EPA 600/R 09/045 I June 2009 I www.epa.gov/ada
United States
Environmental Protection
Agency
Metrics for Nitrate Contamination
of Ground Water at
CAFO Land Application Sites -
Iowa Swine Study
Office of Research and Development
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Metrics for Nitrate Contamination
of Ground Water at
CAFO Land Application Sites -
Iowa Swine Study
Jerry L. Hatf ield
National Soil Tilth Laboratory
Ames, Iowa
Office of Research and Development
National Risk Management Research Laboratory, Ada, Oklahoma 74820
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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
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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, Region-
specific 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 near-
term 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 ($13 OK 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
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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
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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
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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
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Acknowledgements
Dale Bumpers Small Farms Research Center (Booneville, AR) and Southern Plains Area Office (College Station, TX)
of ARS/USD A provided administrative support for the interagency agreement.
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Executive Summary
Nitrate (NO3") 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.
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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 (NO3")
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 etal., 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
(Gardenas 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.
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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 10m (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 corn-
soybean 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.
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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 renectometry (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
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Table 1. Soil Types and Cropping Management Characteristics for Each Site.
Site
1
2
3
4
5
6
7
8
Field
1
1
1
1
2
2
3
3
Soil Type
Coland
clay loam
Webster
clay loam
Clarion
loam
Clarion
loam
Lawler
loam
Coland
clay loam
Clarion
loam
Clarion
loam
Crop
Corn
Corn
Corn
Corn
Corn
Corn
Soybeans
Soybeans
Manure Application
Month
Applied
April
2006
April
2006
April
2006
April
2006
October
2005
October
2005
N Added
(kg ha-1)
112
112
112
112
157
157
0
0
P Added
(kg ha-1)
52
52
52
52
76
76
0
0
Sidedress
N
Applied
(kg ha-1)
56
56
56
56
0
0
0
0
Manure
Applied
in 2005
Yes
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
Clarion
Loam
Coland
Loam
Lawler
Loam
Webster
Clay
Loam
Depth (cm)
0-33
33-84
84-152
0-100
100-152
0-53
53-76
76-152
0-55
55-96
96-152
Texture
Loam
Clay loam
Sandy loam
Clay loam
Sandy loam
Loam
Sandy clay loam
Sandy loam
Silty clay loam
Clay loam
Sandy loam
Clay
(%)
22
27
17
31
19
23
24
7
31
30
23
Bulk Density
(g cm'3)
1.42
1.60
1.75
1.45
1.57
1.42
1.52
1.62
1.37
1.45
1.60
pH
6.2
6.8
7.8
6.7
7.0
6.2
5.8
5.8
7.0
7.1
7.9
Available Water
(cm cm"1)
0.21
0.18
0.18
0.21
0.15
0.21
0.17
0.03
0.20
0.17
0.18
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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.
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Agricultural Experiment Station, 1998). Cornbiomass
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 nr3
and kg nr3, 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.
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4.0
Results
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.
40
o
5
CD
30
20
10
Q.
'O
80
60
40 -
20
vv
Manure
Application
Maximum Temperature u |]1
Minimum Temperature 11 '
100
Figure 2.
150
200
250
300
350
Day of Year
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.
Manure
Application
150
200
Day of Year
250
300
Figure 3.
Daily precipitation during the 2006 growing season
in central Iowa. A bar in the figure indicates date of
the spring manure application.
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.
0
-10-
|-20-
^ -30-
"5.
S -40-
W -50
-60
-70
Manured Field Site 1
20
40 60
P(mgkg-1)
80
100
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.
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
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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.
-10-
'£-20-
r.3o.
Q -40
CO -50
fin
-7f>.
Manured Field Site 1 2006
1— ^H
50
100 150
200
250
300 350
N (mg kg 1)
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.
0
-10
—. -20
•r -so-i
•s.
a -40
CO -50-I
-60
-70
Manured Fields 2006
Sitel
Site 2
- Site3
Site 4
100
200 300
N (mg kg'1)
400
500
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.
Q
0
-10
-20
-40
'o
CO -50
-60
-70
Manured Fields 2006
Sitel
Site 2
SiteS
Site 4
20
40 60
P (g m-3)
80
100
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).
600
T 500 •
01 400
Z 300 •
S
|° 200 ]
'5
CO 100 •
Manure Study 2006
Site 1
Site 2
Site 3
Site 4
160 170 180 190 200 210 220
Day of Year (DOY)
230 240
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.
-------
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.
-10-
— -20-
o
-50 H
-60-
-70
Manure Study 2006
Sites 1-4
-25 -20 -15 -10 -5 0
Differences in Total Soil P (mg kg1)
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.
-10 -
'-20 -
0)
Q -40 -
OT-50-
-60 -
-70
Manure Study 2006
Sites 1-4
-60 -50 -40 -30 -20 -10
Differences in Total Soil N (mg kg"1)
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 m3 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
-------
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.
Q.
&
0
-10
-20
-30
-40
-50
-60
-70
Manure Study 2006
Sites 5-6
-50 -40 -30 -20 -10 0
Differences in Total Soil N (mg kg"1)
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.
0
-10-
-20-
-30-
-40-
OT -50-I
-60-
-70
Manure Study 2006
Sites 5-6
-18 -16 -14 -12 -10 -8 -6-4-2 (
Differences in Total Soil P (mg kg"1)
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.
4600
4400-
4200
4000-
3800-
3600-
3400-
3200
3000
Manure Study 2006
160 180 200 220 240
Day of Year (DOY)
260
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 (Table 1).
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.
-------
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.
250
Manure Management 2006
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).
-------
5.0
Conclusions and Impact
Application of swine manure using CNMPs onto a corn-
soybean 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 1.5m.
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.
-------
6.0
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