Estimated Animal Agriculture Nitrogen and Phosphorus from Manure

About this indicator

Animal agriculture manure is a primary source of nitrogen and phosphorus to surface and groundwater. Manure runoff from cropland and pastures or discharging animal feeding operations and concentrated animal feeding operations (CAFOs) often reaches surface and groundwater systems through surface runoff or infiltration. Permitting discharging CAFOs to limit nitrogen and phosphorus discharge to surface waters, and implementing best management practices outlined in a manure management plan are critical steps to protecting water quality. This indicator shows animal agriculture manure produced in states in 2007 and 2017 (the year of the last Census of Agriculture) and expressed in terms of nitrogen and phosphorus content, rather than total amounts of manure, since different animal types produce manure with differing nitrogen and phosphorus concentrations. Data are for cattle, swine, poultry (chickens and turkeys), sheep, and horses. Data are presented as 1000s of kg of manure nitrogen and phosphorus as well as kilograms of manure nitrogen and phosphorus per km² of farmland.

Sources: The number of animals per state are from USDA’s 2007 and 2017 Census. Estimated manure N and P contents are from Ruddy et al. 2006. 2007 and 2017 farm land acreage is from USDA's National Agricultural Statistics Service: Farm Numbers, Farms and Land in Farms, Final Estimates, 2003-2007; 2017.

Download the Manure data table (xlsx) (17.28 KB)

Sources of data

1. U.S. Department of Agriculture. 2009. 2007 Census of agriculture: United States summary and state data. Vol 1. AC-07-A-51.
2. U.S. Department of Agriculture. 2019. 2017 Census of agriculture: United States summary and state data.
3. Ruddy, B.C., D.L. Lorenz, and D.K. Mueller. 2006. County-level estimates of nutrient inputs to the land surface of the conterminous United States, 1982–2001: U.S. Geological Survey Scientific Investigations Report 2006-5012.
4. U.S. Department of Agriculture. National Agricultural Statistics Service, Farms and Land in Farms, Final Estimates, 2003–2007. Refer to the Table 825 of the U.S. Census Bureau’s 2012 Statistical Abstract, Agriculture: Farms and Farmland.
5. U.S. Department of Agriculture. National Agricultural Statistics Service, Farms and Land in Farms, Final Estimates, 2017., Agriculture: Farms and Farmland.

Data source information

Data were collected for the following animal types: cattle (milk cows, beef cows, steers, heifers, slaughtered cattle), hogs and pigs, chicken (broilers, layers, and pullets), turkeys, sheep, lambs, horses, and ponies. The numbers of animals were collected from the 2007 and 2017 U.S. Department of Agriculture (USDA) Census, except for steers, heifers, and on-farm cattle slaughter, as the USDA Census no longer reports on these cattle categories. Inventory for these animals were estimated per Ruddy et al. 2006. Manure nitrogen and phosphorus production rates (kg/animal/day) for each animal type are also from Ruddy et al. 2006. Farm land acreage is from the National Agricultural Statistics Service. The current definition of a farm, first used for the 1974 census, is any place from which $1,000 or more of agricultural products were produced and sold, or normally would have been sold, during the census year. Acreage designated as ‘‘land in farms’’ consists primarily of agricultural land used for crops, pasture, or grazing. Acres were converted to km² for this indicator in order to be consistent with other indicators.

What to consider when using these data

• The rate of delivery of nitrogen and phosphorus from land-applied fertilizer such as manure to streams is dependent on the amount, timing, and placement of application, as well as best management practices to minimize runoff from fields.
• In cases where certain states did not report total numbers of hogs and pigs or poultry to the 2007 or 2017 USDA Census, the total number of head was estimated based on reported number of head for counties that reported by head, plus an estimate of the number of head for counties that reported by farm size, by using the median value in the ranges reported for each farm size.
• The 2007 and 2017 USDA Census do not differentiate between tom and hen turkeys. Therefore, the averages of the manure nitrogen/phosphorus production rates (kg/animal/day) for tom and hen turkeys provided by Ruddy et al. 2006 were used as estimates of the manure nitrogen/phosphorus production rates for all turkeys.
• Based on a review of the literature, USDA sites, and university extension programs, weaning age is variable with reported average values of 120-220 days (cattle are considered calves until weaning). Heifers not used for breeding are typically slaughtered at 9-10 months. Therefore, it was assumed (consistent with Ruddy et al. 2006) that 50% of the cattle, excluding cows, were slaughtered within their first year of life and that the average lifespan was 170 days.
• All other cattle, excluding cows and slaughtered cattle, were assumed heifers or steers in equal proportions, based on Ruddy et al. 2006 procedures.

References and links to other data sources

1. U.S. Department of Agriculture.  Manure management webpage.
2. U.S. EPA. Animal Feeding Operations - NPDES CAFO Permitting webpage.