Understanding mechanisms of sulfur cycling in Minnesota soils and availability from fertilizer

Study author(s): Daniel Kaiser, University of Minnesota, Department of Soil, Water, and Climate
Growing season(s): 2018, 2019, 2020, 2021, 2022, 2023, 2024, 2025
Minnesota location(s): Becker, Morris, Rosemount, and Waseca

Important: to view the complete findings, including all tables and figures, please download the full research reports using the links to the right.

2025 Growing Season2023 Growing Season2022 Growing Season2020 Growing Season

WHAT IS THIS PROJECT ABOUT?

This project investigates how sulfur (S) fertilizer behaves over time in Minnesota soils under a continuous corn crop. Standard soil tests struggle to reliably track sulfate levels or predict crop yield responses, leaving gaps in understanding how different sulfur fertilizers release nutrients over multiple seasons.

The main problems addressed by this study include:

  • Soil test limitations: Current standard soil tests have difficulty detecting changes in sulfate-S caused by fertilizer applications, often showing high sulfate levels even in fields that actively respond to sulfur fertilization.
  • Uncertainty around elemental sulfur performance: Low-cost elemental sulfur options (like Tiger 90) must be converted into sulfate by soil bacteria (Thiobacillus) before plants can use them. Because these bacteria slow down in cool soil temperatures, elemental sulfur breaks down slowly—sometimes taking 5 to 6 years of annual application to fully build up available sulfur.
  • Lack of long-term carryover data: Farmers need to know how long applied sulfur remains available in the soil profile after applications stop, and whether residual sulfur can sustain yield for subsequent crops.

KEY PROJECT GOALS & FARMER BENEFITS

  1. Comparing fertilizer options: Evaluates quick-acting sulfate fertilizers (potassium sulfate) against slower-releasing elemental sulfur sources (Tiger 90 and Micronized Sulfur Technology / MST) to see which provides the best long-term value.
  2. Determining application longevity: Helps farmers understand how quickly sulfur wears off when yearly applications are stopped. Data shows that stopping sulfate applications drops yields back to un-fertilized levels in 1 to 2 years, whereas elemental sulfur (like MST and Tiger 90) breaks down more slowly and carries over longer.
  3. Optimizing application rates: Demonstrates that applying 10 to 20 lbs of S per acre per year is generally sufficient for medium to fine-textured soils, preventing over-application and lowering input costs.
  4. Predicting crop health: Uses tissue testing (leaf S concentrations and SPAD meter readings) to better link plant nutrient levels to final corn grain yields.

HOW THE STUDY WILL BE CONDUCTED

  • Field sites: Multi-year field trials are conducted at Rosemount and Waseca, Minnesota on continuous corn plots.
  • Split-plot treatment plan: Plots previously treated with sulfur for four consecutive years (2019–2022) were sub-divided starting in 2023. Half of each plot continues to receive annual spring applications of sulfur, while the other half has application halted to measure residual carryover and soil nutrient drawdown.
  • Tested rates & sources: Three sulfur sources (potassium sulfate, Tiger 90, and K-MST) are applied at annual rates of 0, 5, 10, and 20 lbs of S per acre.

Measurements:

  • Early plant vigor is tracked at the V5 growth stage using active sensors (NDRE).
  • Leaf tissue samples are collected at the V10 stage (upper leaf) and R1 stage (ear leaf) to measure S concentration and leaf greenness.
  • Harvest data is collected to evaluate corn grain yield, grain S concentration, and total sulfur removal.
  • Soil samples down to a depth of 2 feet (0–24″) are analyzed every fall to monitor deep soil sulfate levels.
Back To Top