Improper usage of fertilizer can pose serious threats to water quality due to its propensity of permeating into ground and surface water through runoff or simple leaching. Two critical components in commercial fertilizers that present direct risk to water contamination are nitrogen and phosphorus (EPA 2010). According to the EPA’s ‘Source Water Protection Practices Bulletin,’ it is estimated that about 25 percent of all pre-plant nitrogen applied to corn is lost through leaching (entering ground water as nitrate) or denitrification (entering the atmosphere as nitrogen gas). The mobility of phosphorus can also cause severe water quality impairment since as much as 60 to 90 percent of phosphorus moves with the soil. Hence, careful usages of a fertilizer that takes its negative ramifications into consideration and develops an effective application management strategy are vital procedures to reduce the level of water impairments.
The fertilizer metric uses the U.S. Department of Agriculture’s National Agricultural Statistics Service’s cropland database and data from the U.S. Department of Agriculture’s Economic Research Service for the land use and the fertilizer-applied amount (nitrogen, phosphorus, and potassium). By using these data along with GIS software, the potential runoff for each component is estimated in the ten considered states.
Preview of Results
In order to rank the potential for fertilizer run-off for all considered states, geographic information system (GIS) tools were used. The types of land use for all 10 states were found using the U.S. Department of Agriculture’s National Agricultural Statistics Service’s cropland database, which contains data concerning land use to a precision of 900 sq. meters; this data was gathered using satellite imagery in 2013 (USDA 2013). The land use data was then separated into the land use in separate watersheds, which were defined at the sub-region level of the hydrologic unit classification system (HUC-8); this data was acquired from the U.S. Geological Survey’s National Hydrography Dataset (USGS 2014). These datasets were used to calculate the acreage of corn, soybeans, and wheat within each state.
After determining the amount of corn, soybeans, and wheat present in each watershed, data from the U.S. Department of Agriculture’s Economic Research Service was used to determine how much fertilizer was applied to each of the types of crop (USDA 2013). The three tables below display the average amount of nitrogen, phosphorus, and potassium fertilizer (in units of pounds per acre) that was applied to corn, soybeans, and wheat in each of the 10 states. The values were determined by finding the state-specific average amount of fertilizer applied per acre for a certain crop and then multiplying that value by the state-specific percentage of acres of that type of crop that receive any fertilizer. If state-specific data concerning the application of these fertilizers was not available, then the national average values were used.
After the amount of cropland in each watershed and the amount of fertilizer applied per acre of specific types of cropland were calculated, the total amount of fertilizer that was applied in each of the watersheds within the states could be estimated. After estimating the amount of fertilizer that was applied in each watershed, each watershed was ranked from the highest level of fertilizer application to the lowest. There were a total of 542 HUC-8 watersheds that were considered.
- The acreage of corn, soybeans, and wheat within each state are calculated using the U.S. Department of Agriculture’s National Agricultural Statistics Service’s cropland database
- The U.S. Department of Agriculture’s Economic Research Service was used to determine how much fertilizer was applied to each of the types of crop
- After ranking all of watersheds in the 10 considered, the average ranking of each state’s watershed was determined
- Indiana ranks 8th out of the 10 states in the potential for both nitrogen and phosphorus runoff. It ranks 9th in the potential for potassium runoff
- The results of this metric do not indicate that a state will have more, or less, issues with water quality due to fertilizer pollution, but rather it quantifies the potential for nutrient pollution of water bodies within each state
- A state that applies more fertilizer than another state would have more issue related to fertilizer pollution