Soil available and added phosphorus (P) nutrient impacts Ohio’s crop production and environment in several ways. 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. This review on the use of P as a nutrient in fertilizer reveals some ongoing agronomic and environmental management trends:
- Purchased P fertilizer use is trending downward. An average annual reduction of 69,000 tons between the highest use period (1993–1997) to the most recent period (2018–2022) represents 33% less P2O5 used annually by Ohio agriculture.
- Sixty-five percent of Ohio counties had decreasing trends in mean soil test P (STP) levels between 1993 and 2015. Since 2003, 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 STP should continue trending downward which has positive environmental impacts.
- P fertilizer sources by order of greatest use are monoammonium phosphate > mixed nitrogen-phosphorus-potassium > diammonium phosphate = ammonium polyphosphate. These sources represent 95% of the commercial fertilizer sources applied in 2018–2022.
- Organic P nutrient excreted from livestock manure increased 670 tons annually from 2006 to 2022. Recovered manure–sourced P2O5 available for land application from 2018–2022 is 42,212 tons
- P fertilizer recommendations developed in 1995 were modified, resulting in 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).
Phosphorus is a primary nutrient needed by crops. It is also the focus of water quality concerns in the Western Lake Erie Basin and other state waters due to cyanobacteria and other aquatic plant blooms resulting from excessive aquatic P. Agricultural management practices to mitigate P impacts have focused on 4R nutrient management:
- right rate
- right place
- right time
- right source
4Rs nutrient goals are improved crop productivity through efficient nutrient use while minimizing the environmental impacts of off-site movement. The primary P sources used in agriculture are organic—primarily livestock manure—and commercial fertilizer manufactured from rock phosphorus. The following information provides P use trends, background on P recommendation approach changes made in 1995, changes in STP, and sources of P used in Ohio.
Determining P2O5 Available from Fertilizer and Manure
Tracking nutrient-use trends increases knowledge of nutrient-use efficiency and environmental risk. Nutrient Use Geographic Information System (NuGIS) provides methods to quantify nutrient use to meet two primary objectives:
- assess nutrient-use efficiencies and balances in crop production
- identify weaknesses in the balance estimation processes and the datasets used for these estimations
(Nutrient Use Geographic Information System [NuGIS], n.d.)
The NuGIS dataset provides tonnage-use values for fertilizer and manure sources of N, P2O5, and K2O. The current NuGIS dataset is available for 1987–2016, with no immediate plans to update. To provide a recent picture of Ohio P nutrient use, the NuGIS data was supplemented with Ohio Department of Agriculture (ODA) fertilizer tonnage data for 2006–2022 and livestock numbers from the National Agriculture Statistics Service (NASS) for 2006–2020.
NuGIS uses fertilizer-use data from the Association of American Plant Food Control Officials (AAPFCO). ODA participates in and provides fertilizer tonnage data to AAPFCO. Fertilizer tonnage data was requested from ODA for 2006 to 2022. ODA’s data from 2006 to 2016 was compared with the NuGIS data to validate the logic of combining the databases. In that comparison, an R2 value of 0.996 was present in the NuGIS and ODA 2006–2016 P data.
Estimating manure production is an inexact science. Various animal sizes, diet ingredients, water consumption, genetics, bedding materials, and other production factors result in variable manure volume and nutrient content from farm to farm. Not all nutrients excreted in animal manure are available for land application. Animals will deposit some manure in pastures, loafing areas, and open feedlots. While manure from animals grown in confinement is contained in centralized storage, nutrient transformations will impact manure volume and nutrient content. Storage has the greatest impact on nitrogen, where transformations result in lower available N. The total P and K content does not change from levels excreted from the animal, but a portion of P and K settles into the bottom of the storage unit. It is important to note that this settled portion of P and K is not resuspended during normal agitation at application.
Nutrient Use Geographic Information System (NuGIS) developed a methodology to estimate manure nutrients excreted by livestock and recovered from storage for land application. NuGIS uses " livestock inventory and sales data from the Census of Ag, and findings from previously published studies were used to estimate the annual volume of manure generated by several different livestock species, by county. Estimates of average annual manure excretion and nutrient content of that excreted manure are available by livestock species. These estimates are reported per 'Animal Unit,' which represents 1,000 pounds of live animal weight (NuGIS, n.d.)." NuGIS provides values for both excreted and recovered manure. Excreted manure is the output from the animal. Recovered manure is available for land application. The difference between excreted manure and recovered manure represents manure nutrients dropped by the animal in pastures, feedlots or accumulated in storage systems.
Ohio animal unit data from 2006 to 2020 was compared to the NuGIS database numbers from 2006 to 2016. Given that a linear relationship with animal number was found, the NuGIS data was extended for 2017 to 2022 to provide a reasonable estimate of manure P2O5 “excreted” and “recovered” (Figure 1). The yearly average manure excreted P2O5 in 2018–2022 was 70,077 tons, representing the maximum P2O5 available. Recovered manure sourced P2O5 available for land application in the same period is 42,212 tons. This annual average recovered manure P2O5 nutrient available would meet 24% of P2O5 removed in harvested grain and biomass.
Manure and Fertilizer Use
Figure 2 shows tons of P2O5 nutrients applied as commercial fertilizer and excreted by animals in manure from 1987 to 2022. The period of 1987–1996 shows increasing commercial fertilizer use with an annual increase of 7,052 tons of P2O5 (R2=0.33). From 1994 to 2022, a downward trend of 2,624 tons annually is shown (R2=0.42). The highest average annual fertilizer use period was 1993–1997 with 206,000 tons. In the most recent period of 2018–2022, the average annual fertilizer use was 137,000 tons. A comparison of the two periods shows a 33% reduction of 69,000 tons of P2O5 in 2018–2022 compared against fertilizer use in 1993–1997. The average annual manure-excreted P2O5 in the most recent period, 2018–2022, is 70,077 tons.
Nutrient application is one factor in determining P2O5 mass balance. The other factor is nutrient removal through harvested crops. State average yield for corn, soybean, wheat, and corn silage saw increasing trendline yields during this period. Figure 3 shows the estimated nutrient balance considering applied fertilizer and manure P2O5 minus expected crop removal based on the total annual production of corn, soybeans, wheat, hay, and corn silage along with per-bushel (or ton) P2O5 removal rates for each crop. Since 2003, P2O5 removal through crop harvest exceeded applied nutrients, resulting in a net annual removal rate of 8 pounds of P2O5 per acre. Increased yield and less applied P2O5 indicate better nutrient use efficiency.
Soil Test P Trends
When crop removal of P exceeds P applied as fertilizer or manure, we expect STP to decline. There is evidence that this expected observation is occurring. Trends in median soil test results for Ohio counties from 1993 to 2015 are shown in Figure 4 (Dayton, et al., 2020). Sixty-five percent of Ohio counties had decreasing long-term STP trends, whereas 15% had an increasing trend. The tri-state fertilizer guide (Culman, et al., 2020) recommends a maintenance (sufficiency) range of 20–50 parts per million (ppm) Mehlich 3 when a deficient STP of 20 ppm or less is present along with an increased risk of yield loss without added nutrients. Only two counties showed median STP values over the tri-state STP maintenance (sufficiency) range from 1993 to 2015. The decreasing long-term trends in STP and declining trend in P2O5 use (Figure 4) suggest farmers are managing STP and P inputs to maximize yield and profitability while minimizing off-site environmental impacts. Given that the mass balance in Figure 3 shows continued net removal of P, we can expect to see continued declines of STP in the future.
Changes in Nutrient Recommendations
The ability to reduce P nutrient inputs while maintaining crop yields is due to the buffering capacity of soil to provide P to the soil solution for plant uptake. The soil's ability to supply P is measured using a soil test. Determining the amount of nutrients needed to be added to the soil to supplement soil-supplied nutrients is a foundational area of study in soil fertility research. The basis of university fertilizer recommendations is the correlation of the measured soil test value to the crop’s yield responsiveness when more fertilizer is added to the soil.
The change in P nutrient use which occurred around 1995 coincided with a major change in regional nutrient recommendations. Regional universities and the agriculture industry historically provided P application recommendations. Before 1995, these fertilizer recommendations differed to a large degree for given soil test P (STP) values and crop production levels. In instances with the same STP and crop, recommendations for P application by The Ohio State University, Purdue University, Michigan State University, and three independent laboratories differed by 50 or more pounds (Table 1). Conversations between university researchers and the agriculture industry in the 1990s resulted in a consolidated recommendation framework to serve farmers' needs better. Tri-State Fertilizer Recommendation for Corn, Soybeans, Wheat, and Alfalfa, Extension Bulletin E-2567, was published in July 1995 (Vitosh, et al., 1995). Table 1 shows the pre-1995 range of P recommendations for corn and soybean (Wallingford, 1990) and those in the 1995 Tri-state recommendation publication. The 1995 P recommendation from this publication provided a single value on the lower end of the ranges used before 1995. The Tri-state recommendations were validated through field trials in 2014–2019 and re-released without significant changes to the P recommendations in a new publication, Tri-State Fertilizer Recommendations for Corn, Soybean, Wheat, and Alfalfa, Bulletin 974 (Culman, et al., 2020).
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P Sources
Discussions around current water quality issues sometimes point to P fertilizer sources as a contributing factor. The Ohio Department of Agriculture (ODA) database provides details that can be used to group P by source. Ammoniated P fertilizers in various dry and liquid formulations are commonly used in Ohio. Monoammonium phosphate (MAP), often referred to as 11-52-0, and diammonium phosphate (DAP), referred to as 18-46-0, are dry products. Ammonium polyphosphate (APP), often referred to as 10-34-0, is a liquid product. All three products have 100% available total P when reacting with water in the soil. These three base-P sources are mixed with other fertilizers to formulate custom nitrogen-phosphorus-potassium (NPK) blends with varied analyses. The amount of P per unit of NPK fertilizer tends to be low, ranging from 2% to 20%. Figure 5 identifies the percentage of annual sales by product type. MAP, DAP, mixed NPK products, and APP constitute 95% of the P fertilizer used. Comparing the 2006–2010 period to the 2018–2022 period shows a shift to MAP and NPK with a decreased use in DAP and APP sources.
Phosphorus from animal manure is a combination of organic and inorganic forms. Inorganic P is 45%–70%, whereas organic P is the rest (Zhang, 2017). The inorganic P is in orthophosphate form, equivalent to commercial fertilizer forms. Microorganisms easily mineralize the organic P. The rate of mineralization depends upon temperature, moisture, and soil pH. From a practical perspective, a unit of P2O5 in manure is equivalent to fertilizer for managing STP.
Summary
Ohio agriculture reduced P fertilizer use by 69,000 tons, representing a 33% reduction in P2O5 use in 2017–2022 compared against the application of P2O5 in 1993–1997. An estimated 42,212 tons of manure P2O5 provided 24% of the P2O5 applied annually from 2018 to 2022. The combined factors of increased yield, reduced fertilizer application, and better manure utilization led to a net removal of 8 pounds of P2O5 across all Ohio agricultural lands from 2003 to 2022. The trend in reduced median soil test P (STP) levels across most Ohio counties from 1995 to 2015 supports this finding of net removal. P fertilizer recommendations developed in 1995 reduced P fertilizer recommendations while still meeting crop production needs. The tri-state recommendations were validated, and P recommendations were re-released without significant P recommendation changes in a new publication, Tri-State Fertilizer Recommendation for Corn, Soybean, Wheat, and Alfalfa, bulletin 974 (Culman, et al., 2020). Fertilizer sources of MAP, mixed NPK, and DAP=APP represent 95% of the commercial fertilizer source applied in 2018–2022. The average annual manure excreted P2O5 in the most recent period, 2018–2022, is 70,077 tons. Phosphorus from animal manure is a combination of organic and inorganic forms. Generally, the inorganic P is 45%–70%, with organic P making up the rest.
A companion factsheet, Ohio P Use by Crop Reporting District , provides regional trends in P use.
References
Culman, S., Fulford, A., Camberato, J., & Steinke, K. (2020). Tri-state fertilizer recommendations for corn, soybean, wheat, and alfalfa, bulletin 974. College of Food, Agricultural, and Environmental Sciences, The Ohio State University.
extensionpubs.osu.edu/tri-state-fertilizer-recommendations-for-corn-soybean-wheat-and-alfalfa
Dayton, E. A., Shrestha, R.K., Fulford, A. M., Love, K.R., Culman, S. W., & Lindsey, L.E. (2020). Soil test phosphorus and phosphorus balance trends: A county-level analysis in Ohio. Agronomy Journal, 112(3), 1617–1624.
doi.org/10.1002/agj2.20146
Nutrient Use Geographic Information System (NuGIS). (n.d.). The Fertilizer Institute. Retrieved October 31, 2023, from
nugis.tfi.org
U. S. Department of Agriculture (USDA). (n.d.). USDA’s National Agricultural Statistics Service Ohio’s Field Office. Retrieved October 31, 2023, from
nass.usda.gov/Statistics_by_State/Ohio/Publications/Annual_Statistical_Bulletin/index.php
Vitosh, M.L., Johnson, J.W., & Mengel, D.B. (Eds.). (1995). Tri-state fertilizer recommendations for corn, soybeans, wheat, and alfalfa, Extension bulletin E-2567. Michigan State University, The Ohio State University, & Purdue University.
agcrops.osu.edu/sites/agcrops/files/publication-files/Tri-State.pdf
Wallingford, G.W. (1990). Fertilizer recommendations in the Eastern Corn Belt. NC Extension-Industry Soil Fertility Conference (53rd Annual). northcentralfertility.com/proceedings/?action=abstract&id=3543&title=Fertilizer+Recommendations+in+the+Eastern+Corn+Belt&search=years
Zhang, H. (2017). Managing phosphorus from animal manure. Oklahoma Cooperative Extension Service.
extension.okstate.edu/fact-sheets/print-publications/pss/managing-phosphorus-from-animal-manure-pss-2249.pdf