- 

 

 

EPA 600/R 09/045 | June 2009 | www.epa.gov/ada 

Metrics for Nitrate Contamination 

of Ground Water at 

CAFO Land Application Sites ­

Iowa Swine Study 

Office of Research and Development 

National Risk Management Research Laboratory, Ada, Oklahoma 74820 

Office of Research and Development 

National Risk Management Research Laboratory, Ada, Oklahoma 74820 

 

 

Metrics for Nitrate Contamination 

of Ground Water at 

CAFO Land Application Sites ­

Iowa Swine Study 

Jerry L. Hatfield 

National Soil Tilth Laboratory 

Ames, Iowa 
Notice
 


This work was supported through Interagency Agreement DW-12-921711-4 between EPA’s 

Ground Water & Ecosystems Restoration Division, National Risk Management Research 

Laboratory (Elise Striz, Stephen Hutchins, Project Officers) and USDA-ARS’s Conservation 

and Production Research Laboratory (David Brauer, USDA-ARS Contact). Although this 

work was funded substantially by the U.S. Environmental Protection Agency, it has not been 

subjected to Agency review and therefore does not necessarily reflect the views of the Agency, 

and no official endorsement should be inferred. 

Contact information: 

Jerry L. Hatfield, Laboratory Director 

National Soil Tilth Laboratory 

2110 University Boulevard 

Ames, Iowa 50011 

jerry.hatfield@ars.usda.gov 

ii 
 

Foreword
 


The U.S. Environmental Protection Agency is charged by Congress with protecting the Nation’s land, air, and water 

resources. Under a mandate of national environmental laws, the Agency strives to formulate and implement actions 

leading to a compatible balance between human activities and the ability of natural systems to support and nurture 

life. To meet this mandate, EPA’s research program is providing data and technical support for solving environmental 

problems today and building a science knowledge base necessary to manage our ecological resources wisely, 

understand how pollutants affect our health, and prevent or reduce environmental risks in the future. 

The National Risk Management Research Laboratory is the Agency’s center for investigation of technological 

and management approaches for preventing and reducing risks from pollution that threatens human health and the 

environment. The focus of the Laboratory’s research program is on methods and their cost-effectiveness for prevention 

and control of pollution to air, land, water, and subsurface resources; protection of water quality in public water 

systems; remediation of contaminated sites, sediments and ground water; prevention and control of indoor air pollution; 

and restoration of ecosystems. NRMRL collaborates with both public and private sector partners to foster technologies 

that reduce the cost of compliance and to anticipate emerging problems. NRMRL’s research provides solutions 

to environmental problems by: developing and promoting technologies that protect and improve the environment; 

advancing scientific and engineering information to support regulatory and policy decisions; and providing the technical 

support and information transfer to ensure implementation of environmental regulations and strategies at the national, 

state, and community levels. 

This work was supported by EPA’s Office of Research and Development through the Regional Applied Research Effort 

(RARE) Program. This program is designed to 1) provide the Regions with near-term research on high priority, Regionspecific technical needs, 2) improve collaboration between Regions and ORD laboratories, 3) build the foundation 

for future scientific interaction, and 4) develop useful tools for state, local and tribal governments to address nearterm environmental issues. EPA Region 6 and ORD’s Ground Water & Ecosystems Restoration Division (GWERD) 

recognized the need to evaluate whether properly-designed Comprehensive Nutrient Management Plans (CNMPs) 

developed for land application of waste from Concentrated Animal Feeding Operations (CAFOs) are truly protective of 

ground water quality. Funding ($130K total) was awarded to EPA Region 6 (Nancy Dorsey, EPA Region 6 Contact) and 

administered through GWERD (Elise Striz, Stephen Hutchins, Project Officers), and was used by USDA’s Agricultural 

Research Service (David Brauer, USDA-ARS Contact) to conduct two separate site investigations at CAFO facilities 

where CNMPs were being followed. The objective was to conduct comprehensive sampling of soil, soil water, and 

crops for nutrients throughout the growing season to determine which simple soil/crop metrics are the best indicators 

of the potential for nutrients to escape the root zone and become a threat to ground water. This report describes the 

site investigation conducted by Dr. Jerry L. Hatfield for a swine operation in Iowa. The other site investigation was 

conducted by Dr. Philip A. Moore, Jr., and Dr. David Brauer for a dairy farm in Arkansas and is described in the 

companion report. 

Robert W. Puls, Acting Director 

Ground Water and Ecosystems Restoration Division 

National Risk Management Research Laboratory 

iii 

 

Contents
 


Notice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii
 


Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
 


Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
 


Figures and Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi
 


Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii
 


Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii
 


Executive Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix
 


1.0		 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
 


2.0		 Study Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
	
 

3.0		 Data Analyses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
	 

4.0		 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
 


Meteorological Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
 


Variation of Soil Nutrient Concentrations within Sampling Sites . . . . . . . . . . . . . . . . . . . . . . . . . . 7
 


Nutrient Concentrations in the Soil during the Growing Season . . . . . . . . . . . . . . . . . . . . . . . . .8
 


Plant Nutrient Concentrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
 


Nutrient Balance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
 


5.0		 Conclusions and Impact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
 


6.0		 Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
	 

v 
Figures and Tables 

Figure 1. Locations of the eight sites at the Hardin County swine production farm for the 2006 
 

CAFO nutrient sampling study. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
 


Figure 2. Maximum and minimum temperatures during the 2006 growing season in central Iowa. . . . . 7
 


Figure 3. Daily precipitation during the 2006 growing season in central Iowa.. . . . . . . . . . . . . . . . . . . . 7
 


Figure 4. Means and standard deviations of Mehlich III P concentrations over the six sampling 
 

depths for the five sub-samples from Site 1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
 


Figure 5. Means and standard deviations of soil total N concentration over the six sampling depths 
 

for the five sub-samples from Site 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
 


Figure 6. Soil total N concentrations with depth for Sites 1-4 in Field 1.. . . . . . . . . . . . . . . . . . . . . . . . . 8
 


Figure 7. Mehlich III P concentrations with depth for Sites 1-4 in Field 1 . . . . . . . . . . . . . . . . . . . . . . . 8
 


Figure 8. Changes in soil total nitrogen concentrations at the 7.5 cm depth for four sites in Field 1 
 

during the 2006 growing season . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
 


Figure 9. Differences in Mehlich III P concentrations with soil depth in Field 1 between the spring 
 

and fall sampling periods in 2006.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
 


Figure 10. Differences in soil total N concentrations with soil depth in Field 1 between the spring 
 

and fall sampling periods in 2006 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
 


Figure 11. Differences in soil total N concentrations with soil depth in Field 2 between the spring 
 

and fall sampling periods in 2006 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
 


Figure 12. Differences in Mehlich III P concentrations with soil depth in Field 2 between the spring 
 

and fall sampling periods in 2006.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
 


Figure 13. Changes in plant total N concentrations in plant leaves throughout the growing season for 
 

Sites 1-4 in 2006 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 
 

Figure 14. Comparison of measured vs estimated N removal from corn-soybean rotations with 
 

manure nutrient additions for the 2006 study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
 


Table 1. Soil Types and Cropping Management Characteristics for Each Site.. . . . . . . . . . . . . . . . . . . . 4
 


Table 2. Detailed Descriptions of the Soil Types within the Study Site in Central Iowa . . . . . . . . . . . . 4
 


vi 
 

 

 

 

 

 

Abbreviations
 


CAFOs Concentrated Animal Feeding Operations 
 

CNMP Comprehensive Nutrient Management Plan 

DOY Day of Year 

MCL Maximum Contaminant Level 

N Nitrogen 

NMP Nutrient Management Plan 

P Phosphorus 

vii 
Acknowledgements 

Dale Bumpers Small Farms Research Center (Booneville, AR) and Southern Plains Area Office (College Station, TX) 

of ARS/USDA provided administrative support for the interagency agreement. 

viii 
 

Executive Summary
 


Nitrate (NO -

3 ) is the most common chemical contaminant found in ground water and there are increasing indications 

that agriculture contributes to this contamination. In the United States, concentrated animal feeding operations 

(CAFOs) are a common agricultural practice. CAFOs lead to concentrated production of animal waste and manure. 

In most instances, this manure is then utilized as an input for crop production because the manure is relatively rich 

in plant nutrients, including nitrogen (N) and phosphorus (P). Manure disposal on agricultural land by CAFOs is 

usually dictated by a Comprehensive Nutrient Management Plan (CNMP or NMP). The stated intention of the CNMP 

is to utilize the manure as beneficially as possible without a high risk of contaminating surface and ground water. 

The objectives of this research were to monitor changes in soil nutrient composition at various depths in response to 

various scenarios of swine manure applications according to an approved CNMP and determine if site characteristics 

or management protocols that pose a risk to ground water can be identified. 

A study was conducted for one year (2006) on a swine-row crop farm in central Iowa. The row crop operation 

consisted primarily of corn (Zea mays L.) -soybean (Glycine max (L.) Merr.) rotation. Swine production consisted 

of growing-finishing operation of 4,200 head. Swine waste was stored in pits for up to a year before being applied. 

Land application consisted of injecting the effluent into a slit approximately 20 cm below the soil’s surface. Eight 

plots (10 x 10 m) were established. Two plots were in a field in which swine manure effluent was applied in the fall to 

supply a corn crop’s N requirement (approximately 150 kg N ha-1). Four plots were in a field in which swine manure 

effluent was applied in the spring to supply approximately 100 kg N ha-1 with the additional crop N (50 kg ha-1) being 

supplied post-planting as sidedressed fertilizer. The last two plots were in a soybean field; one received swine effluent 

application in 2005 and the other did not. Soil core samples (0-15, 15-30, 30-45, 45-60, and 60-120 cm depths) were 

taken in May (planting time) and October (after harvesting). Soil samples from the top 22.5 cm were also collected 

biweekly throughout the growing season. These samples were analyzed for soluble components (nitrate, ammonium, 

SRP, pH, and EC), as well as exchangeable ammonium and Mehlich III extractable P. Plant samples were also 

collected and analyzed for biomass and N content. 

Detailed soil sampling revealed that soil N and P concentrations were greatest in the upper 20 and 10 cm, respectively. 

In addition, the variations in soil P and N were greater at the soil surface than at lower depths. Concentrations of soil 

P and N at all depths decreased during the growing season. The largest decrease in soil P and N concentrations was 

found in the upper 10 cm, and at 20-40 cm, respectively. Nutrient removal from the soil was also calculated from 

changes in soil concentrations. Changes in soil N concentration indicated that the soybean and corn crop removed 

approximately 140 and 200 N ha-1. Analyses of the plant biomass indicated that approximately 140 and 200 kg N ha-1 

had been accumulated in the soybean and corn crop, respectively. Similarly, P removals based on soil removal versus 

grain and biomass removal were not significantly different and averaged 62 kg ha-1. Thus, crop removal by the two 

methods was in excellent agreement for both P and N. There were no differences in the P or N removal rates between 

the two management practices, one in which all of the N requirement was supplied by manure and another where 

sidedressed N supplemented the amount of N added by manure application. These results suggest that P additions 

to the soil from manure application can be reduced without affecting crop production if sufficient N is added from 

sidedressed fertilizer. 

The results from this study indicate that application of swine manure effluent at this farm according to the existing 

CNMP should supply N and P in sufficient amounts for crop production without leading to a further accumulation 

of N or P in the soil. There were no significant differences in the corn yields between the two manure management 

practices. Sparse rainfall during the early part of the 2006 growing season resulted in weather that was not typical 

of central Iowa. Therefore, far-reaching conclusions from this research may not be possible. The use of soil 

characteristics in the topsoil as indicators of the potential of downward movement of soil N and P will be made more 

difficult by the large variations in soil N and P concentrations in this zone. 

ix 

1.0 

Introduction
 


Modern American farms often have large numbers 

of animals and a relatively limited land base to apply 

the manure. This can lead to the problem of over 

application of nutrients, particularly nitrogen (N) and 

phosphorus (P) to agricultural lands. Nitrate (NO -

3 ) 

is soluble in water, hence, it can be easily leached 

from soils into ground water. As a result, nitrate is the 

most ubiquitous chemical contaminant in the world’s 

ground-water supplies (Spalding and Exner, 1993). 

The U.S. EPA established a maximum contaminant 

level (MCL) of 10 mg NO3-N L-1 for nitrate in drinking 

water (U.S. EPA, 1995). Nolan et al. (1998) estimated 

that 24 percent of the ground water in the United 

States exceeded the U.S. EPA MCL between 1993 and 

1995. Likewise, the European Community (EC) has 

established an upper threshold on drinking water nitrate 

levels of 11.3 mg NO3-N L-1. Approximately 10 million 

people in France depend on ground water with nitrate 

levels above the EC’s upper threshold (Spalding and 

Exner, 1993). Nitrate contamination of ground water 

near intensive vegetable production has been reported in 

Japan (Babiker et al., 2004). 

Surveys of ground water in areas with concentrated 

animal feeding operations (CAFOs) have reported higher 

than normal nitrate levels. In Sussex County, Delaware, 

the number one broiler producing county, 37 percent 

of the wells had nitrate levels above the MCL (Ritter 

and Chirnside, 1984). However, only 3.2 percent of the 

1232 wells sampled in a ten county area of Arkansas, 

another state with numerous poultry CAFOs, had 

nitrate levels above the MCL (Arkansas CES, 1990). 

Steele and McCalister (1991) reported the average 

nitrate-N concentration was only 3 mg NO3-N L-1 in 

areas receiving heavy applications of poultry litter in the 

Ozark region of Arkansas. Waste from poultry CAFOs 

is not the only potential source of nitrate contamination 

in ground water. Nitrate levels were high in ground water 

taken from wells under or near fields on which swine 

waste has been applied (Becker et al., 2003; Gillam et 

al., 1996; Mikkleson, 1995; Sloan et al., 1999). Nitrate 

derived from the N in swine manure that has been 

applied to agricultural fields has been found in shallow 

ground-water wells and this nitrate can be transferred to 

adjacent streams and waterways, thus decreasing surface 

water quality (Israel et al., 2005). 

Rate of N application is an important determinate of 

the leaching potential of nitrates. Results from Adams 

et al. (1994) indicate that manure additions that supply 

N more than twice the crop’s needs are likely to lead to 

nitrate contamination in ground water. However, other 

factors influence the concentration of nitrates in soil 

ground water below the plants’ rooting depth. Both the 

amount and timing of precipitation events and irrigation 

applications relative to time of N applications affect 

the amount of nitrate found deep in the soil profile 

(Gärdenäs et al., 2005; van Es et al., 2006). Leaching 

potential of nitrate through coarse texture soils is greater 

than for finer texture soils (van Es et al., 2006). Source 

of the N, including the type of manure, also influences 

the rate at which nitrate moves through the soil profile 

(Giullard and Kopp, 2004; Wu and Powell, 2007). 

Spalding and Exner (1993) stated that high temperatures, 

abundant rainfall and relatively high organic contents 

in Coastal Plain soils of the southeastern United States 

promote denitrification below the root zone and naturally 

remediate nitrate leaching into ground water. In North 

Carolina, Gilliam (1991) found that high levels of 

nitrates (15-20 mg N L-1) occurred in soil solutions in 

Coastal Plain soils cropped to corn. However, these 

high concentrations were not measured below 4 m. 

Gilliam (1991) attributed these low nitrate levels at 

greater depths to denitrification (soluble organic carbon 

compounds provide an energy source for microbial 

reduction of nitrate). 

Total N excreted in livestock and poultry manure 

represents nearly 35 percent of the U.S. commercial 

fertilizer N use; 30-85 percent of this may be lost to 

atmosphere during manure storage and application 

depending upon the manure management system 

(Hess et al., 2008). Additional losses of the N content 

may occur because of application timing, method, 

and weather conditions (Hess et al., 2008). Given the 

magnitude of these losses, methods and decision support 

tools are needed to identify areas and practices that 

increase the risk of nitrate contamination in ground 

water. Several methods for monitoring nitrate leaching 

have been used in the past. Results from Zotarelli et al. 

(2007) indicate that analyses of soil cores for nitrate 

provided as reliable estimates of nitrate leaching as 

soil lysimeters. Zhu et al. (2002) and Toth et al. (2006) 

demonstrated that passive capillary lysimeters also 

provided reliable estimates of nitrate leaching, while 

being easier to install and maintain than other types of 

lysimeters. The problem with all of these methods for 

use by producers is that they are labor intensive during 

installation and/or sample collection. 

1 
Recent work by U.S. EPA personnel in Oklahoma have 

demonstrated that land application of swine manure 

can cause nitrate contamination of ground water above 

the MCL at depths greater than 10 m (Elise Striz, 

unpublished data). These findings, along with similar 

findings around the country, are raising concerns for 

ground-water degradation on or adjacent to CAFOs. 

Currently, land application of manures from CAFOs 

must follow a comprehensive nutrient management plan 

(CNMP) in most states. One of the main underlying 

assumptions of using a well designed and executed 

CNMP is that ground water will be protected from 

excessive amounts of nitrate or other nutrients. One 

question that occurs is what are the nutrient dynamics 

when these plans are followed for land application? 

There is little information to help understand the 

seasonal changes in nutrient dynamics in soil when 

manure is applied according to a plan, although it is 

assumed that following CNMPs will alleviate potential 

environmental impacts. This study was designed to 

evaluate CNMPs for an integrated row crop-swine 

production system in the Midwestern United States. 

The Midwest environment is unique from other parts of 

the United States in which integrated row crop-swine 

production systems are practiced, like the coastal plains 

of North Carolina. Many Midwestern soils are derived 

from fine-textured glacial deposits, which results in these 

soils being poorly drained (Eidem et al., 1999; Rodvang 

and Simkins, 2001). To facilitate agriculture, many of 

these soils have been artificially drained (McCorvie and 

Lant, 1993). Thus, the hydrology of these Midwestern 

soils is probably very unique. In addition, the existing 

soil conditions impair the ability of shallow lysimeters 

to provide reliable estimates of nutrient composition in 

ground water at and just below the plant rooting depth 

(Hatfield, personal communications). 

This study evaluated N and P dynamics in a cornsoybean production system using swine manure as 

the primary nutrient source. Specific objectives were: 

1) evaluate the seasonal dynamics of N and P in the 

soil profile under CNMP-based applications of swine 

manure; and 2) evaluate the potential for ground-water 

contamination from the nutrient balance in the root zone. 

This study complemented one conducted in Arkansas 

using a different source of manure (dairy) and soils. 

2 
2.0 

Study Design
 


Study sites were established at a cooperator’s farm in 

central Iowa (Hardin County). This farm was chosen 

because CNMPs are an integral part of the swine 

operation. The cropping component of this farm’s 

operation is primarily a two-year rotation of corn and 

soybeans. The farm operator at this site has provided 

detailed records on nutrient content of applied manure, 

rates and timing of manure application, soil tests records, 

crop production, and meteorological data. Manure for 

this study was supplied from deep-pit manure storage 

from a 4,200 head grow-finish production unit. Manure 

is stored for up to a year in the pits underneath the 

building, and then stirred before pumping into the 

application equipment. Manure was applied with a knife 

injection system in the fall or spring when the pits are 

pumped out. According to the CNMPs, swine manure 

is applied to fields in the fall or spring of the year to 

supply the anticipated nutrient requirements of the corn 

crop the following season, approximately 150 kg N ha -1 

(135 pounds N acre-1). Manure was applied with a knife 

injector to a depth of 20 cm; this type of system is 

typical in central Iowa. Manure application rates based 

on the CNMP for these fields are shown in Table 1 and 

nutrient application rates were based on manure samples 

and the application rate made to supply these rates. 

Three areas of the farm, representing different cropping 

strategies and sequences in the cropping rotation, were 

selected to provide details about the metrics of N and 

P movement through the soil profile (Figure 1). These 

fields were tilled with a field cultivation operation in the 

spring before planting with additional soil disturbance 

caused by the injection of the manure. These three areas 

were as follows: 1) CNMP based spring application of 

manure supplying the nitrogen needs for that year’s corn 

(Table 1; Field 2, Sites 5 and 6); 2) CNMP based fall 

manure application rates and sidedressed N during the 

corn’s early season growth (Table 1, Field 1, Sites 1-4) 

to reduce P loads from manure; 3) evaluation of the 

residual N and P levels in the soil profile grown in 

corn in 2005 and in soybeans in 2006, the year of the 

study (Table 1, Field 3, Sites 7 and 8). The difference 

between Sites 7 and 8 is that the N requirement of the 

corn crop in 2005 was supplied by manure and fertilizer 

applications, respectively. The rationale behind the 

management protocol in Field 2 compared to Field 1 

was to reduce the P application from the manure while 

supplying a constant amount of N. The soil type at 

each site is listed in Table 1. Four soil types were found 

among the eight sites and detailed descriptions are given 

in Table 2. The month and amounts of N applied as 

manure are shown in Table 1. Crops were not irrigated 

and long term no-till was not being practiced. 

Sites were identified as 10 x 10 m sampling areas. 

All sites were located with GPS equipment to ensure 

samples were collected from the same area throughout 

the study. Soil samples were collected at each of the 

four corners and in the center of the sampling plot at 

depths of 0-15, 15-30, 30-45, 45-60, and 60-120 cm at 

planting (May 18, 2006, Day of Year, DOY 139) and 

after harvest (October 22, 2006, DOY 297) in 5 cm 

diameter samples. During the growing season (DOY 165 

to 235), biweekly soil samples were collected at 0-7.5, 

7.5-15.0 and 15.0-22.5 cm depths by aggregating five 

2.5 cm diameter soil cores randomly collected from the 

sampling area. At the same time biweekly, soil water 

content measurements were collected to a depth of 

10 cm using a time domain reflectometry (TDR) probe. 

Samples from each soil depth were analyzed for bulk 

density, N, P, K, C, and pH at the Iowa State University 

Soil Testing Laboratory (Missouri Agricultural 

Experiment Station, 1998). Nitrogen content was 

expressed as total N in both inorganic and organic 

forms (Missouri Agricultural Experiment Station, 

1998). Total plant available P was measured with a 

Mehlich III test, which is appropriate for the soils of 

Iowa (Missouri Agricultural Experiment Station, 1998). 

Duplicate samples were analyzed within the National 

Soil Tilth Laboratory as a cross reference to evaluate 

quality of the process and differences in N and P content 

were less than 5 percent between the two laboratories. 

Concentrations were expressed as mg kg-1 (dry weight) 

for all nutrients. Bulk density samples were collected at 

the initial sampling period for each depth by removing 

a 125 cm3 volume of soil with an open sided sampler, 

weighing the sample, drying the soil volume at 105°C 

for 48 hours, reweighing to determine the dry weight, 

and then using that weight to determine the dry mass of 

soil per unit volume of soil. 

Plant samples from the corn sites were collected 

biweekly (DOY 165 to 235) on the first fully expanded 

leaf from the top and the ear leaf after tasseling by 

removing 1 cm2 disk from the center point of the leaf 

to the side of the midrib. Five different leaves were 

sampled from each site during the course of the study 

with different leaves sampled each week. Nutrient 

contents of P and N were obtained from the Iowa 

State University Soil Testing Laboratory (Missouri 

3 
 

Table 1. Soil Types and Cropping Management Characteristics for Each Site. 
 

Site Field Soil Type Crop 

Manure Application Sidedress 

N 

Applied 

(kg ha-1) 

Manure 

Applied 

in 2005 

Month 

Applied 

N Added 

(kg ha-1) 

P Added 

(kg ha-1) 

1 1 Coland 

clay loam Corn April 2006 112 52 56 

2 1 Webster 

clay loam Corn April 2006 112 52 56 

3 1 Clarion 

loam Corn April 2006 112 52 56 

4 1 Clarion 

loam Corn April 2006 112 52 56 

5 2 Lawler 

loam Corn October 2005 157 76 0 

6 2 Coland 

clay loam Corn October 2005 157 76 0 

7 3 Clarion 

loam Soybeans 0 0 0 Yes 

8 3 Clarion 

loam Soybeans 0 0 0 No 

Table 2. Detailed Descriptions of the Soil Types within the Study Site in Central Iowa. Data from Soil Survey of 

Hardin County. 

Soil Type Depth (cm) Texture Clay 

(%) 

Bulk Density 

(g cm-3) pH Available Water 

(cm cm-1) 

Clarion 

Loam 

0-33 Loam 22 1.42 6.2 0.21 

33-84 Clay loam 27 1.60 6.8 0.18 

84-152 Sandy loam 17 1.75 7.8 0.18 

Coland 0-100 Clay loam 31 1.45 6.7 0.21 

Loam 100-152 Sandy loam 19 1.57 7.0 0.15 

Lawler 

Loam 

0-53 Loam 23 1.42 6.2 0.21 

53-76 Sandy clay loam 24 1.52 5.8 0.17 

76-152 Sandy loam 7 1.62 5.8 0.03 

Webster 

Clay 

Loam 

0-55 Silty clay loam 31 1.37 7.0 0.20 

55-96 Clay loam 30 1.45 7.1 0.17 

96-152 Sandy loam 23 1.60 7.9 0.18 

4 
Figure 1. Locations of the eight sites at the Hardin County swine production farm for the 2006 CAFO nutrient sampling study. 

Scale: 0.25 km per cm. 

5 
Agricultural Experiment Station, 1998). Corn biomass 

samples were collected from two plants from the edge 

of the sampling area at the biweekly interval. After 

tasseling, biomass samples were separated into leaves, 

stalks, and ears. Plant biomass samples were dried. These 

data were used to estimate N and P removal from the soil 

into the plant biomass during the season. Biomass plant 

samples were collected at the end of the growing season 

from the soybean sites. Soybean biomass samples were 

divided into vegetative and seed fractions, dried, and 

analyzed for N content at the Iowa State Soil Testing 

Laboratory (Missouri Agricultural Experiment Station, 

1998). 

Meteorological data (maximum and minimum daily 

temperature, and daily precipitation) were collected from 

an automated weather station located on the cooperator’s 

farm within 0.5 km of the field sites. 

3.0 

Data Analyses 

Results were obtained for each soil depth and sampling 

location within the sampling area. These data were then 

evaluated to determine the variation within the sampling 

area. Amounts of soil P and N were expressed as g m-3 

and kg m-3, respectively. These values were derived by 

adjusting the P and N concentrations at each depth by the 

bulk density of the soil obtained at the initial sampling 

period. Differences in soil N and P concentrations were 

determined from the intensive samples collected in the 

spring and fall to evaluate changes over the course of 

the growing season. Statistical differences were deemed 

significant at the 0.05 level. 

6 
Meteorological Conditions 

Maximum and minimum temperatures during the 

growing season were typical of most years in central 

Iowa (Figure 2). Maximum temperatures exceeded 

30°C for a few days during the season. Precipitation, 

however, was characterized by sparse rainfall during the 

early growing season and abundant rainfall during the 

latter part of the growing season (Figure 3). The lack 

of precipitation events created a situation in which the 

upper soil profile was extremely dry through most of the 

early growing season. 

4.0 

Results 

Variation of Soil Nutrient 

Concentrations within Sampling Sites 

The largest variation in total soil P was in the upper 

sampling depth for the five subsamples within Site 1 

for the May sampling date (Figure 4). The standard 

deviation of the mean was larger relative to its mean 

compared to means and standard deviations at lower 

depths. This pattern was observed across all eight sites. 

Figure 4. 	 Means and standard deviations of Mehlich III P 

concentrations over the six sampling depths for the 

five subsamples from Site 1. Site 1 is in Field 1, 

which received spring application of swine manure. 

Soil samples were collected in May 2006. Crop 

management characteristics are summarized in 

Table 1. 

Figure 2.		 Maximum and minimum daily temperatures during 

the 2006 growing season in central Iowa. A bar 

in the figure indicates date of the spring manure 

application. 

Figure 3. 	 Daily precipitation during the 2006 growing season 

in central Iowa. A bar in the figure indicates date of 

the spring manure application. 

An example for changes in soil N concentration 

with depth is shown in Figure 5. Changes in soil N 

concentrations with depth were slightly different 

compared to soil P. Similar to changes in soil P 

concentrations, the highest concentration of N was in the 

upper layer. However, the decrease in N concentration 

from the uppermost layer to the next depth was less 

with soil N compared to soil P. The decline in the total 

N concentration with soil depth was similar among 

Sites 1-4 in Field 1 (Figure 6). These four sites represent 

three different soil types (Table 1). In comparing the 

profile concentrations for N and P among the three 

soils within Field 1 there was no significant difference 

among the soils (data not presented). Variations among 

soils were insignificant for this field for the spring 

and fall sampling periods. Similar trends were found 

for the total P concentrations with depth for Sites 1-4. 

Total P concentration differed significantly among the 

four sites only in the upper sampling depth (Figure 7). 

Concentrations of total P were lower at Site 3. There 

7 
was a rapid decrease in the concentrations of both P and 

N with depth in the profile which is expected since the 

manure is applied in the upper profile and there is a large 

amount of plant residue from the previous crop present 

in these layers as well. 

Figure 5.		 Means and standard deviations of soil total N 

concentrations over the six sampling depths for 

the five subsamples from Site 1. Site 1 is in Field 

1, which received spring manure application. Data 

are from samples collected in May 2006. Cropping 

characteristics are summarized in Table 1. 

Figure 6.		 Soil total N concentrations with depth for Sites 

1-4 in Field 1. Field 1 received spring application 

of swine manure in 2006 (Table 1). Samples were 

collected in May 2006. 

Figure 7.		 Mehlich III P concentrations with depth for Sites 

1-4 in Field 1. Field 1 received a spring swine 

manure application (Table 1). Samples were 

collected in May 2006. 

Nutrient Concentrations in the Soil 

during the Growing Season 

Total soil N concentrations at the 7.5 cm sampling 

depth showed large variations among the four sites 

(1-4) in Field 1 and smaller variations across the season 

(Figure 8). This variability was attributed to differences 

in the initial soil N concentrations among the four sites 

because the patterns remained consistent across the 

season. This depth of the soil profile is most dynamic in 

terms of mineralization processes and during the 2006 

growing season this part of the soil profile was quite 

dry with water contents in the upper 10 cm often near 

0.1 percent of available water. The variation across the 

season and among soils was typical of what we have 

observed in other studies in sampling this soil depth 

(Hatfield and Prueger, 1994). 

Figure 8.		 Changes in the total soil N concentrations at the 

7.5 cm sampling depth for the four sites (1-4) in 

Field 1 during the 2006 growing season. Crop and 

soil management characteristics are presented in 

Table 1. 

8 
Changes in N and P concentrations in the soil profile 

were evaluated for the three different fields and cropping 

strategies present in 2006. For these comparisons, 

data from soil samples collected at the beginning and 

end of the growing season were averaged across sites 

within Fields 1 (Sites 1-4) and 2 (Sites 5-6). There was a 

decrease in P concentrations at all depths for Sites 1-4 in 

Field 1 (Figure 9), which had a reduced application rate 

of spring applied manure supplemented with N sidedress 

application. The change in P within the soil profile was 

greatest with the soil collected closest to the surface. At 

all depths there was a decrease in total soil P, consistent 

with P removal to meet the crop nutrient requirements. 

Figure 9. 	 Differences in Mehlich III P concentrations with 

soil depth in Field 1 between the spring and fall 

sampling periods in 2006. Field 1 received a 

spring application of swine manure (Table 1). 

Concentration values of samples collected in the 

spring were subtracted from those collected in 

the fall and data from Sites 1-4 in Field 1 were 

averaged graphed values. 

Soil N concentrations from the beginning to the end of 

the growing season decreased in Field 1, which received 

the spring manure application (Figure 10). There was a 

decrease in the N concentration in the upper soil profile 

because of uptake from the soil by the crop. However, 

the largest decrease in total soil N concentration was 

found in the 20 - 50 cm depth. This depth typically 

has the highest concentrations of roots to extract N 

(Kramer and Boyer, 1995). This pattern of N extraction 

was exaggerated in 2006 because of the dry year and 

points out the problems in a single year of observations. 

Sampling N concentration using this method is inclusive 

of all sources of N within the soil layer which may not 

be related to the amount of manure applied to the soil. 

Figure 10.		 Differences in soil total N concentrations with 

soil depth in Field 1 between the spring and fall 

sampling periods in 2006. Field 1 received a 

spring application of swine manure (Table 1). 

Concentration values of samples collected in the 

spring were subtracted from those collected in 

the fall and data from Sites 1-4 in Field 1 were 

averaged to obtain graphed values. 

Sites 5 and 6 in Field 2 (Table 1) received fall applied 

manure to supply 157 and 76 kg ha-1 of N and P, 

respectively. Total soil P and N concentrations decreased 

at all depths in the soil profile over the growing season 

(Figures 11 and 12). Removal of N from the soil profile 

was greatest at the 20 - 40 cm depth similar to the other 

sites. The most noticeable change in the P levels was in 

the upper layer of the soil profile in which there was a 

decrease exceeding 15 g m-3 in this layer. These changes 

in P and N concentrations from spring to fall in Field 2 

showed similar patterns to that found for Sites 1-4 in 

Field 1. Thus, there was no difference in the patterns 

of nutrient changes between the fall and spring applied 

manure reflected in the patterns of change within the 

soil profile (Figures 9-12). Although there was less P 

applied to this field as a result of the lower amount of 

manure applied and then supplemented with sidedress N, 

there was no significant difference in the P removal rates 

between the two fields. There was adequate P within 

the soil profile to supply the P requirements for the corn 

crop during this year. In years with a greater amount of 

rainfall there may be a greater difference between these 

two systems. 

Differences in total soil N and P concentrations 

throughout soil profiles were not significant for samples 

collected from Sites 7 and 8. Both fields showed similar 

patterns in the concentration profiles. There was no 

difference in the rooting depth between these two fields 

based on the observations of the soil samples collected 

after harvest. The soybean field with the manure history 

(Site 7) showed an insignificant increase in Mehlich III P 

9 
concentrations in the upper soil depth over the growing 

season. There was no additional P added to the soil 

during this period and these differences can be attributed 

to sampling variation within small areas. Changes over 

the growing season for Sites 7 and 8 showed similar 

patterns to Sites 1-4. 

Figure 11. Differences in total soil N concentrations with 

soil depth in Field 2 between the spring and 

fall sampling periods in 2006. Field 2 received 

a fall application of swine manure (Table 1). 

Concentration values of samples collected in the 

spring were subtracted from those collected in the 

fall and data from Sites 5 and 6 in Field 2 were 

averaged. 

Figure 12.		 Differences in Mehlich III P concentrations with 

soil depth in Field 2 between the spring and 

fall sampling periods in 2006. Field 2 received 

a fall application of swine manure (Table 1). 

Concentration values of samples collected in the 

spring were subtracted from those collected in the 

fall and data from Sites 5 and 6 in Field 2 were 

averaged. 

Soil samples collected from the soybean fields (Field 3) 

did not show any difference within the profile throughout 

the year. This was expected because no manure was 

applied during this season, and any N or P added from 

manure in previous years had been removed by the 

previous year’s crop. 

Plant Nutrient Concentrations 

Changes in the total N concentration in plant leaves 

showed a decrease during the growing season 

(Figure 13). There was no significant difference in the 

N concentrations among Sites 1-4 in Field 1 during this 

study. 

Figure 13. Changes in plant total N concentration in plant 

leaves throughout the growing season for Sites 1-4 

in 2006. Field 1 received spring application of 

swine manure (Table1). 

Nutrient Balance 

Analyses of plant biomass production and its N content 

indicated that N removal in the aboveground biomass for 

Field 1 (Sites 1-4) was 208 kg ha-1, for Field 2 (Sites 5 

and 6) was 197 kg ha-1, and for Field 3 (Sites 7 and 8) 

was 147 kg ha-1. The calculated nutrient removal based 

on the changes in the total N from the soil profile for 

Field 1 (Sites 1-4) was 197 kg ha-1, for Field 2 (Sites 5 

and 6) was 200 kg ha-1, and for Field 3 (Sites 7 and 8) 

was 137 kg ha-1. There is very good agreement between 

the N changes and crop removal rates in this study 

(Figure 14). There was no significant difference between 

Field 1 and Field 2 in the N removal. This is expected 

because there was no significant difference in the yield 

between these two manure management systems with 

a yield of 10,160 kg ha-1 for the two fields. For Field 3 

with the soybean crop the yield for both sites was 

2,500 kg ha-1 with no significant difference between the 

fields. 

10 
The P balance showed a similar good agreement between 

changes in the soil concentration and P content of the 

biomass and grain. In Field 1, the soil-based P removal 

was calculated to be 62 kg ha-1. P removal based on 

biomass and grain content was 65 kg ha-1 for Field 1. 

In Field 2, the soil-based P removal was calculated to 

be 56 kg ha-1 compared to 64 kg ha-1 for calculations 

based on biomass and grain. There was no significant 

difference between the two methods of estimating P 

removal rates. This CNMP is based on reapplying 

nutrients to meet the crop removal, and for the year in 

the study these results demonstrate the effectiveness 

of the method. Even though the crop residue was not 

removed, these nutrients are now present on the surface 

and would be returned to the soil profile as a result of 

residue decay, microbial activity and tillage. However, at 

crop harvest (the endpoint for this study) these nutrients 

can be considered as being removed from the profile. 

These values for removal exceed the amount applied 

with the difference being the extraction from the soil 

profile during the cropping season. 

Figure 14. Comparison of measured versus estimated N 

removal from corn-soybean rotations with manure 

nutrient additions for the 2006 study. Sites 1 are 

(1-4), Site 2 (5-6) and Site 3 (7-8). 

11 
5.0 

Conclusions and Impact
 


Application of swine manure using CNMPs onto a cornsoybean cropping system creates a condition in which 

there is extraction of nutrients from the soil profile to 
 

meet the crop demand. The 2006 growing season was 
 

not typical with the small precipitation events during 
 

the portion of the growing season in which there is the 
 

most rapid vegetative growth and grain production. 

This created a condition in which there was a water 

deficit in the soil profile with the plants extracting water 
 

from within the soil profile to depths exceeding 1.5 m. 
 

Water contents in the soil samples collected at harvest 
 

indicated the soil was near the lower limit of soil water 
 

availability (data not shown), thus there was no water 
 

for transport of nutrients within the soil profile. This 
 

scenario is not atypical of central Iowa where the soil 

profile is dry at the time of harvest. These meteorological 

conditions would create a situation that limits any 

downward movement of nutrients, especially NO3-N. 

However, the extraction of nutrients from the soil profile 

was necessary to offset the amount applied to the soil 
 

via manure and sidedress N to the corn crop and this 
 

practice did not affect yield between the two practices. 
 

Following CNMPs does meet the agronomic demand 
 

for the crop and the P and N removal rates from the soil 

profile were not significant between the two different 
 

manure management systems. In the soybean field that 
 

had portions with and without a history of manure there 

was removal of N and P from the profile to meet the crop 

growth demands for nutrients. The lack of differences 
 

in the nutrient contents for these fields showed that 
 

there was no residual N or P from the previous manure 

application. For both the corn and soybean crop a 

portion of the nutrients removed would be returned to 

the soil through the crop residue (leaves and stalks) that 
 

would be left on the soil profile. The amount returned to 
 

the soil from the residue would replenish the profile of 
 

the amounts removed during the season.
	 

The metrics for ground-water contamination in this study 
 

were not directly assessed because this year with limited 
 

rainfall proved to limit water movement. Techniques for 

sampling shallow ground water in these poorly drained 
 

soils require a minimum of one year of adjustment 
 

time before sample collection and are not possible to 
 

use when the soils are dry. We would conclude from 
 

this one-growing season study that following CNMPs 
 

provides nutrients in adequate supply for the crop with 

the addition of that extracted from the soil profile. 

One of the limitations for this study was the lack of 
 

precipitation during the growing season which allowed 
 

only for a partial assessment of Objective 2. Variation 

in precipitation among years requires multiple years of 

study and other studies being conducted in central Iowa 

suggest that a minimum of five years may be needed 

to account for the variation in precipitation timing and 

amounts during cropping season. These types of studies 

need to be conducted over a range of meteorological 

scenarios to address the variable conditions of soil water 

content induced by different precipitation amounts. We 

would expect a similar result with the crop demand using 

the nutrients applied from the manure source. Producers 

should be aware of the value of developing CNMP for 

fields and the potential variation among soils in their 

response in supplying nutrients to the crop. 

12 
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14 

 

 

 

 

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