Potassium Management Effects and Chloride Cycling in Potato and Corn Cropping Systems

Study author(s): Carl Rosen, University of Minnesota
Growing season(s): 2023, 2024, 2025 (includes 2024)
Minnesota location(s): Various

Note: Complete reports with figures and tables are available for download.

2025 Growing Season2023 Growing Season

CORN

WHAT IS THIS PROJECT ABOUT?

This study investigates how different potassium (K) sources and chloride (Cl) application rates affect crop yield, plant nutrient uptake, soil nutrient levels, and groundwater leaching in a dryland corn-soybean rotation.

Farmers heavily rely on potassium chloride (KCl or 0-0-60) to supply potassium, but this fertilizer delivers large amounts of chloride alongside it. While chloride is a micronutrient, excessive amounts can cause yield losses, particularly in soybeans, which are far more sensitive to chloride toxicity than corn.

This project was conducted to address key agronomic questions:

  • The Chloride Risk: Determining if applying standard rates of KCl causes yield reductions or toxicity in soybeans or corn.
  • Alternative Nutrient Sources: Evaluating whether more expensive non-chloride potassium fertilizers—such as potassium sulfate (K2SO4  or 0-0-50) or liquid dairy manure—are economically or agronomically necessary to avoid chloride toxicity.
  • Nutrient Timing and Carryover: Testing whether applying high rates of KCl only during corn years allows enough chloride to leach out of the root zone before soybeans are planted the following year.
  • Chloride Leaching and Environmental Cycling: Understanding how chloride moves through the soil profile, how much is taken up and held in crop stover, and how much leaches into groundwater during wet versus dry years.

WHAT ARE KEY PROJECT GOALS & POTENTIAL FARMER BENEFITS?

  • Optimized Fertilizer Selection: Helps growers determine if switching from standard KCl to more expensive K2SO4 provides any tangible yield benefit, or saving input costs if cheaper KCl remains safe to use.
  • Improved Rotation Timing: Provides clear recommendations on whether chloride-heavy fertilizers or manures should be applied exclusively prior to corn crops to protect sensitive soybean crops the following season.
  • Manure Value Clarification: Evaluates how manure performs as a potassium and chloride source compared to commercial fertilizers, helping dairy and livestock operations better manage multi-nutrient applications.
  • Environmental & Chloride Cycling Insights: Tracks removal of chloride in grain, chloride leaching deeper into the water table and reveals how stover residue retains chloride from one season to release into the next.

HOW WILL THE STUDY BE CONDUCTED?

  • Field Setup: The research was established on a dryland Waukegan silt loam soil at the Rosemount Research and Outreach Center (RROC) in Rosemount, Minnesota, following a corn-soybean rotation across multiple years (Corn in 2023, Soybeans in 2024, Corn in 2025, and Soybeans in 2026). Sulfur was applied to all plots to eliminate sulfur as a variable in the study.
  • Experimental Treatments: Eleven distinct treatments were arranged in a randomized block design with four replications, testing varying application strategies:
  • Check & Control Plots: A zero-potassium/zero-chloride check treatment and a chloride-only treatment using calcium chloride (CaCl2) to isolate chloride effects without adding potassium.
  • Fertilizer Comparisons: Three application rates of potassium (50, 100, and 150 lbs/acre K2O) applied as either KCl or K2SO4.
  • Manure Treatments: Liquid dairy manure applied to supply target nitrogen (150 lbs/acre N), which co-applied significant rates of K2SO4 and chloride.
  • Application Frequency: Comparing single-year applications (applied only during corn years) against split yearly applications (applied in both corn and soybean years).

Sampling & Analysis:

  • Yield Measurements: Grain, cob, and stover biomass were harvested annually using full-plant tissue samples and plot combines in the corn years and grain and stover in the soybean years.
  • Plant Tissue Testing: Harvested tissues were laboratory-tested for potassium, chloride, sulfur, and calcium concentrations to determine total per-acre nutrient uptake.
  • Soil Testing: Soil samples (0–6 inches and 0–2 feet) were periodically evaluated to monitor available soil potassium and chloride build-up or depletion.
  • Water Leaching Tracking: Deep soil suction lysimeters (installed 6 feet deep) collected sub-surface soil water throughout the growing season to measure daily chloride leaching loads based on a water balance approach using  local rainfall and evapotranspiration data.

POTATO

WHAT IS THIS PROJECT ABOUT?

This project evaluates potassium (K) management strategies and chloride (Cl) cycling in irrigated potato cropping systems on sandy soils. Potassium is required in large amounts for potato yield, tuber bulking, and bruise reduction, but it is often applied as potassium chloride (muriate of potash), which introduces significant amounts of chloride. The study investigates whether alternative application methods, split timing, or switching to potassium sulfate can improve fertilizer efficiency and reduce the negative side effects associated with excessive chloride.

WHAT ARE KEY PROJECT GOALS & POTENTIAL FARMER BENEFITS?

The primary goals and potential benefits to farmers include:

  • Evaluating Potassium Application Rates & Sources: Comparing low-cost potassium chloride against potassium sulfate to see if avoiding chloride improves crop yield, tuber size, and tuber specific gravity.
  • Improving Fertilizer Efficiency: Determining if placing potassium chloride in concentrated bands in the root zone or splitting applications between planting and hilling reduces the total amount of fertilizer required.
  • Reducing Crop Quality Risks: Identifying how chloride impacts internal tuber defects (such as hollow heart and brown center) and tuber processing quality (specific gravity and sugar ends).
  • Tracking Chloride Cycling and Environmental Loss: Measuring chloride removal by the tubers and chloride leaching to 4-foot soil depths to understand environmental risks to freshwater ecosystems and confirm whether high chloride carries over in the soil to subsequent crop years.

HOW WAS THE STUDY CONDUCTED?

The study was conducted at the Sand Plain Research Farm in Becker, MN, using field trial plots of Russet Burbank potatoes grown on loamy sand soil following soybeans over three years (2023, 2024 and 2025). Researchers applied 12 distinct field treatments featuring different rates, timings, placement methods (broadcast vs. banded vs. split), and fertilizer sources (potassium chloride, potassium sulfate, and calcium chloride). Sulfur was applied to all plots to eliminate sulfur as a variable in the study. Throughout the season, data was collected on plant canopy cover, leaflet greenness, stem counts, and tissue nutrient concentrations from leaf petioles, vines, and tubers, and chloride input from irrigation water. At harvest, yield was sorted by size and grade, tubers were evaluated for internal defects and specific gravity, and soil/soil-water samples were collected using lysimeters to measure nutrient uptake and chloride leaching loads.

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