Version 1.0 | August 6, 2021
The Iowa Nutrient Reduction Strategy is a science- and technology-based approach to assess and reduce nutrients delivered to Iowa waterways and the Gulf of Mexico. The strategy outlines opportunities for reducing nutrients in surface water from both point sources, such as municipal wastewater treatment plants and industrial facilities, and nonpoint sources, including agricultural operations and urban areas, in a scientific, reasonable, and cost-effective manner. The Iowa Nutrient Reduction Strategy was developed in response to recommendations provided by the United States Environmental Protection Agency (EPA) in its March 16, 2011, memo, “Working in Partnership with States to Address Phosphorus and Nitrogen Pollution through Use of a Framework for State Nutrient Reduction.” Ongoing action for nutrient load reductions is further supported by the recent EPA recommendations, “Renewed Call to Action to Reduce Nutrient Pollution and Support for Incremental Actions to Protect Water Quality and Public Health,” released September 22, 2016.
This page presents an analysis of changes in nonpoint source and point source efforts to reduce nitrogen and phosphorus loads by 45% and represents the “Land” dimension of the Iowa Nutrient Reduction Strategy Logic Model.
From 2014 to 2020, a comprehensive progress report was released annually by the Iowa Department of Agriculture and Land Stewardship, the Iowa Department of Natural Resources, and Iowa State University. The process of reporting nutrient reduction efforts is transitioning in 2021 to a revised approach by publishing data and findings in a set of web-based dashboards. This web-based update of the “Land” dimension will be followed by dashboards on the “Water”, “Inputs”, and “Human” dimensions throughout 2021, with this cycle recurring annually and may be adjusted as needed. This revised reporting structure aims to increase the timeliness, frequency, and transparency of updates on Iowa Nutrient Reduction Strategy efforts and nutrient loss in Iowa.
This page presents screen reader-friendly versions of the text and tables that are presented in the web-based dashboards.
Tracking Nonpoint Source Nutrient Reduction Practices - Agricultural Conservation Practices
Agricultural Land Use in Iowa Over Time
Iowa’s total land area is 35.7 million acres. Based on data from the USDA Census of Agriculture, nearly 90% of Iowa’s total area is dedicated for agricultural purposes, with total agricultural land averaging 31.4 million acres since 1982. Land area dedicated to field crops — corn, soybeans, and other annual and perennial crops — has remained relatively steady since the 1980s, averaging 27 million acres. Acres enrolled in the United States Department of Agriculture Conservation Reserve Program, which aims primarily to convert environmentally sensitive land from crops to perennial cover, has fluctuated between approximately 1.5 and two million acres in Iowa since the start of the program in 1986.
Records from the United States Department of Agriculture (USDA) Census of Agriculture, the USDA National Agriculture Statistics Service (NASS), and the USDA Farm Service Agency (FSA) were compiled to estimate historical and recent crop acreages from 1992 to 2019. Acreages prior to 1992 were tabulated from digitized documents in the USDA Census of Agriculture Historical Archive. Crop acres from the Census of Agriculture and National Agriculture Statistics Service (NASS) were used for annual values from 1993 to 2010. For both periods, harvested acres were used when available; planted acres were used as an alternative value when harvested acres were not available. NASS survey values were used for years that the Census did not occur. For annual crop acres between 2011 to 2019, planted crop acres were aggregated from Farm Service Agency (FSA) crop acreage reports. In response to a recent increase in availability of historical and recent crop acreages in NASS, this dashboard’s display of crop acreages will be adjusted in late 2021 to reflect the annual crop acreage values provided in NASS (in lieu of combined records from archival, NASS, and FSA databases).
The annual acres enrolled in the Conservation Reserve Program in Iowa were obtained from the FSA crop acreage reports and aggregated by year.
Iowa Cover Crops
During the baseline and benchmark time periods—1980-96 and 2006-10—there were no or very few acres of cover crops in Iowa. The USDA Census of Agriculture reported that 970,000 acres of cover crops were planted Iowa in fall 2016, and the Survey of Agricultural Retailers estimated 1.6 million acres. That survey estimated that 2.2 million acres were planted in fall 2018. Based on county-level data from the 2017 USDA Census of Agriculture, the eastern and southern regions of Iowa show the highest rates of cover crop use.
Of these statewide estimates, public conservation programs accounted for an average of 565,000 acres each year from 2017 to 2019. It should be noted that these publicly funded cover crop acres represent a portion of Iowa’s total cover crop acres; annual publicly funded acres do not represent a total statewide estimate of Iowa cover crops.
|United States Department of Agriculture - Census of Agriculture||379,614||973,112|
|Survey of Agricultural Retailers||1,597,614||2,015,688||2,183,606|
|Portion Funded by Public Conservation Programs||18,702||30,987||69,955||211,235||161,000||275,854||324,097||549,638||597,205||555,400|
There are currently three data sources utilized for tracking the rate of cover crop adoption in Iowa. First, the Survey of Agricultural Retailers, conducted by the Iowa Nutrient Research and Education Council, has estimated annual statewide cover crop acres since 2017 (capturing the cover crops planted in fall of the prior year). Second, the United States Department of Agriculture (USDA) Census of Agriculture provides county-level cover crop acres for fall 2011 and fall 2016, allowing for aggregated statewide totals for those years. Third, state and federal conservation programs (whereby government cost-share is given to farmers and landowners) provides spatially explicit records of publicly funded cover crop acres. All state programs recorded by the Iowa Department of Agriculture and Land Stewardship were included in this analysis of cost-share acres, as well as acres under the federal Environmental Quality Incentive Program and Conservation Stewardship Program.
The map of cover crop distribution in Iowa was created using the USDA Census of Agriculture county-level acres planted in fall 2016. County values were assigned proportionally to Iowa HUC8 watersheds based on the percentage of county land area that intersects each watershed.
|Species Group or Type||Percent of Iowa Cover Crop Acres in 2019|
|Other Type or Species Mix||15%|
No-Till and Conservation Tillage
In the last few decades, the use of no-till and conservation tillage in Iowa has increased dramatically. Conservation tillage represents a range of reduced tillage practices that leave at least 30% of crop residue on the soil surface following harvest and planting. No-till further minimizes soil disturbance by leaving most of the crop residue on the surface.
During the baseline period of 1980-1996, no-till was used on an average of two million acres. In 2012, the USDA Census of Agriculture estimated 6.9 million acres of no-till. Since 2012, no-till acres have increased to approximately 8.2 million acres, according to both the Census and the Survey of Agricultural Retailers. No-till practices account for a higher portion of row crop acres in the rolling landscapes of western Iowa, for example, the Loess Hills region and some southern and northeastern watersheds.
Conservation tillage was practiced on 5.2 million acres during the baseline period, on average, and on an estimated 8.8 million acres in 2012. Since then, conservation tillage has increased to approximately 10 million acres, according to both the Census of Agriculture and the Survey of Agricultural Retailers. The use of conservation tillage is distributed across the state, with higher rates of use in the western, north central, and northeastern regions of Iowa. The increased use of no-till and conservation tillage in row crop operations since the 1980s is paired with a marked decrease in the use of conventional tillage. Conventional tillage was used on an estimated 12 million acres during the baseline period and has decreased to approximately five million acres in 2019.
|Data Source and Practice Name||
1980-1996 Average Annual
2006-2010 Average Annual
|Iowa Nutrient Reduction Strategy - Derived from data from the Conservation Technology Information Center|
|Census of Agriculture|
|Survey of Agricultural Retailers|
Tillage acres were estimated using three data sources. First, the 1980-96 baseline period (displayed here as 1996) and the 2006-10 benchmark period (displayed here as 2010) are derived from the Crop Management Residue Survey, conducted by the Conservation Technology Information Center for Iowa from 1982 to 2011. Methods for using these findings to determine average annual acreages are described in the Iowa Nutrient Reduction Strategy Nonpoint Source Science Assessment and the corresponding Iowa Nutrient Reduction Strategy baseline study, both of which can be found at the Iowa Nutrient Reduction Strategy website.
Statewide acreages for the 2012 and 2017 crop year were estimated using the United States Department of Agriculture Census of Agriculture, which provides county-level data for no-till, conservation tillage, and conventional tillage.
Annual statewide acreages of tillage practices in corn and soybean fields are estimated by the Survey of Agricultural Retailers, conducted by the Iowa Nutrient Research and Education Council, for the 2017, 2018, and 2019 crop years.
Nutrient Management in Iowa - Nitrogen Rates and Phosphorus Application
During the 1980-96 baseline period, corn-soybean rotations received an estimated average of 149 pounds of commercial and manure nitrogen; continuous corn rotations received 199 pounds per acre. This figure was estimated using similar methodology for 2006-10 benchmark period at 151 pounds per acre for corn-soybean rotations and 201 pounds for continuous corn. These estimates were derived from the state fertilizer sales data, which is publicly available from the Iowa Department of Agriculture and Land Stewardship (IDALS), and the USDA Census of Agriculture’s reported animal units in Iowa.
In 2017, the Iowa Nutrient Research and Education Council conducted its first annual Survey of Agricultural Retailers to estimate the extent of in-field practice use, including commercial fertilizer application practices. The annual survey has found that in corn-soybean rotations, corn acres received, on average, between 170 and 178 pounds per acre during the 2017-19 period. On average, continuous corn rotations received between 200 and 202 pounds per acre during that time.
|Category (Pounds Nitrogen Per Acre)||Proportion of Crop Rotation Acres in 2019|
These annual nitrogen fertilizer rates represent statewide averages; however, nitrogen application rates to corn vary across agricultural fields and, in some cases, vary by acre within a field. The percent of total acres that received various levels of commercial nitrogen rates varies by crop rotation. In 2019, for example, 40 percent of corn-soybean acres received 176-200 pounds of commercial nitrogen on their most recent corn year, and 33 percent received 151-175 pounds. Some fields lay at the ends of this distribution, with 12 percent of acres receiving 150 pounds of nitrogen per acre or less and 15 percent receiving 201 pounds per acre or more. There was a similar distribution for continuous corn rotations, with 51 percent of acres receiving 176-200 pounds of commercial nitrogen fertilizer.
These estimates of annual nitrogen applications from 2017-19 represent an increase in fertilizer use since the 1980-96 baseline period. While the 2017-19 estimates of commercial fertilizer rates were obtained via a different data collection process than for the baseline and benchmark time periods, there is complementary evidence from recent fertilizer sales data that commercial fertilizer application rates for corn-soybean operations have increased gradually since before 1990. Increases in Iowa’s corn acres since that time have not met the increase in commercial nitrogen fertilizer sales, supporting the finding that average commercial nitrogen application rates (in pounds per acre) have increased over time.
Phosphorus fertilizer application methods that inject or incorporate it into the soil, compared with broadcasting across the soil surface, reduces potential nutrient losses from the field. The Survey of Agricultural Retailers estimated 14.4 million acres received phosphorus fertilizer incorporated, injected, or knifed into the soil within 24 hours of application for the 2017 crop year, 18.5 million acres for the 2018 crop year, and 18.8 million acres for the 2019 crop year. These estimates account mostly for commercial fertilizer, with a small portion of these acres receiving manure; each year, approximately 80% of surveyed fields received no manure.
In addition, the survey reported 8.6 million acres that received phosphorus fertilizer – commercial or manure – for the 2017 crop year by another method; 4.5 million acres and 4.1 million acres received other forms of application for the 2018 and 2019 crop years, respectively. Soil testing for phosphorus occurred on 81% of fields in 2017, 72% in 2018, and 85% in 2019. The extent of these phosphorus fertilizer practices is unknown for time periods prior to the 2017 survey results.
|Commercial P Incorporated with Planter||2,523,800||862,800||270,500|
|Commercial P Incorporated in Knifed Bands||656,900||627,900||619,600|
|Commercial P Broadcast & Incorporated within 1 week||10,807,000||16,143,900||15,847,400|
|Liquid P (commercial/manure) Injected||416,000||865,400||2,048,900|
|Other P Application Type||8,591,300||4,468,900||4,137,300|
Commercial nitrogen application rates were obtained from the Iowa Nutrient Research and Education Council's Survey of Agricultural Retailers, which has been conducted annually since 2017. The statewide average annual rates of commercial nitrogen fertilizer application were calculated using a stratified, weighted average approach, based on each field's size and the number of observations within each major land resource area in Iowa.
The distributions of varying application rates for continuous corn and corn-soybean rotations were determined using the survey's records for agricultural fields that received only commercial nitrogen fertilizer in 2019.
The total application of commercial nitrogen fertilizer, in tons per year, was estimated from Iowa’s fertilizer sales data and the USDA Census of Agriculture, using the methods described in the NRS Nonpoint Source Science Assessment, which can be accessed at nutrientstrategy.iastate.edu/documents.
To estimate the total plant-available nitrogen from manure applied to crops since the 1980-96 baseline period, researchers evaluated livestock animal unit data, USDA Census of Agriculture data, and published studies on manure nutrient availability. The methodology is described in the NRS Nonpoint Source Science Assessment, which can be accessed at nutrientstrategy.iastate.edu/documents.
Acres of various timing methods for commercial phosphorus application were obtained from the Iowa Nutrient Research and Education Council's Survey of Agricultural Retailers, which has been conducted annually since 2017. The statewide acreages of each phosphorus application method were calculated using a stratified, weighted approach, based on each field's size and the number of observations within each major land resource area in Iowa.
Nutrient Management in Iowa - Nitrogen Application Timing
Nitrogen application timing also affects nitrogen loss. Shifting nitrogen application from fall to spring reduces nitrogen loads by 6% and shifting from spring pre-plant to in-season application (i.e. side-dress) reduces nitrogen loads by 4-7%. The Survey of Agricultural Retailers provides recent estimates of when nitrogen is most commonly applied. In 2019, a split application of spring and side-dress was used on 1.9 million corn acres. That year, 119,000 corn acres received only side-dress application and 5.6 million acres received only spring pre-plant.
Fall-applied anhydrous with nitrapyrin has been shown to reduce nitrogen loads by approximately 9% when compared with applications without an inhibitor. Based on the NRS Nonpoint Source Science Assessment, researchers estimated that during the 2006-10 benchmark period, fall anhydrous was applied annually to 5.7 million acres of corn-soybean and continuous corn acres. Of these acres, nitrification inhibitor was applied to 3.5 million acres. According to the Survey of Agricultural Retailers, farmers’ nitrification inhibitor use has increased since the benchmark period. As a comparison to the 1980-96 baseline period, researchers associated with the NRS Nonpoint Source Science Assessment suggest, based on professional knowledge, that nitrification inhibitor was used on a negligible number of acres due to the recent development of the technology.
|Fall anhydrous plus
|Fall Anhydrous without
|Spring Side-Dress Split, 40-60||2,274,791||3,537,893||4,592,334|
The data showing the timing of commercial nitrogen applications were obtained from the Iowa Nutrient Research and Education Council's Survey of Agricultural Retailers, which has been conducted annually since 2017. The statewide proportions of the data were calculated using a stratified, weighted approach, based on each field's size and the number of observations within each major land resource area in Iowa.
Acres Treated by Bioreactors and Saturated Buffers
Bioreactors and saturated buffers are edge-of-field practices that are made by routing agricultural drainage water through a woodchip trench or vegetated buffer to remove nitrate before the water enters an adjacent stream, ditch, or tile main. At 43% and 53% reduction, respectively, these practices are highly effective at reducing annual nitrate loads to streams. The suitability of bioreactors and saturated buffers for a farm field is highly dependent upon the presence of tile drainage, topography, and soil types.
From 2011 to 2019, at least 46 bioreactors and 24 saturated buffers were installed through cost-share programs in Iowa; using a conservative assumption that these practices each treat 50 acres of drained cropland, at least 33,500 acres are treated, as of the end of 2019.
Multipurpose oxbows are similar edge-of-field practices that were added to the Iowa Nutrient Reduction Strategy in 2019. A naturally occurring oxbows is a floodplain wetland that forms when a stream or river cuts a straighter path through a loop of its meander or when a stream is channelized. Routing agricultural drainage water into a restored oxbow can reduce nitrate concentration in the tile flow before it moves to the adjacent stream. Multipurpose oxbows will be integrated into future Iowa Nutrient Reduction Strategy reports as data collection and reporting is improved. will provide information on practice adoption.
|Bioreactor - Acres Treated by New Practices Annually||150||150||50||150||100||250||400||750||300|
|Saturated Buffer - Acres Treated by New Practices Annually||50||250||200||350||350|
|Cumulative Acres Treated By Bioreactors and Saturated Buffers in Iowa||150||300||350||500||650||1,150||1,750||2,850||3,500|
Acres treated by bioreactors and saturated buffers were summarized using state and federal conservation program data, which provide detailed, spatial records of publicly funded practices. All state programs recorded by the Iowa Department of Agriculture and Land Stewardship were included in this analysis of cost-share practices, as well as practices under the federal Environmental Quality Incentive Program and Conservation Stewardship Program. Due to variable data in early years of bioreactor and saturated buffer construction (e.g. 2011 to approximately 2015), an assumption of 50 acres treated by each practice was used.
Acres Treated by Water Quality Wetlands
Wetlands that are designed for water quality improvement have an effectiveness of 52% nitrogen load reduction. In designing these types of wetlands, agricultural tile drainage is routed through the wetland for nitrate removal. Currently, water quality wetlands require higher financial investment and development time than many other conservation practices but have a lifespan of multiple decades or more. Most of Iowa’s wetlands have been constructed under the Conservation Reserve Enhancement Program (CREP). Other programs and individuals have installed wetlands in Iowa that are similarly sited and constructed, but data currently are not available to assess the full extent of this non-CREP implementation.
Currently, Iowa has 95 water quality wetlands, which have all been constructed since the 1980-96 baseline period of the Iowa Nutrient Reduction Strategy. These wetlands have a cumulative drainage area of 124,000 acres. Iowa experienced its highest rate of installations in 2019, with nine new wetlands capturing nearly 17,000 acres. Program implementation continues, with at least 40 wetlands currently in the planning and construction phases. Wetlands constructed since 2011 (i.e. since the 2006-10 benchmark period of the Iowa Nutrient Reduction Strategy) protect 66,000 acres of agricultural land.
|New Acres Treated Annually||2,488||2,189||634||10,941||14,800||5,962||13,414||8,074||6,965||13,519||6,334||4,940||10,448||4,596||1,945||17,117|
|Cumulative Acres Treated||2,488||4,677||5,311||16,252||31,052||37,014||50,428||58,502||65,467||78,986||85,320||90,260||90,260||100,708||105,304||107,249||124,366|
Acres protected by water quality wetlands were estimated using data from the Iowa Department of Agriculture and Land Stewardship. A majority of these wetlands were installed under the Conservation Reserve Enhancement Program, but some were funded through other programs and partnerships.
Acres Treated by Structural Erosion Control Practices
The Iowa Nutrient Reduction Strategy Nonpoint Source Science Assessment identified a set of structural practices that capture sediment or reduce erosion within or at the edge of an agricultural field that reduce soil-bound phosphorus loss. These practices include terraces, water and sediment control basins (WASCOBs), farm ponds, and grade stabilization structures; their effectiveness at reducing phosphorus loads range from 77% to 85%.
Currently, it is assumed a significant portion of erosion control practices are constructed through the financial assistance of state and federal government cost-share programs and this report presents data from those sources. An estimated 217,000 acres are treated by terraces, WASCOBs, ponds, and grade stabilization that have been installed under government cost-share programs since 2011. Owing to the topography and soils of the southern and northeastern regions of Iowa, erosion control practices are concentrated primarily in those geographic areas.
The BMP Mapping Project is an ongoing effort that will estimate the extent of all erosion control installations—not just those funded by cost-share programs. The project’s data collection is complete for three time periods: the 1980s, 2007-10, and 2016-17. Researchers are completing the final data processing, and results will be published in future Iowa Nutrient Reduction Strategy reports and dashboards. For more information on this effort, see the 2018-19 Iowa Nutrient Reduction Strategy Annual Report.
|Terraces and Water & Sediment Control Basins - Acres Treated by New Practices Annually||32,926||25,369||21,511||26,787||24,668||22,788||17,295||15,725||19,527|
|Grade Stabilization and Ponds - Acres Treated by New Practices Annually||1,823||1,117||1,447||1,187||1,194||1,114||898||908||730|
|Cumulative Acres Treated by Terraces, Water & Sediment Control Basins, Grade Stabilization, and Ponds||34,749||61,235||84,193||112,167||138,029||161,931||180,124||196,758||217,015|
Structural erosion control practices were summarized using state and federal conservation program data, which provide detailed, spatial records of publicly funded cover crop acres. This report accounts for practices installed between 2011 and 2019. All state programs recorded by the Iowa Department of Agriculture and Land Stewardship were included in this analysis of cost-share practices, as well as practices under the federal Environmental Quality Incentive Program and Conservation Stewardship Program. The database for state programs provides an estimate of the acres treated by each erosion control practice. For terraces, water and sediment control basins, and grade stabilization structures, and within each HUC8 watershed, the state database’s mean acres protected per foot installed was applied to the federal cost-share practices to obtain an estimate of total acres treated. For ponds, there were no federal practices to extrapolate, so only state data were used.
Future analysis will include the BMP Mapping Project to capture structural practices that were not funded through public conservation programs. Statewide estimates for the BMP Mapping Project were completed in early 2021; summaries of these findings are in progress.
Tracking Point Source Nutrient Reduction Efforts - Wastewater Treatment and Industrial Facilities
Understanding Point Source Efforts Associated with the Iowa Nutrient Reduction Strategy
The Iowa Nutrient Reduction Strategy identifies 157 industrial and municipal wastewater treatment point source facilities that need to evaluate the amounts of nutrients in their discharges in order to meet the goals of the strategy. Upon receiving a National Pollutant Discharge Elimination System (NPDES) permit under the Strategy, each facility works to develop a feasibility study, which outlines the resources required to achieve nutrient reduction goals. The permits also incorporate requirements for measuring nutrient concentrations in influent and effluent to determine current nutrient removals and provide an empirical basis for feasibility studies.
Point source facilities listed in the strategy are required to monitor raw waste and final effluent for total nitrogen (TN) and total phosphorus (TP). However, some industries (e.g., power plants) that do not have a treatment plant are required to monitor only the final effluent. This extensive monitoring effort has generated one of country’s most complete sets of point source nutrient data, and the extent of this data collection will continue to increase as the remaining permits are issued. This data has enabled the facilities and the Iowa Department of Natural Resources to determine current TN and TP loads associated with these point sources, even before additional nutrient reduction technologies are installed.
A facility uses the data collected during the two-year period after permit issuance to evaluate the feasibility and reasonableness of reducing the amounts of nutrients discharged into surface water. The Iowa Nutrient Reduction Strategy establishes a target of reducing TN and TP from point sources by 66% and 75%, respectively. A facility’s feasibility study must include an evaluation of operational changes that could be implemented to reduce the amounts of TN and TP discharged. If the implementation of operational changes alone cannot achieve the targets, the facility must evaluate new or additional treatment technologies that could achieve reductions in the nutrient amounts discharged. At the end of 2019, 114 feasibility studies had been submitted.
As these feasibility studies are reviewed and approved by the Iowa Department of Natural Resources, the schedules these contain for installing nutrient reduction technologies or optimizing existing treatment are added to the facilities’ NPDES permits by amendment. Once the construction or optimization outlined by the schedules is complete and treatment processes are optimized, facilities will submit twelve months of effluent TN and TP sampling results. Effluent limits based on those sampling results will then be added to facilities’ permits and become enforceable.
|Permits Issued with Feasibility Studies Submitted||Permits Issued, Awaiting Feasibility Studies||Permits Remaining to be Issued|
|Feasibility Studies Submitted||0||0||20||32||31||26||19|
|NRS Permits Amended to Include Construction Schedules||0||0||2||13||14||18||9|
|Permits issued with NRS requirements||20||32||29||24||19||15||11|
|Permits issued with NRS Requirements in Targeted Watersheds||8||7||9||3||3||2||3|
|Number of Facilities|
|NRS Permits with Nitrogen and Phosphorus Limits||61|
|NRS Permits with Nitrogen Limits Only||58|
|NRS Permits with Phosphorus Limits Only||12|
|Facilities Meeting Percent Reduction Targets - Nitrogen||32|
|Facilities Meeting Percent Reduction Targets - Phosphorus||18|
|Total permits with nutrient monitoring (including those not in the NRS)||394|
|Nitrogen Load (tons)||13,170||14,054||15,344||15,228|
|Phosphorus Load (tons)||2,387||2,623||3,256||3,282|
Recommended citation: Iowa Department of Agriculture and Land Stewardship, Iowa Department of Natural Resources, and Iowa State University. (2021, August 6). Tracking the Iowa Nutrient Reduction Strategy. Version 1.0. https://nrstracking.cals.iastate.edu/tracking-iowa-nutrient-reduction-s…