By Greg LaBarge, CPAg/CCA, OSU Extension Field Specialist, Agronomic Crops, Adapted from C.O.R.N. 2024-02
Soil available and added phosphorus (P) nutrient impacts Ohio’s crop production and environment. Fertilizer P can increase crop yields. Yet, excessive P can have negative impacts on water quality, resulting in toxic algal blooms. To properly calibrate the use of P for maximum crop yield efficiency and environmental safety, it is important to monitor P use trends, understand the changes to P recommendations from 1995 to today, review changes in soil test phosphorus (STP), and identify the sources of P used. Two recent factsheets examine P nutrient use at two scales: statewide and regional. The regional results were summarized by Crop Reporting Districts (CRD). The two publications and their links are Phosphorus (P) Nutrient Use in Ohio ANR-0143, found at https://go.osu.edu/ohiop, and Ohio Phosphorus (P) Use by Crop Reporting District ANR-0144, found at https://go.osu.edu/ohiocrdp.
These two reviews of P use reveal several trends impacting agronomic management and environmental outcomes: Ohio purchased P fertilizer use is trending downward. During the highest use period (1993–1997), 206,000 tons of P2O5 were applied annually. In the most recent period (2018–2022), annual applications averaged 137,000 tons. Agriculture reduced the average yearly P2O5 application by 33% between the two periods.
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 annually.
Seven of nine Ohio CRDs show increased availability of P2O5 sourced from manure. CRD 30 and 80 show a decline. The 2017–2022 average annual increase in manure P2O5 is 28 to 355 tons for the seven districts with an increase.
Sixty-five percent of Ohio counties had decreasing trends in mean soil test P (STP) levels between 1993 and 2015. Since 2003, Ohio’s P2O5 removal through crop harvest has exceeded P applied as a nutrient, resulting in a net annual removal of 8 pounds of P2O5 per acre. Continued net removal would indicate that STP should continue trending downward, which has positive environmental impacts.
The P2O5 mass balance of applied nutrients through fertilizer and manure applications minus nutrients removed through crop harvest ranges from -14 to 1 pound per acre in Ohio’s nine CRDs.
P fertilizer recommendations developed in 1995 were modified, resulting in the reduced application of P fertilizer while still meeting crop production needs. Tri-state fertilizer recommendations were validated and re-released without significant changes for P use in a 2020 publication, Ohio State University Extension Bulletin 974 Tri-State Fertilizer Recommendations for Corn, Soybean, Wheat, and Alfalfa (Culman, et al., 2020).
Environmental Implications of CRD Data
