Ohio Phosphorus (P) Use by Crop Reporting District

Using phosphorus (P) crop fertilizer has environmental and agronomic impacts. P is a necessary nutrient for maximizing crop production. P can also contribute to water quality issues and harmful algal blooms. A review of regional data of Ohio, the application of P as fertilizer by the state’s crop reporting districts reveals trends that affect agronomic and environmental management:

• All nine Ohio crop reporting districts (CRDs) show a declining trend in P₂O₅ usage from 1994 to 2022. The reduction rate ranges from 50 to 868 tons per year.
• Seven of nine Ohio CRDs show an increase in manure P₂O₅ availability. CRD 30 and 80 show a decline. The 2017–2022 average annual increase in manure P₂O₅ is 28 to 355 tons.
• The P₂O₅ mass balance of applied nutrients minus nutrients removed through crop harvest is minus 14 to 1 pounds per acre. Only CRD 30 shows an increase of 1 pound per acre.
• Education, practice cost-share programs, and voluntary ag retailer certification programs are supporting better P use.

This fact sheet on regional P use is a companion to the Ohio line fact sheet, Phosphorus Nutrient Use in Ohio, which reviews statewide P trends. Methods described in Phosphorus Nutrient Use in Ohio section “Determining P₂O₅ Available from Fertilizer and Manure” were used to develop regional data based on Ohio Crop Reporting Districts (CRD) defined by the National Agricultural Statistics Service (NASS). Figure 1 shows the nine CRD regions defined by NASS. Regional data provides information that can be useful for agronomic and environmental management questions, including P₂O₅ fertilizer and manure availability data, and an estimate of the mass balance of input versus output. When Ohio’s major watersheds are laid over top of the CRDs some understanding of P use by watershed is gained.

Nutrient Availability: Fertilizer

Annual fertilizer P₂O₅ use has declined statewide by 69,000 tons or 33% when comparing two periods, 1993 to 1997 which was the highest P use period to 2018 to 2022, the most recent period (LaBarge, 2023). Figure 2 shows the average tons of P used by CRDs for their five highest years compared to the most recent five-year period 2018–2022. The highest use years are 1993–1997 for all CRDs except CRD 10, which had the highest usage from 1994 to 1998. The regions with the highest P₂O₅ use in the most recent period (2018–2022) are CRD 50, 10, 20, and 40, representing the major row crop-producing areas. All nine CRDs reduced P use when compared to the most recent five years (2018–2022).

Statewide P₂O₅ trendline data showed an increasing annual use rate of 7,052 tons (1987–1996) and a decreasing rate of 2,424 tons from 1994 to 2022 (LaBarge, 2023). Table 2 shows the trendline change by CRD for these same two periods. For 1987–1996, the most significant annual use increase occurred in CRD 50, 10, and 40. Since 1994, all CRDs have shown a declining rate of P₂O₅ fertilizer usage, with CRDs 10, 40, 50, and 20 having the greatest annual tonnage decreases.

Table 1 (click to download PDF). Annual change in trendline fertilizer usage by crop reporting district (CRD).

Nutrient Availability: Organic Nutrients

Organic nutrients in the form of livestock manures are an important P nutrient source. Ohio animal unit numbers have an overall upward linear trend from 2006 to 2020 (LaBarge, 2023). Trendlines for Ohio animal unit numbers were developed for each CRD to estimate the amount of P₂O₅ excreted and recovered for agricultural use from 2017 to 2022 (Table 2). More information on manure excreted and recovered tonnage development can be found in Phosphorus Nutrient Use in Ohio. The recovered P₂O₅ tonnage estimate is used for mass balance calculations, as shown in Figure 3.

Table 2 (click to download PDF). Estimated excreted and recovered tons of P2O5 from 2017 to 2022.

P₂O₅ Mass Balance

Nutrient application is one factor when determining nutrient mass balance. The other factor is nutrient removal through harvested crops. State and CRD average yields for corn, soybean, wheat, and corn silage saw increased trendline yields from 1987 to 2022. Figure 3 shows the annual mass balance trend for CRD 10 from 1987 to 2022 as an example. Contact the author for graphics of Ohio’s other CRDs. Mass balance is determined by taking the fertilizer and manure P₂O₅ applied and subtracting the calculated value of P₂O₅ removed in the harvested grain and biomass. The crops considered were corn, soybeans, wheat, hay, and corn silage, along with per bushel (or ton) P₂O₅ removal rates. Since 2003, statewide P₂O₅ removal through crop harvest has exceeded applied nutrients, resulting in a net annual removal of 8 pounds of P₂O₅ per acre (LaBarge, 2023). Table 2 summarizes the annual net balance for all nine CRDs from 2003 to 2022. CRDs 50 and 70 show the highest annual net removal at minus 14 pounds of P₂O₅ per acre. CRDs 10, 80, and 90 have a net annual removal of minus 11 pounds of P₂O₅ per acre.

Environmental Implications of CRD Data

Ohio's nonpoint source goals for improving water quality are related to nutrient management and reducing erosion. Agriculture is among the top reasons for the impairment of Ohio's water through nutrient enrichment, sedimentation/siltation, and organic enrichment (Ohio Environmental Protection Agency [OEPA], 2022). Nonpoint source nutrients, specifically phosphorus (P), have been in the spotlight for the Lake Erie basin. Mass balance studies (OEPA, 2020) show that 90% of P enters Lake Erie through the Maumee River basin from nonpoint sources. Due to agricultural land use covering 76% of the Maumee watershed, the nonpoint focus has fallen on agriculture practices (OEPA, 2020). While Lake Erie gets the primary press with annual harmful algal blooms, water quality issues from P in water bodies across Ohio, plus impacts on the Gulf of Mexico from the Ohio River basin watershed portion of the state, continue (OEPA, 2020).

Figure 4 shows the map of CRDs, along with Ohio's major watersheds. Regional P use trends help to identify the current and future environmental health of those watersheds. For example, CRDs10 and 20 represent nutrient application activity in the Western Lake Erie Basin. The Great Miami River is impacted by CRD 40 and 70, and CRD 50 represents most of the acreage in the Scioto River basin. Soil test P is one factor that can mitigate the amount of P loss at the edge of field (LaBarge & Cochran, 2023). The negative mass balance trends identified in Table 2 would result in lower soil test phosphorus (STP) values over time. Evidence that this is occurring can be found in previous studies that found 65% of Ohio counties had decreasing trends in mean STP levels between 1993 and 2015 (LaBarge, 2023). Future trends in STP are expected to continue to decline where crop removal exceeds the application of P.

Reason for Reduced P Use

Several factors have impacted farmer decisions in nutrient use since 1987. One factor was a 1995 collaborative effort to regionalize P recommendations (LaBarge, 2023). A second factor is the higher per-unit cost for P fertilizer since 2018. A third factor is increased education on fertilizer use resulting in the Fertilizer Applicator Certification in 2014. Farmers are required to use the Tri-State Fertilizer Recommendations for Corn, Soybean, Wheat, and Alfalfa, Bulletin 974 for their P recommendations when participating in Natural Resource Conservation Service cost-share programs, the 2017 4R Certified Ag Retailer voluntary third-party audit program, and the 2019 Ohio H2Ohio program. Increased farmer knowledge of P use, technical assistance programs, and economic returns are all driving reductions in P use.

References

LaBarge, G & Cochran, R. (2023). Understanding how soil test phosphorus impacts water quality [Fact sheet]. Ohioline.
ohioline.osu.edu/factsheet/anr-0111

LaBarge, G. (2023). Phosphorus nutrient use in Ohio [Fact sheet]. Ohioline.
ohioline.osu.edu/factsheet/anr-0143

Ohio Environmental Protection Agency (OEPA). (2022). Ohio 2022 integrated water quality monitoring and assessment report.
epa.ohio.gov/static/Portals/35/tmdl/2022intreport/Full-2022-IR.pdf

Ohio Environmental Protection Agency (OEPA). (2020). Nutrient mass balance study for Ohio's major rivers 2020.
epa.ohio.gov/static/Portals/35/documents/Nutrient-Mass-Balance-Study-2020.pdf