Methodology

Animal feeding operations identification

EWG received a list of permitted animal feeding operations, or AFOs, from the Wisconsin DNR (WIDNR, 2018), which listed the dominant animal type and number of animal units, or AU, for each operation. This dataset was used for all counties except Kewaunee, for which EWG used a dataset derived from 2020 WPDES Annual Reports (Midwest Environmental Advocates, 2021).

Animal units listed in the WIDNR dataset were converted to animal counts using the WIDNR Animal Unit Calculation Worksheet. Dominant animal types included “dairy” (1 AU = 1.4 mature dairy cows), “heifers” (1 AU = .85 dairy heifers), “beef” (1 AU = 1 beef cow), “poultry” (1 AU = .01 layers) and “swine” (1 AU = .4 swine). A more detailed breakdown of animal types and sizes was provided for permitted operations in Kewaunee County, which also listed “dairy calves” (1 AU = .2 dairy calf) and “beef calves” (1 AU = .2 beef calf). EWG removed four operations that had no AU listed, leaving 51 permitted operations in the nine counties.

To identify unpermitted operations, EWG scanned 2018 National Aerial Imagery Program, or NAIP, photography to locate and attribute AFOs with an “animal type” (cattle, dairy, beef, poultry or swine), “size” and “access to pasture” designation. Size was defined using a small (50 to 199 cows), medium (200 to 499) or large (more than 500) designation for cattle operations, and a barn count for poultry and swine. We could not confidently assign dairy and beef to small cattle operations, so they were assigned a “cattle” animal type. We gave a “dairy” or “beef” designation to each medium or large cattle operation.

Multiple geographic information system, or GIS, analysts (at least three and up to five) independently attributed each operation, and we accepted the majority animal type, size and pasture designation. Where a majority consensus did not exist, at least two GIS analysts together revisited the operation to agree upon final attribution. The total number of operations we identified in each county is shown in Table 1 below. 

Table 1. Count of animal feeding operations identified or permitted in nine Wisconsin counties.

^{Source: EWG/MEA via Wisconsin Department of Nature Resources and NAIP imagery (2018).} 

Animal counts

The 2017 Agricultural Census was used to guide the number of animals allocated to each unpermitted operation, based on its size designation. To calculate the number of animals assigned to small operations, for example, we divided the total number of cattle and calves housed in farms between 50 and 199 cows by the number of farms in this same size category. We performed this same calculation for medium operations (cattle and calves in farms with 200 to 499 cows) and large operations (more than 500 cows) for each of the nine counties. When the large rate exceeded 1,000 cows, this rate was reduced to 1,000 cows per large operation. For small cattle operations for which a dairy-versus-beef distinction could not be assigned, we assumed the ratio of beef to milk cows listed in the 2017 Agricultural Census for each small operation in that county.

All but 21 of the 1,850 unpermitted operations were cattle operations. For the very few swine and poultry operations identified, a similar rate was calculated using the 2017 census. The number of hogs housed in operations with more than 100 hogs was divided by the number of operations with more than 100 hogs to define a swine count per farm in each county. The census does not provide a size breakdown for poultry operations. Instead, we assumed the total number of layers in each county (divided by the number of layer operations) for all poultry operations identified. Overall, the contribution of poultry and swine to overall animal counts and manure generation was nominal.

Table 2 lists EWG/MEA cattle counts compared to the 2017 Agricultural Census. In all but two counties (Adams and Kewaunee), EWG/MEA animal counts came in below census inventories.

Table 2. Total estimated cattle and calves in nine Wisconsin counties. 

^{Source: EWG/MEA via Wisconsin Department of Nature Resources, NAIP imagery (2018), and USDA-NASS 2017 Census of Agriculture.}   

Manure nutrients

We estimated manure nutrients using literature values from the Wisconsin NRCS Nutrient Management Technical Note and SnapPlus software. When provided for permitted facilities, animal size categories (dairy heifer versus mature dairy cow) were used to estimate manure nutrients. We estimated manure nutrients for unpermitted operations using the following assumptions:

• Dairy – 1,400-pound mature lactating dairy cow
• Beef – 1,100-pound high-energy beef cow
• Swine – 150-pound grow-finish pig
• Poultry – Layer

Table 3 summarizes the manure nutrient values used. Animals were assumed to be present 365 days a year. To estimate manure volumes, we assumed a ratio of solid to liquid manure based on AFO size. Small- and medium-sized beef operations were considered to produce 100 percent solid manure, whereas a 75/25 solid-to-liquid ratio was assumed for large beef operations. We assumed a 75/25, 50/50 and 25/75 solid-to-liquid ratio for small, medium and large dairy operations, respectively. All poultry manure was assumed to be solid and all swine manure liquid.

Table 3. Literature values used for manure nutrient estimation.

^{Source: EWG/MEA via SnapPlus and Wisconsin NRCS Conservation Planning Technical Note 1.}

Unrecoverable manure

For cattle operations with an “access to pasture” flag, manure nutrients were reduced by 50 percent, assuming half of this manure is deposited on pasture and is therefore unrecoverable. This reduction was substantial, with 1,414 of 1,879 cattle operations receiving a pasture designation. There was a direct correlation between access to pasture and operation size, with 85 percent of all small operations, 66 percent of medium, and 36 percent of large operations having some access to pasture. Total nitrogen, or N, and phosphorus, or P205, contained within stored manure was reduced by 24 percent and 26 percent, respectively, accounting for unrecoverable manure.

Crop nutrient needs

Nitrogen

The Agricultural Conservation Planning Framework, or ACPF, database provided crop rotation history for each field in the nine-county area from 2014 to 2019. Each field received an N recommendation for each year, based on the current and previous crop grown, the dominant soil type in the field, derived from USDA gSSURGO database, and leading crop nutrient recommendations. The SnapPlus Wisconsin Soil Classifications for Nutrient Management Planning was used to match dominant soil types within each field to a corresponding soil texture and yield potential.

Table 4 shows a summary of the N rates used. A .05 MRTN rate was used for corn and wheat, assuming a lower cost for manure than commercial fertilizer. A first-year corn-following-alfalfa credit of 140 pounds per acre and 90 pounds per acre was assumed for loamy and sandy soil fields, respectively, and a second-year corn-following-alfalfa credit of 50 pounds per acre was assumed for loamy soil fields.

Phosphorus

Six-year average county crop yields (NASS Surveys, 2014-2019) were used to estimate the average amount of phosphorus removed annually from each field and for each year in the rotation. Although statewide yields are shown in Table 5, the analysis utilized county-specific crop yields to estimate phosphorus removal rates for each field.

As crop rotations in the ACPF are derived from the NASS Cropland Data Layer, or CDL, we could not distinguish between corn for grain and corn silage. Therefore, the average of phosphorus removal rates for “corn for grain” and “corn for silage” were used for all fields and years planted to corn.

Table 4. Nitrogen fertilizer recommendations for major crops in Wisconsin.

^{Source: EWG/MEA via SnapPlus and University of Wisconsin Extension.}

Table 5. Phosphorus removal rates for major crops in Wisconsin.

^{Source: EWG/MEA via USDA-NASS Crop Yield Surveys and Wisconsin NRCS Conservation Planning Technical Note 1.}

Modeling manure application

Manure application was simulated for each year between 2014 and 2019. Manure was spatially applied from AFO to fields using the methods described in Porter and James, 2020. Briefly, manure is spatially applied from AFO to proximal fields moving outward from each AFO until no manure nutrients remain.

A recent improvement to this approach allows for manure allocation to be modeled for each year in the analysis, rather than using a six-year average nutrient recommendation for each field. This allows for manure to be applied using year one manure N availability, while tracking the percentage of residual (year two) N remaining on each field. Any residual N remaining on each field is subtracted (credited) from its current year nutrient requirement. This occurs when consecutive years of crops with an N recommendation are grown.

Manure allocation was modeled for three scenarios, described by:

Scenario 1: Application to non-legume crops only – corn, wheat, potatoes and small grains – to meet the recommended amount of N fertilizer for each field.

Scenario 2: Application to non-legume crops plus alfalfa – corn, wheat, potatoes, small grains and alfalfa – to meet the recommended amount of N fertilizer for each field.

Wisconsin rules allow manure application to alfalfa up to the amount of N that can be removed. This is seen as increasing spreadable acres during the growing season when manure storage may be limited. Despite challenges with timing, risk of soil compaction and damage to alfalfa stands, alfalfa can remove relatively high rates of nutrients and can benefit from secondary micronutrients in manure. Therefore, some manure application to alfalfa likely occurs.

Manure N application rates for alfalfa were derived from the USDA Wisconsin Nutrient Management Technical Note. In all but one county, Adams, average alfalfa yields fell between 2.6 and 3.5 tons per acre, equating to a manure N application rate of 155 pounds per acre. A 100 pound per acre N application rate was assumed for alfalfa in Adams County.

Scenario 3: Application to all crops – corn, wheat, potatoes, small grains, alfalfa and soybean – at the average annual phosphorus removal capacity of each field. Average annual phosphorus removal for each field was estimated by summing the phosphorus removal for each year in a six-year rotation (2014-2019), then dividing by six.

No losses were assumed for manure phosphorus, which means the estimated amount of phosphorus in stored manure was available for field application. In contrast, a significant portion of manure nitrogen is lost during manure application. This is reflected in the year one and year two N availabilities calculated for each AFO. For scenarios 1 and 2, manure was applied based on year one N availability, while crediting any residual, or year 2, manure N present on each field from a previous years’ application.

Contribution from commercial fertilizer

Wisconsin does not publish county-level fertilizer sales. In lieu of this dataset, statewide sales from 2017 to 2018, which include both farm and non-farm uses, were apportioned to each of the nine counties based on their respective percentage of statewide fertilizer and lime expenditures, as reported in the 2017 Agricultural Census. Statewide sales in 2017-2018 for both N and P205 fell within 1 percent of the five-year average.

Table 6. Estimated commercial nitrogen and phosphorus sold (in tons) in each of the nine counties.

^{Source: EWG/MEA via Wisconsin Department of Agriculture, Trade, and Consumer Protection and USDA-NASS 2017 Census of Agriculture.}

Results from manure allocation scenarios

Table 7. Scenario 1: Manure N relative to annual county N recommendations for non-legume crops.

^{Source: EWG/MEA via Wisconsin Department of Agriculture, Trade, and Consumer Protection, University of Wisconsin Extension, USDA-ARS Agricultural Conservation Planning Framework.}

Table 8. Scenario 2: Manure N relative to annual county N recommendations for non-legume crops plus alfalfa

^{Source: EWG/MEA via Wisconsin Department of Agriculture, Trade, and Consumer Protection, University of Wisconsin Extension, USDA-ARS Agricultural Conservation Planning Framework.}

Table 9. Scenario 3: Manure phosphorus relative to annual county phosphorus removal rates

^{Source: EWG/MEA via Wisconsin Department of Agriculture, Trade, and Consumer Protection, University of Wisconsin Extension, USDA-ARS Agricultural Conservation Planning Framework.}

References

Borchardt, Mark A., et al. Sources and Risk Factors for Nitrate and Microbial Contamination of Private Household Wells in the Fractured Dolomite Aquifer of Northeastern Wisconsin. Environmental Health Perspectives. 2021.

Laboski, C. A. M., and J. B. Peters. Nutrient application guidelines for field, vegetable, and fruit crops in Wisconsin. Madison: Cooperative Extension of the University of Wisconsin-Extension. 2012.

Mathewson, P.D., Evans, S., Byrnes, T., Joos, A., & Naidenko, O.V., Health and economic impact of nitrate pollution in drinking water: a Wisconsin case study. Environmental Monitoring Assessment. 2020.

Mitchell, Paul D. Preliminary Assessment of the Potential Economic Impacts of Proposed Changes to NR 151 for Agricultural Operations, University of Wisconsin – Madison. 2021. Available at: https://widnr.widen.net/s/lhcsbgkpsl/uw_nitratereport_091521

Porter, S.A.; James, D.E. Using a Spatially Explicit Distribution Model to Assess the Contribution of Animal Agriculture to Minnesota’s Agricultural Nitrogen Budget. Agronomy. 2020, 10(4), 1–15.

Raff, Z. and Meyer, A. CAFOs and Surface Water Quality: Evidence from Wisconsin. American Journal of Agricultural Economics. 2021. Available at: https://onlinelibrary.wiley.com/doi/abs/10.1111/ajae.12222

SnapPlus. Wisconsin’s Nutrient Management Planning Software. University of Wisconsin—Madison Department of Soil Science. Available at: https://snapplus.wisc.edu/.

Soil Survey Staff. The Gridded Soil Survey Geographic (gSSURGO) Database for Wisconsin. United States Department of Agriculture, Natural Resources Conservation Service. 2020. Available at: https://gdg.sc.egov.usda.gov/.

Tomer, M.D., Porter, S.A., James, D.E., Boomer, K.M.B., Kostel, J.A. & McLellan, E. Combining precision conservation technologies into a flexible framework to facilitate agricultural watershed planning. Journal of Soil and Water Conservation. 2013. 68, 113A-120A.

USDA-NASS. County Agricultural Production. United States Department of Agriculture-National Agriculture Statistics Service: Washington, D.C., 2020. Available at: https://www.nass.usda.gov/Surveys/Guide_to_NASS_Surveys/County_Agricultural_Production/index.php

USDA NASS, 2017 Census of Agriculture, Available at: https://www.nass.usda.gov/Publications/AgCensus/2017/.

USDA NRCS Technical Note. Nutrient Management TN-Conservation Planning-WI-1. Available at: https://datcp.wi.gov/Documents/NM590TechNoteApp23.pdf.

Wisconsin Department of Agriculture, Trade, and Consumer Protection. Commercial Fertilizer Dealers Annual Tonnage Summaries. Available at: https://dnr.wisconsin.gov/topic/SurfaceWater/Congress.html.

Wisconsin Groundwater Coordinating Council. Report to the Legislature. 2021. Available at: https://dnr.wi.gov/topic/groundwater/documents/GCC/Report/GCCFullReport2021.pdf.