Potassium (K) is a primary macronutrient essential for crop growth. In agriculture, K is supplied by soil-derived potassium, supplemented by nutrient applications from organic sources—primarily livestock manure—and by commercial fertilizers manufactured from mined deposits of potassium chloride (KCl) originating from ancient seabeds (Mertz-Myers, 2025).
Potassium uptake by plants occurs primarily through diffusion, a process driven by nutrient concentration gradients near the root surface (Rakkar, 2024). Soil testing measures the soil’s ability to supply K. Fertilizer recommendations are based on correlations between soil test levels and the amount of added K required to achieve a yield response in a given crop. Tracking soil-test trends helps guide long-term nutrient management to support increasing crop yields.
This fact sheet summarizes trends in the use of K sources applied for Ohio crop production, the mass balance of nutrient additions and removal at a state and regional scale and state soil test K trends.
Nutrient Use
Monitoring nutrient-use trends helps evaluate nutrient-use efficiency and identify opportunities for improved nutrient management. The Nutrient Use Geographic Information System (NuGIS, n.d.) provides county-level estimates of fertilizer and manure nutrient use with two main objectives:
- Assessing nutrient use efficiencies and balances in crop production.
- Identifying weaknesses in nutrient balance estimation methods and datasets.
NuGIS provides annual tonnage estimates for fertilizer- and manure-derived nitrogen, phosphorus, and potassium from 1987–2016. To extend these estimates through 2024, Ohio Department of Agriculture fertilizer tonnage data (ODA, 2024) along with crop and livestock inventory data from the National Agricultural Statistics Service (NASS, 2024) were analyzed using the NuGIS framework. Methods used to assemble the data are described in Phosphorus (P) nutrient use in Ohio (LaBarge, 2023).
Applied K2O from Fertilizer and Manure
Commercial K fertilizer used in Ohio crop production is primarily potassium chloride (0-0-60). Potassium in manure is largely present in ionic form and is considered nearly 100% plant available during the year of application. First-year availability of potassium from manure is 80%–90%. Commercial K fertilizer and manure are both valuable resources to meet the potassium needs of crops.
Figure 1 shows commercial fertilizer and manure-derived K2O applied from 1987–2024. Commercial fertilizer applications averaged 279,000 tons annually, ranging from 231,000 to 327,000 tons, with a long-term decreasing trend of 1,600 tons per year. Manure-derived K2O increased by an average of 654 tons per year over the same period. During 2020–2024, manure contributed an average of 52,000 tons of K2O annually—enough to supply approximately 16% of statewide crop-removal needs.
Nutrient application is only one component of nutrient-use efficiency; nutrient removal through harvested crops is equally important. Figure 2 illustrates Ohio’s annual estimated K2O balance, accounting for fertilizer inputs, manure inputs, and crop removal based on annual production of corn, soybeans, wheat, hay, and corn silage. Removal estimates use standard per-bushel or per-ton K2O removal coefficients.
The statewide K2O mass balance shows an average of 1 pound of K2O removed per acre annually (Figure 2), indicating that the nutrient is applied at a crop removal rate where nutrient removed is replaced by applied fertilizer or manure. From 1987 to 2024, state average yields for major crops have increased despite overall decline in potassium applied, suggesting improved potassium nutrient-use efficiency with closer attention to nutrient management.
Ohio K Use by Region
Looking at potassium nutrient use by region reveals regional differences influenced by the major crops grown. Figure 3 shows Ohio’s nine crop reporting districts (CRDs). CRDs 10, 20, 40, and 50 are the primary row-crop-producing regions in the state, producing 84% of corn, 78% of soybeans, and 84% of wheat bushels annually during the period 2020–2024. CRDs 30, 60, 70, 80, and 90 grew 67% of the tons of hay produced annually in the state during the period from 2020 to 2024. These differences in regional crop and livestock systems influence K fertilizer use and mass balance.
One difference across regions is the annual mass balance of K2O nutrient use by CRDs over the past 20 years, from 2005 to 2024. K2O mass balance was calculated by estimating the annual amount of K2O applied from fertilizer and manure, then subtracting the amount of K2O removed by corn, soybean, wheat, corn silage, and forage crops. Positive values indicate that nutrient applications exceeded the K2O subtracted through crop removal. Negative values indicate that the K2O subtracted through crop removal exceeded the applied K2O. Figure 3 shows the annual mass balance of K2O in lb per acre. A negative number, shown in parentheses, indicates that more potassium was removed than added in manure and fertilizer applications. For example, CRD 60 shows that the K2O nutrient removed averages 21 pounds per acre higher than the K2O nutrient applied. Persistent negative mass balances are expected to result in declining soil-test K levels over time.
Figure 4 compares the average K2O fertilizer use across two five-year periods: 1992–1996 and 2020–2024. CRDs 10, 20, 40, and 50 account for 76% of statewide K fertilizer use. These regions are dominated by row-crop production and confinement livestock systems, resulting in greater manure-K application to cropland. Other regions have more forage-based and pasture-based livestock systems, leading to different nutrient-cycling dynamics. Generally, all districts show lower potassium fertilizer use during 2020–2024 than during 1992–1996.
Soil Test Trends
Figure 5 shows median soil-test K values for Ohio across five sampling periods from 2001–2020 (Soil Test Summary, n.d.). According to Tri-State Fertilizer Recommendations (Culman, 2020), the maintenance range for potassium in most Ohio soils is 120–170 ppm. This maintenance range is generally applied across both row and forage crops.
The 2020 sample data show a near doubling of the percentage of samples (13%) below 80 ppm and a slight increase of the percentage of samples (28%) in the 81–120 ppm range compared with previous years. Samples that fall within the Tri-State maintenance range of 121–160 ppm have remained constant, averaging 28% of all samples across all years. Samples measuring greater than 161 ppm have declined. The increasing proportion of samples below the critical level of 120 ppm suggests that annual potassium applications should be considered to maintain crop productivity. Farmers should closely monitor soil tests for indications of low potassium soil and crop response.
Overall, long-term potassium use in Ohio reflects a generally balanced system in which fertilizer and manure applications closely match crop removal, supporting continued gains in crop yields and nutrient-use efficiency. However, regional patterns and soil test trends reveal emerging concerns:
- Forage-dominated districts consistently remove more K than they apply.
- Statewide soil test data show a growing share of fields falling below the critical potassium threshold.
These declines indicate that, despite stable statewide averages, localized K depletion is increasing and may limit crop productivity if not addressed in nutrient management plans. Continued monitoring of soil test levels, attention to regional nutrient balances, and appropriately timed potassium applications are essential to maintaining potassium availability to support Ohio’s diverse crop and livestock systems.
References
Culman, S., Fulford, A., Camberato, J., & Steinke, K. (2020). Tri-State fertilizer recommendations, Bulletin 974. The Ohio State University.extensionpubs.osu.edu/content/sample/e974.pdf
LaBarge, G. (2023). Phosphorus (P) nutrient use in Ohio. Ohioline. Ohio State University Extension.
ohioline.osu.edu/factsheet/anr-0143
Mertz-Myers, M. (2025). Understanding potash. The Fertilizer Institute.
tfi.org/media-center/2025/03/10/understanding-potash
National Agricultural Statistics Service (NASS). (2024). USDA’s national agricultural statistics service Ohio field office. United States Department of Agriculture.
nass.usda.gov/Statistics_by_State/Ohio/Publications/Annual_Statistical_Bulletin/index.php
ODA. (2024). Ohio commercial fertilizer tonnage data. Personnel communication.
Rakkar, M., & LaBarge, G. (2024). Potassium uptake and Ohio crop response. Ohioline. Ohio State University Extension.
ohioline.osu.edu/factsheet/anr-0147
Nutrient Use Geographic Information System (NuGIS). (n.d.).
nugis.tfi.org.
Soil Test Summary. (n.d.). Soil test levels in North America.
soiltest.tfi.org