Manure and Fertilizer Inputs to Land in the Chesapeake Bay 

Watershed, 1950–2012

Scientific Investigations Report 2018–5022

U.S. Department of the Interior

U.S. Geological Survey
Cover: Soybean farm in northern Maryland, August 15, 2014. Photograph by Alex Demas, U.S. Geological Survey.
Manure and Fertilizer Inputs to Land in the 

Chesapeake Bay Watershed, 1950–2012

By Jennifer L.D. Keisman, Olivia H. Devereux, Andrew E. LaMotte, Andrew J. 

Sekellick, and Joel D. Blomquist

Scientific Investigations Report 2018–5022

U.S. Department of the Interior

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

RYAN K. ZINKE, Secretary

U.S. Geological Survey

James F. Reilly II, Director

U.S. Geological Survey, Reston, Virginia: 2018

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Suggested citation:

Keisman, J.L.D., Devereux, O.H., LaMotte, A.E., Sekellick, A.J., and Blomquist, J.D., 2018, Manure and fertilizer 

inputs to land in the Chesapeake Bay watershed, 1950–2012: U.S. Geological Survey Scientific Investigations Report 

2018–5022, 37 p., https://doi.org/10.3133/sir20185022.

ISSN 2328-0328 (online)

ISSN 2328-031X (print)
Contents

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

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

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

Methods ..........................................................................................................................................................5

Land Use, Crops, and Animals............................................................................................................5

Fertilizer and Manure Inputs to Land ................................................................................................6

Best Management Practices..............................................................................................................7

Results .............................................................................................................................................................8

Land Use/Land-Use Change ...............................................................................................................8

Fertilizer and Manure Inputs to Land ................................................................................................8

1950–82 ..........................................................................................................................................8

1982–2012 ......................................................................................................................................8

Agricultural Land Use and Farming Practices...............................................................................13

Nutrient Input Intensity......................................................................................................................19

Relating Agricultural Practices to Fertilizer and Manure Inputs................................................19

Effects of Best Management Practice (BMP) Implementation on Manure and 

Fertilizer Inputs ......................................................................................................................19

Expected Reductions in Fertilizer and Manure Inputs ........................................................19

Animal Best Management Practice (BMP) Implementation..............................................26

Land-Use Change Best Management Practices (BMPs) ...................................................26

Summary........................................................................................................................................................29

References Cited..........................................................................................................................................30

Appendix 1

Inputs of nitrogen (N) to the Chesapeake Bay watershed’s 53 8-digit hydrologic 

units (HUC8s) from manure, fertilizer, and the two sources combined.................................32

Appendix 2

Inputs of phosphorus (P) to the Chesapeake Bay watershed’s 53 8-digit hydrologic 

units (HUC8s) from manure, fertilizer, and the two sources combined.................................35

iii
iv

Figures

1. Map showing location of the Chesapeake Bay watershed, with 8-digit

hydrologic units (HUC8s) and aggregated regions identified ...............................................3

2. Graph showing phasing in of reduction credit for poultry phytase

implementation, 1997–2002 .........................................................................................................7

3. Graph showing reported implementation of agricultural land-use change best

management practices (BMPs) for major regions of the Chesapeake Bay

watershed, 1985–2012..................................................................................................................9

4. Graphs showing A, nitrogen, and B, phosphorus inputs to the Chesapeake Bay

watershed from manure and fertilizer, 1950–2012.................................................................12

5. Boxplots showing range and variability of the change in agricultural A,

nitrogen inputs, and B, phosphorus inputs from 1950–82 and 1982–2012 in the

Chesapeake Bay watershed at the 8-digit hydrologic unit (HUC8) scale .........................13

6. Graphs showing change in agricultural A, nitrogen inputs, and B, phosphorus

inputs for each 8-digit hydrologic basin (HUC8) in the Chesapeake Bay

watershed from 1982 to 2012 ....................................................................................................14

7. Graphs showing spatial variability of A, major crop groups, and B, major

animal groups in the Chesapeake Bay watershed in 1982 and 2012 .................................18

8. Maps showing input intensity of A, nitrogen (N) and B, phosphorus (P) on

agricultural acres in the Chesapeake Bay watershed in 1982............................................20

9. Maps showing input intensity change from 1982 to 2012 for A, nitrogen (N) and

B, phosphorus (P) in the Chesapeake Bay watershed.........................................................21

10. Graphs showing nitrogen fertilizer use on harvested cropland by proportion of

cropland devoted to A, grain corn, and B, silage corn in the Chesapeake Bay

watershed ....................................................................................................................................22

11. Graphs showing expected effect of best management practices (BMPs) on A,

nitrogen (N) and B, phosphorus (P) applications to land in the Chesapeake Bay

watershed, 1985–2012................................................................................................................23

12. Graphs showing A, expected percent change in manure-phosphorus

(manure-P) applications due to best management practices (BMPs) from 1985

to 2012 (dark blue bars), and B, 2012 poultry populations (light blue bars) in the

Chesapeake Bay watershed.....................................................................................................27

13. Graph showing reported implementation of agricultural land-use change best

management practices (BMPs) for major regions of the Chesapeake Bay

watershed, 1985–2012................................................................................................................28

14. Map showing implementation of agricultural land-use change best

management practices (BMPs) as of 2012 (percent of eligible acres) in the

Chesapeake Bay watershed.....................................................................................................29
v

Tables

1. 8-Digit hydrologic units (HUC8s) of the Chesapeake Bay watershed, grouped 

by region.........................................................................................................................................4

2. Watershed regions: size and area distribution........................................................................5

3. Sources of data used in this report ...........................................................................................6

4. Animal number to animal unit (AU) conversion assumptions used by the 

Chesapeake Bay Program, and revised assumptions used and described 

in the Methods section of this report........................................................................................6

5. Percent of land area in each land-use class in the Chesapeake Bay watershed,

1982 and 2012...............................................................................................................................10

6. Changes over time in agricultural nitrogen (N) and phosphorus (P) inputs to

seven distinct regions of the watershed, 1950–2012 ............................................................11

7. Changes in farmland area (acres) in the Chesapeake Bay watershed,

1950–2012 .....................................................................................................................................15

8. Changes in spatial variability of harvested cropland in the Chesapeake Bay

watershed in 1950, 1982, and 2012 ...........................................................................................16

9. Percentage of acres harvested for six dominant crop types in the Chesapeake

Bay watershed, 1950–2012........................................................................................................16

10. Annual percentage of animal biomass (in animal units) for the five major 

animal types produced in the Chesapeake Bay watershed, 1950–2012............................17

11. Intensity of agricultural nutrient inputs to seven major regions in the

Chesapeake Bay watershed in 1950, 1982, and 2012............................................................21

12. Expected change in nitrogen (N) and phosphorus (P) applications in the

Chesapeake Bay watershed with and without best management practice (BMP)

implementation, 1985–2012 .......................................................................................................24

13. Spatial variability in expected changes in manure and fertilizer inputs due to

best management practice (BMP) implementation in the Chesapeake Bay

watershed, 1985–2012................................................................................................................25

14. Dairy precision feeding implementation rates in the Chesapeake Bay

watershed, 2007–12....................................................................................................................27
vi

Conversion Factors

Inch/Pound to International System of Units

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

Area

acre 0.004047 square kilometer (km2)

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2) 

Mass

pound, avoirdupois (lb) 0.4536 kilogram (kg) 

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F = (1.8 × °C) + 32.

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows: 

 °C = (°F – 32) / 1.8.

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD83).
vii

Abbreviations

AU Animal unit

BMP Best management practice

CBP Chesapeake Bay Program

CBPO EPA Chesapeake Bay Program Office

COA Census of Agriculture

EPA U.S. Environmental Protection Agency

HUC Hydrologic unit code

HUC8 8-digit hydrologic unit

N Total Nitrogen

NAWQA USGS National Water-Quality Assessment Project 

NWALT National Water-Quality Assessment Wall-to-Wall Anthropogenic Land-Use 

 Trends

P Total Phosphorus

TMDL Total Maximum Daily Load

USDA U.S. Department of Agriculture

USGS U.S. Geological Survey

Manure and Fertilizer Inputs to Land in the Chesapeake 

Bay Watershed, 1950–2012

By Jennifer L.D. Keisman1, Olivia H. Devereux2, Andrew E. LaMotte1, Andrew J. Sekellick1, and 

Joel D. Blomquist1

Abstract

Understanding changing nutrient concentrations in 

surface waters requires quantitative information on changing nutrient sources in contributing watersheds. For example, 

the proportion of nutrient inputs reaching streams and rivers is directly affected by when and where those nutrients 

enter the landscape. The goal of this report is to contribute 

to the U.S. Geological Survey’s efforts to describe spatial 

and temporal patterns in nutrient inputs to the landscape in 

the Chesapeake Bay watershed, thereby informing efforts 

to understand changes in riverine and estuarine conditions. 

The magnitude, spatial variability, and changes over time in 

nutrient inputs from manure and fertilizer were evaluated in 

the context of changes in land use and agricultural practices 

from 1950 through 2012 at three spatial scales: the entire 

Chesapeake Bay watershed, the 53 8-digit hydrologic units 

(HUC8s) that are contained within the watershed, and a set 

of 7 regions that were determined by aggregating geographically similar HUC8s. The expected effect of agricultural best 

management practices (BMPs) on agricultural nutrient inputs 

from 1985 through 2012 was also investigated. Nitrogen (N) 

and phosphorus (P) inputs from manure increased gradually 

over time at the scale of the entire watershed. Fertilizer-N 

inputs showed steeper increases, with greater inter-annual 

fluctuations. Fertilizer-P inputs were less variable, increasing 

moderately from 1950 through the mid-1970s, and declining thereafter. Nutrient inputs and farming practices varied 

geographically within the watershed, with implications for the 

potential impact of these inputs on downstream water quality and ecosystem health. Both temporal and spatial patterns 

in the intensity of agricultural nutrient inputs were consistent 

with the magnitude and concentration of livestock and poultry 

populations and the intensity of row crop agriculture. Reported 

implementation of the animal and land-use change BMPs that 

were evaluated were expected to have little effect on agricultural N inputs. Animal BMPs were expected to have a more 

measurable impact on manure-P inputs, particularly in areas 

with large poultry populations. Understanding these patterns is 

1

 U.S. Geological Survey.

2

 Devereux Consulting, Inc.

important for explaining the changes that have been observed 

in nutrient loads to the rivers and streams of the Chesapeake 

Bay watershed, and their impacts on the water quality and 

ecosystem health of Chesapeake Bay itself. 

Introduction

The Chesapeake Bay watershed covers about 

64,000 square miles (mi2), stretching across seven jurisdictions made up of six states (Delaware, Maryland, New York, 

Pennsylvania, Virginia, and West Virginia) as well as Washington, D.C. The watershed drains into an estuary covering a 

surface area of about 4,400 mi2, with a mean depth of about 

21.3 feet (ft) (Kemp and others, 2005). Pressures such as 

increasing population, agricultural production, and urban 

development across the watershed have degraded water quality and living resources in the Chesapeake Bay, leading to 

the establishment of a Total Maximum Daily Load (TMDL) 

regulating the amount of nitrogen, phosphorus, and sediment 

that jurisdictions may discharge into the watershed’s rivers, 

streams, and tidal waters (U.S. Environmental Protection 

Agency, 2010). In order to comply with the Chesapeake Bay 

TMDL, jurisdictions are implementing best management 

practices (BMPs) designed to reduce the amount of nitrogen, 

phosphorus, and sediment draining to tidal waters. 

Nitrogen (N) and phosphorus (P) inputs from agriculture (for example, manure and inorganic fertilizer combined) 

currently constitute the largest source of nutrient inputs to 

the landscape in the Chesapeake Bay watershed (Boesch and 

others, 2001; U.S. Environmental Protection Agency, 2010a), 

as well as the predominant source of nutrients delivered to 

Chesapeake Bay (Ator and others, 2011). Manure inputs can 

occur in feed lots, manure storage structures, or pasture, or can 

be applied to cropland as fertilizer, while inorganic fertilizer 

is generally applied to cropland. Understanding the absolute 

magnitude and spatial variability of manure and inorganic fertilizer inputs can inform further analysis of the relative impact 

of nutrient loads to Chesapeake Bay from different regions; 

a pound of N or P applied to land in the far western edge of 

the watershed does not have the same impact on Chesapeake 

Bay’s water quality as a pound applied to land closer to the 
2 Manure and Fertilizer Inputs to Land in the Chesapeake Bay Watershed, 1950–2012

Bay’s shoreline (Linker and others, 2013). Variable landscape 

conditions including soil erodibility, soil drainage properties, 

physiographic region, and rainfall patterns also lead to the 

variable contributions from uplands to streams and the Bay 

(Ator and Garcia, 2016). Understanding how the amount and 

location of manure and fertilizer inputs have changed over 

time may help managers understand the causes of improving or degrading water quality across the watershed, thereby 

informing their decisions regarding the future level of implementation and placement of BMPs.

Purpose and Scope 

The purpose of this report is to document the magnitude 

of N and P inputs to land from manure and inorganic fertilizer 

from 1950 through 2012 in the Chesapeake Bay watershed, 

and to describe changes in spatial variability over time. Inputs 

from other sources, such as biosolids from wastewater treatment plants that may be spread on fields in agricultural areas, 

are not considered in this report. Land-use change is explored 

– as are temporal and spatial patterns in agricultural land use 

and farming practices contributing to manure and fertilizer 

inputs – in order to better understand observed patterns in 

manure and fertilizer inputs. Both the amount of past implementation (1985–2012) and the expected effects of BMPs that 

directly affect manure and fertilizer inputs are also described. 

The term “expected effects” refers to the effects of BMPs as 

estimated from modeling scenarios provided by the Chesapeake Bay Program (CBP). The actual effects of these BMPs 

on nutrient inputs from manure and fertilizer may not yet be 

fully realized.

Inputs of N and P from manure and fertilizer are presented for the Chesapeake Bay watershed as a whole, and 

at the subbasin, or 8-digit, scale of the Watershed Boundary 

Dataset (U.S. Geological Survey and U.S. Department of Agriculture, Natural Resources Conservation Service, 2013). These 

subbasins were delineated using science-based hydrologic 

principles and assigned unique hydrologic unit codes (HUCs). 

There are a total of 53 8-digit scale hydrologic units (HUC8s) 

in the Chesapeake Bay watershed (fig. 1; table 1). HUC8s 

are also aggregated to seven categories corresponding to key 

regions of interest within the watershed (table 2). Changes 

in N and P inputs are compared with changes in agricultural 

land-use practices, such as the cultivation of crops and animal 

populations, and with the reporting of certain agricultural 

BMPs between 1985 and 2012.
Introduction 3

Eastern Shore

Regions

EXPLANATION

Hampton Roads

James River

Maryland Western Shore

Potomac River

Susquehanna River

Virginia Western Shore

Chesapeake Bay

Chesapeake Bay

watershed boundary

Maryland

Washington, D.C.

New York

Pennsylvania

Delaware

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50 100 MILES

0 50 100 KILOMETERS

0

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NEW YORK

Chesapeake Bay

watershed

boundary

PENNSYLVANIA

D.C. WEST

VIRGINIA

VIRGINIA

NJ

ATLANTIC OCEAN

Chesapeake Bay

MARYLAND

DE

80°

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0 10 20 30 40 50 MILES

0 10 20 30 40 50 KILOMETERS

Figure 1. Location of the Chesapeake Bay watershed, with 8-digit hydrologic units (HUC8s) and aggregated regions identified. 

[Integers shown for each HUC8 correspond to those listed in table 1.]
4 Manure and Fertilizer Inputs to Land in the Chesapeake Bay Watershed, 1950–2012

Table 1. 8-Digit hydrologic units (HUC8s) of the Chesapeake Bay watershed, grouped by region. The column labeled “HUC8 number” 

corresponds to those on the map of the Chesapeake Bay watershed shown in figure 1; the column labeled “8-digit code” contains the 

U.S. Geological Survey 8-digit identifier for each HUC8.

Region HUC8 name HUC8 number 8-digit code Area 

(square miles)

Susquehanna

Upper Susquehanna 1 02050101 2,287

Chenango 2 02050102 1,606

Owego-Wappasening 3 02050103 1,044

Tioga 4 02050104 1,382

Chemung 5 02050105 1,210

Upper Susquehanna-Tunkhannock 6 02050106 2,004

Upper Susquehanna-Lackawanna 7 02050107 1,766

Upper West Branch Susquehanna 8 02050201 1,597

Sinnemahoning 9 02050202 1,034

Middle West Branch Susquehanna 10 02050203 784

Bald Eagle 11 02050204 773

Pine 12 02050205 981

Lower West Branch Susquehanna 13 02050206 1,810

Lower Susquehanna-Penns 14 02050301 1,448

Upper Juniata 15 02050302 991

Raystown 16 02050303 962

Lower Juniata 17 02050304 1,450

Lower Susquehanna-Swatara 18 02050305 1,876

Lower Susquehanna 19 02050306 2,482

Eastern Shore

Chester-Sassafras 20 02060002 1,083

Choptank 21 02060005 801

Nanticoke 22 02080109 791

Tangier 23 02080110 651

Pocomoke-Western Lower Delmarva 24 02080111 842

Maryland 

Western Shore

Gunpowder-Patapsco 25 02060003 1,303

Severn 26 02060004 294

Patuxent 27 02060006 879

Potomac

South Branch Potomac 28 02070001 1,480

North Branch Potomac 29 02070002 1,343

Cacapon-Town 30 02070003 1,205

Conococheague-Opequon 31 02070004 2,277

South Fork Shenandoah 32 02070005 1,672

North Fork Shenandoah 33 02070006 1,034

Shenandoah 34 02070007 352

Middle Potomac-Catoctin 35 02070008 1,237

Monocacy 36 02070009 970

Middle Potomac-Anacostia-Occoquan 37 02070010 1,255

Lower Potomac 38 02070011 1,350
Methods 5

Table 1. 8-Digit hydrologic units (HUC8s) of the Chesapeake Bay watershed, grouped by region. The column labeled “HUC8 number” 

corresponds to those on the map of the Chesapeake Bay watershed shown in figure 1; the column labeled “8-digit code” contains the 

U.S. Geological Survey 8-digit identifier for each HUC8.—Continued

Region HUC8 name HUC8 number 8-digit code Area 

(square miles)

Virginia 

Western Shore

Great Wicomico-Piankatank 39 02080102 516

Rapidan-Upper Rappahannock 40 02080103 1,557

Lower Rappahannock 41 02080104 1,002

Mattaponi 42 02080105 904

Pamunkey 43 02080106 1,460

York 44 02080107 220

James

Upper James 45 02080201 2,211

Maury 46 02080202 838

Middle James-Buffalo 47 02080203 2,023

Rivanna 48 02080204 768

Middle James-Willis 49 02080205 945

Lower James 50 02080206 1,250

Appomattox 51 02080207 1,606

Hampton Roads Lynnhaven-Poquoson 52 02080108 176

Hampton Roads 53 02080208 401

Table 2. Watershed regions: size and area distribution.

[HUC8, 8-digit hydrologic unit]

Region Number of HUC8s Acres Square miles Percent of total

Susquehanna 19 17,591,020 27,486 43

Eastern Shore 5 2,667,233 4,168 6

Maryland Western Shore 3 1,585,094 2,477 4

Potomac 11 9,070,399 14,173 22

Virginia Western Shore 6 3,621,594 5,659 9

James 7 6,169,892 9,640 15

Hampton Roads 2 369,345 577 1

Total 53 41,074,577 64,180 100

Methods 

Data on land use, farmland area and use, cultivated 

crop types, livestock and poultry numbers, and manure 

and fertilizer inputs were combined to investigate changing spatial patterns over time in agricultural nutrient inputs 

and factors affecting those inputs (table 3). Patterns were 

explored at three spatial scales – the Chesapeake Bay watershed, HUC8, and seven regions of interest – and for 2 time 

periods: the entire period of record (1950–2012) and the 

most recent 30 years of record (1982–2012). Sizes and locations of HUC8s were obtained from the Watershed Boundary Dataset (WBD), a nationally standardized collection of 

hydrologic unit data developed and maintained cooperatively 

by the U.S. Department of Agriculture (USDA), the U.S. 

Geological Survey (USGS), and the Environmental Protection 

Agency (EPA). Data on reported BMP implementation for the 

years 1985–2012, along with the results of modeling scenarios 

described below, were used to explore the expected effects of 

BMP implementation on nutrient inputs to the watershed for 

each year from 1985 to 2012.

Land Use, Crops, and Animals

Changes in land use from 1982 to 2012 were described 

based on the USGS National Water-Quality Assessment Wallto-Wall Anthropogenic Land-Use Trends (NWALT) dataset 

(Falcone, 2015). NWALT land use classes were aggregated 

to four major categories as follows: “developed” and “semideveloped” classes were combined into one “developed” 
6 Manure and Fertilizer Inputs to Land in the Chesapeake Bay Watershed, 1950–2012

Table 3. Sources of data used in this report.

Data Source Time period

Fertilizer use Sekellick, 2017 1-year increments 1950–2012

Manure production Sekellick, 2017 5-year increments 1950–2012

Crop acres and yields; animal populations LaMotte, 2015 5-year increments 1950–2012

Land use, land-use change Falcone, 2015 1974, 1982, 1987, 1992, 2012

Best management practice implementation Devereux and others, 2017 1-year increments 1985–2012

category; “low use” and “very low use, conservation” classes 

were combined into one “natural” category; the “crops” and 

“pasture/hay” production subclasses were combined into an 

“agriculture” category; and the “wetlands,” “mining/extraction,” and “grazing potential” production subclasses were 

combined into an “other” category. The proportion of land in 

each of these four categories was evaluated at both the watershed scale and the HUC8 scales. To further explore changes 

in agricultural land use and agricultural practices, data from 

the USDA Census of Agriculture (COA) were used to quantify changes in the amount of cropland and pasture, in crops 

cultivated, and in animal populations (LaMotte, 2015). The 

COA reports data at the county scale. To facilitate analysis at 

the HUC8 scale, COA data were re-allocated from county to 

HUC8s by distributing the animal inventory equally across the 

agricultural pixels of a county, and then summing by HUC8. 

This assumed that animals were co-located with cropland and 

pasture.

Certain crop types tend to be co-located with livestock 

and (or) poultry populations, which may have implications for 

both manure and commercial fertilizer usage (Beegle, 2013). 

To illustrate this pattern for the Chesapeake Bay watershed, 

crop data from the COA were grouped into the following 

categories: forage (hay, alfalfa, and silage hay), silage corn, 

grain corn, and soybeans. To compare livestock and poultry 

populations with crop types, animals were grouped into cows 

(beef, dairy, other), hogs, and poultry (layers, pullets, broilers, 

and turkeys). 

In order to evaluate the relative contribution of each 

animal to total animal biomass in the watershed, the head 

counts for five animal types (cows, poultry, horses, sheep, and 

hogs) were converted to animal units (AUs) using methods 

developed by the CBP Partnership (table 4) (Chesapeake Bay 

Program, 2013), with some modifications to accommodate differences between the animal categories used by the CBP and 

those used in the USGS dataset. For example, the average of 

the CBP’s animal unit conversion assumptions for layers and 

pullets was used to estimate chicken AUs in the USGS dataset. 

Fertilizer and Manure Inputs to Land

Changes in manure and fertilizer-N and -P inputs as 

well as in N and P input intensity (a measure of nutrient input 

per acre of cropland) were compared within and among the 

Table 4. Animal number to animal unit (AU) conversion 

assumptions used by the Chesapeake Bay Program (Chesapeake 

Bay Program, 2013), and revised assumptions used and described 

in the Methods section of this report.

[CBP, Chesapeake Bay Program; USGS, U.S. Geological Survey; N/A, not 

applicable]

Animal type Animals per AU, 

CBP

Animals per AU, 

USGS

Broilers 455 455

Layers 250 N/A

Pullets 352.5 N/A

Chickens N/A 301.25

Turkeys 67 67

Angora goats 15.38 N/A

Milk goats 15.38 N/A

Beef 1.14 1.14

Dairy 0.74 0.74

Other cattle 2.08 2.08

Hogs and pigs for breeding 2.67 2.67

Hogs for slaughter 9.09 N/A

Horses 1 1

Sheep and lambs 10 10

53 HUC8s and seven regions. Data on fertilizer and manure 

inputs to the Chesapeake Bay watershed were obtained from 

Sekellick (2017). Historical crop, agricultural land-use, 

livestock, and poultry data were derived from the USDA 

COA for the Census Years from 1950 through 2012. These 

data are a subset of the data presented in LaMotte (2015). The 

NWALT dataset was used to derive areas that were defined as 

agricultural. NWALT consists of five land-use rasters covering the years 1974, 1982, 1992, 2002, and 2012. Agricultural 

pixels were defined based on NWALT second-level classes 

43 (crops), 44 (pasture/hay), and 45 (grazing potential). Crop 

pixels were defined by NWALT second-level class 43 (crops). 

County-level census input estimates were evenly distributed 

across agricultural or crop pixels for each county by dividing 

the county total by the number of thematic pixels. Pixels (and 

their associated agricultural census values) were then summed 

for each 8-digit HUC and each of the seven distinct regions 

in the Chesapeake Bay watershed. Examining changes at both 
Methods 7

the HUC8 scale and the regional scale provided an additional 

layer of information on geographic shifts in nutrients within 

the watershed.

Temporal and spatial patterns in the magnitude of manure 

and inorganic fertilizer inputs to the Chesapeake Bay watershed were evaluated for 1950–2012. At finer geographic scales 

within the watershed, changes in manure and fertilizer inputs 

between 1982 and 2012 were evaluated in order to coincide 

(approximately) with the 1985–2012 period for which the 

CBP had evaluated nutrient inputs and BMP implementation. 

Changes in input amounts during 1992, 2002, and 2012 for 

N (Appendix 1) and for P (Appendix 2) were compiled as 

supplementary material to support further analysis to explain 

observed changes in water quality. Linear regression was 

performed in R3.3.2 (R Core Team, 2016) to explore relations 

between fertilizer usage and the cultivation of different crop 

types across the watershed.

Best Management Practices

Data on the reported implementation of BMPs were 

retrieved from the Chesapeake Bay Program Office (CBPO) 

databases in July 2016 (Chesapeake Bay Program, 2013). 

These datasets were collected for use as inputs to the Phase 

5.3.2 version of the CBP’s Chesapeake Bay Watershed Model 

(U.S. Environmental Protection Agency, 2010). The Chesapeake Bay jurisdictions report the BMP data to the CBPO 

annually. The spatial scale varies depending on the BMP, 

state preference, and year. Some BMPs are reported at very 

specific scales, such as county, whereas others are reported at 

the HUC4 scale. The CBPO disaggregates the BMP data to the 

CBP Phase 5.3.2 Watershed Model land-river segments. BMPs 

were further assigned to HUC8s according to the HUC8 in 

which most of the land-river segment’s area was located. Both 

the spatial and temporal distribution in BMP implementation 

from 1985 (the first year for which these data are available) to 

2012, as well as their expected effects, were quantified. The 

resulting dataset includes the BMP name, the amount of that 

BMP implemented, land-use or animal type, and HUC8 to 

which the implementation was assigned. 

To estimate the expected effect of BMP implementation 

on changes in N and P over time, output from the CBP Phase 

5.3.2 Scenario Builder (Chesapeake Bay Program, 2013) was 

also obtained from the CBPO and allocated to the HUC8 

scale. Output consisted of the results of a set of “No Action” 

and “Progress” scenarios run for each year between 1985 

and 2012. No Action scenarios produced manure and fertilizer input datasets consistent with real-world estimates, based 

on the assumption that no BMPs were in place in each given 

year. In the Progress scenarios, manure and fertilizer input 

datasets were modified by applying assumptions of the effect 

of reported BMPs, based on the expectation that all BMPs 

reported by and credited to the jurisdictions were in place and 

functioning.

Only the animal and agricultural land-use change BMPs 

that affect nutrient inputs to land were included in this analysis. There are three animal BMPs tracked by the states that 

reduce N and (or) P inputs to the land by reducing the nutrient 

concentration in animals’ manure: changes in feed for poultry 

and swine, and dairy precision feeding and (or) forage management. Feed changes for poultry and swine include phytase, 

an enzyme added to animal feed to increase the amount of P 

that can be absorbed into the animal’s biomass. This increased 

efficiency of P absorption enables manufacturers to add less P 

to the feed, and also reduces the P content of manure (Chesapeake Bay Program, 2015). The intensity and effect of swine 

phytase implementation was not evaluated because implementation was not reported by the major jurisdictions until after 

2012. Another animal BMP – manure transport – also affects 

local manure inputs. Manure can be transported from the 

location in which it was generated by the animal, to another 

location to be applied to the land. This is commonly done in 

areas that have a high number of animals and little row cropland. Manure may be transported among farms and out of the 

watershed. 

For purposes of estimating the effect of poultry phytase 

implementation on manure-P inputs to the land, the CBP gradually increased the calculated benefit of phytase implementation over a 5-year period from 1997 through 2002 as follows: 

benefits were assumed to begin for all poultry as of 1997, and 

the full effect of that implementation (indicated by a reduction in P content of manure) was gradually phased in between 

1997 and 2002. The credited reduction in the P content of 

poultry manure due to phytase implementation was increased 

from 4 percent to 21 percent for broilers and turkeys, and from 

3 percent to 16 percent for layers and pullets (fig. 2).

The agricultural land-use change BMPs described in this 

report eliminate the manure and fertilizer applied to cropland, hay, and pasture land uses by converting these lands to 

agricultural land uses that do not receive manure or fertilizer, 

and (or) to natural land uses like forest or wetlands, thereby 

eliminating manure and fertilizer input to these areas. Landuse changes over time for reasons other than BMP implementation are excluded; thus, the intensity and expected effects 

25

20

15

10

5

0

1997

1998

Year

2000 2002 2004 2006 2008 2010 2012 2014

1999 2001 2003 2005 2007 2009 2011 2013

Percent of phosphorus

reduction credit

EXPLANATION

Layers and pullets

Broilers and turkeys

Figure 2. Phasing in of reduction credit for poultry phytase 

implementation, 1997–2002.
8 Manure and Fertilizer Inputs to Land in the Chesapeake Bay Watershed, 1950–2012

of BMP implementation described are distinguished from the 

effects of other changes in land use such as urban development 

or re-forestation. The total amount of BMP acres in a HUC8 

can exceed the total agricultural area because more than one 

type of BMP can occur on the same acre of land. 

Results

Land Use/Land-Use Change

In 1982, 58 percent of the watershed was considered to 

be in a “natural” condition (parks and other areas showed no 

evidence of regular human usage; Falcone, 2015), with the 

remainder divided between agriculture (28 percent), urban 

development (11 percent), or other uses (3 percent). About 

6 percent of the watershed’s total area was developed between 

1982 and 2012 (about 4 percent from natural areas and 2 percent from agriculture). Overall, developed land area increased 

by about 49 percent – from about 4.58 million acres to about 

6.83 million acres - between 1982 and 2012. 

Consistent with the pattern at the watershed scale, most 

Chesapeake HUC8s were dominated by natural areas in both 

1982 and 2012 (fig. 3; table 5). However, eight HUC8s3

contained a greater proportion of land in agriculture than in 

any other use in 1982, and six HUC8s4 contained more area 

in developed than in either the natural, agricultural, or other 

land-use categories. 

All 53 HUC8s experienced some degree of urbanization 

between 1982 and 2012; in most of these cases urbanization 

occurred through the development of both agricultural and 

natural lands. However, the proportion of land in agriculture 

was unchanged or had increased slightly (less than 0.5 percent) in three5

 HUC8s by 2012. In these cases, development 

of natural areas accounted for urbanization. Natural land area 

was unchanged or increased (up to 2 percent) in five HUC8s6. 

In these cases, urbanization occurred through development of 

agricultural areas. 

By 2012, a total of 13 HUC8s contained more developed 

land than agricultural land. These HUC8s were categorized 

as “predominantly urban” in order to reflect the differential 

impact that development had on their manure and fertilizer 

input patterns.

3

 Chester-Sassafras, Choptank, Lower Susquehanna, Middle PotomacCatoctin, Monocacy, Nanticoke, Shenandoah, Tangier.

4

 Gunpowder-Patapsco, Hampton Roads, Lynnhaven-Poquoson, Middle 

Potomac-Anacostia-Occoquan, Patuxent, Severn.

5

 North Branch Potomac, Sinnemahoning, Upper West Branch Susquehanna.

6

 Chenango, Nanticoke, Pine, Tioga, Upper Susquehanna.

Fertilizer and Manure Inputs to Land

N inputs to land in the Chesapeake Bay watershed from 

manure and inorganic fertilizer combined increased by over 

90 percent between 1950 and 1982, and peaked at about 

960 million pounds in 2000 before decreasing to 812 million 

pounds in 2012. Increases over time in P inputs were less dramatic (about 13 percent) between 1950 and 1982, but P inputs 

decreased by about 26 percent between 1982 and 2012. 

Temporal shifts in agricultural N and P inputs were 

largely driven by changing patterns in inorganic fertilizer use 

(fig. 4). Fertilizer-N inputs increased sharply from 1950–71, 

after which they declined by 14 million pounds from 1971 

to 2012, but with inter-annual fluctuations of as much as 

117 million pounds. Fertilizer-P inputs increased by about 

27 million pounds from 1950 to 1971 and then declined by 

about 106 million pounds, with inter-annual fluctuations of 

as much as 27 million pounds. Estimates of manure inputs 

were derived directly from livestock and poultry populations 

(Sekellick, 2017), and it was assumed that manure remained 

where it was produced (the potential impact of manure transport is discussed later in this report). Based on this assumption, manure inputs increased moderately and gradually over 

time, in concert with animal populations. 

The greater variability observed in fertilizer inputs 

reflects a more complex matrix of drivers, such as crop type, 

acreage, and projected yields, as well as fertilizer prices, 

weather, and manure availability (Stuart and others, 2015).

1950–82

N inputs from agriculture increased from 1950 to 

1982 in 50 out of the 53 HUC8s throughout the watershed 

(not shown), and in all regions of the watershed in general 

(table 6). P inputs increased in 25 HUC8s, and in 4 out of 

7 regions, with the greatest percent increase occurring in the 

Eastern Shore region. The largest percent decrease was seen 

in the Hampton Roads (Virginia) region, reflecting the highly 

urban nature of the Lynnhaven-Poquoson and Hampton Roads 

HUC8s.

1982–2012

In contrast to the prior period, 25 HUC8s (about half) 

experienced increasing agricultural N inputs from 1982 to 

2012, with a narrower distribution and a median change close 

to zero (fig 5). Only seven HUC8s had increased P inputs; 

changes ranged from a decrease of 7.9 million pounds to an 

increase of 1.2 million pounds. 

Reductions in both N and P inputs resulted primarily 

from a decline in fertilizer use (fig. 6); inputs of N and P from 

manure increased over this period in almost half of the HUC8s 

studied. The changes in the spatial distribution of inputs 
Results 9

Figure 3. Percent of land area in the natural, agriculture, and developed land-use classes in A, 1982, and B, 2012 in the Chesapeake Bay 

watershed. Percent land area in the “other” category not shown.

Hampton Roads

Lynnhaven−Poquoson

Appomattox

Lower James

Middle James−Willis

Rivanna

Middle James−Buffalo

Maury

Upper James

York

Pamunkey

Mattaponi

Lower Rappahannock

Rapidan−Upper Rappahannock

Great Wicomico−Piankatank

Lower Potomac

Middle Potomac−Anacostia−Occoquan

Monocacy

Middle Potomac−Catoctin

Shenandoah

North Fork Shenandoah

South Fork Shenandoah

Conococheague−Opequon

Cacapon−Town

North Branch Potomac

South Branch Potomac

Patuxent

Severn

Gunpowder−Patapsco

Pocomoke−Western Lower Delmarva

Tangier

Nanticoke

Choptank

Chester−Sassafras

Lower Susquehanna

Lower Susquehanna−Swatara

Lower Juniata

Raystown

Upper Juniata

Lower Susquehanna−Penns

Lower West Branch Susquehanna

Pine

Bald Eagle

Middle West Branch Susquehanna

Sinnemahoning

Upper West Branch Susquehanna

Upper Susquehanna−Lackawanna

Upper Susquehanna−Tunkhannock

Chemung

Tioga

Owego−Wappasening

Chenango

Upper Susquehanna

0 25 50 75 100

A. 1982

0 25 50 75 100

B. 2012

Percent of land area Percent of land area

Natural Agriculture Developed

EXPLANATION

Susquehanna Potomac James

Hampton 

Roads

Virginia

Western

Shore

Maryland

Western

Shore

Eastern

Shore

8-digit hydrologic unit (HUC8) name

Figure 3. Reported implementation of agricultural land-use change best management practices (BMPs) for major regions of the 

Chesapeake Bay watershed, 1985–2012. [Bars represent accumulated implementation as of a given year; the black line represents the 

percent of the total (as of 2012) BMP implementation for all regions.]
10 Manure and Fertilizer Inputs to Land in the Chesapeake Bay Watershed, 1950–2012

Table 5. Percent of land area in each land-use class in the Chesapeake Bay watershed, 1982 and 2012.

[HUC8, 8-digit hydrologic unit]

Region HUC8 name

Natural

(percent)

Developed

(percent)

Agriculture 

(percent)

Other

(percent)

1982 2012 1982 2012 1982 2012 1982 2012

Susquehanna

Upper Susquehanna 64 66 4 5 30 28 1 1

Chenango 62 64 5 5 32 30 1 1

Owego-Wappasening 62 60 12 15 26 25 0 0

Tioga 63 64 2 3 34 32 1 1

Chemung 61 61 7 8 31 30 1 1

Upper Susquehanna-Tunkhannock 59 59 5 7 35 33 1 1

Upper Susquehanna-Lackawanna 55 51 21 27 22 21 1 1

Upper West Branch Susquehanna 80 79 7 8 11 12 2 2

Sinnemahoning 96 95 1 1 3 3 0 0

Middle West Branch Susquehanna 95 94 2 2 3 3 0 0

Bald Eagle 72 70 8 11 19 18 0 1

Pine 88 88 1 2 11 10 0 0

Lower West Branch Susquehanna 66 65 6 9 28 26 0 0

Lower Susquehanna-Penns 59 57 8 11 32 31 1 1

Upper Juniata 68 66 10 12 21 21 1 1

Raystown 71 70 3 5 25 24 1 1

Lower Juniata 72 70 4 7 24 23 1 0

Lower Susquehanna-Swatara 41 39 18 25 40 35 1 1

Lower Susquehanna 22 16 18 30 60 52 1 1

Eastern Shore

Chester-Sassafras 22 18 10 18 61 57 7 7

Choptank 19 19 6 9 59 56 16 16

Nanticoke 28 28 5 8 54 50 14 14

Tangier 27 26 8 13 32 28 33 33

Pocomoke-Western Lower Delmarva 42 41 5 8 38 36 15 15

Maryland 

Western Shore

Gunpowder-Patapsco 18 15 47 58 32 24 2 3

Severn 25 10 59 77 11 9 4 4

Patuxent 31 17 35 55 28 22 5 6

Potomac

South Branch Potomac 82 81 1 2 15 15 1 1

North Branch Potomac 78 77 8 9 12 12 2 2

Cacapon-Town 86 86 1 1 12 12 1 1

Conococheague-Opequon 45 38 10 21 43 40 1 1

South Fork Shenandoah 54 51 9 14 35 34 1 1

North Fork Shenandoah 62 59 5 8 32 31 2 1

Shenandoah 32 24 15 26 51 48 2 2

Middle Potomac-Catoctin 29 24 21 34 47 39 3 3

Monocacy 25 24 11 20 63 53 2 3

Middle Potomac-Anacostia-Occoquan 23 15 57 69 17 14 2 2

Lower Potomac 54 37 19 38 21 19 6 6
Results 11

Table 5. Percent of land area in each land-use class in the Chesapeake Bay watershed, 1982 and 2012.—Continued

[HUC8, 8-digit hydrologic unit]

Region HUC8 name

Natural

(percent)

Developed

(percent)

Agriculture 

(percent)

Other

(percent)

1982 2012 1982 2012 1982 2012 1982 2012

Virginia 

Western Shore

Great Wicomico-Piankatank 65 43 9 31 18 18 8 8

Rapidan-Upper Rappahannock 57 51 4 11 37 36 2 2

Lower Rappahannock 60 54 11 19 24 23 5 5

Mattaponi 74 65 4 13 16 16 6 6

Pamunkey 68 62 4 11 22 21 6 6

York 60 45 17 33 14 13 9 9

James

Upper James 87 87 3 3 10 9 1 1

Maury 73 72 4 5 22 21 2 2

Middle James-Buffalo 76 73 7 11 16 15 1 1

Rivanna 65 59 12 19 21 21 2 2

Middle James-Willis 70 61 9 19 16 15 4 5

Lower James 45 37 33 43 14 12 8 8

Appomattox 70 62 8 17 18 17 4 4

Hampton Roads Lynnhaven-Poquoson 6 5 84 88 5 1 5 5

Hampton Roads 16 13 42 48 16 13 25 26

Table 6. Changes over time in agricultural nitrogen (N) and phosphorus (P) inputs to seven distinct regions of the watershed, 

1950–2012 (regions are defined in table 2).

Region

N Input 

(million pounds)

N-Input change,

in percent

P Input 

(million pounds)

P-Input change,

in percent

1950 1982 2012 1950–82 1982–2012 1950 1982 2012 1950–82 1982–2012

Susquehanna 201 350 321 74 -8 91 100 70 10 -30

Eastern Shore 34 135 144 296 6 24 38 31 60 -19

Maryland Western 

Shore 19 27 22 42 -19 7.8 7.3 5.6 -6 -23

Potomac 116 212 198 82 -7 54 60 48 12 -20

Virginia Western 

Shore 36 68 58 88 -14 21 20 11 -5 -45

James 41 66 62 61 -6 19 20 15 6 -26

Hampton Roads 1.8 3.8 7.1 114 89 1.4 1.2 1.2 -19 6

Total 449 863 812 92 -6 218 247 182 13 -26
12 Manure and Fertilizer Inputs to Land in the Chesapeake Bay Watershed, 1950–2012

1950

1950

1955

1955

1960

1960

1965

1965

1970

1970

1975

1975

1980

1980

1985

1985

1990

1990

1995

1995

2000

2000

2005

2005

2010

2010

1,200

1,100

1,000

900

800

700

600

500

400

300

200

100

0

400

350

300

250

200

150

100

50

0

Nitrogen input, in million pounds Phosphorus input, in million pounds

A

B

Manure nitrogen

Fertilizer nitrogen

Manure phosphorus

Fertilizer phosphorus

EXPLANATION

Year

Year

EXPLANATION

Figure 4. A, nitrogen, and B, phosphorus inputs to the Chesapeake Bay watershed from manure and fertilizer, 1950–2012. [Note 

difference in scales of y axes.]
Results 13

70

60

50

40

30

20

10

0

-10

-20

1950–1982

Nitrogen Phosphorus

1982–2012 1950–1982 1982–2012

25th percentile (25 percent of the

data values are less than this value)

Median

Data value within 1.5 times the IQR

outside the quartile

Outlier

75th percentile (75 percent of the

data values are less than this value)

Interquartile

range (IQR)

A B

EXPLANATION

Change in nutrient input, in million pounds

Figure 5. Range and variability of the change in agricultural A, nitrogen inputs, and B, phosphorus inputs from 1950–82 and 1982–2012 in 

the Chesapeake Bay watershed at the 8-digit hydrologic unit (HUC8) scale.

throughout the watershed during this period are also shown in 

figure 6. For example, manure-N inputs in the upper part of 

the Susquehanna region declined by about 30 million pounds, 

whereas manure-N inputs in HUC8s in the lower Susquehanna 

region increased by about 26 million pounds. The Potomac 

region also experienced a shift in the spatial distribution of 

manure inputs, in this case from the eastern HUC8s to the 

western HUC8s.

Agricultural Land Use and Farming Practices

In 1950, there were about 23.3 million acres (36,500 mi2) 

of land in farms in the Chesapeake Bay watershed, of which 

3.4 million acres were in permanent pasture and 11.2 million 

acres were in cropland. Sixty-seven percent of cropland was 

further categorized as harvested cropland. Between 1950 and 

1982, acres of land in farms declined 37 percent, acres of land 

in permanent pasture declined 60 percent, and acres of total 

cropland (“harvested cropland” + “pastured cropland” + “other 

cropland”) declined 21 percent. The amount of cropland and 

the amount of land in farms continued to decline between 

1982 and 2012, whereas acres of permanent pasture increased 

(table 7). Farms lost an additional 13 percent of land area 

overall, with steeper declines in cropland. The amount of total 

cropland declined to a greater degree than did the amount of 

harvested cropland. 

The distinction between total cropland and harvested 

cropland is relevant for understanding patterns in manure and 

fertilizer inputs. The COA’s “harvested cropland” category 

includes only the acreage from which crops were harvested 

and (or) hay was cut in a given Census year. The “total cropland” category also includes land on which crops were planted 

but failed to mature, as well as additional lands that could 

have been used for crops but were not in the given Census 
14 Manure and Fertilizer Inputs to Land in the Chesapeake Bay Watershed, 1950–2012

Hampton Roads

Lynnhaven−Poquoson

Appomattox

Lower James

Middle James−Willis

Rivanna

Middle James−Buffalo

Maury

Upper James

York

Pamunkey

Mattaponi

Lower Rappahannock

Rapidan−Upper Rappahannock

Great Wicomico−Piankatank

Lower Potomac

Middle Potomac−Anacostia−Occoquan

Monocacy

Middle Potomac−Catoctin

Shenandoah

North Fork Shenandoah

South Fork Shenandoah

Conococheague−Opequon

Cacapon−Town

North Branch Potomac

South Branch Potomac

Patuxent

Severn

Gunpowder−Patapsco

Pocomoke−Western Lower Delmarva

Tangier

Nanticoke

Choptank

Chester−Sassafras

Lower Susquehanna

Lower Susquehanna−Swatara

Lower Juniata

Raystown

Upper Juniata

Lower Susquehanna−Penns

Lower West Branch Susquehanna

Pine

Bald Eagle

Middle West Branch Susquehanna

Sinnemahoning

Upper West Branch Susquehanna

Upper Susquehanna−Lackawanna

Upper Susquehanna−Tunkhannock

Chemung

Tioga

Owego−Wappasening

Chenango

Upper Susquehanna

−16 −12 −8 −4 0 4 8 12 16

Nitrogen input change, in million pounds

−10 −8 −6 −4 −2 0 2 4 6 8 10

Phosphorus input change, in million pounds

Susquehanna Potomac James

Hampton 

Roads

Virginia

Western

Shore

Maryland

Western

Shore

Eastern

Shore

8-digit hydrologic unit (HUC8) name

Fertilizer Manure

EXPLANATION

A B

-8%

+6% -19%

-19%

-7%

-14%

-6%

+89% +6%

-26%

-45%

-20%

-23%

-30%

Figure 6. Change in agricultural A, nitrogen inputs, and B, phosphorus inputs for each 8-digit hydrologic unit (HUC8) in the Chesapeake 

Bay watershed from 1982 to 2012. [Note difference in scale of x-axes. Values represent the net percent (%) change in nitrogen and 

phosphorus inputs for each region.]
Results 15

Table 7. Changes in farmland area (acres) in the Chesapeake Bay watershed, 1950–2012 (LaMotte, 2015).

Year Land in farms Permanent pasture Total cropland Harvested cropland

1950 23,334,852 3,377,433 11,159,254 7,482,192

1954 22,088,307 3,731,581 9,984,922 7,391,219

1959 20,311,352 3,312,373 9,416,986 6,853,237

1964 18,611,753 3,208,865 8,739,063 6,456,300

1969 15,334,086 1,431,457 8,792,797 5,558,307

1974 14,510,378 1,425,626 8,524,465 6,027,832

1978 14,948,207 1,368,512 8,919,869 6,448,196

1982 14,612,749 1,334,687 8,771,036 6,693,000

1987 13,611,260 1,209,840 8,490,874 6,061,504

1992 12,680,759 1,106,232 8,072,613 5,942,293

1997 13,307,174 1,161,225 8,340,054 6,259,273

2002 13,045,746 1,380,533 7,872,550 6,087,411

2007 12,578,008 1,920,215 7,010,680 5,855,584

2012 12,671,236 2,072,482 6,732,108 5,992,953

year (U.S. Department of Agriculture, National Agricultural 

Statistics Service, 2014). Where manure availability exceeds 

crop need, it may be applied to other cropland and pasture 

in addition to harvested cropland (MacDonald and others, 

2009; Ribaudo and others, 2003; Kellogg and others, 2000). 

However, purchasing fertilizer in excess of crop need has an 

economic cost. Thus, changes in fertilizer inputs may be more 

closely tied to harvested cropland than to total cropland.

Of the 789,000 acres of harvested cropland acreage lost 

in the watershed between 1950 and 1982, the vast majority 

(637,000 acres, or 81 percent) was lost from the Susquehanna

region of the watershed. These losses and additional losses 

from the Potomac, James, and Maryland Western Shore 

regions were partly counteracted by gains in the Eastern Shore 

and the Virginia Western Shore regions (table 8). 

The same patterns were observed at the HUC8 scale: 

acres of harvested cropland increased in just 12 of the 

53 HUC8s from 1950 to 1982, 10 of which were located in 

either the Eastern Shore or Virginia Western Shore regions. 

The period from 1982 to 2012 also showed increases in 12 of 

the 53 HUC8s. However, spatial variability shifted: previous gains in harvested cropland were reversed on the Eastern Shore and Virginia Western Shore, and increases were 

instead distributed among the Susquehanna (three HUC8s), 

James (three HUC8s), and Potomac (six HUC8s) regions. The 

continuing urbanization of the Maryland Western Shore and 

the Hampton Roads (Virginia) regions was reflected in additional losses of more than 30 percent of harvested cropland 

between 1982 and 2012.

Harvested cropland in the Chesapeake Bay watershed is 

divided among approximately 25 crop types (LaMotte, 2015). 

Six of these – barley, corn, hay, oats, soybeans, and wheat – 

accounted for between 96 and 99 percent of acres harvested 

in any given Census year (table 9). In this context, “acres 

harvested” represents the sum of acres reported for each crop 

in the COA whereas “harvested cropland” represents the acres 

of cropland that are allocated to harvested crops each year. 

Harvesting more than one crop each year on the same acreage 

(double cropping) can result in more “acres harvested” than 

“harvested cropland.” 

Between 1950 and 2012, the prevalence of barley, oats, 

and wheat declined throughout the watershed, whereas the 

proportion of harvested acres dedicated to corn, hay, and soybeans increased from 67 to 88 percent of all acres harvested. 

Although the remaining 19 crops accounted for 1 percent or 

less of acres harvested in the Chesapeake Bay watershed, 

some of these were more prominently represented at local 

scales. Between 1950 and 2012, harvested cropland declined 

by about 20 percent, whereas acres harvested declined 11 percent. In other words, more intensive use of cropland may have 
16 Manure and Fertilizer Inputs to Land in the Chesapeake Bay Watershed, 1950–2012

Table 8. Changes in spatial variability of harvested cropland in the Chesapeake Bay watershed in 1950, 1982, and 2012.

Region

Harvested cropland 

(acres)

Change in harvested cropland 

(percent)

Regional 

change

Contribution to 

watershed change

1950 1982 2012 1950–1982 1982–2012 1950–1982 1982–2012

Susquehanna 3,657,711 3,021,069 2,710,568 -17 -10 -81 -44

Eastern Shore 816,855 1,046,129 934,303 28 -11 29 -16

Maryland Western Shore 321,082 243,995 169,273 -24 -31 -10 -11

Potomac 1,623,361 1,362,971 1,272,728 -16 -7 -33 -13

Virginia Western Shore 482,212 568,846 482,495 18 -15 11 -12

James 534,202 407,856 394,851 -24 -3 -16 -2

Hampton Roads 46,767 42,135 28,735 -10 -32 -1 -2

Table 9. Percentage of acres harvested for six dominant crop types in the Chesapeake Bay watershed, 1950–2012.

Year Harvested 

cropland

Acres 

harvested

Percent of acres harvested

Barley Corn Hay Oats Soybeans Wheat

1950 7,482,192 6,963,107 4 25 40 8 2 17

1954 7,391,219 7,014,994 4 26 41 9 4 12

1959 6,853,237 6,612,321 4 25 43 8 6 10

1964 6,456,300 6,261,867 4 27 43 6 8 9

1969 5,558,307 5,209,184 5 32 39 5 9 7

1974 6,027,832 5,980,615 4 35 35 4 11 9

1978 6,448,196 6,302,192 4 36 38 3 12 5

1982 6,693,000 6,893,963 3 38 34 3 14 7

1987 6,061,504 6,281,869 3 33 39 3 14 7

1992 5,942,293 6,312,714 3 31 37 2 17 8

1997 6,259,273 6,507,061 2 31 38 1 18 8

2002 6,087,411 6,275,296 2 30 42 1 17 7

2007 5,855,584 6,033,221 2 34 39 1 17 7

2012 5,992,953 6,174,823 2 32 37 1 19 8
Results 17

partially compensated for the reduction of agricultural land 

allocated to crop production in the watershed.

Patterns of nutrient inputs and decisions regarding 

crop cultivation may be affected by the magnitude of animal 

biomass, as well as by the production of different animal 

types. Biomass (in AUs) was relatively stable in the watershed 

between 1950 and 2012, despite the declines in farmland in 

general, and in permanent pasture acreage in particular, that 

occurred. Whereas changes in animal biomass between Census 

years ranged from -11 to +23 percent, the net change over 

the entire period was less than 1 percent. The proportion of 

AUs represented by cows declined by about 11 percent from 

1950 to 2012, whereas the proportion of AUs represented by 

poultry increased by about 14 percent (table 10). The concentration of nutrients varies among animal types; for example, 

poultry manure contains a higher P fraction per pound than 

cow manure (American Society of Agricultural and Biological 

Engineers, 2005).

The coupled nature of crop and animal production is 

reflected in the changing nature of corn and hay production 

Table 10. Annual percentage of animal biomass (in animal units) for the five major animal types produced in the Chesapeake Bay 

watershed, 1950–2012.

Year Animal units

Animal biomass

(percent)

All cows All poultry Horses Sheep Hogs

1950 2,946,787 74 4 7 2 14

1954 3,003,566 82 3 1 1 13

1959 2,984,522 80 2 3 2 13

1964 2,665,731 86 3 0 1 10

1969 3,281,758 65 22 2 1 10

1974 2,929,712 79 8 2 1 10

1978 2,965,039 73 10 3 1 14

1982 3,239,750 72 11 3 1 13

1987 3,133,925 69 14 3 1 13

1992 3,181,345 67 15 3 1 14

1997 3,216,803 65 18 3 0.5 13

2002 3,160,248 63 17 5 0.5 14

2007 3,055,029 62 19 5 0.4 14

2012 2,963,812 63 18 6 0.5 13

across the watershed. Whereas acres harvested of corn grown 

for grain (“grain corn”) changed less than 1 percent between 

1950 and 2012, cultivation of corn grown for silage (“silage 

corn”) increased from 295,518 to 491,518 acres harvested, or 

about 66 percent. Similarly, in 1950, silage hay accounted for 

1 percent of all hay acres harvested. By 2012, that proportion 

had increased to 21 percent.

The spatial variability in cultivation of both major 

crop groups and animal groups in 1982 and 2012 is shown 

in figure 7. Poultry and poultry feed (grain corn and soybeans) dominate agricultural land on the Eastern Shore; 

about 45 percent of the entire watershed’s poultry inventory, 

35 percent of its soybean acreage, and 24 percent of its grain 

corn acreage were produced in this region in 2012. Cultivation of forage and silage crops was more broadly distributed 

across the remaining five regions, as were cow populations. 

The Lower Susquehanna HUC8 contains large proportions 

of all three animal groups (including 41 percent of the entire 

watershed’s hog inventory) and all four crop types. 
18 Manure and Fertilizer Inputs to Land in the Chesapeake Bay Watershed, 1950–2012

200,000

20,000

200,000

400

200,000

140

120

100

80

60

40

20

200,000

Soy, in acres Poultry,

in thousands

Grain corn,

in acres

Hogs,

in thousands

Silage corn,

in acres

Cows,

in thousands

Hay, silage hay,

alfalfa, in acres

100,000

10,000

100,000

300

200

100

100,000

100,000

Susquehanna Eastern

Shore

Potomac James Hampton

Roads

Virginia

Western

Shore

Maryland

Western

Shore

8-digit hydrologic unit (HUC8) name

0

0

0

0

0

0

0

Upper Susquehanna

Chenango

Owego-Wappasening

Tioga

Chemung

Upper Susquehanna-Tunkhannock

Upper Susquehanna-Lackawanna

Upper West Branch Susquehanna

Sinnemahoning

Middle 

West Branch Susquehanna

Bald Eagle

Pine

Lower West Branch Susquehanna

Lower Susquehanna-Penns

Upper Juniata

Raystown

Lower Juniata

Lower Susquehanna-Swatara

Lower Susquehanna

Chester-Sassafras

Choptank

Nanticoke

Tangier

Pocomoke-Western Lower Delmarva

Gunpowder-Patapsco

Severn

Patuxent

South Branch Potomac

North Branch Potomac

Cacapon-Town

Conococheague-Opequon

South Fork Shenandoah

North Fork Shenandoah

Shenandoah

Middle Potomac-Catoctin

Monocacy

Lower Potomac

Great Wicomico-Piankatank

Rapidan-Upper Rappahannock

Lower Rappahannock

Mattaponi

Pamunkey

York

Upper James

Maury

Middle James-Buffalo

Rivanna

Middle James-Willis

Lower James

Appomattox

Lynnhaven-Poquoson

Hampton Roads

Middle Potomac-Anacostia-Occoquan

EXPLANATION

1982

2012

EXPLANATION

1982

2012

A

B

Figure 7. Spatial variability of A, major crop groups, and B, major animal groups in the Chesapeake Bay watershed in 1982 and 2012. 

[Note difference in scale of x-axes.]
Results 19

Nutrient Input Intensity

Declines over time in pasture and cropland, combined 

with stable or increasing animal inventories and fertilizer 

inputs and the changing proportion of crops harvested per 

acre of harvested cropland, indicate that the amount of N and 

P input per acre of total cropland (“nutrient input intensity”) 

may have increased over time. The spatial pattern of nutrient 

input intensity on agricultural acreage across the watershed 

in 1982 is shown in figure 8. N input intensity increased in 

all 7 regions of the watershed (table 11), and in 44 HUC8s 

between 1982 and 2012 (fig. 9). During the same period, 

P input intensity increased in 4 regions and 22 HUC8s across 

those regions. Five of the HUC8s with increasing P input 

intensity were clustered in the Maryland Western Shore and 

the Hampton Roads (Virginia) regions, where sharp declines 

in agricultural land coincided with gains in fertilizer-P use 

associated with new residential development. Elsewhere, 

the input intensity of fertilizer-P declined whereas manure-P 

input intensity either increased (Susquehanna, Eastern Shore, 

Potomac, James) or was stable (Virginia Western Shore).

Relating Agricultural Practices to Fertilizer and 

Manure Inputs

Manure inputs in any given HUC8 are a direct result of 

local animal populations, therefore they are not expected to 

vary as a result of changes in either the amount of cropland or 

the crops being cultivated. However, because nutrient requirements differ among crop types, changes in fertilizer inputs 

over time may be more closely related to changes in crop production. This relation may be confounded by the availability 

of animal manure; where appropriate and economical, manure 

can reduce the need for commercial fertilizer (MacDonald and 

others, 2009). Alternatively, excess manure must be disposed 

of and may be spread on cropland in excess of crop nutrient 

need or transported to other areas. 

Corn has a high N requirement relative to other major 

agronomic crops (Basden and others, 2006), and it is often 

suggested that increases in corn cultivation in particular result 

in increased fertilizer-N inputs. In the case of the Chesapeake 

Bay watershed, fertilizer-N inputs increased each year from 

1950 to 1974 on harvested cropland across all HUC8s, independent of the amount of acreage in any given crop, including 

corn. However, commercial fertilizer-N usage leveled off at 

the watershed scale during the mid-1970s, indicating a shift 

that may have tied fertilizer inputs more closely to crop need. 

When data prior to 1974 were excluded from the analysis7

, HUC8s with a greater proportion of harvested cropland 

in grain corn tended to have greater fertilizer-N input intensity 

per acre of harvested cropland, but the relation was weak 

but significant (r2 = 0.18, p<0.001) and visual inspection 

7

 Lynnhaven-Poquoson was also excluded; its fertilizer-N application intensity is an order of magnitude greater than any other HUC8 in the post-1974 

period.

revealed a deviation from this tendency in the more urbanized HUC8s. When the 13 predominantly urban HUC8s 

identified previously were excluded, this relation improved 

(r2 = 0.31, p<0.001) (fig. 10A). In contrast, there was a very 

slight (but still significant) negative correlation between silage 

corn cultivation and fertilizer-N input intensity (r2 = 0.12, 

p<0.001) (fig. 10B). Silage corn tends to be grown in close 

proximity to cow production, and its high N requirements may 

be met more by applications of readily available manure than 

by the purchase of inorganic fertilizer.

Effects of Best Management Practice (BMP) 

Implementation on Manure and Fertilizer Inputs

This section describes the aggregated expected effect 

of the four BMPs that affect nutrient inputs to land. Landuse change BMPs, dairy precision feeding and (or) forage 

management, and manure transport can have direct effects on 

both N and P inputs; poultry phytase reduces the P content of 

manure. Local manure transport can reduce manure input in 

one HUC8 while increasing it in another HUC8. Reports of 

manure transport implementation indicate that of the approximately 2.6 billion pounds of poultry manure transported 

between 1998 and 2012, about 35 percent was transported out 

of the Chesapeake Bay watershed (Devereux and others 2017).

Expected Reductions in Fertilizer and Manure 

Inputs

BMPs were expected to have a relatively minor impact 

on N and P inputs from manure and fertilizer between 1985 

and 2012. The modeling scenarios generated by use of the 

CBP’s Phase 5.3.2 Scenario Builder indicated that a reduction 

in N inputs to land of about 41 million pounds (3.6 percent), 

and 9 million pounds (3.9 percent) in P inputs to land would 

have occurred in the Chesapeake Bay watershed between 

1985 and 2012 without any implementation of BMPs (No 

Action scenario). It is important to note that Scenario Builder 

estimates N and P inorganic fertilizer based on crop need, 

resulting in different estimates of the magnitude of fertilizer use than those described earlier in this report. In spite of 

this discrepancy, Scenario Builder simulations are useful for 

estimating relative (percent) changes in fertilizer use due to 

changes on the landscape. 

When reported BMP implementation was considered 

(Progress scenario), an additional 0.8-percent decrease in 

N inputs (9 million pounds), and an additional 5.2-percent 

decrease in P inputs (12 million pounds) were predicted 

(fig. 11). Lower fertilizer usage accounted for 8.9 of the 

expected 9-million-pound additional reduction in agricultural 

N inputs. Some of the nutrient reduction is due to the loss of 

agricultural land, which has the effect of reducing fertilizer 

inputs. With fewer crops, there is less fertilizer purchased and 
20 Manure and Fertilizer Inputs to Land in the Chesapeake Bay Watershed, 1950–2012

EXPLANATION

N input, in pounds

per acre, 1982

>150

A B

Chesapeake Bay

watershed

boundary

Chesapeake Bay

watershed

boundary

50 to 80

>80 to 90

>90 to 100

>100 to 150

EXPLANATION

P input, in pounds

per acre, 1982

>45

14 to 18

>18 to 25

>25 to 35

>35 to 45

Figure 8. Input intensity of A, nitrogen (N) and B, phosphorus (P) on agricultural acres in the Chesapeake Bay watershed in 1982. 

[Inputs are the sum of manure and fertilizer in pounds per acre of cropland.] 

applied. Where animal populations do not change, the manure 

is still applied to land, sometimes at a higher application rate 

than is required by the crop. 

Reductions in manure-P usage were solely responsible 

for the expected additional reduction in agricultural P inputs; 

the model actually simulated a small (3-percent) increase in 

fertilizer-P inputs as a result of BMP implementation. This 

result reflects the simulated effect of manure transport out of 

the watershed; farmers may replace manure P with commercial fertilizer according to crop need. 

BMPs were expected to generate negligible additional 

change (less than 0.5 percent) in N inputs in 33 out of the 

53 HUC8s in the Chesapeake Bay watershed. Among the 

remainder, BMPs reduced N inputs by anywhere from 

0.6 to 4 percent, with the greatest reduction expected in the 

Choptank HUC8 (table 12).

Lower fertilizer-N inputs were the sole driver of these 

small expected N reductions – more than compensating for 

increasing manure-N inputs – in five of the seven Chesapeake 

regions (table 13), and were the primary driver (accounting for 

more than half) of expected N-input reductions in 41 HUC8s 

distributed across all regions of the watershed. The Progress 

scenario predicted increased manure-N inputs as a result of 

BMP implementation in 25 HUC8s. This result is likely due 

to the transport of manure into these HUC8s from basins with 

excess manure production.

In the Susquehanna and Eastern Shore regions, expected 

N reductions were almost evenly split between manure and 

fertilizer sources. In the Susquehanna region, larger than 

expected manure-N reductions in the Swatara and Lower 

Susquehanna HUC8s accounted for the greater influence of 

manure on N reductions in this region. In the Eastern Shore 

region, larger than expected decreases in manure-N inputs in 

the Nanticoke, Tangier, and Pocomoke-Western Lower Delmarva countered relatively small increases in manure-N inputs 

in the Chester-Sassafras and Choptank HUC8s.

Expected reductions in P inputs from implementation 

of these four BMPs (poultry feed additives, dairy precision 

feeding, manure transport, and land-use change) ranged 

from no appreciable change in 17 HUC8s up to an additional 

51-percent reduction in the Sinnemahoning HUC8. In contrast 

to N-input changes, decreases in manure-P inputs were the 
Results 21

Table 11. Intensity of agricultural nutrient inputs to seven major regions in the Chesapeake Bay watershed in 1950, 1982, and 2012.

Region

Nitrogen-input intensity

(pounds per acre of total cropland)

Phosphorus-input intensity

(pounds per acre of total cropland)

1950 1982 2012 1950 1982 2012

Susquehanna 40 93 103 18 27 23

Eastern Shore 31 123 144 22 35 31

Maryland Western Shore 36 86 119 15 23 30

Potomac 45 104 140 21 29 34

Virginia Western Shore 45 90 111 26 27 21

James 41 88 133 19 26 31

Hampton Roads 30 84 240 25 26 42

Chesapeake Bay watershed 40 98 121 20 28 27

A B

Chesapeake Bay

watershed

boundary

EXPLANATION

<-20

>-20 to 0

Chesapeake Bay

watershed

boundary

Change in N input, 

in pounds per acre of 

cropland, 1982–2012

>20 to 40

>0 to 20

>40 to 80

>80 to 150

>150

EXPLANATION

Change in P input,

in pounds per acre of 

cropland, 1982–2012

-20 to -10

>0 to 20

>-10 to 0

>20 to 40

>40 to 80

>80

Figure 9. Input intensity change from 1982 to 2012 for A, nitrogen (N) and B, phosphorus (P) in the Chesapeake Bay watershed. [Inputs 

are the sum of manure and fertilizer in pounds per acre of cropland.]

Results 21
22 Manure and Fertilizer Inputs to Land in the Chesapeake Bay Watershed, 1950–2012

0.0 0.2 0.4 0.6 0.8 1.0

0

50

100

150

Grain corn

Nitrogen, in pounds per acre

0.0 0.2 0.4 0.6 0.8 1.0

0

50

100

150

Silage corn

Nitrogen, in pounds per acre

r

2 = 0.31

r

2 = 0.12

B

A

Simple linear 

regression

Simple linear 

regression

Figure 10. Nitrogen fertilizer use on harvested cropland by proportion of cropland devoted to A, grain corn, and B, silage corn in the 

Chesapeake Bay watershed. [Data are by Census of Agriculture for each 8-digit hydrologic unit (HUC8) from 1974 to 2012. Predominantly 

urban HUC8s are excluded.]
Results 23

900

1,100

1,300

1,500

1985 1990 1995 2000 2005 2010 2015

Nitrogen input (million pounds)

100

150

200

250

300

1985 1990 1995 2000 2005 2010 2015

Year

Phosphorus input (million pounds)

No BMPs

With BMPs

EXPLANATION

A

B

Figure 11. Expected effect of best management practices (BMPs) on A, nitrogen (N) and B, phosphorus (P) applications to land in the 

Chesapeake Bay watershed, 1985–2012. [Note difference in scales of y axes.]
24 Manure and Fertilizer Inputs to Land in the Chesapeake Bay Watershed, 1950–2012

Table 12. Expected change in nitrogen (N) and phosphorus (P) applications in the Chesapeake Bay watershed with and without best 

management practice (BMP) implementation, 1985–2012. 

[HUC8, 8-digit hydrologic unit; ND, not determined]

Region HUC8 name

Change in N applied, 1985–2012

(percent)

Change in P applied, 1985–2012

(percent)

Without BMPs With BMPs Without BMPs With BMPs

Susquehanna

Upper Susquehanna -41 -42 -48 -49

Chenango -37 -38 -42 -42

Owego-Wappasening -36 -37 -45 -45

Tioga -9 -9 -6 -8

Chemung -23 -23 -29 -29

Upper Susquehanna-Tunkhannock -28 -28 -40 -40

Upper Susquehanna-Lackawanna -8 -9 -2 -3

Upper West Branch Susquehanna -8 -8 -22 -22

Sinnemahoning 169 169 225 173

Middle West Branch Susquehanna ND ND ND ND

Bald Eagle 0 -1 5 4

Pine ND ND ND ND

Lower West Branch Susquehanna -13 -13 3 0

Lower Susquehanna-Penns -2 -3 25 16

Upper Juniata 26 25 36 35

Raystown -4 -4 1 0

Lower Juniata -3 -4 6 2

Lower Susquehanna-Swatara 15 14 33 26

Lower Susquehanna -6 -7 -4 -11

Eastern Shore

Chester-Sassafras -5 -6 5 0

Choptank 26 22 22 12

Nanticoke 0 -3 -14 -24

Tangier 6 3 -5 -19

Pocomoke-Western Lower Delmarva 6 5 6 -6

Maryland 

Western Shore

Gunpowder-Patapsco -22 -22 -34 -34

Severn ND ND ND ND

Patuxent -4 -4 -26 -26

Potomac

South Branch Potomac 25 22 62 39

North Branch Potomac -3 -3 17 8

Cacapon-Town 16 15 29 19

Conococheague-Opequon 4 3 5 2

South Fork Shenandoah 7 5 7 -3

North Fork Shenandoah 8 6 2 -6

Shenandoah -21 -21 -31 -31

Middle Potomac-Catoctin -19 -19 -32 -32

Monocacy -30 -30 -30 -31

Middle Potomac-Anacostia-Occoquan 17 17 -21 -21

Lower Potomac 11 11 -11 -11
Results 25

Table 12. Expected change in nitrogen (N) and phosphorus (P) applications in the Chesapeake Bay watershed with and without best 

management practice (BMP) implementation, 1985–2012.—Continued

[HUC8, 8-digit hydrologic unit; ND, not determined]

Region HUC8 name

Change in N applied, 1985–2012

(percent)

Change in P applied, 1985–2012

(percent)

Without BMPs With BMPs Without BMPs With BMPs

Virginia 

Western Shore

Great Wicomico-Piankatank 3 3 -27 -27

Rapidan-Upper Rappahannock -8 -8 -11 -12

Lower Rappahannock -3 -3 -21 -22

Mattaponi 7 7 -20 -20

Pamunkey -4 -4 -27 -28

York 17 17 -54 -54

James

Upper James -4 -4 -18 -19

Maury 19 19 7 6

Middle James-Buffalo 18 18 2 1

Rivanna -17 -17 -33 -33

Middle James-Willis -21 -21 -29 -33

Lower James 25 25 -14 -14

Appomattox 16 16 1 -5

Hampton Roads Lynnhaven-Poquoson ND ND ND ND

Hampton Roads -6 -6 -28 -29

Chesapeake Bay 

watershed -4 -4 -4 -9

Table 13. Spatial variability in expected changes in manure and fertilizer inputs due to best management practice (BMP) 

implementation in the Chesapeake Bay watershed, 1985–2012.

[N, nitrogen; P, phosphorus]

Region

Change due to BMPs, 1985–2012 

(pounds)

Manure N Fertilizer N Manure P Fertilizer P

Susquehanna -1,252,690 -1,589,212 -4,133,321 154,201

Eastern Shore -1,367,777 -1,853,734 -4,807,370 435,302

Maryland Western Shore 0 -9,074 -6,953 527

Potomac 1,716,842 -4,702,115 -3,449,915 -256,347

Virginia Western Shore 71,244 -124,050 -38,681 -2,112

James 386,729 -618,295 -376,222 22,473

Hampton Roads 4,089 -9,348 -8,175 2,630
26 Manure and Fertilizer Inputs to Land in the Chesapeake Bay Watershed, 1950–2012

sole driver of expected P reductions in 5 of the 7 Chesapeake 

regions and accounted for the majority of expected reductions 

in 42 HUC8s. Implementation of these BMPs was expected 

to increase fertilizer-P usage in all but 2 regions8, and in 

26 HUC8s distributed across all 7 regions of the watershed.

Animal Best Management Practice (BMP) 

Implementation

The reductions in manure-N and manure-P inputs 

described above can be fully attributed to animal BMPs, 

as only these BMPs affect nutrient concentrations and (or) 

amounts of manure. However, based on BMP implementation 

reported to the CBP (Devereux and others, 2017), rates for 

dairy precision feeding/forage management were so low that 

it would be unlikely that they affected manure nutrient concentrations (table 14). The 100-percent implementation level 

of poultry phytase is more likely to have affected manure-P 

reductions, although increasing poultry populations could 

theoretically mask the overall effect of phytase on manure-P 

inputs from poultry. Because manure transport can also affect 

local manure-P inputs, expected reductions cannot be attributed solely to poultry phytase implementation in this dataset. 

However, the greatest expected reductions in manure-P inputs 

tend to occur in those HUC8s containing the largest poultry 

populations (fig. 12). 

The most notable exception to this pattern is the 

Sinnemahoning HUC8. Results from the Scenario Builder 

model indicated that manure-P inputs in the Sinnemahoning 

increased almost hundredfold, even with BMP implementation, between 1985 and 2012. However, based on data from 

LaMotte (2015), this analysis indicated that the Sinnemahoning ranked among the lowest for poultry inventories 

among all HUC8s in the watershed in 2012. Between 2007 

and 2012, its poultry inventory declined from 2,483 to 1,792 

individuals, and livestock populations also remained low. 

This anomaly was caused by a protocol used by the CBP to 

account for poultry populations that were reported only at 

the state level in the USDA COA due to privacy restrictions. 

The LaMotte (2015) dataset included only those animals 

that were reported at the county scale, whereas the CBP used 

an algorithm to allocate poultry reported at the state level 

to local areas around the watershed. As a result, the CBP 

8

The Potomac and Virginia Western Shore.

Phase 5.3.2 Scenario Builder dataset assumed a large allocation of poultry to Cameron County, Pennsylvania (thus to the 

Sinnemahoning HUC8), whereas LaMotte (2015) did not. 

Land-Use Change Best Management Practices 

(BMPs)

Between 1985 and 2012, reported implementation of 

agricultural land-use change BMPs increased from 60 to about 

651,000 acres per year across the watershed, for an accumulated total of almost 4.5 million acres in 2012. However, 

85 percent of the cumulative increase occurred during the last 

6 years of the period, from 2006 to 2012 (fig. 13). Although 

major jurisdictions have reported BMP implementation to the 

CBP since the late 1990s, the establishment of the Chesapeake 

Bay TMDL in 2010 provided incentive to improve BMP 

reporting. At that time, jurisdictions were permitted to update 

past reporting of BMP implementation as far back as 2006 

(Chesapeake Bay Program Watershed Technical Work Group, 

2013). In recent years, the CBP has developed new tools to 

improve the counting and reporting of BMP implementation, however, verification of historical BMP implementation 

records remains challenging (National Research Council, 

2011). It is likely that the increase in implementation observed 

in recent years is at least partially a consequence of increased 

reporting rather than increased implementation.

The vast majority of land-use change BMP acreage was 

located in the regions including the most agricultural acreage (the Susquehanna, Potomac, and Eastern Shore regions). 

However, when implementation was adjusted to account for 

the amount of eligible9 acreage in each HUC8, the resulting measure of implementation intensity of land-use change 

BMPs (such as implementation per acre of eligible land) in 

the agricultural sector varied both within and among regions, 

from as low as 2.6 percent in the Chenango HUC8 to as much 

as 32 percent in the Sinnemahoning HUC8 (fig. 14), and did 

not necessarily occur in those HUC8s with the most agricultural activity. For example, the lower part of the Susquehanna region and the central part of the Potomac region have 

relatively high agricultural N- and P-input intensities (see 

figure 8), but show some of the lowest agricultural land-use 

change BMP implementation intensities (percent of eligible 

acres).

9

Acres determined to be appropriate for implementation of agricultural 

land-use change BMPs.
Results 27

Table 14. Dairy precision feeding implementation rates in the Chesapeake Bay watershed, 2007–12 (Devereux and others, 2017).

[BMP, best management practice]

Year BMP Region

Amount 

implemented 

(animal units)

Animal 

units 

available 

Percent 

implementation

2007 Dairy precision feeding; forage management Susquehanna 352 29,166 1

2008 Dairy precision feeding; forage management Susquehanna 3,634 39,186 9

2009 Dairy precision feeding; forage management Susquehanna 6,724 38,589 17

2010 Dairy precision feeding; forage management Susquehanna 1,710 72,043 2

2011 Dairy precision feeding; forage management Susquehanna 3,199 31,351 10

2012 Dairy precision feeding; forage management Susquehanna 5,541 514,766 1

2012 Dairy precision feeding; forage management Potomac 98 69,645 0

Hampton Roads

Lynnhaven−Poquoson

Appomattox

Lower James

Middle James−Willis

Rivanna

Middle James−Buffalo

Maury

Upper James

York

Pamunkey

Mattaponi

Lower Rappahannock

Rapidan−Upper Rappahannock

Great Wicomico−Piankatank

Lower Potomac

Middle Potomac−Anacostia−Occoquan

Monocacy

Middle Potomac−Catoctin

Shenandoah

North Fork Shenandoah

South Fork Shenandoah

Conococheague−Opequon

Cacapon−Town

North Branch Potomac

South Branch Potomac

Patuxent

Severn

Gunpowder−Patapsco

Pocomoke−Western Lower Delmarva

Tangier

Nanticoke

Choptank

Chester−Sassafras

Lower Susquehanna

Lower Susquehanna−Swatara

Lower Juniata

Raystown

Upper Juniata

Lower Susquehanna−Penns

Lower West Branch Susquehanna

Pine

Bald Eagle

Middle West Branch Susquehanna

Sinnemahoning

Upper West Branch Susquehanna

Upper Susquehanna−Lackawanna

Upper Susquehanna−Tunkhannock

Chemung

Tioga

Owego−Wappasening

Chenango

Upper Susquehanna

−100 −75 −50 −25 0

Expected manure-P reduction, in percent

0 5,000 10,000 15,000 20,000 25,000

2012 poultry population, in thousands

Susquehanna Potomac James

Hampton 

Roads

Virginia

Western

Shore

Maryland

Western

Shore

Eastern

Shore

8-digit hydrologic unit (HUC8) name

A B

Figure 12. A, expected percent change in manure-phosphorus (manure-P) applications due to best management practices (BMPs) 

from 1985 to 2012 (dark blue bars), and B, 2012 poultry populations (light blue bars) in the Chesapeake Bay watershed. [In general, BMP 

effects on manure-P inputs were expected only in basins where poultry populations were located. Exceptions were the Tioga, Upper 

Susquehanna-Lackawanna, and Sinnemahoning Basins.]
28 Manure and Fertilizer Inputs to Land in the Chesapeake Bay Watershed, 1950–2012

600,000

500,000

400,000

300,000

200,000

100,000

0

100.0

90.0

80.0

70.0

60.0

50.0

0.0

40.0

30.0

20.0

10.0

1985198619871988198919901991199219931994199519961997199819992000200120022003200420052006200720082009201020112012

Year

Acres implemented

Percent of total acres implemented

Susquehanna

Virginia Western Shore

Potomac

Maryland Western Shore

Eastern Shore

Hampton Roads

James

Percent of total

EXPLANATION

Figure 13. Reported implementation of agricultural land-use change best management practices (BMPs) for major regions of the 

Chesapeake Bay watershed, 1985–2012. [Bars represent annual implementation; black line represents the cumulative total of BMP 

acreage for all regions.]
Summary 29

EXPLANATION

Chesapeake Bay

watershed

boundary

Percent of agricultural

acres implemented,

2012

2.6 to 4.4

4.5 to 5.0

5.1 to 10.0

10.1 to 20.0

20.1 to 31.9

Figure 14. Implementation of agricultural land-use change best management practices (BMPs) as of 2012 (percent of eligible acres) in 

the Chesapeake Bay watershed.

Summary

The U.S. Geological Survey (USGS) serves as an integral part of the effort to advance the understanding of factors 

affecting aquatic conditions in the Chesapeake Bay watershed 

and estuary. Understanding temporal and spatial patterns in 

manure and fertilizer inputs, as well as in associated agricultural practices, enables further interpretation of the results of 

research on changes in riverine and estuarine aquatic conditions. To that end, this report evaluates the magnitude and spatial variability of nitrogen (N) and phosphorus (P) inputs from 

manure and fertilizer from 1950 through 2012 at three spatial 

scales: the entire Chesapeake Bay watershed, 7 regions within 

the watershed, and the 53 8-digit hydrologic units (HUC8s) 

that are contained within the watershed. Changes over time in 

natural, developed, and agricultural land use were also characterized, as were temporal and spatial variability in agricultural land-use practices such as livestock and poultry populations, and the cultivation of different crop types. Relations 

between land-use change, agricultural practices, and manure 

and fertilizer inputs were explored. In addition, data on the 

reported implementation of land-use change and animal best 

management practices (BMPs) from 1985–2012 were used to 

describe temporal and spatial patterns in BMP implementation 

intensity, and modeling scenarios from the Chesapeake Bay 

Program (CBP) Scenario Builder were used to estimate the 

expected effect of these BMPs on manure and fertilizer inputs 

across the watershed. 

Inputs of N and P to the watershed from manure 

increased moderately and steadily between 1950 and 2012, 

reflecting a small increase in animal inventory as measured 

in Animal Units (AUs), but with a shift from cows to poultry. 

Fertilizer-N inputs increased dramatically but experienced 

large inter-annual variability, whereas inputs of fertilizer-P 

decreased slightly. Patterns were more varied at the HUC8 

scale, particularly in the latter part of the data record. Fertilizer 

inputs decreased in most areas throughout the Bay watershed 

from 1982–2012, whereas manure input increased in almost 

half of the HUC8s studied. Manure inputs also were re-distributed, most notably from the northern to the southern Susquehanna region, and from the central to the western part of the 

Potomac region. These patterns were consistent with changes 

in farming practices. Decreases in pasture and cropland were 
30 Manure and Fertilizer Inputs to Land in the Chesapeake Bay Watershed, 1950–2012

accompanied by reduced agricultural nutrient inputs per acre 

of farmland in some areas, whereas other areas experienced 

an increase in the intensity of agricultural practices even as 

the actual amount of land in farms declined. Greater intensity 

of N inputs tended to occur in row-crop-dominated regions 

and in areas that saw large increases in poultry populations, 

whereas N-input intensity was lower and was more likely to 

decline over time in regions dominated by forage crops and 

cows. Nutrient input patterns in predominantly urban HUC8s 

deviated from those in predominantly agricultural HUC8s.

Exploratory analysis of this dataset identified a positive 

correlation between fertilizer-N use and the proportion of 

acres planted in grain corn. The proportion of acres planted in 

silage corn did not exhibit this pattern. Corn silage is usually produced in close proximity to cow populations, possibly increasing the usage of manure rather than fertilizer for 

meeting crop N requirements. These findings can be used to 

evaluate whether increased cultivation of corn, which often 

has greater N requirements than other crops, results in larger 

fertilizer-N inputs.

Finally, the reported implementation of BMPs that affect 

agricultural nutrient inputs was expected to reduce N inputs by 

less than 1 percent, and P inputs by just over 5 percent, across 

the watershed. The greater influence on P inputs, due almost 

entirely to reduced manure-P inputs, was concentrated in areas 

with high poultry populations, and most likely resulted from 

the addition of the phytase enzyme to poultry feed. Reported 

implementation of agricultural land-use change BMPs 

increased substantially after 2005, but this may have been at 

least partially due to improved mechanisms for BMP reporting rather than solely due to increased implementation on the 

ground. Implementation of land-use change BMPs also varied 

geographically, ranging from less than 3 percent to just over 

30 percent of eligible acres. The intensity of land-use change 

BMP implementation was not consistently aligned with areas 

experiencing the greatest intensity of manure and fertilizer 

nutrient inputs.

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separate files, accessed August 17, 2017, at http://dx.doi.

org/10.3133/ds948.

Kellogg, R.L., Lander, C.H., Moffitt, D.C., and Gollehon, N., 

2000, Manure nutrients relative to the capacity of cropland 

and pastureland to assimilate nutrients: spatial and temporal trends for the United States: United States Department 

of Agriculture publication number nps00-0579, accessed 

August 17, 2017, at https://www.nrcs.usda.gov/wps/portal/

nrcs/detail/national/technical/nra/?cid=nrcs143_014126.

Kemp, W.M., Boynton, W.R., Adolf, J.E., Boesch, D.F., 

Boicourt, W.C., Brush, G., Cornwell, J.C., Fisher, T.R., 

Glibert, P.M., Hagy, J.D., Harding, L.W., Houde, E.D., 

Kimmel, D.G., Miller, W.D., Newell, R.I.E., Roman, M.R., 

Smith, E.M., and Stevenson, J.C., 2005, Eutrophication of 

Chesapeake Bay: historical trends and ecological interactions: Marine Ecology Progress Series, v. 303, p. 1–29, 

accessed August 17, 2017, at http://www.int-res.com/articles/feature/m303p001.pdf. 

LaMotte, A.E., 2015, Selected items from the Census of 

Agriculture at the county level for the conterminous United 

States, 1950-2012: U.S. Geological Survey data release, 

http://dx.doi.org/10.5066/F7H13016.

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2013, Development of the Chesapeake Bay watershed 

Total Maximum Daily Load Allocation: Journal of the 

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no. 5, p. 986–1,006, DOI 10.1111/jawr.12105, accessed 

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MacDonald, J.M., Ribaudo, M.O., Livingston, M.J., Beckman, J., and Huang, W., 2009, Manure use for fertilizer and 

for energy: Report to Congress: United States Department 

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2, 2017, at https://www.ers.usda.gov/publications/pubdetails/?pubid=42740.

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of program strategies and implementation: Washington, 

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Sciences, 258 p., accessed April 27, 2015, at https://www.

chesapeakebay.net/channel_files/21727/2011_nas_report.

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Ribaudo, M.O., Gollehon, N.R., and Agapoff, J., 2003, Land 

application of manure by animal feeding operations: Is 

more land needed?: Journal of Soil and Water Conservation, v. 58, no. 1, p 30–38, accessed May 14, 2018, at http://

www.jswconline.org/content/58/1/30.abstract. 

Sekellick, A.J., 2017, Nitrogen and phosphorus from fertilizer 

and manure in the Chesapeake Bay watershed, 1950–2012: 

U.S. Geological Survey data release, http://doi.org/10.5066/

F7TQ6011.

Stuart, D., Basso, B., Marquart-Pyatt, S., Reimer, A., Robertson, G.P., and Zhao, J., 2015, The need for a coupled human 

and natural systems understanding of agricultural nitrogen 

loss: Bioscience, v. 65, no. 6, p. 571–578, accessed August 

17, 2017, at https://doi.org/10.1093/biosci/biv049.

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Geographic Area Series, Part 51: United States Department of Agriculture National Agricultural Statistics Service 

(NASS), May 2014, Report AC-12-A-51, accessed May 9, 

2017, at https://www.agcensus.usda.gov/Publications/2012/

Full_Report/Volume_1,_Chapter_1_US/usv1.pdf.

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Standards and Procedures for the National Watershed 

Boundary Dataset (WBD) (4th ed.): Techniques and Methods 11–A3, 63 p., accessed August 17, 2017, at http://pubs.

usgs.gov/tm/11/a3/.
Appendix 1

Inputs of nitrogen (N) to the Chesapeake Bay watershed’s 53 8-digit hydrologic units (HUC8s) from manure, fertilizer, 

and the two sources combined. Inputs, as well as changes in those inputs, between the decades 1992–2002 and 2002–12 are 

provided.
Appendix 1. Inputs of nitrogen (N) to the Chesapeake Bay watershed’s 53 8-digit hydrologic units (HUC8s) from manure, fertilizer, and the two sources combined. Inputs, as well 

as changes in those inputs, between the decades 1992–2002 and 2002–12 are provided.

Region HUC8 name HUC8 code

Manure-N 

(million pounds)

Fertilizer-N 

(million pounds)

Combined 

(million pounds)

1992 2002 2012

Change 

1992–

2002

Change 

2002–12 1992 2002 2012

Change 

1992–

2002

Change 

2002–12

Change 

1992–2002

Change 

2002–12

Susquehanna

Upper Susquehanna 02050101 13.10 10.98 7.68 -2.12 -3.29 6.80 5.48 3.43 -1.31 -2.05 -3.43 -5.35Chenango 02050102 11.33 9.52 7.81 -1.81 -1.71 6.86 5.44 4.30 -1.42 -1.14 -3.24 -2.85Owego-Wappasening 02050103 5.37 4.83 3.61 -0.54 -1.21 2.48 2.90 1.29 0.42 -1.61 -0.12 -2.82Tioga 02050104 7.71 7.33 7.01 -0.38 -0.32 3.71 2.86 3.14 -0.85 0.27 -1.23 -0.05Chemung 02050105 5.36 4.99 4.67 -0.38 -0.32 4.82 3.86 4.12 -0.96 0.27 -1.34 -0.05Upper Susquehanna-Tunkhannock 02050106 13.56 11.04 7.47 -2.52 -3.58 4.70 5.71 3.95 1.01 -1.76 -1.51 -5.34Upper Susquehanna-Lackawanna 02050107 3.84 3.85 3.93 0.01 0.08 4.75 7.19 6.53 2.44 -0.66 2.44 -0.58Upper West Branch Susquehanna 02050201 1.87 1.78 1.42 -0.10 -0.35 1.64 2.93 1.68 1.29 -1.25 1.19 -1.61Sinnemahoning 02050202 0.31 0.30 0.31 -0.01 0.01 0.15 0.25 0.19 0.10 -0.07 0.09 -0.05Middle West Branch Susquehanna 02050203 0.52 0.68 1.04 0.16 0.36 0.24 0.37 0.26 0.13 -0.11 0.30 0.25Bald Eagle 02050204 3.30 3.72 4.30 0.42 0.58 2.01 3.04 2.16 1.03 -0.88 1.45 -0.30Pine 02050205 1.59 1.59 1.32 0.00 -0.27 0.71 0.84 0.65 0.13 -0.19 0.13 -0.46Lower West Branch Susquehanna 02050206 8.63 9.88 10.09 1.25 0.21 5.53 9.09 6.73 3.56 -2.36 4.81 -2.15Lower Susquehanna-Penns 02050301 12.24 14.24 16.57 2.00 2.33 6.52 9.45 7.73 2.93 -1.72 4.93 0.60Upper Juniata 02050302 5.81 6.48 7.74 0.67 1.27 3.43 4.72 4.00 1.29 -0.72 1.96 0.55Raystown 02050303 5.45 5.04 5.93 -0.41 0.88 2.94 3.56 3.29 0.62 -0.28 0.21 0.61Lower Juniata 02050304 11.77 14.22 14.13 2.45 -0.09 4.67 5.89 4.46 1.22 -1.43 3.66 -1.51Lower Susquehanna-Swatara 02050305 24.81 28.42 33.18 3.61 4.76 9.30 13.42 12.57 4.12 -0.85 7.73 3.91Lower Susquehanna 02050306 74.36 72.62 75.15 -1.74 2.53 27.94 46.15 37.27 18.22 -8.89 16.48 -6.36

Eastern Shore

Chester-Sassafras 02060002 5.93 6.34 7.34 0.41 1.00 36.78 34.39 24.54 -2.39 -9.85 -1.98 -8.85Choptank 02060005 7.11 8.76 12.49 1.65 3.72 24.99 21.36 15.52 -3.62 -5.84 -1.97 -2.12Nanticoke 02080109 23.05 25.21 24.48 2.17 -0.73 17.88 18.16 15.53 0.28 -2.63 2.45 -3.36Tangier 02080110 10.76 10.88 12.99 0.12 2.11 8.05 7.61 4.07 -0.44 -3.54 -0.32 -1.43Pocomoke-Western Lower Delmarva 02080111 14.33 14.95 17.35 0.61 2.40 14.92 14.41 9.32 -0.51 -5.09 0.11 -2.68

Maryland 

Western Shore

Gunpowder-Patapsco 02060003 5.41 4.04 2.66 -1.37 -1.38 12.83 13.26 10.50 0.43 -2.76 -0.94 -4.14Severn 02060004 0.22 0.17 0.13 -0.05 -0.04 1.38 1.42 1.34 0.04 -0.08 -0.01 -0.12Patuxent 02060006 2.27 1.61 1.14 -0.66 -0.47 9.22 7.99 6.23 -1.23 -1.75 -1.89 -2.23

Appendix 1 33
Appendix 1. Inputs of nitrogen (N) to the Chesapeake Bay watershed’s 53 8-digit hydrologic units (HUC8s) from manure, fertilizer, and the two sources combined. Inputs, as well 

as changes in those inputs, between the decades 1992–2002 and 2002–12 are provided.—Continued

Region HUC8 name HUC8 code

Manure-N 

(million pounds)

Fertilizer-N 

(million pounds)

Combined 

(million pounds)

1992 2002 2012

Change 

1992–

2002

Change 

2002–12 1992 2002 2012

Change 

1992–

2002

Change 

2002–12

Change 

1992–2002

Change 

2002–12

Potomac

South Branch Potomac 02070001 12.52 14.11 15.01 1.59 0.90 1.94 1.73 1.17 -0.21 -0.55 1.38 0.35North Branch Potomac 02070002 4.25 4.91 5.03 0.66 0.12 1.08 1.20 0.73 0.11 -0.47 0.77 -0.35Cacapon-Town 02070003 5.53 6.59 7.17 1.06 0.57 1.01 1.04 0.55 0.03 -0.49 1.09 0.08Conococheague-Opequon 02070004 24.35 26.48 26.16 2.13 -0.31 16.08 17.72 12.21 1.64 -5.51 3.77 -5.82South Fork Shenandoah 02070005 38.06 41.11 35.33 3.05 -5.78 11.88 11.57 9.46 -0.32 -2.10 2.73 -7.88North Fork Shenandoah 02070006 20.84 22.94 19.55 2.10 -3.39 4.39 4.26 3.86 -0.13 -0.40 1.97 -3.79Shenandoah 02070007 3.16 3.01 2.75 -0.15 -0.25 2.42 2.70 1.76 0.28 -0.94 0.13 -1.19Middle Potomac-Catoctin 02070008 11.26 8.83 7.13 -2.43 -1.70 10.25 10.20 8.58 -0.05 -1.63 -2.47 -3.33Monocacy 02070009 10.92 9.19 6.69 -1.73 -2.51 18.80 17.40 11.29 -1.40 -6.11 -3.13 -8.62Middle Potomac-Anacostia-Occoquan 02070010 3.13 2.77 2.43 -0.35 -0.34 9.34 11.17 10.76 1.83 -0.41 1.48 -0.75Lower Potomac 02070011 1.94 1.61 1.23 -0.33 -0.38 11.11 11.08 9.11 -0.04 -1.97 -0.37 -2.35

Virginia 

Western Shore

Great Wicomico-Piankatank 02080102 0.24 0.21 0.18 -0.02 -0.03 3.70 3.45 3.92 -0.25 0.48 -0.28 0.45Rapidan-Upper Rappahannock 02080103 13.87 13.06 11.54 -0.81 -1.51 11.26 10.23 9.12 -1.03 -1.11 -1.84 -2.63Lower Rappahannock 02080104 1.04 1.05 0.78 0.01 -0.27 10.06 9.52 10.67 -0.54 1.15 -0.53 0.89Mattaponi 02080105 1.29 1.16 0.96 -0.13 -0.21 6.19 5.04 5.86 -1.14 0.81 -1.27 0.61Pamunkey 02080106 5.77 5.06 4.38 -0.72 -0.67 11.55 9.33 9.72 -2.22 0.38 -2.94 -0.29York 02080107 0.13 0.11 0.10 -0.02 -0.00 1.45 1.34 1.24 -0.12 -0.10 -0.14 -0.10

James

Upper James 02080201 5.32 4.87 5.03 -0.45 0.16 3.43 3.63 2.45 0.20 -1.18 -0.25 -1.02Maury 02080202 5.29 5.58 5.71 0.29 0.13 2.11 2.08 1.78 -0.04 -0.30 0.25 -0.17Middle James-Buffalo 02080203 8.21 7.77 8.16 -0.45 0.39 5.55 5.12 3.81 -0.43 -1.32 -0.88 -0.92Rivanna 02080204 3.61 2.79 2.76 -0.82 -0.03 1.83 1.68 1.32 -0.15 -0.35 -0.97 -0.39Middle James-Willis 02080205 4.43 4.57 4.01 0.14 -0.56 3.00 3.17 2.44 0.16 -0.73 0.30 -1.29Lower James 02080206 1.87 1.52 0.83 -0.35 -0.69 10.55 9.79 9.62 -0.76 -0.17 -1.11 -0.86Appomattox 02080207 9.20 9.99 9.07 0.79 -0.92 6.89 6.29 4.79 -0.61 -1.50 0.19 -2.42

Hampton Roads Lynnhaven-Poquoson 02080108 0.05 0.01 0.01 -0.04 0.00 1.89 2.67 2.13 0.78 -0.54 0.74 -0.54 Hampton Roads 02080208 0.73 0.67 0.35 -0.06 -0.32 5.59 5.13 4.61 -0.46 -0.53 -0.52 -0.85

34 Manure and Fertilizer Inputs to Land in the Chesapeake Bay Watershed, 1950–2012
Appendix 2

Inputs of phosphorus (P) to the Chesapeake Bay watershed’s 53 8-digit hydrologic units (HUC8s) from manure, fertilizer, 

and the two sources combined. Inputs, as well as changes in those inputs, between the decades 1992–2002 and 2002–12 are 

provided.
36 Manure and Fertilizer Inputs to Land in the Chesapeake Bay Watershed, 1950–2012 Appendix 2. Inputs of phosphorus (P) to the Chesapeake Bay watershed’s 53 8-digit hydrologic units (HUC8s) from manure, fertilizer, and the two sources combined. Inputs, as well as changes in those inputs, between the decades 1992–2002 and 2002–12 are provided. Region HUC8 name HUC8 code Manure-P (million pounds) Fertilizer-P (million pounds) Combined (million pounds) 1992 2002 2012 Change 1992– 2002 Change 2002–12 1992 2002 2012 Change 1992– 2002 Change 2002–12 Change 1992–2002 Change 2002–12 Susquehanna Upper Susquehanna 02050101 2.39 2.21 1.60 -0.18 -0.61 2.31 1.35 0.54 -0.95 -0.81 -1.13 -1.40 Chenango 02050102 2.01 1.87 1.57 -0.15 -0.30 2.19 1.26 0.64 -0.93 -0.62 -1.08 -0.90 Owego-Wappasening 02050103 1.03 1.02 0.76 -0.01 -0.26 0.81 0.70 0.19 -0.11 -0.51 -0.12 -0.80 Tioga 02050104 1.50 1.70 1.62 0.20 -0.08 1.28 0.67 0.48 -0.62 -0.19 -0.42 -0.30 Chemung 02050105 1.09 1.10 1.03 0.01 -0.07 1.62 0.93 0.65 -0.70 -0.28 -0.69 -0.30 Upper Susquehanna-Tunkhannock 02050106 2.87 2.51 1.65 -0.37 -0.86 1.62 1.17 0.52 -0.45 -0.66 -0.82 -1.50 Upper Susquehanna-Lackawanna 02050107 0.96 1.00 1.05 0.03 0.06 1.59 1.38 0.86 -0.20 -0.52 -0.17 -0.50 Upper West Branch Susquehanna 02050201 0.44 0.43 0.34 -0.01 -0.10 0.54 0.56 0.22 0.02 -0.34 0.01 -0.40 Sinnemahoning 02050202 0.07 0.07 0.07 0.00 0.00 0.05 0.04 0.03 0.00 -0.02 0.00 0.00 Middle West Branch Susquehanna 02050203 0.11 0.14 0.25 0.03 0.10 0.08 0.08 0.03 -0.01 -0.04 0.03 0.10 Bald Eagle 02050204 0.69 0.80 0.98 0.11 0.17 0.69 0.62 0.28 -0.07 -0.34 0.04 -0.20 Pine 02050205 0.32 0.40 0.32 0.08 -0.08 0.25 0.17 0.09 -0.07 -0.09 0.01 -0.20 Lower West Branch Susquehanna 02050206 2.15 2.61 2.73 0.46 0.12 1.91 1.87 0.88 -0.03 -1.00 0.42 -0.90 Lower Susquehanna-Penns 02050301 3.45 4.04 4.83 0.59 0.80 2.25 1.94 1.01 -0.31 -0.93 0.28 -0.10 Upper Juniata 02050302 1.13 1.32 1.63 0.19 0.31 1.18 0.96 0.52 -0.22 -0.44 -0.03 -0.10 Raystown 02050303 1.15 1.14 1.40 -0.02 0.27 1.02 0.74 0.43 -0.28 -0.31 -0.30 0.00 Lower Juniata 02050304 2.77 3.77 3.68 1.00 -0.09 1.62 1.22 0.58 -0.40 -0.64 0.60 -0.70 Lower Susquehanna-Swatara 02050305 6.57 7.90 9.12 1.33 1.22 3.15 2.64 1.65 -0.51 -0.99 0.82 0.20 Lower Susquehanna 02050306 21.85 20.67 21.23 -1.17 0.56 8.98 9.25 4.97 0.27 -4.27 -0.91 -3.70

Eastern Shore

Chester-Sassafras 02060002 1.44 1.62 1.91 0.18 0.30 7.57 5.94 3.47 -1.64 -2.46 -1.46 -2.20Choptank 02060005 2.07 2.55 3.67 0.47 1.12 5.00 3.51 2.22 -1.49 -1.28 -1.02 -0.20Nanticoke 02080109 7.00 7.50 7.28 0.51 -0.22 3.12 2.27 1.35 -0.85 -0.92 -0.35 -1.10Tangier 02080110 3.29 3.27 3.89 -0.03 0.62 1.66 1.32 0.66 -0.34 -0.66 -0.37 0.00Pokomoke-Western Lower Delmarva 02080111 4.39 4.47 5.19 0.08 0.72 3.68 3.01 1.35 -0.67 -1.66 -0.59 -0.90

Maryland 

Western Shore

Gunpowder-Patapsco 02060003 1.36 0.97 0.62 -0.38 -0.35 2.83 2.29 2.70 -0.53 0.41 -0.92 0.10Severn 02060004 0.05 0.04 0.03 -0.01 -0.01 0.31 0.24 0.41 -0.07 0.16 -0.08 0.10Patuxent 02060006 0.58 0.40 0.26 -0.18 -0.14 1.98 1.38 1.57 -0.60 0.20 -0.78 0.10
Appendix 2. Inputs of phosphorus (P) to the Chesapeake Bay watershed’s 53 8-digit hydrologic units (HUC8s) from manure, fertilizer, and the two sources combined. Inputs, as 

well as changes in those inputs, between the decades 1992–2002 and 2002–12 are provided.—Continued

Region HUC8 name HUC8 code

Manure-P 

(million pounds)

Fertilizer-P 

(million pounds)

Combined 

(million pounds)

1992 2002 2012

Change 

1992–

2002

Change 

2002–12 1992 2002 2012

Change 

1992–

2002

Change 

2002–12

Change 

1992–2002

Change 

2002–12

Potomac

South Branch Potomac 02070001 3.95 4.33 4.52 0.38 0.19 0.87 0.33 0.28 -0.54 -0.05 -0.16 0.10North Branch Potomac 02070002 1.14 1.35 1.44 0.21 0.09 0.36 0.22 0.16 -0.14 -0.06 0.07 0.00Cacapon-Town 02070003 1.67 1.90 2.16 0.23 0.27 0.37 0.19 0.12 -0.18 -0.08 0.05 0.20Conococheague-Opequon 02070004 5.97 6.83 6.66 0.86 -0.17 4.71 3.50 1.90 -1.21 -1.60 -0.35 -1.80South Fork Shenandoah 02070005 11.28 12.12 10.41 0.84 -1.71 3.51 3.04 1.39 -0.47 -1.65 0.37 -3.40North Fork Shenandoah 02070006 6.13 6.68 5.67 0.54 -1.01 1.30 1.12 0.57 -0.18 -0.56 0.37 -1.60Shenandoah 02070007 0.84 0.82 0.71 -0.02 -0.11 0.91 0.60 0.34 -0.31 -0.26 -0.33 -0.40Middle Potomac-Catoctin 02070008 2.80 2.27 1.80 -0.53 -0.47 2.50 2.13 1.76 -0.36 -0.38 -0.89 -0.80Monocacy 02070009 2.50 2.32 1.55 -0.18 -0.76 4.14 3.13 1.81 -1.01 -1.32 -1.19 -2.10Middle Potomac-Anacostia-Occoquan 02070010 0.83 0.73 0.62 -0.10 -0.11 2.54 2.52 2.48 -0.01 -0.05 -0.12 -0.20Lower Potomac 02070011 0.58 0.42 0.32 -0.16 -0.10 2.78 2.36 1.49 -0.41 -0.87 -0.57 -1.00

Virginia 

Western Shore

Great Wicomico-Piankatank 02080102 0.06 0.05 0.05 -0.01 -0.01 1.10 0.91 0.57 -0.19 -0.34 -0.20 -0.30Rapidan-Upper Rappahannock 02080103 3.95 3.61 3.31 -0.33 -0.30 3.34 2.70 1.33 -0.64 -1.37 -0.97 -1.70Lower Rappahannock 02080104 0.27 0.26 0.21 -0.01 -0.05 2.98 2.51 1.56 -0.47 -0.94 -0.48 -1.00Mattaponi 02080105 0.35 0.30 0.26 -0.05 -0.04 1.83 1.33 0.85 -0.50 -0.48 -0.55 -0.50Pamunkey 02080106 1.66 1.46 1.17 -0.20 -0.29 3.42 2.46 1.42 -0.96 -1.04 -1.16 -1.30York 02080107 0.03 0.02 0.02 -0.01 0.00 0.43 0.35 0.19 -0.08 -0.16 -0.09 -0.20

James

Upper James 02080201 1.50 1.38 1.38 -0.12 0.00 1.02 0.93 0.38 -0.09 -0.55 -0.20 -0.50Maury 02080202 1.57 1.67 1.69 0.10 0.02 0.63 0.55 0.26 -0.08 -0.29 0.03 -0.30Middle James-Buffalo 02080203 2.52 2.34 2.54 -0.17 0.20 1.63 1.34 0.57 -0.30 -0.76 -0.47 -0.60Rivanna 02080204 1.08 0.84 0.79 -0.24 -0.05 0.54 0.43 0.20 -0.10 -0.23 -0.34 -0.30Middle James-Willis 02080205 1.32 1.32 1.18 0.01 -0.14 0.88 0.82 0.37 -0.06 -0.44 -0.05 -0.60Lower James 02080206 0.64 0.51 0.26 -0.14 -0.24 3.07 2.50 1.49 -0.56 -1.02 -0.70 -1.30Appomattox 02080207 2.65 2.94 2.72 0.29 -0.22 2.03 1.64 0.72 -0.39 -0.92 -0.10 -1.10

Hampton Roads Lynnhaven-Poquoson 02080108 0.02 0.00 0.00 -0.02 0.00 0.50 0.63 0.38 0.13 -0.25 0.12 -0.20 Hampton Roads 02080208 0.26 0.24 0.12 -0.02 -0.12 1.61 1.30 0.73 -0.31 -0.56 -0.33 -0.70

Appendix 2 37
For additional information, contact:

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Keisman and others—Manure and Fertilizer Inputs to Land in the Chesapeake Bay Watershed, 1950–2012—Scientific Investigations Report 2018–5022

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https://doi.org/10.3133/sir20185022 Printed on recycled paper