Sulfur and Micronutrients Fertilizer Guide

Sulfur has become the fourth major nutrient in modern row crop systems. Atmospheric sulfur deposition from rain — the "free S" that older agronomists relied on — has declined 80–90% since the Clean Air Act. Zinc, boron, and manganese deficiencies are increasingly common, particularly in high-yield systems and no-till soils. Here is what to know.

Sulfur: The Fourth Major Nutrient

Product	S Content	Form	2026 Price
Ammonium sulfate (21-0-0-24S)	24% S	Dry granule	$380–$450/ton
Elemental sulfur (90% S)	90% S	Prilled/granule	$140–$200/ton
ATS (12-0-0-26S liquid)	26% S	Liquid	$0.28–$0.38/gal
Gypsum (CaSO₄)	18% S + Ca	Dry/prilled	$45–$80/ton applied

Sulfur deficiency symptoms: yellowing of newest (youngest) leaves — the opposite of nitrogen deficiency, which shows on oldest leaves first. This distinction helps diagnose the problem correctly in the field.

Corn responds to sulfur at rates of 10–20 lbs S/acre in deficient soils; soybeans respond at 8–15 lbs S/acre. Sandy soils, soils with low organic matter, and fields with no manure history are highest risk.

Zinc Fertilizer

Zinc is the most commonly deficient micronutrient in U.S. corn production. Zinc deficiency reduces corn yield 10–20% in severe cases and causes characteristic white striping on young leaves (white bud).

• Deficiency threshold: soil Zn below 1.0 ppm (DTPA extraction) indicates probable yield response
• Most cost-effective product: zinc sulfate (36% Zn) at $800–$1,100/ton. Apply 1–3 lbs Zn/acre to deficient soils.
• Avoid over-application: zinc accumulates and can become toxic above 4 lbs Zn/acre per year on many soils
• High-pH soils (above 7.2) reduce zinc availability regardless of soil content — chelated forms may be required

Boron Fertilizer

Boron deficiency is most common in alfalfa, canola, sunflower, and sugar beets. In corn and soybeans, deficiency is less frequent but occurs on leached sandy soils.

• Deficiency threshold: below 0.5 ppm water-soluble B in soil
• Most common product: Solubor (20% B) at $1,200–$1,600/ton; foliar boron at $4–$10/acre for in-season correction
• Boron has a narrow deficiency-toxicity range — do not apply without soil test confirmation

Manganese Fertilizer

Manganese deficiency is most common in soybean production, particularly on high-pH, high-organic-matter soils. Symptoms include interveinal chlorosis on young soybean leaves.

• Manganese sulfate (32% Mn) at $700–$950/ton; foliar Mn at $3–$8/acre
• Foliar application is more efficient than soil application on high-pH soils where Mn is chemically bound

Frequently Asked Questions

Do corn and soybeans need sulfur fertilizer?

Increasingly yes. Atmospheric S deposition has declined 80–90% since the 1980s as a result of Clean Air Act emissions controls. On sandy soils or fields with low organic matter and no manure history, corn and soybean response to 10–15 lbs S/acre is well-documented. Soil test before applying — over-application of sulfur is rare but possible.

What is the cheapest sulfur fertilizer per pound of S?

Elemental sulfur (90% S, prilled) at $140–$200/ton is the cheapest source per pound of S at $0.08–$0.11/lb S. However, elemental S must be oxidized by soil bacteria before becoming plant-available — this can take 4–8 weeks in cold soils. For immediate availability, ammonium sulfate or ATS liquid is more reliable.