Manure Nitrogen Loadings from Confined Livestock
Source: Natural Resources Conservation Service
Map Description:
Pounds of manure nitrogen loadings per watershed were estimated using data on livestock populations from the 1992 Agriculture Census. The average number of livestock present on each farm and the average length of time they lived on the farm were estimated for 16 types of livestock, adjusting the estimates to reflect the number of livestock held in confinement. Assuming all manure from confined operations was applied to the land, nitrogen loadings were estimated by multiplying the livestock population times the average amount of manure produced by each type of livestock, and then multiplying times an estimate of the average nitrogen content of the manure for each type of livestock. An additional adjustment was made for typical losses of nitrogen during storage and from volatilization during application. County totals for manure nitrogen were obtained by aggregating over the farms in the county. Watershed totals were obtained by multiplying county estimates by county-watershed conversion factors derived from a GIS calculation of the percentage of each county in each watershed. (Weights were adjusted using NRI information on the presence or absence of pastureland and cropland in each county-watershed polygon.)

A variety of algorithms were used to create watershed values, generating a variety of units (pounds per watershed, index scores per watershed, etc.). To facilitate comparisons among the maps, the classes shown in each map were based on a consistent set of watershed rankings. The 200 watersheds with the highest scores are shown with the darkest color. The next highest 200 watersheds are shown with a slightly lighter color, and so on.

Taken from a poster presentation at the 52nd Annual SWCS Conference (July 1997), "Potential Priority Watersheds for Protection of Water Quality from Nonpoint Sources Related to Agriculture" by R.L. Kellogg, S. Wallace, K. Alt, and D.W. Goss. Revised October 1997.

Cautions for this Product:
Analyses do not show which watersheds will have water quality impairments related to agricultural production. The simulation models estimate soil loss, chemical loss, or vulnerability indexes for conditions at the edge of the field and the bottom of the root zone. Not included in the indicators are dynamics of fate and transport from the farm field to a water body. Dilution from runoff and recharge on noncropland areas in the watershed will also reduce the potential for actual water quality impairments.

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