National Water-Quality Assessment Program

County-Level Estimates of Nitrogen and Phosphorus from 

Commercial Fertilizer for the Conterminous United States, 

1987–2006

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2012-5207

County-Level Estimates of Nitrogen and 

Phosphorus from Commercial Fertilizer for the 

Conterminous United States, 1987–2006

By Jo Ann M. Gronberg and Norman E. Spahr

National Water-Quality Assessment Program 

Scientific Investigations Report 2012-5207

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2012

For more information on the USGS—the Federal source for science about the Earth, its natural and living 

resources, natural hazards, and the environment, visit http://www.usgs.gov or call 1–888–ASK–USGS.

For an overview of USGS information products, including maps, imagery, and publications, 

visit http://www.usgs.gov/pubprod

To order this and other USGS information products, visit http://store.usgs.gov

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Gronberg, J.M., and Spahr, N.E., 2012, County-level estimates of nitrogen and phosphorus from commercial fertilizer 

for the Conterminous United States, 1987–2006: U.S. Geological Survey Scientific Investigations Report 2012-5207, 

20 p.
iii

Forward

The U.S. Geological Survey (USGS) is committed to providing the Nation with reliable scientific information 

that helps to enhance and protect the overall quality of life and that facilitates effective management of water, 

biological, energy, and mineral resources (http://www.usgs.gov/). Information on the Nation’s water resources 

is critical to ensuring long-term availability of water that is safe for drinking and recreation and is suitable 

for industry, irrigation, and fish and wildlife. Population growth and increasing demands for water make the 

availability of that water, measured in terms of quantity and quality, even more essential to the long-term 

sustainability of our communities and ecosystems.

The USGS implemented the National Water-Quality Assessment (NAWQA) Program in 1991 to support 

national, regional, State, and local information needs and decisions related to water-quality management and 

policy (http://water.usgs.gov/nawqa). The NAWQA Program is designed to answer: What is the quality of our 

Nation’s streams and groundwater? How are conditions changing over time? How do natural features and 

human activities affect the quality of streams and groundwater, and where are those effects most pronounced? 

By combining information on water chemistry, physical characteristics, stream habitat, and aquatic life, the 

NAWQA Program aims to provide science-based insights for current and emerging water issues and priorities. 

From 1991 to 2001, the NAWQA Program completed interdisciplinary assessments and established a baseline 

understanding of water-quality conditions in 51 of the Nation’s river basins and aquifers, referred to as Study 

Units (http://water.usgs.gov/nawqa/studies/study_units.html).

National and regional assessments are ongoing in the second decade (2001–2012) of the NAWQA Program as 

42 of the 51 Study Units are selectively reassessed. These assessments extend the findings in the Study Units 

by determining water-quality status and trends at sites that have been consistently monitored for more than a 

decade, and filling critical gaps in characterizing the quality of surface water and groundwater. For example, 

increased emphasis has been placed on assessing the quality of source water and finished water associated 

with many of the Nation’s largest community water systems. During the second decade, NAWQA is addressing 

five national priority topics that build an understanding of how natural features and human activities affect 

water quality, and establish links between sources of contaminants, the transport of those contaminants 

through the hydrologic system, and the potential effects of contaminants on humans and aquatic ecosystems. 

Included are studies on the fate of agricultural chemicals, effects of urbanization on stream ecosystems, 

bioaccumulation of mercury in stream ecosystems, effects of nutrient enrichment on aquatic ecosystems, and 

transport of contaminants to public-supply wells. In addition, national syntheses of information on pesticides, 

volatile organic compounds (VOCs), nutrients, trace elements, and aquatic ecology are continuing. 

The USGS aims to disseminate credible, timely, and relevant science information to address practical and 

effective water-resource management and strategies that protect and restore water quality. We hope this 

NAWQA publication will provide you with insights and information to meet your needs and will foster increased 

citizen awareness and involvement in the protection and restoration of our Nation’s waters.

The USGS recognizes that a national assessment by a single program cannot address all water-resource 

issues of interest. External coordination at all levels is critical for cost-effective management, regulation, 

and conservation of our Nation’s water resources. The NAWQA Program, therefore, depends on advice 

and information from other agencies—Federal, State, regional, interstate, Tribal, and local—as well as 

nongovernmental organizations, industry, academia, and other stakeholder groups. Your assistance and 

suggestions are greatly appreciated.

William H. Werkheiser

USGS Associate Director for Water 
iv

This page intentionally left blank.
v

Contents

Forward...........................................................................................................................................................iii

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Purpose and Scope .......................................................................................................................................2

Description of the Association of American Plant Food Control Officials Fertilizer Sales Data ......2

Estimation of State-Level Farm and Nonfarm Portions of Fertilizer Sales ...........................................3

Distribution to the County Level ..................................................................................................................8

Description of the County-Level Fertilizer Nutrient-Input Dataset......................................................11

Evaluation of the Farm and Nonfarm Fertilizer Data..............................................................................12

Temporal Variability at the State Level............................................................................................12

Spatial Distribution of Nonfarm-to-Total Fertilizer Ratios ............................................................12

Comparison to Independent Estimates of Nonfarm Fertilizer Application and Land Use ......14

Summary........................................................................................................................................................17

References Cited..........................................................................................................................................17

Appendixes ...................................................................................................................................................19

Appendix 1. Total Number of Fertilizer Products and Number of Nonfarm Fertilizer 

Products Summarized from the Association of American Plant Food Control 

Officials Data, by State, 1987–2006.....................................................................................19

Appendix 2. Product Tonnage as Reported in Raw Association of American Plant Food 

Control Officials Data, by State, 1987–2006.......................................................................19

Appendix 3. Location of States With at Least One Year (1987–2006) of Association of 

American Plant Food Control Officials (AAPFCO) Fertilizer Product Tonnage 

Data Estimated from Previous Years or from Surrounding States, and Summary 

of States and Years with Estimated AAPFCO Fertilizer Product Tonnage Data, 

1987–2006................................................................................................................................19

Appendix 4. Location of Counties with Association of American Plant Food Control 

Officials Fertilizer Product Tonnage data Reported at the County Level, 

1987–2006................................................................................................................................19

Appendix 5. Farm and Nonfarm Nitrogen and Phosphate Tonnage, by State, 1987–2006......19

Appendix 6. Nitrogen and Phosphorus Tonnage Based on National and State 

Farm and Nonfarm Proportions, by State, 1987–2006 .....................................................19
vi

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Area

square foot (ft2) 0.09290 square meter (m2)

square mile (mi2) 2.590 square kilometer (km2)

Mass

pound, avoirdupois (lb) 0.4536 kilogram (kg) 

ton, short (2,000 lb) 907.2 kilogram (kg) 

Abbreviations used in this report

AAPFCO Association of American Plant Food Control Officials

LULC Land Use and Land Cover

NAWQA National Water-Quality Assessment

NLCD National Land Cover Data

SIR Scientific Investigations Report

TIGER Topologically Integrated Geographic Encoding and Referencing system

USGS U.S. Geological Survey

Figures

1. Method for selecting annual data for each state ....................................... 3

2. Summary of results of the selection process for including states used to

derive the national farm and nonfarm proportions for each year (1987−2006) ...... 6

3. Process to calculate the national farm and nonfarm rates for each fertilizer

product, and calculate farm and nonfarm nitrogen and phosphate tonnage, for

each state, for each year .................................................................. 7

4. Distribution of state-level farm nitrogen to the county level by using county

weights based on fertilizer expenditure ................................................ 9

5. Distribution of state-level nonfarm nitrogen to the county level by using

county weights based on population...................................................... 10

6. Spatial distribution of state- and national-based median nonfarm-to-total

ratios during 1987–2006 for nitrogen and phosphorus ................................. 13

7. Ratio of estimated nonfarm nitrogen input rate to the recommended lawn

application rate, by state,1987–2006 ...................................................... 15

8. Nonfarm-to-total fertilizer ratio (median, 25th and 75th percentile) versus

urban land-use percentage, 1987–2006, for nitrogen and phosphorus ............... 16

Tables

1. Attribute labels and definitions for the tblFarmNonfarmCountyNitrogen and

tblFarmNonfarmCountyPhosphorus data files .......................................... 11
County-Level Estimates of Nitrogen and Phosphorus from 

Commercial Fertilizer for the Conterminous United States, 

1987–2006

By Jo Ann M. Gronberg and Norman E. Spahr

Abstract

The U.S. Geological Survey’s National Water-Quality 

Assessment program requires nutrient input for analysis of the 

national and regional assessment of water quality. Detailed 

information on nutrient inputs to the environment are needed 

to understand and address the many serious problems that 

arise from excess nutrients in the streams and groundwater of 

the Nation. This report updates estimated county-level farm 

and nonfarm nitrogen and phosphorus input from commercial 

fertilizer sales for the conterminous United States for 1987 

through 2006. Estimates were calculated from the Association 

of American Plant Food Control Officials fertilizer sales data, 

Census of Agriculture fertilizer expenditures, and U.S. Census 

Bureau county population. A previous national approach for 

deriving farm and nonfarm fertilizer nutrient estimates was 

evaluated, and a revised method for selecting representative 

states to calculate national farm and nonfarm proportions was 

developed. A national approach was used to estimate farm 

and nonfarm fertilizer inputs because not all states distinguish 

between farm and nonfarm use, and the quality of fertilizer 

reporting varies from year to year. For states that distinguish 

between farm and nonfarm use, the spatial distribution of 

the ratios of nonfarm-to-total fertilizer estimates for nitrogen 

and phosphorus calculated using the national-based farm and 

nonfarm proportions were similar to the spatial distribution 

of the ratios generated using state-based farm and nonfarm 

proportions. In addition, the relative highs and lows in the 

temporal distribution of farm and nonfarm nitrogen and 

phosphorus input at the state level were maintained—the 

periods of high and low usage coincide between national- and 

state-based values. With a few exceptions, nonfarm nitrogen 

estimates were found to be reasonable when compared to 

the amounts that would result if the lawn application rates 

recommended by state and university agricultural agencies 

were used. Also, states with higher nonfarm-to-total fertilizer 

ratios for nitrogen and phosphorus tended to have higher urban 

land-use percentages.

Introduction

In 1991, the U.S. Geological Survey (USGS) began full 

implementation of the National Water-Quality Assessment 

(NAWQA) program to assess the status and trends of the 

Nation’s surface and groundwaters (Leahy and Thompson, 

1994). As part of this national and regional assessment of 

water quality, Ruddy and others (2006) derived county-level 

fertilizer nutrient input from commercial fertilizer sales data 

for 1987–2001. Historically, several methods have been used 

to estimate county-level nutrients in fertilizer (Alexander and 

Smith, 1990; Battaglin and Goolsby, 1995), but Ruddy and 

others (2006) were the first to make a distinction between 

farm and nonfarm portions at the county level. Because farm 

and nonfarm sales are not distinguished for all states, Ruddy 

and others (2006) developed a procedure to estimate nonfarm 

fertilizer sales for all states from the Association of American 

Plant Food Control Officials (AAPFCO) fertilizer sales data 

by summing farm and nonfarm sales for each fertilizer product 

for selected states and converting these to proportions. These 

proportions were then applied to the annual reported sales 

of each fertilizer product to estimate farm and nonfarm sales 

within each state. State totals were then allocated to each 

county within the state on the basis of Census of Agriculture 

fertilizer expenditures for farm fertilizer and U.S. Census 

Bureau county population for nonfarm fertilizer.

Analysis of estimates from Ruddy and others (2006) and 

the computer programs used to produce the estimates revealed 

that allocation of fertilizer to farm and nonfarm portions was 

not calculated as described in the SIR 2006-5012 report. 

Instead of using only states that reported nonfarm sales for at 

least 11 fertilizer products to eliminate states with limited or 

erroneous data on nonfarm sales, as described in Ruddy and 

others (2006), all states were used to calculate the national 

farm and nonfarm proportions of each fertilizer product. By 

using all states, the calculation inflated the farm tonnage 

estimates, and therefore, the nonfarm proportion was lower 

than would be expected from using the procedure described in 
2 County-Level Estimates of Nitrogen and Phosphorus from Commercial Fertilizer for the Conterminous United States, 1987–2006

the report. At the state level, for 1987 through 2001, average 

estimates of farm nitrogen input, based on using all states to 

calculate the national farm and nonfarm proportions, were 

higher by 2 to 4 percent, and estimates of nonfarm nitrogen 

were lower by 23 to 55 percent compared to estimates based 

on using only states that reported nonfarm sales for at least 11 

fertilizer products; estimates of farm phosphorus were higher 

by 2 to 4 percent, and estimates of nonfarm phosphorus were 

lower by 29 to 50 percent.

The method described in Ruddy and others (2006)—

using only states that reported nonfarm sales for at least 11 

fertilizer products—would include some states with limited 

nonfarm sales data: Alabama for 1992, Colorado for 1998 and 

2003, Kansas for 2002, 2003, and 2005, South Dakota for 

2002, Vermont for 1989, and Wyoming for 1992. This method 

would also exclude some states with significant data (large 

nonfarm tonnage), including California for 1996 through 

2006, Montana for 1990 through 1993, and Washington for 

1997. In addition, the described method would not screen out 

states that contained errors or estimates. 

To rectify these shortcomings, the method for selecting 

states to estimate the national farm and nonfarm proportions 

of each fertilizer product in Ruddy and others (2006) was 

reevaluated and a new approach developed. This necessitated 

an analysis of AAPFCO fertilizer sales data to develop a better 

understanding of the information available.

Purpose and Scope

This report provides background information and a 

description of the AAPFCO fertilizer sales data and presents 

the revised method for selecting representative states to 

calculate national farm and nonfarm proportions of fertilizer 

products. In addition, this report provides updated estimates 

of county-level nitrogen and phosphorus from fertilizer for 

both farm and nonfarm use for the conterminous United States 

for 1987 through 2006, a description of the methods used to 

derive these values, and an evaluation of the farm and nonfarm 

fertilizer estimates.

These estimates of nitrogen and phosphorus provide 

information on the largest nonpoint sources of nutrients in 

the Nation, information that is critical for characterizing the 

nutrient inputs to surface water basins and groundwater areas. 

These estimates consequently provide a means for explaining 

the occurrence of nutrients in surface water and groundwater 

for national and regional assessments of water quality, and for 

evaluating agricultural management practices.

Description of the Association of 

American Plant Food Control Officials 

Fertilizer Sales Data

Annual fertilizer sales data are compiled by AAPFCO 

(Association of American Plant Food Control Officials, 2010). 

Gaither and Terry (2004) provide a detailed description of the 

AAPFCO data reporting system. Ruddy and others (2006) 

provide a summary of the data set. Reported annual sales data 

compiled by AAPFCO include state, county, quantity (in tons) 

sold, a fertilizer code (for the type of fertilizer), an optional 

code distinguishing the intended use as farm or nonfarm, 

and the individual percentage content of nitrogen-phosphatepotash for the fertilizer, hereinafter referred to as N-P-K 

percent content. Each “fertilizer product” is defined by the 

unique combination of the 9-digit field containing the N-P-K 

percent content and the 3-digit AAPFCO field containing 

the fertilizer code. The total number of fertilizer products 

reported, and the number reported for nonfarm use, also varies 

from state to state and from year to year (appendix 1). There 

are over 90,000 fertilizer products reported in the AAPFCO 

data set. 

The temporal distribution of the state fertilizer product 

tonnage totals, as reported in raw AAPFCO data, for farm, 

nonfarm, uncoded (use code is not populated with a valid 

value), and nonfarm-to-total ratio are shown in appendix 2. 

These graphs show that reporting practices vary from state 

to state. Some states regularly distinguish between farm and 

nonfarm tonnage (appendix 2, California, Florida, Illinois, and 

Indiana, to name a few), while other states do not (appendix 2, 

Arkansas, Georgia, Montana, and Iowa). Farm tonnage 

is usually a much larger portion of the total tonnage than 

nonfarm tonnage, except in some northeastern states.

Reporting of nonfarm sales is inconsistent for some 

states. The following are examples of deviations from the 

norm for particular state data: 

• From 1987 to 2000, Arkansas did not distinguish 

between farm and nonfarm sales. Beginning in 2001, 

they distinguished between farm and nonfarm sales, 

and nearly all the tonnage was allocated to farm use. In 

2002, nearly all the tonnage was allocated to nonfarm 

use, however (appendix 2, page 3). From 2003 to 2006, 

all tonnage was allocated to farm use.

• In the first half of the data record (1987–96), Nevada 

reported less than 50 percent of the tonnage as 

nonfarm (appendix 2, page 26). From 1997 through 

2006, except for 2000 when more than 80 percent 

of the tonnage was reported as nonfarm, all tonnage 

was reported as nonfarm. Census of Agriculture data 
Estimation of State-Level Farm and Nonfarm Portions of Fertilizer Sales 3

for 1997 and 2002 indicate over 11 million dollars in 

fertilizer expenditures for Nevada (U.S. Department 

of Agriculture, National Agriculture Statistics Service, 

1999 and 2004), making it highly unlikely that 100 

percent of the fertilizer was nonfarm. 

• New Hampshire usually reports less than 40 percent of 

fertilizer tonnage as nonfarm (appendix 2, page 27). In 

2003, 100 percent of the fertilizer product tonnage was 

reported as nonfarm. 

• Ohio usually does not report nonfarm tonnage 

(appendix 2, page 33). In 2004 and 2005 minor 

amounts of tonnage were reported as nonfarm.

• Rhode Island usually reports less than 40 percent of 

fertilizer tonnage as nonfarm (appendix 2, page 37). 

In 1989 and 1990 more than 70 percent was reported 

as nonfarm tonnage, and in 2003 all fertilizer product 

tonnage was reported as nonfarm. 

State data are sometimes estimated from previous years 

or from surrounding states. These are usually characterized by 

constant nonfarm-to-total tonnage ratios (appendix 2). States 

with estimated values were identified from the Data Sources 

documentation from AAPFCO (David Terry, AAPFCO, 

written commun., 2008) and are summarized in appendix 3.

Although AAPFCO data contain county-level 

information for some states (appendix 4), many state 

regulators/reporters do not consider county sales data a 

reflection of point of contact with soils. Distribution centers 

and farms are getting larger, and reported sales in a county can 

represent distribution and use in many counties (David Terry, 

University of Kentucky and Joe Slater, University of Missouri, 

oral commun. July 24, 2008). Also, farmers can use fertilizer 

in a different county from where it was sold.

Estimation of State-Level Farm and 

Nonfarm Portions of Fertilizer Sales

The initial step to obtaining the county-level nutrient 

input was to estimate the state-level farm and nonfarm 

portions of the fertilizer sales data. States with data that met 

screening criteria were used to determine the national farm 

and nonfarm proportions of each fertilizer product for each 

year. These proportions were applied to fertilizer sales data for 

all states. The departure from Ruddy and others (2006) was in 

the procedure to select states used to determine the national 

farm and nonfarm proportions.

This revised method took a more comprehensive 

approach to selecting state sales data from the AAPFCO data 

base to calculate the national farm and nonfarm proportions. 

The annual sales data for each state were subject to a 

screening procedure consisting of four steps: (1) identify 

and eliminate records with nonfarm tonnage not reported, 

(2) identify and eliminate records with estimated values, (3) 

identify and eliminate records with large inconsistencies that 

indicate errors in the use codes, and (4) for each state, identify 

and eliminate records from years that have a lower reported 

nonfarm tonnage in comparison to the nonfarm tonnage from 

other years (fig. 1).

Figure 1. Method for selecting annual data for each state.

Reported nonfarm Yes

tonnage is low—

do not use.

Error in reported No

nonfarm data—

do not use.

Yes Estimated data—

do not use.

Nonfarm tonnage No

not reported—

do not use.

Yes

No

Yes

No

Use state/year data to derive

national farm and nonfarm 

proportions (figure 2)

Is nonfarm

tonnage low in

comparison to

other years?

Is nonfarm

tonnage 

consistent with

other years?

Is reported

tonnage

estimated?

Is nonfarm

tonnage

reported?

Annual farm and nonfarm 

fertilizer product tonnage for 

state (appendix 2)

Information on estimated 

data (appendix 3)

Selection Method

Figure 1. Method for selecting annual data for each state.
4 County-Level Estimates of Nitrogen and Phosphorus from Commercial Fertilizer for the Conterminous United States, 1987–2006

The graphs showing farm, nonfarm, and uncoded 

fertilizer product tonnage and ratios of nonfarm-to-total 

tonnage (appendix 2), and the table of the number of fertilizer 

products by state and by year (appendix 1), were reviewed to 

identify general patterns of use for each state. Deviations in 

those patterns were indications of potential errors.

Once the records with missing, estimated, and erroneous 

nonfarm tonnage were identified and eliminated from the 

data set, the statistical distribution of nonfarm tonnage was 

calculated and graphed to find a reasonable lower limit of the 

remaining nonfarm tonnage for each state. For each state, a 

yearly value below one tenth of the average yearly value was 

assumed to reflect incomplete coding of the sales data. For a 

given state, any year with nonfarm tonnage below the limit 

was not used in the farm-nonfarm processing. A summary of 

this evaluation of the data available for each state and for each 

year is shown in figure 2. 

National totals of farm and nonfarm sales from the 

selected states (fig. 2) were computed for each fertilizer 

product for each year. Following the methodology of Ruddy 

and others (2006) any fertilizer product not specifically 

coded as nonfarm was set to “farm.” In addition, six fertilizer 

products identified as only for farm use (Joe Slater, AAPFCO, 

written commun., 2008) were recoded to “farm” if found to be 

coded otherwise. There were no fertilizer products identified 

as having only nonfarm use. These totals were converted 

to national farm and nonfarm proportions (or rates), which 

were applied to the annual sales of each fertilizer product in 

each state to estimate farm and nonfarm tonnage. By using 

the fertilizer N-P-K percent content information, the farm 

and nonfarm tonnage for each the fertilizer product was 

then converted to farm and nonfarm nitrogen and phosphate 

estimates for each state and year. This procedure, from Ruddy 

and others (2006), is summarized below and illustrated in 

figure 3:

A. Calculate national farm and nonfarm rates for each 

fertilizer product from selected states (to be applied to all 

states) for each year. 

1. Using data from the selected states, sum farm and 

nonfarm tonnage for each fertilizer product.

2. Calculate national farm and nonfarm rates from 

tonnage for each fertilizer product:

a. farm rate = farm tonnage / (farm tonnage + 

nonfarm tonnage) 

b. nonfarm rate = (1 – farm rate) 

B. Calculate farm and nonfarm nitrogen and phosphate 

tonnage for each state for each year. 

1. Derive nitrogen and phosphate percentage from 

N-P-K values.

2. Obtain the farm and nonfarm rates from step A, by 

matching AAPFCO data by fertilizer product (If 

fertilizer product is unique to states not used in step 

A, then farm rate = 1).

3. For each state, for each fertilizer product, calculate:

a. Farm nitrogen tonnage = Fertilizer product 

tonnage * (nitrogen percentage * 0.01) * farm 

rate

b. Farm phosphate tonnage = Fertilizer product 

tonnage * (phosphate percentage * 0.01) * farm 

rate

c. Nonfarm nitrogen tonnage = Fertilizer product 

tonnage * (nitrogen percentage * 0.01) * 

nonfarm rate

d. Nonfarm phosphate tonnage = Fertilizer product 

tonnage * (phosphate percentage * 0.01) * 

nonfarm rate

4. For each state, sum tonnage calculated from each 

fertilizer product for farm nitrogen, farm phosphate, 

nonfarm nitrogen and nonfarm phosphate.

Further refinements were accomplished by examining 

the results from the initial processing for inconsistencies 

that could be caused by possible data coding errors in 

the AAPFCO data. These were identified by looking for 

abnormal nonfarm tonnage with respect to adjacent years, 

abnormal nonfarm nitrogen with respect to a recommended 

lawn application of 1 pound per 1,000 square feet (Florida 

Department of Agriculture and Consumer Services, 2007; 

Mugass, 1995; Rosen and Horgan, 2005; and University of 

California, 2004), and unusually high nonfarm proportion 

with respect to adjacent years. To aid in identifying the errors 

and the causes, farm and nonfarm tonnage contributing to 

the calculation of the nonfarm proportions were examined. 

Several issues were identified from the additional screening: 

• Estimates of nonfarm nitrogen in several states were 

unusually high in 2006 compared to other years. This 

large discrepancy in nonfarm nitrogen was likely 

caused by a high nonfarm use of urea (fertilizer 

product 460000000.066) in South Dakota. An 
Estimation of State-Level Farm and Nonfarm Portions of Fertilizer Sales 5

evaluation of the pattern of urea farm and nonfarm 

use from other states for 2003 through 2006 (North 

Dakota, South Dakota, Montana account for almost 

half of the urea use, 1987–2006) revealed that this high 

nonfarm use is anomalous and inconsistent with the 

extremely small amount of residential and urban land 

use in South Dakota. To address this issue, the USE 

field for one entry of 109,000 tons of urea in South 

Dakota for 2006 was recoded from nonfarm to farm.

• Nonfarm nitrogen and phosphate estimates in Georgia 

were unusually high in 2004 compared to other 

years. This large discrepancy was likely caused by 

allocating 88,000 tons of a single fertilizer product 

(080120180.000) to nonfarm use. Georgia did not 

report nonfarm sales in 2004 and, therefore, does not 

contribute to the national calculation of the farm and 

nonfarm proportions for this year. In fact, with the 

exception of Georgia, only a few states reported use 

of this fertilizer product and the amounts were small. 

The national nonfarm proportion for 2004 for this 

fertilizer product was solely based on 1 ton of nonfarm 

use reported in Vermont. This proportion caused 

88,000 tons to be allocated as nonfarm use in Georgia. 

Because all other tonnage from 2003 through 2006 

has been reported as farm use, it is believed that this 

fertilizer product should be allocated to farm usage. To 

address this, the USE field for one entry of 1 ton of this 

fertilizer product in Vermont was recoded as “farm” 

so that when the 2004 national farm and nonfarm 

proportions were applied, the Georgia tonnage was 

assigned to farm use.

• Estimates of nonfarm phosphate in Missouri were 

unusually high in 2005 compared to other years. This 

large discrepancy was likely caused by a change in 

reporting fertilizer sales by Missouri. From 1987 

through 2004, Missouri differentiated between farm 

and nonfarm usage (appendix 2, page 23). During these 

years, Missouri always reported mono ammonium 

phosphate (fertilizer product 110550000.209) as 

farm tonnage. In 2005, when Missouri stopped 

differentiating between farm and nonfarm tonnage, 

it was no longer a significant contributor toward the 

national nonfarm proportion. To address this, the 2005 

nonfarm proportion for this fertilizer product was set 

equal to the 2004 value.

• Nonfarm phosphate estimates in Oregon were 

unusually high in 2004 and 2005 compared to other 

years. This large discrepancy was likely caused by 

a change in reporting fertilizer sales by Oregon. In 

2004 and 2005, Oregon reported nonfarm tonnage that 

was over six times the amount previously reported 

(appendix 2, page 35). In addition, all nonfarm tonnage 

was reported by using one fertilizer product. To 

address this, Oregon data were not used in calculating 

the national nonfarm proportions for 2004 and 2005.

• Nonfarm nitrogen and phosphate estimates in Texas 

were unusually high in 2004 through 2006 compared to 

other years. Also, in 2005 and 2006, nonfarm nitrogen 

was unusually high with respect to a recommended 

lawn application of 1 pound per 1,000 square feet. 

This large discrepancy was likely caused by a change 

in the method of fertilizer sales reporting by Texas. 

From 1987 through 2003, Texas did not populate the 

USE field; therefore, farm and nonfarm use could not 

be distinguished. In 2004 through 2006, Texas reported 

all nonfarm tonnage as use of one fertilizer product. To 

address this, Texas data were not used in calculating 

the national nonfarm proportions in 2004 through 

2006. 

• Nonfarm nitrogen and phosphate estimates in Arizona 

were unusually high in 2004 compared to other years. 

Also, in 2004, nonfarm nitrogen was unusually high 

with respect to a recommended lawn application of 1 

pound per 1,000 square feet. This large discrepancy 

was likely caused by large tonnage of two fertilizer 

products (150050030.000 and 210020040.000) being 

allocated to nonfarm use because of a national nonfarm 

proportion based on small amounts of these fertilizer 

products reported in only a few states. To address 

this, the USE field was set to “farm” for both of these 

fertilizer products.

The farm and nonfarm nitrogen and phosphate estimates 

for each state and year were recalculated after implementation 

of the above data refinements and are shown in appendix 5. 

The revised data were compared to the 1987–2001 values from 

Ruddy and others (2006): average state-level farm nitrogen 

estimates were 3 to 6 percent lower, and nonfarm nitrogen 

estimates were 6 to 82 percent higher; average state-level farm 

phosphorus estimates were 2 to 3 percent lower, and nonfarm 

phosphorus estimates were 32 to 114 percent higher. 
6 County-Level Estimates of Nitrogen and Phosphorus from Commercial Fertilizer for the Conterminous United States, 1987–2006

Figure 2. Summary of results of the selection process for including states used to derive the national farm and nonfarm proportions for 

each year (1987−2006).

STATE

Alabama

Arizona

Arkansas

California

Colorado

Connecticut

Delaware

Florida

Georgia

Idaho

Illinois

Indiana

Iowa

Kansas

Kentucky

Louisiana

Maine

Maryland

Massachusetts

Michigan

Minnesota

Mississippi

Missouri

Montana

Nebraska

Nevada

New Hampshire

New Jersey

New Mexico

New York

North Carolina

North Dakota

Ohio

Oklahoma

Oregon

Pennslyvania

Rhode Island

South Carolina

South Dakota

Tennessee

Texas

Utah

Vermont

Virginia

Washington

West Virginia

Wisconsin

Wyoming

Figure 2. Summary of results of the selection process for including states used to derive the national farm and nonfarm proportions

for each year (1987−2006).

1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006

Eliminated during further review

Reported nonfarm tonnage is low in comparison to reported nonfarm tonnage from other years for the state

Error in reported nonfarm data

Nonfarm tonnage not reported; estimated data

Estimated data

Nonfarm tonnage not reported

Data used in calculations to derive national farm and nonfarm proportions

EXPLANATION

Data not used in calculations to derive national farm and nonfarm proportions
Estimation of State-Level Farm and Nonfarm Portions of Fertilizer Sales 7

Figure 3. Process to (A) calculate the national farm and nonfarm rates for each fertilizer product, and (B) calculate farm and 

nonfarm nitrogen and phosphate tonnage, for each state, for each year. Figure 3. Process to (A) calculate the national farm and nonfarm rates for each fertilizer product, and (B) calculate farm and 

nonfarm nitrogen and phosphate tonnage for each state, for each year.

Numbers in upper left corner of boxes correspond to 

description of steps in the text.

AAPFCO, Association of American Plant Food Control Officials

N-P-K, percentage content of nitrogen-phosphate-potash

fert, fertilizer product

tons, tonnage

%, percentage

EXPLANATION

Yes

No

For each state, from each 

fertilizer products, sum:

farm nitrogen tons

farm phosphate tons

nonfarm nitrogen tons

nonfarm phosphate tons

For each state, for each fertilizer product, calculate:

Farm nitrogen tons = fert tons * (nitrogen% * 0.01) * farm rate

Farm phosphate tons = fert tons * (phosphate% * 0.01) * farm rate

Nonfarm nitrogen tons = fert tons * (nitrogen% * 0.01) * nonfarm rate

Nonfarm phosphate tons = fert tons * (phosphate% * 0.01) * nonfarm rate

Does fertilizer

product have farm

and nonfarm rate?

Obtain national farm and nonfarm

rates from step A, by matching 

AAPFCO data by fertilizer product

Derive nitrogen and phosphate

percentage from N-P-K

Generate “fertilizer product”

from AAPFCO fertilizer code and N-P-K 

Read AAPFCO data: 

state, fertilizer code, N-P-K,

use, tonnage

Calculate farm

and nonfarm tonnage

for each state

4)

3)

2)

1)

B.

farm rate = 1

nonfarm rate = 0

National farm and nonfarm 

rate for each fertilizer product 

based on selected states 

farm rate = farm tons /

 (farm tons + nonfarm tons)

nonfarm rate = (1 - farm rate)

Calculate national farm 

and nonfarm rates 

for each fertilizer product,

For each fertilizer product,

using the selected states, sum:

farm tonnage

nonfarm tonnage

Generate “fertilizer product”

from AAPFCO fertilizer code and N-P-K 

Read AAPFCO data: 

state, fertilizer code, N-P-K,

use, tonnage

Read list of selected states

(figure 2)

Calculate

national farm and

nonfarm rates 

2)

1)

A.
8 County-Level Estimates of Nitrogen and Phosphorus from Commercial Fertilizer for the Conterminous United States, 1987–2006

Distribution to the County Level

State-level farm and nonfarm estimates of nitrogen and 

phosphate were distributed to the county level by using the 

methods established in Ruddy and others (2006). The method 

based on fertilizer expenditures was adopted by Ruddy and 

others (2006) and this report to distribute farm fertilizer for 

all states because it is thought to produce a more realistic 

point-of-use spatial distribution of the fertilizer than the raw 

data based on county point-of-sale. State-level farm nitrogen 

and phosphate were distributed to the county in proportion to 

fertilizer expenditure (Ruddy and others, 2006) as shown in 

figure 4:

FFCUik = FFSSi (FCEik/FSEi) (1)

where

FFCUik is the estimated nutrient input from farmfertilizer use in county k of State i, in tons 

of nitrogen or phosphate;

FFSSi is total farm-fertilizer sales for State i, in tons 

of nitrogen or phosphate;

FCEik is fertilizer expenditure for county k of State i, 

in dollars; and 

FSEi is total fertilizer expenditure for State i, in 

dollars.

County-level fertilizer expenditure data were obtained 

from the 1987, 1992, 1997, and 2002 Censuses of Agriculture 

(U.S. Department of Commerce, Bureau of the Census, 

1989 and 1995; U.S. Department of Agriculture, National 

Agriculture Statistics Service, 1999 and 2004). For intervening 

years, state and county fertilizer expenditures were estimated 

by linear interpolation. In cases where fertilizer expenditures 

were not disclosed for a county in a particular Census of 

Agriculture year, an interpolation was done between the 

nearest census years that had disclosed values. If nondisclosed 

values occurred at either end of the time span, the nearest 

disclosed value was used for all previous or subsequent years 

(Ruddy and others, 2006). The 2002 fertilizer expenditure 

values were used for 2002 through 2006. At the time of 

processing, 2007 fertilizer expenditure data were not available. 

Ruddy and others (2006) developed a relation between 

effective population and nonfarm fertilizer sales, which was 

used to distribute state sales of nonfarm fertilizer to the county 

level: 

EPCik = Aik × minimum (Pik, 700)1.3 (2) 

where

EPCik is the effective population of county k in State 

i;

Aik is the area of county k in State i, in square 

kilometers; and 

Pik is the population density of county k in State 

i, in persons per square kilometer.

State-level nonfarm fertilizer was allocated to the county 

level in proportion to effective population (Ruddy and others, 

2006) as shown in figure 5:

NFCUik = NFSSi (EPCik/EPSi) (3)

where

NFCUik is the estimated nutrient inputs from nonfarmfertilizer use in county k of State i, in tons 

of nitrogen or phosphate; 

NFSSi is total nonfarm-fertilizer sales for State i, in 

tons of nitrogen or phosphate; and 

EPSi is the sum of EPCik for State i.

Population data for 1990 and 2000 and estimates for 

1987–89, 1991–99, and 2001–2006 were compiled from the 

U.S. Census Bureau (2003a, 2004a, 2004b, 2008) and Hitt 

(1992). County areas for 1987–2001 were derived from a 

30-meter-resolution grid of 1990 counties (http://water.usgs.

gov/lookup/getspatial?sir2012-5207_co1990g). This grid 

was created from 1990 county data set (U.S. Department of 

Commerce, Bureau of the Census, 1993) with the shoreline 

defined by the medium-resolution digital vector U.S. shoreline 

(National Oceanic and Atmospheric Administration, 1994) 

and the enhanced National Land Cover Data 1992 (NLCDe 

92; Nakagaki and others, 2007) because the counties, as 

defined by the U.S. Department of Commerce, Bureau of the 

Census (1993) extended into the oceans and Great Lakes. 

County areas for 2002–2006 were derived from a 30-meterresolution grid of 2001 counties (http://water.usgs.gov/lookup/

getspatial?sir2012-5207_co2001g) created by updating the 

1990 county data set with 2000 and 2004 TIGER/line files 

(U.S. Census Bureau, Geography Division, 2003b, and 2005) 

and defining the shoreline with the U.S. shoreline and the 

NLCDe 92 revised with 2000 population data to indicate 

urban development between 1992 and 2000 (NLCDep0905; 

Hitt, 2008).

County-level nutrient values of nitrogen and phosphate, 

calculated in tons, were multiplied by 907.2 to convert tons 

to kilograms. Phosphate values were subsequently multiplied 

by 0.4365 to convert kilograms of phosphate to kilograms of 

phosphorus. 
Distribution to the County Level 9

Figure 4. Distribution of state-level farm nitrogen to the county level by using county weights 

based on fertilizer expenditure.

Step 1: Calculate farm county weights

State ID 

(i )

County ID 

(k)

County fertilizer 

expenditure (FCEik ) ÷

State fertilizer 

expenditure (FSEi ) = Farm county weight (FCEik /FSEi )

10 001 8,799 23,780 0.37

10 003 3,329 23,780 0.14

10 005 11,652 23,780 0.49

Step 2: Calculate county farm nitrogen tonnage

State ID 

(i )

County ID 

(k)

Farm county weight 

(FCEik /FSEi ) x

State farm nitrogen

tonnage (FFSSi ) = County farm nitrogentonnage (FFCUik )

10 001 0.37 1,651.51 611.06

10 003 0.14 1,651.51 231.21

10 005 0.49 1,651.51 809.24

Figure 4. Distribution of state-level farm nitrogen to the county level, by using county weights based on 

fertilizer expenditure. (See equation 1 in text.)

Farm county weights

10001

37 percent

10005

49 percent

10003

14 percent

10005

10001

10003
10 County-Level Estimates of Nitrogen and Phosphorus from Commercial Fertilizer for the Conterminous United States, 1987–2006

Figure 5. Distribution of state-level nonfarm nitrogen to the county level by using county weights 

based on population.

Step 1: Calculate population density

State ID 

(i )

County ID 

(k) Population ÷ Area (Aik ) = Population density 

(Pik ) 

10 001 134,424 1,545.65 87

10 003 513,471 1,113.85 461

10 005 167,903 2,448.51 69

Step 2: Calculate effective population of county

State ID 

(i )

County ID 

(k) Area (Aik ) x

minimum [population

density (Pik ) , 700]

1.3 = Effective population

of county (EPCik )

10 001 1,545.65 332 513,200

10 003 1,113.85 2,903 3,233,126

10 005 2,448.51 244 596,905

Step 3: Calculate nonfarm county weights

State ID 

(i )

County ID 

(k)

Effective population

of county (EPCik ) ÷ Sum of EPCik (EPSi ) = Nonfarm county 

weight (EPCik /EPSi )

10 001 513,200 4,343,231 0.12

10 003 3,233,126 4,343,231 0.74

10 005 596,905 4,343,231 0.14

Step 4: Calculate county nonfarm nitrogen tonnage

State ID 

(i )

County ID 

(k)

Nonfarm county 

weight (EPCik /EPSi ) x

State nonfarm 

nitrogen tonnage

(NFSSi ) 

=

County nonfarm 

nitrogen tonnage

(NFCUik )

10 001 0.12 133.56 16.03

10 003 0.74 133.56 98.83

10 005 0.14 133.56 18.70

Figure 5. Distribution of state-level nonfarm nitrogen to the county level, by using county weights based 

on population. (See equations 2 and 3 in text.)

Nonfarm county weights

10003

74 percent

10005

14 percent

10001

10005 12 percent

10001

10003
Description of the County-Level Fertilizer Nutrient-Input Dataset 11

Description of the County-Level 

Fertilizer Nutrient-Input Dataset

The fertilizer nutrient-input data described in 

this report are in two files in a Microsoft Access 

database: tblFarmNonfarmCountyNitrogen, and 

tblFarmNonfarmCountyPhosphorus. The database 

is available on line at http://water.usgs.gov/lookup/

getspatial?sir2012-5207_county_fertilizer. The data files 

contain estimates of nitrogen and phosphorus from farm and 

nonfarm fertilizer use, in kilograms, for each county in the 

conterminous United States for the period of 1987 to 2006. 

Counties are identified by state, county, and state and county 

Federal Information Processing System (FIPS) code, sorted 

alphabetically by state and numerically by FIPS code within 

each state. Attribute definitions for the two files are listed in 

table 1.

Table 1. Attribute labels and definitions for the tblFarmNonfarmCountyNitrogen and tblFarmNonfarmCountyPhosphorus data files.

[NA, not applicable]

tblFarmNonfarmCountyNitrogen tblFarmNonfarmCountyPhosphorus

Attribute

label Attribute definition Units Attribute label Attribute definition Units

FIPS_ST The Federal Information Processing 

Standards (FIPS) 2-digit code of the 

State or State equivalent

NA FIPS_ST The Federal Information Processing 

Standards (FIPS) 2-digit code of the State 

or State equivalent

NA

FIPS_CO The Federal Information Processing 

Standards (FIPS) 3-digit code of the 

county or county equivalent in the 

designated state

NA FIPS_CO The Federal Information Processing 

Standards (FIPS) 3-digit code of the 

county or county equivalent in the 

designated state

NA

STATE The Federal Information Processing 

Standards (FIPS) 2-character 

abbreviation of the name of the State or 

State equivalent

NA STATE The Federal Information Processing 

Standards (FIPS) 2-character abbreviation 

of the name of the State or State equivalent

NA

CO County name NA CO County name NA

farmN1987 Nitrogen from farm fertilizer, 1987 kilograms farmP1987 Phosphorus from farm fertilizer, 1987 kilograms

nonfN1987 Nitrogen from nonfarm fertilizer, 1987 kilograms nonfP1987 Phosphorus from nonfarm fertilizer, 1987 kilograms

farmN1988 Nitrogen from farm fertilizer, 1988 kilograms farmP1988 Phosphorus from farm fertilizer, 1988 kilograms

nonfN1988 Nitrogen from nonfarm fertilizer, 1988 kilograms nonfP1988 Phosphorus from nonfarm fertilizer, 1988 kilograms

farmN1989 Nitrogen from farm fertilizer, 1989 kilograms farmP1989 Phosphorus from farm fertilizer, 1989 kilograms

nonfN1989 Nitrogen from nonfarm fertilizer, 1989 kilograms nonfP1989 Phosphorus from nonfarm fertilizer, 1989 kilograms

farmN1990 Nitrogen from farm fertilizer, 1990 kilograms farmP1990 Phosphorus from farm fertilizer, 1990 kilograms

nonfN1990 Nitrogen from nonfarm fertilizer, 1990 kilograms nonfP1990 Phosphorus from nonfarm fertilizer, 1990 kilograms

farmN1991 Nitrogen from farm fertilizer, 1991 kilograms farmP1991 Phosphorus from farm fertilizer, 1991 kilograms

nonfN1991 Nitrogen from nonfarm fertilizer, 1991 kilograms nonfP1991 Phosphorus from nonfarm fertilizer, 1991 kilograms

farmN1992 Nitrogen from farm fertilizer, 1992 kilograms farmP1992 Phosphorus from farm fertilizer, 1992 kilograms

nonfN1992 Nitrogen from nonfarm fertilizer, 1992 kilograms nonfP1992 Phosphorus from nonfarm fertilizer, 1992 kilograms

farmN1993 Nitrogen from farm fertilizer, 1993 kilograms farmP1993 Phosphorus from farm fertilizer, 1993 kilograms

nonfN1993 Nitrogen from nonfarm fertilizer, 1993 kilograms nonfP1993 Phosphorus from nonfarm fertilizer, 1993 kilograms

farmN1994 Nitrogen from farm fertilizer, 1994 kilograms farmP1994 Phosphorus from farm fertilizer, 1994 kilograms

nonfN1994 Nitrogen from nonfarm fertilizer, 1994 kilograms nonfP1994 Phosphorus from nonfarm fertilizer, 1994 kilograms

farmN1995 Nitrogen from farm fertilizer, 1995 kilograms farmP1995 Phosphorus from farm fertilizer, 1995 kilograms

nonfN1995 Nitrogen from nonfarm fertilizer, 1995 kilograms nonfP1995 Phosphorus from nonfarm fertilizer, 1995 kilograms

farmN1996 Nitrogen from farm fertilizer, 1996 kilograms farmP1996 Phosphorus from farm fertilizer, 1996 kilograms

nonfN1996 Nitrogen from nonfarm fertilizer, 1996 kilograms nonfP1996 Phosphorus from nonfarm fertilizer, 1996 kilograms

farmN1997 Nitrogen from farm fertilizer, 1997 kilograms farmP1997 Phosphorus from farm fertilizer, 1997 kilograms

nonfN1997 Nitrogen from nonfarm fertilizer, 1997 kilograms nonfP1997 Phosphorus from nonfarm fertilizer, 1997 kilograms

farmN1998 Nitrogen from farm fertilizer, 1998 kilograms farmP1998 Phosphorus from farm fertilizer, 1998 kilograms

nonfN1998 Nitrogen from nonfarm fertilizer, 1998 kilograms nonfP1998 Phosphorus from nonfarm fertilizer, 1998 kilograms
12 County-Level Estimates of Nitrogen and Phosphorus from Commercial Fertilizer for the Conterminous United States, 1987–2006

Evaluation of the Farm and Nonfarm 

Fertilizer Data

Annual totals of state-level farm and nonfarm nitrogen 

and phosphorus fertilizer were evaluated by comparing results 

using the national farm and nonfarm proportions to results 

for states where reporting includes farm and nonfarm usage 

for ten or more years. Nonfarm usage was also compared to 

independent estimates of nonfarm fertilizer applications and 

land use.

Temporal Variability at the State Level

A comparison of farm and nonfarm nitrogen and 

phosphorus estimates based on national farm and nonfarm 

proportions versus specific state reported farm and nonfarm 

product use is shown in appendix 6. These figures show the 

year-to-year variability of the farm and nonfarm nitrogen and 

phosphorus estimates based on national and state proportions. 

The most useful way to examine the graphs is not to look at 

the differences between the national-based and state-based 

values, but to look at the relative change from year to year. In 

general, the periods of high and low usage coincide between 

the national- and state-based values. The national processing 

tends to smooth the values from year to year, limiting the 

spikes and dips seen in the state processing, and filling gaps 

in the state reporting. The inconsistent reporting of nonfarm 

usage in many states is apparent, however.

Spatial Distribution of Nonfarm-to-Total 

Fertilizer Ratios

Nonfarm-to-total fertilizer ratios for nitrogen and 

phosphorus were calculated by using state-based farm and 

nonfarm proportions for 1987 through 2006 for states with 

sufficient data (at least 10 years of data for the calculation of 

the national-based farm and nonfarm proportions, shown in 

figure 2). Median values for each state were then determined 

from the nonfarm-to-total fertilizer ratios. The same was 

done for the same states by using the national-based farm 

and nonfarm proportions. Comparisons of the results from 

these two approaches helped to determine if applying national 

farm and nonfarm proportions for each fertilizer product to 

each state maintained the spatial distribution of the nonfarm 

fertilizer ratios. The medians of the state- and nationalbased nonfarm-to-total ratios for nitrogen and phosphorus 

are shown in figure 6. The broad regional distribution of the 

nonfarm ratios appeared to be maintained for both nitrogen 

and phosphorus. Higher nonfarm ratios were present in the 

Northeast region and South Atlantic division of the South 

region. Lower nonfarm ratios were present in the West North 

Central division of the Midwest region and the Pacific division 

of the Northwest region. Regions and divisions are from the 

U.S. Census Bureau, Geographic Division (2011).

Table 1. Attribute labels and definitions for the tblFarmNonfarmCountyNitrogen and tblFarmNonfarmCountyPhosphorus

data files.—Continued

[NA, not applicable]

tblFarmNonfarmCountyNitrogen tblFarmNonfarmCountyPhosphorus

Attribute

label Attribute definition Units Attribute label Attribute definition Units

farmN1999 Nitrogen from farm fertilizer, 1999 kilograms farmP1999 Phosphorus from farm fertilizer, 1999 kilograms

nonfN1999 Nitrogen from nonfarm fertilizer, 1999 kilograms nonfP1999 Phosphorus from nonfarm fertilizer, 1999 kilograms

farmN2000 Nitrogen from farm fertilizer, 2000 kilograms farmP2000 Phosphorus from farm fertilizer, 2000 kilograms

nonfN2000 Nitrogen from nonfarm fertilizer, 2000 kilograms nonfP2000 Phosphorus from nonfarm fertilizer, 2000 kilograms

farmN2001 Nitrogen from farm fertilizer, 2001 kilograms farmP2001 Phosphorus from farm fertilizer, 2001 kilograms

nonfN2001 Nitrogen from nonfarm fertilizer, 2001 kilograms nonfP2001 Phosphorus from nonfarm fertilizer, 2001 kilograms

farmN2002 Nitrogen from farm fertilizer, 2002 kilograms farmP2002 Phosphorus from farm fertilizer, 2002 kilograms

nonfN2002 Nitrogen from nonfarm fertilizer, 2002 kilograms nonfP2002 Phosphorus from nonfarm fertilizer, 2002 kilograms

farmN2003 Nitrogen from farm fertilizer, 2003 kilograms farmP2003 Phosphorus from farm fertilizer, 2003 kilograms

nonfN2003 Nitrogen from nonfarm fertilizer, 2003 kilograms nonfP2003 Phosphorus from nonfarm fertilizer, 2003 kilograms

farmN2004 Nitrogen from farm fertilizer, 2004 kilograms farmP2004 Phosphorus from farm fertilizer, 2004 kilograms

nonfN2004 Nitrogen from nonfarm fertilizer, 2004 kilograms nonfP2004 Phosphorus from nonfarm fertilizer, 2004 kilograms

farmN2005 Nitrogen from farm fertilizer, 2005 kilograms farmP2005 Phosphorus from farm fertilizer, 2005 kilograms

nonfN2005 Nitrogen from nonfarm fertilizer, 2005 kilograms nonfP2005 Phosphorus from nonfarm fertilizer, 2005 kilograms

farmN2006 Nitrogen from farm fertilizer, 2006 kilograms farmP2006 Phosphorus from farm fertilizer, 2006 kilograms

nonfN2006 Nitrogen from nonfarm fertilizer, 2006 kilograms nonfP2006 Phosphorus from nonfarm fertilizer, 2006 kilograms
Evaluation of the Farm and Nonfarm Fertilizer Data 13

Figure 6. Spatial distribution of state- and national-based median nonfarm-to-total ratios during 1987–2006 for (A) nitrogen 

and (B) phosphorus.

Ratios based on state data to generate farm and nonfarm proportions

[Number of years varies by state (10 to 20)]

Figure 6. Spatial distribution of state- and national-based median nonfarm-to-total ratios during 1987–2006 for (A) nitrogen, and

(B) phosphorus.

Ratios based on state data to generate farm and nonfarm proportions

[Number of years varies by state (10 to 20)]

Ratios based on national data to generate farm and nonfarm proportions

[All states based on 20 years of data]

A. Nitrogen

B. Phosphorus

Ratios based on national data to generate farm and nonfarm proportions

[All states based on 20 years of data]

<0.01

0.01 to 0.03

0.03 to 0.05

0.05 to 0.10

>0.10

Median ratio of nonfarm

to total nitrogen 

EXPLANATION

Insufficient state data

<0.01

0.01 to 0.03

0.03 to 0.05

0.05 to 0.10

>0.10

Median ratio of nonfarm

to total phosphorus 

EXPLANATION

Insufficient state data
14 County-Level Estimates of Nitrogen and Phosphorus from Commercial Fertilizer for the Conterminous United States, 1987–2006

Comparison to Independent Estimates of 

Nonfarm Fertilizer Application and Land Use

Recommended lawn application rates vary from about 

1 to 4 pounds of nitrogen per 1,000 square feet for different 

areas of the country (Florida Department of Agriculture and 

Consumer Services, 2007; Mugass, 1995; Rosen and Horgan, 

2005; and University of California, 2004). A comparison of 

the nonfarm nitrogen fertilizer values with these recommended 

application rates provides an independent measure of the 

nonfarm estimates. A comparison of the nonfarm phosphorus 

fertilizer values was not done because it was difficult to find a 

recommended application rate for phosphorus.

The nonfarm-fertilizer values for each state and year 

were compared to values that would be obtained if the lower 

bound of recommended use rates—one pound of nitrogen 

for each 1,000 square feet—were followed for urban land in 

each state. Land use was derived from the enhanced National 

Land Cover Data 1992 (NLCDe 92; Nakagaki, 2007), which 

was developed by overlaying satellite imagery-based 1992 

National Land Cover Data (NLCD 92; Vogelmann and others, 

2001) with selected classifications from aerial-photographybased Land Use and Land Cover (LULC) data (Price and 

others, 2007). For this comparison, the urban land use was 

estimated by summing four land-use classes from the NLCDe 

92: low-intensity residential; LULC residential, not classified 

as forest, water, or urban by NLCD 92; LULC residential, 

classified as forest by NLCD 92; and urban and recreational 

grasses. The ratios of observed nonfarm-fertilizer values to 

recommended values calculated from the land-use data are 

shown as box plots of annual values for each state in figure 7. 

Most states had ratios of less than one. Ratios greater than 

one indicate that the nonfarm-fertilizer application rates are 

in excess of the low end of the recommended application 

rates, whereas ratios less than one indicate nonfarm-fertilizer 

application rates less than the low end of recommended 

application rates. The low ratios are consistent with the fact 

that the actual area of fertilizer application is only a small 

portion of the urban area. For example, vegetation often 

accounts for only 20 to 70 percent of the cover in low intensity 

residential (Nakagaki and others, 2007). Estimates of nitrogen 

input rate from nonfarm fertilizer for Arizona and Georgia 

were much lower when compared to the recommended lawn 

application rate, suggesting that the nonfarm-fertilizer values 

were underestimated. Nitrogen input rates from nonfarm 

fertilizer for North Dakota and South Dakota could be 

overestimated. 

The plausibility of the nonfarm fertilizer use estimates 

was assessed by comparing the proportion of nonfarm 

fertilizer use (relative to total fertilizer use) in each state to the 

proportion of developed land in urban use. Ratios of nonfarmto-total (nonfarm to nonfarm plus farm) fertilizer estimates for 

nitrogen and phosphorus were calculated for each state and 

year. These ratios were then compared to the urban land-use 

percentage ((urban land area divided by the sum of urban and 

agricultural land area) * 100) in each state (fig. 8). Agricultural 

land was estimated by summing six NLCDe 92 land use 

classes: orchards/vineyards/other, LULC orchards/vineyards/

other, pasture/hay, row crops, small grains, and fallow. The 

data show that increases in nonfarm-to-total fertilizer ratios 

for nitrogen and phosphorus correspond to an increase in 

urban land-use percentages. This systematic trend is consistent 

with the hypothesis that the nonfarm portion of total fertilizer 

should increase as the urban area increases, and indicates that 

the calculated national nonfarm ratios provide a useful method 

to estimate nonfarm fertilizer use at the state level. Similar 

to figure 7, nonfarm-to-total fertilizer ratios for Arizona and 

Georgia were low compared to the other states with similar 

urban land-use percentages, and nonfarm-to-total ratios for 

North and South Dakota could be high.
Evaluation of the Farm and Nonfarm Fertilizer Data 15

Figure 7. Ratio of estimated nonfarm nitrogen input rate to the recommended lawn application rate, by state,1987–2006.

0.01

0.1

1

10

ALARAZCACOCTDEFLGAIAIDILINKSKYLAMAMDMEMIMNMOMSMTNCNDNENHNJNMNVNYOHOKORPARISCSDTNTXUTVAVTWAWIWVWY

Ratio of nonfarm input rate to recommended lawn application rate

Federal Information Processing Standard state abbreviation

Figure 7. Ratio of estimated nonfarm nitrogen input rate to the recommended lawn application rate, by state, 1987–2006. 

Median

75th percentile

90th percentile

Data outside 90th

or 10th percentile

25th percentile

10th percentile

1 to 1 ratio for application 

rate of 1 pound of nitrogen 

per 1,000 square feet
16 County-Level Estimates of Nitrogen and Phosphorus from Commercial Fertilizer for the Conterminous United States, 1987–2006

Figure 8. Nonfarm-to-total fertilizer ratio (median, 25th and 75th percentile) versus urban land-use percentage, 

1987–2006, for (A) nitrogen and (B) phosphorus (Alaska, Hawaii, and the District of Columbia are not included).

0.001

0.01

0.1

1

0.1 1 10 100

Urban land-use percentage

Ratio of nonfarm-to total-nitrogen input estimates

ND

SD MT

NE

KS MN

ID

MO

OK

WI

AR

IL

WY

MSTX

INCO

RI

MA

CT NJ

NH

FL

ME

AZ

MD

CA

VA

NY

NC

DE

PA

UT

SC

NV

TN

WV

WA

NM

OH

OR

MIAL

VT

LA

KY

GA

IA

Figure 8. Nonfarm-to-total fertilizer ratio (median, 25th and 75th percentile) versus urban land-use percentage, 1987–2006, for 

(A) nitrogen, and (B) phosphorus (Alaska, Hawaii, and the District of Columbia are not included).

A. Nitrogen

0.001

0.01

0.1

1

0.1 1 10 100

Urban land-use percentage

Ratio of nonfarm-to-total phosphorus input estimates

ND SD MT NE

KS

MN ID

MO

OK

WIAR

IL

WY

MSTX

IN

CO

RI

MA

CT NJ

NH

FL

ME

AZ

MD

CA

VA

NY

NC

DE

PA

UT

SC

NV

TN

WV

WA

NM OH

OR

MI

AL VT

LA

KY

GA

IA

B. Phosphorus

ME

EXPLANATION

Federal Information Processing Standard state abbreviation

75th percentile

Median

25th percentile
References Cited 17

Summary

County-level nitrogen and phosphorus from fertilizer, 

for both farm and nonfarm use, were estimated for the 

conterminous United States for 1987 through 2006. A 

national approach to estimate state-level farm and nonfarm 

portions of the fertilizer sales data was used because not all 

states distinguish between farm and nonfarm use. Data from 

selected states were used to derive national farm and nonfarm 

proportions for each fertilizer product. These proportions were 

applied to fertilizer sales data from all states. The selection of 

states used in determining the farm and nonfarm proportions 

differs from what was reported by Ruddy and others (2006). 

The revised method excludes the use of estimated state data as 

well as inconsistent or erroneous values. State totals of farm 

fertilizer were distributed to counties by using county weights 

based on fertilizer expenditure, and state totals of nonfarm 

fertilizer were distributed to counties by using county weights 

based on effective population, as described by Ruddy and 

others (2006). 

Comparison of fertilizer inputs determined with the 

national proportions versus proportions developed from 

individual state reported data showed that periods of relative 

highs and lows were coincident between the national- and 

state-based values. Use of the national proportions also tended 

to reduce the extreme high values found in some individual 

state reported values. The national processing also was able 

to extrapolate values for states that do not report nonfarm 

use. The regional distribution of the nonfarm ratios also were 

maintained by using the national approach. 

Nonfarm nitrogen values were found to be 

reasonable estimates when compared to lawn application 

recommendations. Exceptions were North Dakota and South 

Dakota, where values could be overestimated for several 

years, and Arizona and Georgia, where values could be 

underestimated. At the state level, increases in nonfarmto-total fertilizer ratios for nitrogen and phosphorus also 

corresponded to an increase in urban land-use percentages, 

with the exception of underestimated values for Arizona and 

Georgia.

References Cited

Alexander, R.B., and Smith, R.A., 1990, County level 

estimates of nitrogen and phosphorus fertilizer use in the 

United States, 1945 to 1985: U.S. Geological Survey OpenFile Report 90-130, 12 p., available online at http://pubs.

usgs.gov/of/ofr90130/.

Association of American Plant Food Control Officials, 2010, 

Commercial fertilizer, available online at http://www.

aapfco.org/publications.html.

Battaglin, W.A., and Goolsby, D.A., 1995, Spatial data in 

geographic information system format on agricultural 

chemical use – Land use, and cropping practices in the 

United States: U.S. Geological Survey Water-Resources 

Investigations Report 95-4176, 86 p., available online at 

http://pubs.usgs.gov/wri/wri944176/.

Florida Department of Agriculture and Consumer Services, 

2007, “Consumer Fertilizer Task Force, Legislation/Rules,” 

Rule 5E01.003(2) Labeling Requirements for urban turf 

fertilizers (July 31, 2007), accessed July 16, 2008, at http://

consensus.fsu.edu/Fertilizer-Task-Force/legislation.html.

Gaither, Kellye, and Terry, D.L., 2004, Uniform fertilizer 

tonnage reporting system — version 4 — Instruction 

manual: Association of American Plant Food Control, 87 p.

Hitt, K.J., 1992, 1990 point population coverage for the 

Conterminous United States, available at http://water.usgs.

gov/lookup/getspatial?uspop90. 

Hitt, K.J., 2008, Enhanced National Land Cover Data 1992 

revised with 2000 population data to indicate urban 

development between 1992 and 2000 (NLCDep0905), 

digital data, available at http://water.usgs.gov/lookup/

getspatial?nlcdep0905.

Leahy, P.P., and Thompson, T.H., 1994, Overview of the 

National Water-Quality Assessment Program: U.S. 

Geological Survey Open-File Report 94-70, 4 p., available 

online at http://pubs.usgs.gov/of/1994/ofr-94-070/.

Mugass, R.J., 1995, “Responsible Fertilizer Practices for 

Lawns,” University of Minnesota Extension, FO-06551, 

accessed July 16, 2008, at http://www.extension.umn.edu/

distribution/horticulture/DG6551.html.

Nakagaki, N., Price, C.V., Falcone, J.A., Hitt, K.J., and 

Ruddy, B.C., 2007, Enhanced national land cover data 1992 

(NLCDe 92), digital data, available at http://water.usgs.gov/

lookup/getspatial?nlcde92.

National Oceanic and Atmospheric Administration (NOAA), 

National Ocean Service (NOS), Office of Coast Survey, 

and the Strategic Environmental Assessments (SEA) 

Division of the Office of Ocean Resources Conservation 

and Assessment (ORCA), 1994, NOS80K/ALLUS80K 

medium-resolution digital vector U.S. shoreline, digital 

map, accessed August 25, 2005 at http://woodshole.er.usgs.

gov/pubs/of2005-1048/data/basemaps/usa/nos80k/nos80k.

htm.

 Price, C.V., Nakagaki, N., Hitt, K.J., and Clawges, R.M., 

2007, Enhanced Historical Land-Use and Land-Cover Data 

Sets of the U.S. Geological Survey: U.S. Geological Survey 

Data Series 240, digital data set, available at http://pubs.

usgs.gov/ds/2006/240.
18 County-Level Estimates of Nitrogen and Phosphorus from Commercial Fertilizer for the Conterminous United States, 1987–2006

Rosen, C.J., and Horgan, B.P., 2005, “Preventing Pollution 

Problems from Lawn and Garden Fertilizers,” University 

of Minnesota Extension, FO-2923, accessed July 16, 2008, 

at http://www.extension.umn.edu/distribution/horticulture/

DG2923.html.

Ruddy, B.C., Lorenz, D.L, and Mueller, D.K., 2006, Countylevel estimates of nutrient inputs to the land surface of the 

Conterminous United States, 1982-2001: U.S. Geological 

Survey Scientific Investigations Report 2006-5012, 17 p., 

available online at http://pubs.usgs.gov/sir/2006/5012/.

U.S. Census Bureau, 2003a, “Intercensal estimates by 

demographic characteristics (1990-1999),” Population 

Estimates Data Sets, County population datasets (June 23, 

2003), accessed July 5, 2005, at http://www.census.gov/

popest/.

U.S. Census Bureau, Geologic Division, 2003b, TIGER 

products, Topologically Integrated Geographic Encoding 

and Referencing system, 2000 TIGER/Line Files, accessed 

February 24, 2003 at http://www.census.gov/geo/www/

tiger/index.html.

U.S. Census Bureau, 2004a, 2000 Census of Population and 

Housing, Population and Housing Unit Counts, PHC-3-1, 

United States Summary, Washington, D.C. 

U.S. Census Bureau, 2004b, “Archives, 1980s,” Population 

Estimates Archives (August 13, 2004), accessed August 30, 

2005, at http://www.census.gov/popest/.

U.S. Census Bureau, 2005, TIGER products, Topologically 

Integrated Geographic Encoding and Referencing system, 

2004 TIGER/Line Files, accessed April 13, 2005 at http://

www.census.gov/geo/www/tiger/index.html.

U.S. Census Bureau, 2008, “County population, population 

change and estimated components of population change: 

April 1, 2000 to July 1, 2007 (CO-EST2007-alldata),” 

Population Estimates Data Sets, County population datasets 

(March 20, 2008), accessed July 15, 2008, at http://www.

census.gov/popest/.

U.S. Census Bureau, Geographic Division, 2011, Geographic 

Terms and Concepts - Census Divisions and Census 

Regions (February 18, 2011), accessed July 17, 2012 at 

http://www.census.gov/geo/www/2010census/gtc/gtc_

census_divreg.html.

U.S. Department of Agriculture, National Agriculture 

Statistics Service, 1999, 1997 Census of Agriculture – State 

and County Data, Volume 1: Geographic Area Series, 

Washington, D.C., available at http://www.agcensus.usda.

gov/Publications/1997/index.asp.

U.S. Department of Agriculture, National Agriculture 

Statistics Service, 2004, 2002 Census of Agriculture – State 

and County Data, Volume 1: Geographic Area Series, 

Washington, D.C., available at http://www.agcensus.usda.

gov/Publications/2002/index.asp.

U.S. Department of Commerce, Bureau of the Census, 1989, 

1987 Census of Agriculture, Volume 1: Geographic Area 

Series, available at http://agcensus.mannlib.cornell.edu/

AgCensus/censusParts.do?year=1987.

U.S. Department of Commerce, Bureau of the Census, 1993, 

1:100,000-scale counties of the United States, digital map, 

accessed September 1, 2005 at http://water.usgs.gov/lookup/

getspatial?county100.

U.S. Department of Commerce, Bureau of the Census, 

1995, 1992 Census of Agriculture, Volume 1: Geographic 

Area Series, available at http://www.agcensus.usda.gov/

Publications/1992/index.asp.

University of California, 2004, Agriculture and Natural 

Resources “The UC Guide to Healthy Lawns” (January 28, 

2004), accessed July 16, 2008 at http://www.ipm.ucdavis.

edu/TOOLS/TURF/MAINTAIN/fertamt.html. 

Vogelmann, J.E., Howard, S.M., Yang, L., Larson, C.R., 

Wylie, B.K., and Van Driel, N., 2001, Completion of the 

1990’s National Land Cover Data Set for the conterminous 

United States from Landsat Thematic Mapper data and 

ancillary data sources: Photogrammetric Engineering and 

Remote Sensing, v. 67, p. 650-662. 
Appendixes 19

Appendixes

Appendixes are available for download in PDF format at http://pubs.usgs.gov/sir/2012/5207/.

Appendix 1. Total Number of Fertilizer Products and Number of Nonfarm Fertilizer Products Summarized from the Association of 

American Plant Food Control Officials Data, by State, 1987–2006.

Appendix 2. Product Tonnage as Reported in Raw Association of American Plant Food Control Officials Data, by State, 1987–2006.

Appendix 3. (A) Location of States With at Least One Year (1987–2006) of Association of American Plant Food Control Officials 

(AAPFCO) Fertilizer Product Tonnage Data Estimated from Previous Years or from Surrounding States, and (B) Summary of States and 

Years with Estimated AAPFCO Fertilizer Product Tonnage Data (shaded), 1987–2006. 

Appendix 4. Location of Counties with Association of American Plant Food Control Officials Fertilizer Product Tonnage data Reported 

at the County Level, 1987–2006.

Appendix 5. Farm and Nonfarm Nitrogen and Phosphate Tonnage, by State, 1987–2006 (blue line on plot B represents 1 pound of 

nitrogen per 1,000 square feet of urban area).

Appendix 6. Nitrogen and Phosphorus Tonnage Based on National (red) and State (green) Farm and Nonfarm Proportions, by State, 

1987–2006.
20 County-Level Estimates of Nitrogen and Phosphorus from Commercial Fertilizer for the Conterminous United States, 1987–2006

This page intentionally left blank.
Publishing support provided by the U.S. Geological Survey Science

Publishing Network, Sacramento and Tacoma Publishing Service Centers

For more information concerning the research in this report, contact the

 Director, California Water Science Center

U.S. Geological Survey

6000 J Street, Placer Hall

Sacramento, California 95819

http://ca.water.usgs.gov
Printed on recycled paper

Gronberg and Spahr— County-Level Estimates of Nitrogen and Phosphorus from Commercial Fertilizer, 1987–2006—Scientific Investigations Report 2012-5207