your soil tests. The most economical method for P and K applications is to apply only enough fertilizer for that year’s yield. Trying to build and maintain high levels has been shown to be inefficient and less profitable.⁹

Sulfur

In most environments, 15–25 pounds of sulfate-sulfur per acre is sufficient to prevent deficiencies, particularly in soils that are sandy or low in organic matter. Using fertilizer sources that release sulfur slowly can help maintain availability throughout the season. Since responses vary by region, growers should monitor local trial data and deficiency symptoms before committing to routine applications.¹⁰

Calcium and magnesium

Calcium and magnesium deficiencies are rare, and lime applications typically supply adequate amounts of calcium and magnesium for soybeans.¹¹

Nitrogen

Most soybean fields do not need added nitrogen because biological fixation supplies the crop’s needs. In soils with low organic matter or poor nodulation, applications of 40 to 60 pounds per acre can support early growth. Higher rates should be avoided because they may suppress nodulation and reduce long-term nitrogen efficiency.¹²

Micro nutrients

Micro nutrient applications should be made only when soil tests or tissue samples indicate a deficiency. For example, iron chelate is recommended at planting in high-pH soils prone to iron deficiency chlorosis. Where soil acidity limits nutrient availability, lime should be applied well in advance of planting at rates that bring pH back into the optimal range of 6.0–6.8.¹³

Experts are available to help you make your soybean fertilizer decisions. Reach out to your seed retailer, a nearby extension office agent or a seed company professional like your regional BASF representative.

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Endnotes

1. Iowa State University Extension and Outreach. “Nutrient Requirements – Soybean.” Integrated Crop Management: Crops, ISU Extension and Outreach, https://crops.extension.iastate.edu/encyclopedia/nutrient-requirements-soybean
2. Kaiser, Dan. “Is It Worth Applying Sulfur to Your Soybean Crop?” Minnesota Crop News, University of Minnesota Extension, 8 Apr. 2024, blog-crop-news.extension.umn.edu/2024/04/is-it-worth-applying-sulfur-to-your.html.
3. Kaiser, Daniel E., and Carl J. Rosen. “Magnesium for Crop Production.” University of Minnesota Extension, reviewed 2024, extension.umn.edu/micro-and-secondary-macronutrients/magnesium-crop-production.
4. University of Minnesota Extension. “Soybean Fertilizer Guidelines.” University of Minnesota Extension, extension.umn.edu/crop-specific-needs/soybean-fertilizer-guidelines#nitrogen-1078560.
5. Oldham, Larry, and Keri Jones. “Soybeans: Liming and Fertilization.” Mississippi State University Extension, extension.msstate.edu/publications/soybeans-liming-and-fertilization.
6. Slaton, Nathan, Trenton Roberts, and Jeremy Ross. “Fertilization and Liming Practices.” Arkansas Soybean Handbook: MP 197, University of Arkansas System Division of Agriculture, Cooperative Extension Service, Feb. 2013, https://www.uaex.uada.edu/publications/pdf/mp197/chapter5.pdf
7. “Sulfur’s Role in Soybean Success.” Crop Nutrition, The Mosaic Company, https://www.cropnutrition.com/resource-library/sulfurs-role-in-soybean-success/
8. Slaton, Roberts, and Ross. “Fertilization and Liming Practices.”
9. Sawyer, John E. “Nitrogen Fertilizer and Swine Manure Application to Soybean.” Iowa State University Extension, https://www.agronext.iastate.edu/soilfertility/info/nfertswmanure01.pdf
10. University of Minnesota Extension. “Soybean Fertilizer Guidelines.”
11. Hardy, David, et al. “Fertilization and Nutrient Management.” NC State Extension Publications: North Carolina Soybean Production Guide, 31 July 2025, AG-835, content.ces.ncsu.edu/north-carolina-soybean-production-guide/soybean-fertilization-and-nutrient-management.
12. Camberato, Jim, Shaun Casteel, and Kurt Steinke. Sulfur Deficiency in Corn, Soybean, Alfalfa, and Wheat. Purdue University Extension, AY-379-W, https://www.extension.purdue.edu/extmedia/AY/AY-379-W.pdf
13. Sawyer, John E. Nitrogen Fertilizer and Swine Manure Application to Soybean. Iowa State University Extension, 2001, https://www.agronext.iastate.edu/soilfertility/info/nfertswmanure01.pdf
14. Oldham and Jones. “Soybeans: Liming and Fertilization.”