- 

 

 

EPA 600/R 09/044 | June 2009 | www.epa.gov/ada 

Metrics for Nitrate Contamination 

of Ground Water at 

CAFO Land Application Sites ­

Arkansas Dairy 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 -

Arkansas Dairy Study 

Philip A. Moore 

University of Arkansas 

Fayetteville, Arkansas 

David Brauer 

Conservation and Production Research Laboratory 

Bushland, Texas 
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:
	

Philip A. Moore, Jr.
	

USDA-ARS, Plant Sciences 115, University of Arkansas, Fayetteville, AR 72701. 

Phone: 479-575-5724. 

Fax: 479-575-7465. 

E-mail: philipm@uark.edu. 

Mention of a trade name, proprietary product, or specific equipment does not constitute a 

guarantee or warranty by the USDA and does not imply its approval to the exclusion of other 

products that may be suitable. 

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. Philip A. Moore, Jr., and Dr. David Brauer for a dairy farm in Arkansas. The other site 

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

 

Contents
 

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

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

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

Diagrams and Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi
 

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

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

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

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

2.0		 Materials and Methods. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
	

Site Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
	

Soil Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
	

Lysimeter Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
	

Effluent Application and Collection of Applied Effluent Samples . . . . . . . . . . . . . . . . . . . . . . . . . . 4
 

Forage Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
	

Statistical Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
	

3.0		 Results and Discussion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
	

Precipitation Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
	

Lysimeter Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
	

Soil Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
 

Forage Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
 

Metrics for Nitrate Leaching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
 

4.0		 Conclusions and Recommendations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
	

5.0		 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
 

v 
Diagrams and Figures
 

Diagram 1.Schematic showing location of plots within Fields 1 and 2. . . . . . . . . . . . . . . . . . . . . . . . . . . 3
	

Diagram 2.Stainless steel lysimeter installation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
 

Figure 1. Daily precipitation between June 1, 2004 (Day -56) and September 1, 2005 (Day 401). . . . . 6 

Figure 2. Lysimeter nitrate concentrations as a function of time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 

Figure 3. Concentrations of total N (TN) in lysimeter ground water samples as a function of time. . . . 7 

Figure 4. Ammonium concentrations in lysimeter ground water samples as a function of time. . . . . . . 8 

Figure 5. Relationship between concentrations of nitrate, organic N, and ammonium N and total N 

concentrations in lysimeter ground water samples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 

Figure 6. Concentrations of soluble reactive P in lysimeter ground water samples as a function of 

time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 

Figure 7. Concentrations of total P in lysimeter ground water samples as a function of time. . . . . . . . . 9 

Figure 8. Soil nitrate concentrations in samples taken from 0-5 cm depth as a function of time. . . . . . . 10 

Figure 9. Concentrations of soil inorganic N for samples taken from 0-5 cm depth as a function of 

time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 

Figure 10. Depth distribution of soil nitrate (panel A) and inorganic N (panel B). . . . . . . . . . . . . . . . . . . 10 

Figure 11. Depth distribution of soluble reactive P (panel A) and Mehlich III P (panel B) 

concentrations in soil samples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

Figure 12. Forage nitrate concentrations as a function of time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

Figure 13. Relationship between lysimeter nitrate and forage nitrate concentrations. . . . . . . . . . . . . . . . 12 

vi 
CAFOs Concentrated Animal Feeding Operations 

HUA High Use Area 

LSD Least Significant Difference 

MCL Maximum Contaminant Level 

N Nitrogen 

NH -N 4 Ammonium Nitrogen 

NMP Nutrient Management Plan 

NO -N 3 Nitrate Nitrogen 

P Phosphorus 

Abbreviations
 

vii 
Acknowledgements 

The authors wish to thank Scott Becton, Suzanne Horlick and Jerry Martin for their contributions to this work. The 

authors also appreciate Dr. Charles MacKown (USDA/ARS, El Reno, OK) for conducting forage nitrate assays. 

viii 
 

 

Executive Summary
 

Nitrate is the most common chemical contaminant found in ground water. Recent research by U.S. EPA has shown 

that land application of manure can cause nitrate contamination of ground water above the maximum contaminant 

levels (MCLs) of 10 mg NO3-N/L at significant depths. This finding and similar ones across the nation are raising 

concerns about the potential for manure to degrade ground water quality near concentrated animal feeding operations 

(CAFOs). The objectives of this research were to determine if nutrient management plans (NMPs) for CAFOs are 

inherently protective of ground water and which metrics can be used as red flags to identify when the land application 

practices pose a risk to ground water. 

A study was conducted for one year (August 2004 to July 2005) on a typical dairy farm in northwest Arkansas. The 

dairy had 250 cows and utilized 27 ha (67 acres) for manure application. Effluent from the holding pond was sprayed 

onto four 4.05 ha (10-acre) fields each year. According to the farmer’s NMP, effluent applications were to occur 

during the growing season after the soil had dried considerably, which did not occur until August in 2004. Four small 

(10 x 10 m) plots were established in each of two of these spray fields. Stainless steel lysimeters were installed to 

a depth of 1 m and sampled weekly. Three soil cores were taken periodically from seven depths (0-5, 5-10, 10-20, 

20-40, 40-60, 60-80 and 80-100 cm). Soil samples were collected 20 times throughout the year. These samples were 

analyzed for soluble components as well as exchangeable ammonium and Mehlich III extractable P. Plant samples 

were also analyzed for nitrate. 

Nitrate levels in lysimeter samples were high, with peaks in excess of 100 mg NO3-N/L. The amount of N applied 

via effluent averaged 280 kg N/ha (250 lbs N/acre), which was not believed to be sufficient to cause such high levels. 

Lysimeter P concentrations were also very high. Beginning in November, it was observed that the farmer utilized 

the 4.05 ha fields as a loafing area or high use area (HUA) for his cows. We estimate that at the observed stocking 

rate (31 cows/ha) as much as 840 kg N/ha (750 lbs N/acre) was being added to these fields via direct waste deposits 

from the cows. When coupled with the effluent application, the total N loading to these fields was approximately 

1100 kg N/ha (1000 lbs N/acre) in one year. 

When state officials were contacted to determine if direct deposits were taken into account when determining 

maximum N application rates for farms spreading liquid manures in Arkansas, we discovered that these deposits by 

the cows were not accounted for. Currently, the Arkansas Phosphorus Index is being revised. During this revision 

we will attempt to change regulations so that growers cannot apply effluent to a HUA unless the direct deposits are 

properly accounted for. The best predictor of high nitrate in the lysimeter samples was leaf tissue nitrate concentration 

with R-square of 0.82. Since nitrate toxicity in cows is a problem that will negatively affect production, dairy farmers 

could easily be convinced to monitor this parameter. High nitrate levels in forage would allow them to know which 

fields were receiving too much N, and allow them to alter applications accordingly. 

ix 

Animal agriculture is important to the economy of both 

Arkansas and the nation. Modern 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). High concentrations 

of nitrate in drinking water can cause problems if 

consumed by infants possibly resulting in a serious 

illness called methemoglobinemia or “blue-baby 

disease.” Blue-baby disease is due to conversion of 

nitrate to nitrite by the immature gastrointestinal tract, 

which results in low oxygen levels in the blood. 

As a result of this potential human health threat, the 

U.S. EPA established a maximum contaminant level 

(MCL) of 10 mg nitrate-nitrogen (NO3-N)/L for nitrate 

in drinking water (U.S. EPA, 1995). Unfortunately, 

Nolan et al. (1998) reported that U.S. EPA MCL was 

exceeded 24 percent of the time in the United States 

when data from 1400 wells sampled between 1993 and 

1995 were analyzed. Approximately 20 percent of the 

population of France (10 million people) depends on 

ground water with nitrate levels above the European 

Community’s upper threshold of 11.3 mg NO3-N/L 

(Spalding and Exner, 1993). Nitrate contamination of 

ground water near intensive vegetable production has 

been reported in Japan (Babiker et al., 2004). 

Several surveys of ground-water nitrate levels have been 

completed in the past in areas considered prone to high 

nitrate, including areas with high poultry production, like 

Arkansas (Arkansas CES, 1990; Steele and McCalister, 

1991) and Delaware (Ritter and Chirnside, 1984). The 

number of wells with nitrate levels greater than 10 mg 

NO3

-N/L was relatively low in Arkansas (Steele and 

McCalister, 1991). This was not the case in Delaware, 

particularly in the number one broiler producing county 

(Sussex County) where 37 percent of the wells had 

nitrate levels above the MCL (Ritter and Chirnside, 

1984). Ritter and Chirnside (1984) concluded that 

nitrate leaching from poultry manure was likely the 

major source of the high ground-water nitrate levels in 

this county. Only 3.2 percent of the 1232 wells sampled 

in a ten county area of Arkansas had nitrate levels 

above the MCL and most of these were in the poultry 

1.0 

Introduction
 

producing areas (Arkansas CES, 1990). However, Steele 

and McCalister (1991) reported the average nitrate 

concentration was only 3 mg NO3-N/L in areas receiving 

heavy applications of poultry litter in western Arkansas. 

Adams et al. (1994) studied nitrate leaching in a Captina 

silt loam soil in northwest Arkansas for 1 year after 

being fertilized with various rates (0, 5, 10 and 20 Mg/ha 

or approximately 2.5 to 10 tons/acre) of poultry litter and 

laying hen manure, which corresponded to N application 

rates of 0, 220, 440 and 880 kg N/ha. Lysimeter data 

taken from 1.2 m depth showed that only the 10 and 

20 Mg/ha rates resulted in soil solution nitrate values in 

excess of 10 mg NO3-N/L with maximum concentrations 

of 24 and 37 mg NO3-N/L, respectively. Adams et al. 

(1994) concluded that if manure application rates are 

made at the recommended rates in Arkansas, less than 

11 Mg/ha or 5 tons/acre (Daniels et al., 2008), then 

excessive nitrate leaching should not occur. These 

results confirmed those of Marriott and Bartlett (1975), 

who showed that manure application rate played an 

important role in nitrate leaching. They indicated that 

manure could be applied at twice the crop’s N needs 

with minimal threat of nitrate leaching to the ground 

water, provided the manure is applied to a deep welldrained soil and the crop is harvested. 

Although rate of N application is an important 

determinant of the leaching potential of nitrates, other 

factors also influence the concentration of nitrates in soil 

water below the plants’ rooting depth. Both the amount 

of and the timing of precipitation events and irrigation 

water 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). 

There may be a value in the use of estimates of crop 

evapotranspiration to scheduling irrigation amounts and 

frequency to limit the amount of nitrate leaching through 

the soil profile (Gärdenäs et al., 2005). 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 

1 
nitrates (15-20 mg NO3

-N/L) 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). 

Several methods for monitoring nitrate leaching have 

been used in the past. Nitrate analyses of soil cores 

provided estimates of nitrate leaching as reliable as two 

different types of soil lysimeters (Zotarelli et al., 2007). 

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 these methods is that they are labor intensive during 

installation and/or sample collection, thus limiting their 

use by farmers.
	

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

demonstrated that land application of swine manure can 

cause nitrate contamination of soil 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 soil and groundwater degradation on or adjacent to concentrated animal 

feeding operations (CAFOs). Currently, land application 

of manures from CAFOs must follow a nutrient 

management plan (NMP) in most states. In Arkansas, 

NMPs for liquid manures have been regulated for over 

a decade by Regulation 5, which states that manure 

applications will be based on the N needs of the crop. 

One of the main underlying assumptions of using a well 

designed and executed NMP is that ground water will 

be protected from excessive amounts of nitrate or other 

nutrients. 

In the southern United States, attention has focused 

on the potential of animal manure from poultry and 

integrated poultry and beef cattle operations contributing 

to ground-water contamination because of the number 

of these operations. In 1997, poultry and beef cattle 

production comprised 50 percent of the agricultural 

income in Arkansas and over 90 percent of the animal 

manure production (VanDevender, 1997). Dairy farms 

in Arkansas, on the other hand, accounted for 2 percent 

of the farm income and 5 percent of the animal manure 

production. The stocking rate of cattle (number of 

head/ha or acre) tends to be greater with dairy than 

beef cattle. Dairy cattle routinely require supplemental 

feeding with both energy- and protein-rich feeds, thus 

leading to an importation of nutrients to the farm. A 

disproportionate amount of these nutrients are fed 

to dairy cattle during that period of the year when 

forages are dormant. The potential for nutrient runoff or leaching is greater when cattle are being fed 

on dormant grasslands (Owens and Shipitalo, 2006). 

The amount of water soluble P in dairy manure is 

relatively high (Shigaki et al., 2006). Several studies 

have indicated that the amount of soluble P applied as 

manure is directly associated with the potential for P 

losses in run-off (DeLaune et al., 2004a; 2004b). Soupir 

et al. (2006) indicated that nutrients are more readily 

lost from direct deposition of dairy manure onto the 

soil than losses from other application methods. These 

previous findings indicate that there is the potential for 

ground-water contamination on or adjacent to southern 

dairy operations, especially when rainfall exceeds 

evapotranspiration and soils are permeable to water. 

The objectives of this research were to determine 

if an NMP, when properly executed, consistently 

protects ground water, and, if not, to determine what 

soil/crop/manure metrics could be utilized to predict 

potential ground water degradation. 

2 
2.0 

Materials and Methods
 

Site Selection 

The site selected for this study was a dairy farm 

located in Washington County in northwest Arkansas. 

The initial meeting with the landowner was made on 

July 20, 2004. The dairy had approximately 250 cows 

on 27.1 ha (67 acres, 47 acres were grazed; 20 acres 

were hayed). Lagoon effluent from the farm was 

applied to four 4.05 ha (10-acre) fields of bermudagrass 

(Cynodon dactylon (L.) Pers). Two of the four fields, 

designated as Field 1 or 2, were randomly chosen for 

the study. Within each of the two fields, four plots 

(10 x 10 m) were established (Diagram 1). According to 

the Washington County Soil Survey (USDA, 1969), the 

soil type in both fields was exclusively a Jay silt loam 

(fine-silty, mixed, active, thermic Oxyaquic Fragiudalf) 

on 1-3 percent slope. Characteristics of soil recovered 

from coring to 1 m depth were consistent with this 

determination (data not shown). According to the 

Washington County Soil Survey (USDA, 1969) the Jay 

series consists of well-drained, slowly permeable soils 

that have a subsoil fragipan between 0.4 and 1.0 m of 

the soil surface. A full description of the Jay silt loam 

is available (NRCS, 2000). No attempt was made to 

determine the depth at which the fragipan occurred. The 

landowner was able to utilize these fields according to 

his management scheme, thus cattle were not excluded 

from the plots. Rainfall data were obtained from a 

USGS gauge station located near the fields (USGS, 

2009). 

Diagram 1. Schematic showing location of plots within 

Fields 1 and 2. 

Soil Samples 

Three soil cores (5 cm in diameter) were collected 

from each plot on each sampling date. The cores were 

divided into 7 discrete samples by depth (0-5, 5-10, 

10-20, 20-40, 40-60, 60-80 and 80-100 cm). Soils 

from each depth of the three cores were combined for 

each plot. Thus, there were a total of 56 soil samples 

(8 plots x 7 depths) taken at each sampling time. First 

soil samples were taken on July 24, 2004. Soil samples 

were collected 19 additional times over the next year, 

with the bulk of the samples being collected just after 

dairy effluent applications. Collection of soil samples 

terminated prior to effluent application in 2005. 

Soluble reactive phosphorus, nitrate-N, and 

ammonium-N were extracted using a 1:10 (soil:water) 

extraction for one hour (Self-Davis et al., 2000). A 

sequential KCl extraction was conducted on the soil 

for exchangeable ammonium. Nitrate (+nitrite) was 

determined using the Cd reduction method on filtered 

(0.45 m) samples (Method 418-F; APHA, 1992). 

Soluble reactive P samples were also filtered (0.45 m), 

and acidified to pH 2.0 with HCl. Soluble reactive 

P was determined using the ascorbic acid technique 

(APHA Method 424-G; APHA, 1992). Ammonium was 

determined with the salicylate-nitroprusside technique 

on filtered (0.45 m), acidified samples (Method 351.2; 

U.S. EPA, 1979). Soil samples were also analyzed 

for Mehlich III P (Mehlich, 1984). Levels of soil 

constituents were expressed as mg per kg of dry soil. 

These concentrations were converted to pounds per 

acre assuming 2,000,000 pounds of soil per acre-foot of 

topsoil. 

Lysimeter Samples 

One stainless steel lysimeter (50 cm long and 5 cm 

in diameter) was installed within each of the four 

10 x 10 m 2 plots in each field on August 2, 2004 

(Diagram 2). Both the equipment and installation 

were essentially as described by Adams et al. (1994). 

Installation began by digging a hole of sufficient size to 

accommodate an armor valve box (approximately 15 cm 

in diameter and 20 cm in height). From the bottom 

of this hole a second hole was dug at a 45-degree 

angle to the soil surface, in which the stainless steel 

lysimeter and the attached vacuum tubes were placed. 

Excavated topsoil and subsoil were kept separately. 

After placement of the lysimeter, the hole was filled 

with the removed material starting with excavated 

subsoil. Such an installation minimizes the disturbance 

3 
to the soil immediately above the sample collection 

chamber. Leachate from the sample collection chamber 

was collected by the application of a vacuum. Attempts 

to gather ground-water samples from the lysimeters 

were made on a weekly basis. Between September 9, 

2004 and October 31, 2004, ground-water samples were 

obtained from less than half of the lysimeters. During 

November 2004, ground-water samples were obtained 

from over half of the lysimeters, but not all. From 

December 1, 2004 through May 14, 2005, groundwater samples were obtained from all lysimeters. After 

May 14, 2005, the number of lysimeters with groundwater samples declined until only two lysimeters in 

Field 2 had samples. Attempts to gather ground-water 

samples were terminated prior to effluent application in 

2005. Chemicals present in the soil water at a depth of 

1 m are likely to continue to percolate downward until 

reaching ground water because a vast majority (over 

95 percent) of roots and associated organic C are located 

at a soil depth of less than 0.9 m in bermudagrass 

dominated agro-ecosystems (Carreker et al. 1977; 

Franzluebbers and Stuedemann, 2005). Lysimeter 

samples were analyzed for pH, electrical conductivity 

(EC), total organic C (TOC), total nitrogen (TN), 

ammonium (NH +

4 ), nitrate (NO -3 ), soluble reactive 

phosphorus (SRP), and total P (TP). Ammonium was 

determined with the salicylate-nitroprusside technique 

(Method 351.2; U.S. EPA, 1979). Soluble reactive P 

samples were filtered (0.45 m), acidified to pH 2.0 

with HCl and frozen. Soluble reactive P was determined 

using the ascorbic acid technique (Method 424-G; 

APHA, 1992). Total N and total organic C were 

analyzed using a Skalar total N and C analyzer. Total P 

and metals were determined using a Spectro inductively 

coupled argon plasma emission spectrometer following 

acid digestion. 

Diagram 2. Stainless steel lysimeter installation. 

Effluent Application and Collection of 

Applied Effluent Samples 

Effluent applications were made according to an 

approved NMP. Application amounts were based 

on N needs of the forage. Liquid manure from the 

holding pond was applied via a travel gun on Field 2 

on August 3, 2004 and on Field 1 on August 18, 2004. 

Length of effluent application was 1 hr 45 min for 

Field 1 and 2 hr for Field 2. The pressure at which 

the liquid was sprayed was 207 kPa (30 pounds per 

square inch) on both fields. Four shallow plastic pans 

(16.5 x 30.5 cm) were placed in each of the four plots 

during effluent application. The effluent collection area 

represented approximately 2 percent of the plot area. 

The volume of effluent captured in each was recorded. 

The captured effluent was analyzed for total N and 

nitrate concentrations. The captured effluent had an 

average total N content of 651 and 514 mg N/L for 

Fields 1 and 2, respectively. Nitrate concentrations were 

0.30 and 0.38 mg NO3

-N/L, respectively, for effluent 

collected on Fields 1 and 2. These results indicate 

that most of the N in the effluent was not in the nitrate 

form. The average application rate applied to the plots 

in Field 1 was 602,100 L/ha (or 64,100 gallons/acre). 

The amount of effluent captured in the collection pans 

in the plots in Field 2 was considerably less, averaging 

330,000 L/ha (or 35,100 gallons/acre). Using the total N 

content of the collected effluent, N application rates of 

391 and 168 kg N/ha (or 349 and 151 lbs N/acre) were 

calculated for Fields 1 and 2, respectively. The average 

total N application rate for both fields was 280 kg N/ha 

(or 250 lbs N/acre). 

What was captured in the pans was probably 

representative of what the plots received, but may not 

have been representative of what was applied to the 

entire field. The traveling gun was spraying effluent 

on Field 2 for a slightly longer period of time than on 

Field 1, 2 hours versus 1.75 hours (see above). Hence, 

Field 2 should have had slightly more manure applied 

than Field 1. The reason for discrepancy between 

what was applied to the field and what fell on the plots 

is probably the non-uniform application which was 

made by the gun. The location of the plots, direction 

and speed of wind, etc., relative to the position of the 

traveling gun in the field were not the same. Very few, 

if any, growers spreading liquid manure in Arkansas 

have center pivot irrigation systems. They have 

traveling guns, like the one this grower utilized. Hence, 

uneven applications within fields are probably typical of 

on-farm situations. No weather station was installed at 

the experimental site. Daily precipitation amounts were 

obtained from the USGS stream gauge 07048600, which 

was located within 10 km of the research site (USGS, 

2009). 

4 
Forage Samples 

Leaf tissue was collected from vegetation growing in 

each of the 8 plots every 30-40 days. Above ground 

biomass was clipped within 2 cm of the soil surface 

from 10 randomly selected areas within each plot, each 

approximately 15 cm in diameter. A sub-sample from 

the leaf material collected from each plot was dried at 

60°C for 48 hours, ground to pass a 40-mesh screen and 

nitrate-N was determined via nitrate reductase assay 

(MacKown and Weik, 2004). 

Statistical Analyses 

Data were analyzed by analysis of variance using SAS 

(SAS Institute, 1985). The experimental unit was a plot 

within one of the two fields. The experimental design 

included sampling dates, plots within field and fields as 

the main factors. In the statistical analyses, missing data 

from a sampling date were treated as missing values. 

Least significant differences (LSD) at P = 0.05 are 

included in figures and text for mean comparison tests. 

Days mentioned in text and accompanying figures refer 

to days after the study was initiated, i.e. July 27, 2004. 

5 
 

 

 

3.0 

Results and Discussion
 

Precipitation Data 

Daily precipitation from June 1, 2004 to September 1, 

2005 is presented in Figure 1. Sufficient rainfall 

occurred in June and July 2004 (Day -56 to Day 0) to 

prevent the application of effluent to the bermudagrass 

fields until early August, as to comply with the soil 

moisture parameters of the farm’s NMP. A substantial 

rainfall event occurred immediately after the effluent 

applications. Approximately 8-10 cm of water were 

applied to the fields by effluent application and rainfall 

between August 1 (Day 5) and September 9, 2004 

(Day 44), the date that the first soil water samples were 

obtained from the lysimeters. Little rainfall fell during 

the fall of 2004. Several rainfall events occurred around 

December 1, 2004 (Day 127) and February 1, 2005 

(Day 189). Frequent rainfalls of over 1 cm occurred 

between April 1 and July 1, 2005 (Days 248-339). 

Figure 1.		 Daily precipitation between June 1, 2004 (Day -56) 

and September 1, 2005 (Day 401). Time zero is 

July 27, 2004. Daily precipitation was obtained 

from USGS gauge station 07048600 located on 

the White River near Fayetteville AR. This gauge 

station is located within 10 km of the experimental 

site. 

Lysimeter Data 

The first lysimeter ground-water samples were 

collected on September 9, 2004, approximately three 

to four weeks after effluent applications were made. 

Nitrate levels in the lysimeters were exceedingly high 

(Figure 2), exceeding 200 mg NO3-N/L at Day 44 of 

the study (September 9, 2004). Nitrate levels were 

above 100 mg NO3-N/L from Day 0 to Day 150 (midDecember 2004). Nitrate levels steadily decreased 

until around Day 200 (February 2005), then increased 

again. The average nitrate concentration in Field 1 was 

significantly (P < 0.05) higher than Field 2 (149 versus 

90 mg NO3

-N/L). This may have been due to the higher 

N application rate in the plots in Field 1 versus Field 2. 

Ground-water samples were collected from at least one 

lysimeter in Field 2 for a longer period of time compared 

to Field 1, thus accounting for the data beyond Day 320 

for Field 2. Trends in total N levels in lysimeter samples 

were similar to those of nitrate (Figure 3). 

Figure 2.		 Lysimeter nitrate concentrations as a function of 

time. Time zero is July 27, 2004, date of the first 

soil sampling. Days 100, 200 and 300 correspond 

to November 4, 2004, February 12, 2005 and 

May 23, 2005, respectively. Effluent applications 

occurred on August 3 and 18, 2004 for Fields 2 and 

1, respectively, or Day 6 and 21, respectively. Data 

are means across four plots (n = 4) within each 

field at a sampling date (LSD = 22.0 mg N/L). 

The discovery of higher than expected nitrate values 

at the beginning of the study was hard to explain at 

first, since N applications from effluent appeared 

to be insufficient to cause such elevated levels. As 

stated earlier, Adams et al. (1994) only found a high 

of 37 mg NO3

-N/L in a soil fertilized with manure 

containing 880 kg N/ha; an N application rate far in 

excess of what was applied to these fields. Moore et 

al. (2000) measured much lower nitrate levels in soil 

solutions on two typical poultry/beef farms in northwest 

Arkansas during a two year study, with the highest 

observed nitrate concentrations being 2.8 mg NO3-N/L, 

roughly 100 fold lower than the peak values found in 

this study. 

6 
 

 

 

Figure 3.		 Concentrations of total N (TN) in lysimeter 

ground-water samples as a function of time. 

Time zero is July 27, 2004, date of the first soil 

sampling. Days 100, 200 and 300 correspond 

to November 4, 2004, February 12, 2005 and 

May 23, 2005, respectively. Effluent applications 

occurred on August 3 and 18, 2004 for Fields 2 

and 1, respectively. Data are means across four 

plots within each field (n = 4) at a sampling date 

(LSD = 29.4 mg/L). 

Beginning in early November 2004, it was observed 

that the dairy farmer was using the two fields where 

effluent was applied for a loafing area for the cattle. 

Within a month of using this area for this purpose, the 

soil surface was covered in a layer of manure that was 

1-2 cm deep (direct deposits from the dairy cows). The 

assumption was made that using the effluent application 

fields for loafing areas was a direct violation of the 

nutrient management plan. However, personnel from 

USDA/NRCS and the University of Arkansas indicated 

that no such restrictions were in place and they routinely 

did not account for direct deposits of N and P when 

evaluating or developing NMP for effluent applications. 

The grower at this farm was using the two 4.05 ha 

(10-acre) spray fields as the dairy loafing area in the 

winter for all of his cows. Hence, 250 cows were 

being kept on roughly 8.1 ha (20 acres) all day, 

except when the cows were moved to and from the 

milking parlor. Thus, the stocking rate was about 

31 cows/ha (or 12.5 cows/acre). A typical dairy 

cow weighing 500 kg (1,100 lbs) excretes roughly 

0.23 kg N/day (0.5 lbs N/day) in manure and urine 

(USDA, 1992). Therefore, approximately 7 kg N/ha 

(6 lbs N/acre) were being added each day by the cattle 

via direct deposits. These fields were used as a loafing 

area for 3 to 4 months during the year of the study. 

Responses from the farmer indicate that use of these 

fields as a loafing area for 3 to 4 months annually had 

been a common practice for several years. If the fields 

were used as a loafing area for 90 to 120 days, then the 

total direct deposit of N from cattle would be 620 to 

820 kg N/ha (560 to 750 lbs N/acre). These estimates 

indicate that direct deposit of manures added three times 

the average amount of N that was added via effluent 

applications (i.e. 280 kg N/ha or 250 lbs N/acre). 

Thus, the total annual N loading on these fields was 

at least 800 kg N/ha and could easily have exceeded 

1,000 kg N/ha. 

As mentioned earlier, nitrate concentrations in ground 

water have been shown to be directly influenced by the 

amount of manure applied (Adams et al., 1994; Marriott 

and Bartlett, 1975). Results of Adams et al. (1994) 

indicated that N application rates from poultry litter 

additions had to exceed 440 kg N/ha for ground-water 

samples taken at 120 cm to exceed 10 mg NO3

-N/L. 

Results of Adams et al. (1994) predict that lysimeter 

NO3-N concentrations in this study should have been 

less than 10 mg NO3-N/L if N was being added only 

from the effluent applications. Lysimeter NO3-N 

concentrations in this study typically exceeded that 

observed by Adams et al. (1994) suggesting that the N 

application rate was in excess of the previous study’s 

highest rates, 880 kg N/ha. Therefore, total N input of 

at least 1,000 kg N/ha seems plausible, based on the 

observed nitrate-nitrogen concentrations in lysimeter 

samples. 

If most of the N additions to these soils were occurring 

from direct manure deposits during the winter, why did 

lysimeter nitrate values decline during this time period 

(Figure 2)? One possible explanation is that manure 

deposited on the soil surface during the winter did not 

start to break down until warmer weather in spring. The 

dominant N forms in dairy manure were not nitrate. 

Nitrate is the form of soil N most susceptible to leaching. 

Thus, significant mineralization of the N in the manure 

would have to occur to produce nitrate for leaching 

to be detected. This mineralization could account for 

the increases in lysimeter nitrate and total N levels 

beginning between Days 225 and 250 (mid-March 

2005) in Field 1 and between Days 275 and 300 (midJune 2005) in Field 2. Neither of these increases in 

lysimeter concentrations was due to additional effluent 

applications. Precipitation amounts during the winter 

months of 2005 were less than historical means 

(Figure 1), thus downward movement of nitrate and 

other N compounds into the soil profile would have been 

minimal. As spring progressed, warmer temperatures 

coincided with increases in precipitation. Increased 

precipitation and temperatures would have promoted 

both N transformation and downward movement of 

soluble water N compounds, thus explaining increases in 

lysimeter N concentrations after Day 250. 

Although the total N concentrations in lysimeter samples 

followed the same patterns as nitrate, the values were 

7 
 

 

about 25 percent higher (Figure 3). Total N is higher 

because it includes other forms of N, such as ammonium 

and organic N forms. Mean total N concentrations 

for Field 1 were higher than for Field 2 (189 versus 

108 mg N/L), as was the case for nitrate, and consistent 

with the higher N application rate on Field 1. Differences 

in average lysimeter concentrations between the 

two fields suggest that the addition of N via effluent 

application was sufficient to alter ground-water levels of 

nitrate and total N. 

Lysimeter ammonium values were less than those 

for nitrate (Figure 4). Twice during the experiment, 

ammonium values from the lysimeters in Field 1 

exceeded 4 mg N/L. One event occurred around 

Day 130 (early December 2004) and the other was 

observed around Day 230 (mid-March 2005). It is 

unclear what caused these spikes; they did not coincide 

with either effluent applications or high amounts of 

rainfall. The mean ammonium concentrations in soil 

solutions were significantly higher in Field 1 than 

Field 2 (4.4 versus 0.6 mg NH4

-N/L). These higher 

concentrations in the plots in Field 1 may have been due 

to the higher application rate of effluent, and thus, N. 

Figure 4.		 Ammonium concentrations in lysimeter 

ground-water samples as a function of time. 

Time zero is July 27, 2004, date of the first soil 

sampling. Days 100, 200 and 300 correspond 

to November 4, 2004, February 12, 2005 and 

May 23, 2005, respectively. Effluent applications 

occurred on August 3 and 18, 2004 for Fields 2 

and 1, respectively. Data are means across four 

plots within each field (n = 4) at sampling date 

(LSD = 1.97 mg/L). 

The amount of nitrate in the lysimeters was highly 

correlated with total N, as was organic N (Figure 5). 

However, ammonium was poorly correlated to total N 

concentrations. The slopes from these three relationships 

indicate that about 77 percent of the total N was nitrate, 

22 percent was organic N and 1 percent was ammonium. 

Figure 5.		 Relationship between concentrations of 

nitrate, organic N, and ammonium N to total N 

concentrations in lysimeter ground-water samples. 

Regression equations and regression coefficients 

(R) are presented in figure. 

It is somewhat unusual for shallow lysimeters installed 

in soils in northwest Arkansas to have ground-water 

samples for a majority of the year as observed in this 

study. Normally lysimeter samples can only be taken a 

few weeks of the year following heavy rainfall events. 

The soils in these two fields were a Jay silt loam, which 

is known to have a fragipan in the subsoil. The fragipan 

restricts the downward movement of water, thus leading 

to a perched water table in the subsoil for at least a 

portion of the year. Therefore, it is quite possible that 

the lysimeters were sampling water from this perched 

water table and that is the reason why lysimeter samples 

could be collected for a large part of the year. 

The chemical composition of the lysimeter samples, 

which contained high concentrations of nitrate and low 

levels of ammonium, indicate that the soil solution 

remained oxidized (under anaerobic conditions ammonia 

will not be oxidized to nitrate). This is somewhat 

surprising, since the deeper soil samples were often dark 

grey to blue in color, which normally indicates anaerobic 

conditions. However, the average iron and manganese 

concentrations in soil solution were only 0.21 and 

0.14 mg/L, respectively (data not shown), which also 

indicate oxidized conditions. Had anaerobic conditions 

been present, then denitrification should have occurred, 

since plenty of organic C was present. Concentrations of 

total organic C were typically near 50 mg C/L or above 

(data not shown). 

Soluble reactive P levels in the lysimeters were 

typically between 0.5 and 2.0 mg P/L, but increased to 

around 7 mg P/L in Field 1 halfway through the study 

(Figure 6). Soluble reactive P levels were significantly 

higher in Field 1 than Field 2 (1.60 versus 1.02 mg P/L). 

As with total N and nitrate concentrations, the 

8 
 

differences in soluble reactive P between the two fields 

indicate that the P additions via the effluent application 

were sufficiently large to affect ground-water sample 

concentrations. Typically, soil water P values taken from 

lysimeters at 1 m depth are much lower in northwest 

Arkansas, ranging between 0.01 to 0.05 mg P/L (Philip 

Moore, unpublished data). Total P concentrations of 

water samples taken from the lysimeters were also high 

(Figure 7). Total P values were only slightly higher than 

those for soluble reactive P (Figures 6 and 7), indicating 

that most of the P in the lysimeter samples was soluble 

reactive P. These data indicate that this soil was 

saturated with P. 

Figure 6.		 Concentrations of soluble reactive P in lysimeter 

ground-water samples as a function of time. 

Time zero is July 27, 2004, date of the first soil 

sampling. Days 100, 200 and 300 correspond 

to November 4, 2004, February 12, 2005 and 

May 23, 2005, respectively. Effluent applications 

occurred on August 3 and 18, 2004 for Fields 2 

and 1, respectively. Data are means across four 

plots within each field (n = 4) at a sampling date 

(LSD = 1.97 mg/L). 

As with N, a lot of the P present in these fields probably 

originated from direct deposits. A 500 kg dairy cow 

excretes roughly 0.03 kg P/day. If the field were used as 

loafing areas for four months with an average density of 

31 cows/ha, then roughly 110 kg P/ha (100 lbs P/acre) 

would have been deposited. While significant amounts 

of N may be lost via gaseous emissions, such as 

ammonia volatilization or possibly denitrification, the 

only loss mechanisms for P would be runoff or leaching. 

Soil Data 

One set of soil samples was taken prior to effluent 

application on Field 2. Three sets of soil samples were 

taken prior to effluent application on Field 1, and one set 

was collected the day after effluent application (i.e., 

August 19, 2004). Soil nitrate concentrations in the 

surface layer (0-5 cm) were high throughout the study 

(Figure 8). There appeared to be a definite response of 

soil nitrate concentrations in the surface layer to the 

effluent application in Field 1. Soil nitrate levels at 

the soil surface (0-5 cm) in Field 1 varied between 60 

and 100 mg NO3

-N/kg soil over the first four sampling 

dates, three prior to effluent application and one day 

after. Soil nitrate levels then increased over two-fold, 

exceeding 150 mg NO3-N/kg soil, during September and 

October 2004 (Days 30-100). This peak in soil nitrate 

levels appeared to occur in response to precipitation 

that occurred during September and October. Warm 

temperatures and adequate moisture are necessary 

for soil microbes to convert the N in the effluent to 

nitrate. Such a trend was less apparent in Field 2. Soil 

nitrate levels in the soil surface (0-5 cm) in Field 2 

averaged almost 200 mg NO3

-N/kg at the beginning of 

the study, and increased slightly in the samples on the 

second sampling date, which was 2 days after effluent 

application. Surface concentrations of soil nitrate 

decreased to approximately 80 mg NO3-N/kg soil by 

the fourth sampling date (Day 23). As with Field 1, 

soil nitrate concentrations in the surface layer (0-5 cm) 

increased between the fourth and fifth sampling dates 

and remained at an elevated level to approximately 

Day 100 (Figure 8). These results are consistent with 

a higher rate of N addition via the effluent to Field 1 

compared to Field 2. Soil inorganic N (nitrate plus 

ammonium) followed similar trends, but peaked between 

250 and 300 mg N/kg (Figure 9). Comparisons of 

the concentration of soil nitrate relative to inorganic 

Figure 7.		 Concentrations of total P in lysimeter groundwater samples as a function of time. Time zero is 

July 27, 2004, date of the first soil sampling. Days 

100, 200 and 300 correspond to November 4, 2004, 

February 12, 2005 and May 23, 2005, respectively. 

Effluent applications occurred on August 3 and 18, 

2004 for Fields 2 and 1, respectively. Data are 

means across four plots within each field (n = 4) at a 

sampling date (LSD = 2.43 mg/L). 

9 
 

 

 

 

N indicate that nitrate was the dominant inorganic 

N species in the soil, as was found in the lysimeter 

samples. 

Figure 8.		 Soil nitrate concentrations in samples taken 

from 0-5 cm depth as a function of time. Time 

zero is July 27, 2004, date of the first soil 

sampling. Days 100, 200 and 300 correspond 

to November 4, 2004, February 12, 2005 and 

May 23, 2005, respectively. Effluent applications 

occurred on August 3 and 18, 2004 for Fields 2 

and 1, respectively. Data are means across four 

plots (n = 4) within each field at a sampling date 

(LSD = 15.5 mg/L). 

Figure 9.		 Concentrations of soil inorganic N for samples 

taken from 0-5 cm depth as a function of time. 

Time zero is July 27, 2004, date of the first soil 

sampling. Days 100, 200 and 300 correspond 

to November 4, 2004, February 12, 2005 and 

May 23, 2005, respectively. Effluent applications 

occurred on August 3 and 18, 2004 for Fields 2 

and 1, respectively. Data are means across four 

plots within each field (n = 4) at a sampling date 

(LSD = 21.7 mg/L). 

Most of the soil nitrate and inorganic N was concentrated 

near the soil surface (Figures 10A and 10B). These 

data represent the means over the 20 samplings. The 

average nitrate concentration at the soil surface was 

exceedingly high in both fields - around 100 mg N/kg. 

Nitrate levels decreased in the soil profile to a minimum 

value of around 10 mg N/kg at the 20-40 cm depth, and 

then increased again as depth increased. Such increases 

in soil nitrate at depths greater than 40 cm are consistent 

with the existence of a layer at or below 1 m that was 

impeding the downward movement of soil water and 

nitrates. Soil inorganic N (which includes ammonium) 

followed the same trends (Figure 10B), but was higher, 

175 mg N/kg at the surface. 

Figure 10. Depth distribution of soil nitrate (panel A) and 

inorganic N (panel B). Data are means across 

four plots within each field and 20 sampling dates 

(n = 80). LSD values for comparing means are 

8.34 and 11.6 mg/L for soil nitrate and inorganic N, 

respectively. 

The water soluble soil P values were above 150 mg P/kg 

(300 pounds/acre) in the surface layer and decreased 

with depth to near zero at the 60-80 cm depth and 

below (Figure 11A). These values at the surface are 

extremely high and represent a “worst-case scenario” 

for the potential for P losses via run-off. Likewise, 

Mehlich III values between 1,250 and 1,500 mg P/kg in 

the surface layer (2,500 to 3,000 lbs P/acre) are higher 

than necessary for optimum crop growth (Figure 11B). 

Unlike soil N concentrations, there was no increase in 

soil P values at lower soil depths. The distribution of soil 

P in the upper 40 cm was unusual for pastures. Typically, 

there is a sharp decline in soil P values with depth 

(Brauer et al., 2005). 

In the past, Arkansas has made recommendations for 

NMPs where liquid manure is applied based on N. 

Hence, if the soil P values exceeded levels necessary 

for optimum crop growth, manure applications 

would still have been allowed. However, the state is 

10 
currently changing the policy for farms permitted under 

Regulation 5 (farms with liquid manure) so that they will 

have to use the Arkansas Phosphorus Index to determine 

application rates. At these levels of soil P, manure 

applications would not be allowed by the Arkansas P 

Index. 

Figure 11.		 Depth distribution of soluble reactive P (panel A) 

and Mehlich III P (panel B) concentrations in 

soil samples. Data are means across four plots 

within each field and 20 sampling dates (n = 80). 

LSD values for comparing means are 5.46 and 

39.7 mg/L for soluble reactive P and Mehlich III P, 

respectively. 

Forage Data 

As in the case of soil samples, one set of forage samples 

was collected prior to effluent application on Field 2 and 

three sets of samples were collected from Field 1 prior 

to effluent application. Nitrate concentrations in forage 

started out very high (near 3,200 mg NO3-N/kg forage 

in Field 1) at the beginning of the study (Figure 12). 

These high levels of nitrate may have been due to the 

nitrogen inputs from direct deposit of manures during 

the winter when the fields were used as a loafing area. 

Bermudagrass forage is usually considered a low risk 

for inducing nitrate toxicity in cattle because it does not 

tend to accumulate enough nitrate to induce toxicity 

(Strickland et al., 2008). In other studies, nitratenitrogen concentrations in bermudagrass forage did 

not exceed more than 400 mg NO3

-N/kg (dry weight) 

with N fertilizer application up to 100 kg N/ha (Hojjati 

et al., 1972). N fertilizer application rates of 200 to 

400 kg N/ha increased concentrations to 1,200 to 

1,600 kg NO3-N/kg. Toxicity of cattle to nitrates is low 

if the forage is less than 3,000 mg NO3-N/kg (Strickland 

et al., 2008). Forage nitrate concentrations in samples 

from Field 1 declined over the first four sampling dates, 

the last of which were collected the day after effluent 

application. Forage nitrate concentrations in samples 

from Field 1 were higher than the initial levels over 

the next four sampling dates. These increases in forage 

nitrate concentrations corresponded to increases in 

soil nitrate levels in the samples from the surface layer 

(0-5 cm). An increase in forage nitrate concentrations 

for samples from Field 2 during the early part of the 

study was not readily discernible. In general, forage 

nitrate concentrations decreased to a minimum of 26 mg 

NO3

-N/kg forage at Day 220 (February 26, 2005) and 

increased to over 2,000 mg NO3-N/kg by Day 274 

(April 21, 2005) in Field 1. The forage on this site 

was bermudagrass, which is a warm season grass. In 

northwest Arkansas, bermudagrass will become dormant 

around November 1 and will resume growth by May 1. 

During the winter months, nitrate, as well as other water 

soluble constituents, is leached from the forage, thus 

explaining the decrease in nitrate concentrations during 

the winter. 

Figure 12. Forage nitrate concentrations as a function of 

time. Time zero is July 27, 2004, date of the first 

soil sampling. Days 100, 200 and 300 correspond 

to November 4, 2004, February 12, 2005 and 

May 23, 2005, respectively. Effluent applications 

occurred on August 3 and 18, 2004 for Fields 2 

and 1, respectively. Data are means across four 

plots within a field (n = 4). Equation and regression 

coefficient (R) appear in figure. 

Metrics for Nitrate Leaching 

Prior to conducting this study we hypothesized that soil 

nitrate would be the best metric for predicting nitrate 

leaching. However, the relationship between soil nitrate 

concentrations at 80-100 cm and lysimeter nitrate levels 

was poor (y = -0.79x + 172, r = 0.08 (P > 0.10), data not 

shown). The best relationship between soil nitrate and 

lysimeter nitrate was with the samples taken from the 

0-5 cm depth (y = 0.56x + 92, r = 0.42 (P < 0.05), data 

not shown). Although this relationship is statistically 

significant, its predictive power is poor. 

11 
The best indicator of high concentrations of nitrate 

in soil solution was the forage nitrate concentrations 

(Figure 13). Many growers often have their hay analyzed 

for nitrate to make sure there is little or no potential 

for nitrate toxicity in their cattle. Forage nitrate 

concentrations followed the same seasonal patterns as 

did lysimeter nitrate concentrations, with the highest 

levels observed at the beginning and ending of study; 

i.e., during summer (Figure 13). 

Figure 13. Relationship between lysimeter nitrate and forage 

nitrate concentrations. Data are means across 

four plots within a field (n = 4) at eight sampling 

dates. Regression equation and coefficient (R) are 

presented in figure. 

12 
4.0 

Conclusions and Recommendations
 

The lysimeter nitrate concentrations and soil P 

concentrations observed in this study were orders of 

magnitude higher than what is normally observed 

in poultry/beef farms located in northwest Arkansas. 

The reason for these higher nutrient levels did not appear 

to be the effluent applications; but rather, they appeared 

to be due to direct manure deposits from dairy cattle 

as a result of using the fields as the loafing area for the 

cows during winter months. Beginning in November 

the surface of these fields became entirely covered with 

cow manure. Although the levels of nitrate found in 

lysimeters were often in excess of 100 mg NO3-N/L, it 

is not known if ground-water contamination actually 

occurred, since deeper wells were not installed to 

investigate this. 

When representatives from USDA/NRCS and University 

of Arkansas Cooperative Extension Service were 

interviewed about the mechanics of the NMP for liquid 

manures using Regulation 5, we discovered that the 

amount of nutrients deposited directly from the animals 

was not taken into consideration. Under normal grazing 

conditions, this practice would not cause a problem, 

since manure rates from grazing animals is normally 

less than what is applied via effluent. However, in dairy 

loafing areas, when dozens of dairy cows consuming a 

complete ration are stocked at a high number of animals 

per land area, then excessive nutrient applications can 

result. 

In hindsight, accumulation of N and P in the soils at 

this farm should have been expected. The 250 dairy 

cows on this farm would be expected to generate about 

21,000 kg N and 2,800 kg P in their manure annually, 

based on USDA estimates referenced earlier in this 

report. These amounts of excreted N and P calculate to 

be annual loading rates in excess of 700 kg N/ha and 

100 kg P/ha, assuming that only the 27 ha on the farm 

were available for deposition. 

The use of pastures or hay fields as HUA may be a 

difficult situation to correct for many dairy farmers. 

The cows must be kept within certain proximity of 

the dairy when days are short. In this case, these four 

fields receiving the effluent were the four closest fields 

to the milking parlor. The solution would be to spread 

the cows out over a greater area (make more fields 

into loafing areas), so that the manure concentrations 

would be reduced. In addition, the effluent from the 

holding pond should be applied to other fields that 

are not used for loafing. This is also problematic, 

since it requires piping the liquid manure greater 

distances on the farm, which increases the grower’s 

cost. However, this is one fairly simple solution that 

is easily implemented. Dr. Karl VanDevender is an 

Agricultural Engineer with the University of Arkansas 

Cooperative Extension Service and is in charge of 

Extension activities involving liquid manure applications 

in Arkansas. His recommendation for this problem is 

as follows: “Growers should decide whether they want 

to keep a field in pasture or use it as a HUA or loafing 

area. If it is kept in pasture, then the cow density and 

use duration should be kept down to the point where 

forage is maintained. These pastures would be subject 

to Phosphorus Index if additional manure (effluent) is 

applied, just as they would for a beef cattle operation. If 

the grower decides to make it a HUA, then he/she should 

design and manage to 1) minimize the area, 2) divert 

runoff water while it is clean, 3) scrape/clean surface as 

needed to avoid low spots, ponding, excessive manure 

accumulations, and 4) treat filter runoff water from HUA 

with filter strips and grass waterways.” This advice 

appears to be sound and well grounded. Efforts will also 

be made to restrict effluent applications on dairy loafing 

areas in the revised Arkansas P Index. It also appears that 

annual loading rates of N and P need to be considered at 

the farm level when NMPs are being developed. If such 

calculations had been performed in the preparation of 

this farm’s NMP, it should have been obvious that the 

31 ha was insufficient land area for application of the 

amount of waste created to avoid the buildup of nutrients 

in the soil. 

The best metric to be indicative of nitrate leaching was 

the forage nitrate concentration. Since growers do not 

want to feed cattle forages containing excessive nitrate 

levels, they would be willing to pay for forage nitrate 

analyses. Hence, we recommend that forage nitrate be 

routinely measured on spray fields receiving effluent 

to determine if excessive nitrate leaching is occurring. 

This would also serve a dual purpose of protecting 

cattle from poor quality vegetation. Forage sampling 

for nitrate analyses just prior to harvesting would 

provide indicators of utility of the hay for dairy cows 

and if future effluent application protocol needed to be 

adjusted. 

13 
 

5.0 

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