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1-1-2002

Review and Interpretation: Nitrogen Management

Strategies to Reduce Nitrate Leaching in TileDrained Midwestern Soils

Dana L. Dinnes

USDA-ARS Natl. Soil Tilth Lab.

Douglas L. Karlen

USDA-ARS Natl. Soil Tilth Lab.

Dan B. Jaynes

USDA-ARS Natl. Soil Tilth Lab.

Thomas C. Kaspar

USDA-ARS Natl. Soil Tilth Lab.

Jerry L. Hatfield

USDA-ARS Natl. Soil Tilth Lab.

See next page for additional authors

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Dinnes, Dana L.; Karlen, Douglas L.; Jaynes, Dan B.; Kaspar, Thomas C.; Hatfield, Jerry L.; Colvin, Thomas S.; and Cambardella,

Cynthia A., "Review and Interpretation: Nitrogen Management Strategies to Reduce Nitrate Leaching in Tile-Drained Midwestern

Soils" (2002). Publications from USDA-ARS / UNL Faculty. Paper 263.

http://digitalcommons.unl.edu/usdaarsfacpub/263
Authors

Dana L. Dinnes, Douglas L. Karlen, Dan B. Jaynes, Thomas C. Kaspar, Jerry L. Hatfield, Thomas S. Colvin,

and Cynthia A. Cambardella

This article is available at DigitalCommons@University of Nebraska - Lincoln: http://digitalcommons.unl.edu/usdaarsfacpub/263
REVIEW AND INTERPRETATION

Nitrogen Management Strategies to Reduce Nitrate Leaching in Tile-Drained

Midwestern Soils

Dana L. Dinnes,* Douglas L. Karlen, Dan B. Jaynes, Thomas C. Kaspar, Jerry L. Hatfield,

Thomas S. Colvin, and Cynthia A. Cambardella

ABSTRACT ricultural fields, and increased use of manufactured N

fertilizers. Balancing the amount of N needed for optimum plant growth while

minimizing the NO Less than 50 yr ago, corn (Zea mays L.) was generally 3 that is transported to ground and surface waters

remains a major challenge for everyone attempting to understand grown in rotation with cereal crops and forage legumes

and improve agricultural nutrient use efficiency. Our objectives for such as alfalfa (Medicago sativa L.), red clover (Trifothis review are to examine how changes in agricultural management lium pratense L.), and sweetclover (Melilotus spp.).

practices during the past century have affected N in midwestern soils Through biological N fixation, the legumes generally

and to identify the types of research and management practices needed increased the amount of residual N in the soil profile.

to reduce the potential for nonpoint NO3 leakage into water resources. Cycling of this residual, biologically fixed N along with Inherent soil characteristics and management practices contributing N mineralized from SOM added with animal manure

to nonpoint NO3 loss from midwestern soils, the impact of NO3 loading or deposited through rainfall was the primary process on surface water quality, improved N management strategies, and through which corn and other grain crops obtained N. research needs are discussed. Artificial drainage systems can have a Following World War II, increased availability of significant impact on water quality because they behave like shallow, commercial N fertilizer and decreased demand for for- direct conduits to surface waters. Nonpoint loss of NO3 from fields

age crops led to a significant reduction in crop rotations to water resources, however, is not caused by any single factor. Rather,

it is caused by a combination of factors, including tillage, drainage, and a general substitution of purchased N for biological

crop selection, soil organic matter levels, hydrology, and temperature N. In Iowa, forage pasture represented more than 33.6%

and precipitation patterns. Strategies for reducing NO3 loss through (3 389 160 ha) of the state’s total cropped area at the

drainage include improved timing of N application at appropriate end of World War II (U.S. Dep. of Commerce, Bureau

rates, using soil tests and plant monitoring, diversifying crop rotations, of the Census, 1945). By 1997, forage pasture area in using cover crops, reducing tillage, optimizing N application tech- Iowa comprised only 12.8% (1 393 451 ha) of the state’s niques, and using nitrification inhibitors. Nitrate can also be removed total cropped area (USDA Natl. Agric. Stat. Serv., from water by establishing wetlands or biofilters. Research that is 1997). Incorporation of legumes into a crop rotation focused on understanding methods to minimize NO3 contamination was no longer needed as commercial N inputs gradually of water resources should also be used to educate the public about replaced biological N fixation. the complexity of the problem and the need for multiple management The increased availability of commercial N also facili- strategies to solve the problem across agricultural landscapes.

tated specialization and a national trend for separating

crop and animal production enterprises. Animal manure

no longer served as an important crop nutrient resource, Nitrogen is essential for growth and reproduction and meadow legumes were not required on farms that of all life forms, and except for legume crops and began to specialize in corn and soybean [Glycine max virgin soils with relatively high soil organic matter (L.) Merr.] production. Although there is considerable (SOM), soil N must usually be supplemented to sustain variation among years and regions in N fertilizer usage, food, feed, and fiber production. During the past 20 yr, the net result of this farming-system change was a na- public concern regarding N movement from agricultural tional average increase in commercial N fertilizer use nonpoint sources into broader water resources has in- of 2.4 kg ha1 yr1 (Fig. 1) between the mid-1960s and creased as problems such as hypoxia (Rabalais et al., the late 1990s. The rise in commercial N fertilizer usage 1996) became more evident. To understand current within Midwest states (Illinois, Iowa, Indiana, Michigan, questions about N management in the U.S. northern Minnesota, Missouri, Nebraska, Ohio, and Wisconsin) Corn and Soybean Belt, it is necessary to examine the has slowed, with average use of commercial N fertilizer changes that have occurred in agriculture during the past increasing by 4 kg ha1 (0.5 kg ha1 yr1 ) from 1991 to century. These changes include the use of less diversified 1999 (Fig. 2). However, the trend of steadily increased crop rotations, separation of crop production and animal usage of commercial N fertilizer may change if fossil fuel enterprises, changes in tillage intensity, drainage of ag- prices increase substantially and the fertilizer industry is

USDA-ARS Natl. Soil Tilth Lab., 2150 Pammel Dr., Ames, IA 50011. Abbreviations: LCD, localized compaction and doming; LSNT, lateReceived 27 Apr. 2001. *Corresponding author (dinnes@nstl.gov). spring nitrate test; NIR, near infrared; PSNT, presidedress soil nitrate

test; SI–CD, subirrigation with controlled drainage; SOM, soil organic

Published in Agron. J. 94:153–171 (2002). matter; WTM, water table management.

153
154 AGRONOMY JOURNAL, VOL. 94, JANUARY–FEBRUARY 2002

Fig. 1. Average U.S. commercial N fertilizer use for corn production

for the years 1964–1998.

Fig. 2. Average commercial N fertilizer use in the Midwest for corn

production for the years 1991–1997. unable to develop lower-cost energy sources or new

strategies for fertilizer N production. An alternative to wet condition of these soils was modified by installation commercial N fertilizer inputs would be to reconsider of artificial drainage, tillage to prepare a seedbed for some of the traditional N management practices, espe- agricultural crops, and a change from perennial to sea- cially if they can be made more efficient and predictable sonal vegetation (Hewes and Frandson, 1952). With by applying 21st century technologies. these changes, the potential for mineralization of N from In addition to decreased diversity in crop rotation, the stored organic matter and N loading of surface wa- separation of crop and animal production enterprises, ters increased significantly. As stated by Randall (1997), and use of more commercial N fertilizers, an even more “Soils high in organic matter can mineralize a substantial dramatic change affecting N cycling within many mid- amount of nitrate-N which is susceptible to loss in sub- western soils was the installation of artificial subsurface surface tile drainage, especially when wet years follow drainage lines. Subsurface drainage lines began to be very dry years.” Collectively, the unintended side effect installed in the late 1800s in the Midwest, intensified of these changes in cultural practices and N management in the next century (Hewes and Frandson, 1952), and strategies has been an apparent reduction in N-cycling continues today. By 1987, more than 20.8 106 ha in efficiency compared with natural ecosystems or crop the states of Illinois, Indiana, Iowa, Ohio, Minnesota, production systems that have little to no reliance on Michigan, Missouri, and Wisconsin had been artificially commercial N inputs. drained (Zucker and Brown, 1998) in contrast to ap- Each agricultural region has its own specific environ- proximately 2 106 ha being irrigated in the same states mental challenges or imbalances associated with land (USDA Natl. Agric. Stat. Serv., 1999). Subsurface artifi- use decisions and crop production practices. In the Mid- cial drainage thus preceded and occurred in coincidence west, artificially drained areas, increased use of synthetic with other management changes in midwestern agricul- fertilizers, and decreased diversity in crop rotation are ture, most likely catalyzing other crop production and among the most notable causes of this region’s problem field management changes. with N contamination of water resources. The objectives Drainage was deemed necessary and strongly pro- of this review are to (i) examine the scope of the NO3 moted for the betterment of farmers, communities, and leaching problems associated with artificially drained the nation as a whole because natural surface drainage midwestern soils, (ii) discuss current strategies for reduc- was limited throughout much of the region. As a result, ing NO3 losses from these soils, and (iii) identify future the landscape was significantly changed, and many areas research needs to develop new strategies for reducing that were previously classified as prairie potholes could NO3 leaching losses. The desired impact of research on now be converted to row crop production. Artificial field- and watershed-scale NO3 loss and opportunities drainage and an increased availability of N fertilizers for improving overall water quality by increasing N use are two of the most prominent practices that facilitated efficiency are discussed. a tremendous increase in the intensity of agricultural

production throughout the midwestern USA. These

changes had enormous positive impact on the agricul- NITRATE LEACHING LOSSES FROM

AGRICULTURAL SYSTEMS tural economy and the expansion of agricultural exports.

However, they drastically altered the farming practices We will focus the attention of this paper on the NO3

that had evolved within the midwestern landscape and form of N because a number of leaching and drainage

contributed to changes in soil and water quality that studies have consistently found that NO3 is the dominant

had an impact far beyond farm fields. form of N present in the soil water (Willrich, 1969; Baker

The ecosystem effects of artificial subsurface drainage et al., 1975; Kladivko et al., 1991; Jacinthe et al., 1999).

in the Midwest were compounded because many of the Soil NO3 can be derived from both organic and inorganic

soils that had developed under a subhumid climate, in N. Whether the N source is animal manure or commerareas of low relief and poor surface drainage, had high cial N fertilizer, overapplication or ill-timed application

(5–6%) levels of organic matter. The predominately of either source can provide too much plant-available
DINNES ET AL.: STRATEGIES TO REDUCE NITRATE LEACHING IN MIDWESTERN SOILS 155

N and increase the potential for NO3 leaching (Hatfield surface waters (Hatfield et al., 1998; Hatfield et al.,

and Cambardella, 2001). Animal manure N sources pro- 1999).

vide many physical, chemical, and biological benefits to Current practices of N fertilizer management are ofthe soil environment beyond that of inorganic commer- ten very inefficient compared with natural systems, thus

cial N sources (Hatfield and Cambardella, 2001), and a increasing the potential for contamination of water rethorough discussion of these aspects and the N dynamics sources (Sanchez and Blackmer, 1988; Kanwar et al.,

of manures would be very extensive. Therefore, within 1993, 1996; Randall, 1997; Randall et al., 1997a; Cambarthis review, we will not specifically discuss manure man- della et al., 1999). As a result, first-year recoveries of

agement issues. Instead, we will focus on commercial fertilizer N by corn have been reported to be 35% (Bijerfertilizer and soil or crop management impacts on NO3 iego et al., 1979), 14 to 65% (Meisinger et al., 1985), 23

leaching. to 45% (Kitur et al., 1984), 24 to 26% (Olson, 1980),

Nitrate contributes to surface water degradation 15 to 33% (Sanchez and Blackmer, 1988), and 45 to 59%

when it flows into subsurface drainage lines that dis- (Reddy and Reddy, 1993). Based on these N fertilizer

charge into streams and lakes or when it leaches below recovery studies, one factor contributing to low fertilizer

the active plant-root zone and into shallow ground water N recovery is that in any given year, corn plants can

resources that connect to surface water bodies through obtain up to 85% of their N from mineralized SOM.

natural processes such as baseflow. The intensification The potential impact of soil-derived N can be illusof row crop production as a whole, not just the increased trated by estimating the amount of plant-available N

use of N fertilizers, has been identified as the primary associated with the SOM in many midwestern soils. Assuming there is approximately 4.5 106 cause for increased NO3 contamination of surface waters kg of soil per

during the past several decades (Keeney and DeLuca, hectare in the surface 30 cm and an average 10:1 C/N

ratio for the SOM, there would be 4500 kg N ha1 1993). This is especially true for continuous corn produc- for

tion, which has repeatedly been identified as providing 1% SOM. Therefore, crops grown on a soil with 3%

the greatest amount of NO3 to streams through subsur- SOM, which would be about average for the subhumid

face drainage (Kanwar et al., 1993; Weed and Kanwar, Midwest, would have the potential to obtain 13 500 kg

N ha1 1996; Randall et al., 1997a). just from the SOM. Obviously, only a small

Field drainage systems can have a significant impact percentage of this soil-derived N would be available at

on water quality because they behave like shallow, di- any given point in time because it must first be mineralrect pipelines or conduits to surface waters. They in- ized by microbes to a plant-available form such as NH4

crease the speed with which water moves off the land- or NO3 and the amount mineralized may not be enough

scape by short-circuiting natural water flow into shallow to meet crop N needs during rapid growth periods.

ground water. Nutrients and pesticides are often trans- Schepers and Mosier (1991) stated that for a given

ported with subsurface drainage water directly into climatic region, a general estimate of N mineralization

streams or lakes (Baker and Johnson, 1981; Buhler et could be made based on SOM content. They estimated

al., 1993; Jayachandran et al., 1994; Kladivko et al., 1991; that assuming 2% of the total organic N in the surface

Randall et al., 1997a). Numerous studies have shown 30 cm is mineralized annually, a soil with 1% SOM

significant edge-of-field losses of NO3 (Hanway and content could be expected to mineralize approximately

45 kg N ha1 yr1 Laflen, 1974; Gast et al., 1978; Miller, 1979; Benoit, 1973; . It is important to remember that these

Logan et al., 1980; Baker and Johnson, 1981; Bergstro ̈ m, are general estimates because the amount of organic N

1987; Kanwar et al., 1988; Drury et al., 1996). One exam- made available through mineralization processes will

ple is a study reported by Baker et al. (1975) where vary greatly over time due to factors such as temperathey found average NO3–N concentrations of 21 mg L ture, precipitation, and tillage (Doran, 1980; Franzlueb- 1

in subsurface drainage water leaving fields planted to bers et al., 1995; Wienhold and Halvorson, 1999). Howcorn–soybean or corn–oat (Avena sativa L.) rotations. ever, because of their high SOM levels, these estimates

Similarly, for a 5130-ha watershed located on the Des illustrate that midwestern soils have a high potential for

Moines lobe in central Iowa, Jaynes et al. (1999) re- providing N throughout the entire growing season.

ported flow-weighted NO3–N concentrations in field With regard to N management, including both fertiland county agricultural drainage lines that were often izer and manure application, the SOM-N pool is exgreater than the USEPA maximum contamination level tremely important for midwestern soils. Routine soil

(MCL) for drinking water of 10 mg L and crop management decisions not only affect the min- 1

, especially from

April through July. Combining stream flow and NO3–N eralization process per se, but also the rates and timing

concentration data for this intensively row-cropped ag- of N release through interactions between the microbial

ricultural watershed showed that total NO3–N losses communities and practices such as drainage or tillage

ranged from 4 to 66 kg ha1 yr1

. The variation in NO3–N and/or residue management. As a result, fertilizer N

losses among years was directly linked to variation in that is not taken up by the crop to which it was applied

annual precipitation (Hatfield et al., 1998). Those water- can have many different fates. If rainfall is below normal

shed-scale measurements also showed that 45% of the for midwestern conditions, NO3 can accumulate within

average annual precipitation was drained from the soil the soil profile. It can also be leached below the active

profile through the subsurface drainage lines. This em- plant root zone; lost through denitrification; or incorphasizes the importance of these drainage lines as a porated, cycled, and stabilized within many different

primary pathway for herbicide and NO3 movement to SOM-N pools. These factors significantly affect N man-
156 AGRONOMY JOURNAL, VOL. 94, JANUARY–FEBRUARY 2002

agement in midwestern soils. For example, in Iowa to these processes increases as the time between N applialone, Swoboda (1990) reported that failure to account cation and crop uptake increases. This is true for residfor residual N caused farmers to annually spend approxi- ual N as well as applied N (Magdoff, 1991; Karlen et

mately $100 million on excess N fertilizer applications. al., 1998), especially in years that do not produce optimal

This is not only an on-farm economic waste, but also yields (Power et al., 1998). Limiting the amount of inoran environmental waste with regard to both water qual- ganic N within the soil at the end of a crop’s growing

ity and the fossil energy needed to manufacture N fer- season and before the next crop has established an extilizer. tensive root system is a key factor for reducing N losses.

Nonpoint contamination is a major water quality con- Therefore, although timing, method of N application,

cern throughout the Midwest (Humenik et al., 1987), and accounting for mineralizable soil N are important

and use of N fertilizers on artificially drained agricul- for reducing potential NO3 leaching, Power and Scheptural land has been implicated as a major contributor ers (1989) concluded that the most important factor was

to this problem (USEPA, 1992; U.S. Geological Survey, to apply the correct amount of N fertilizer.

1995; CAST, 1999). The 1992 national water quality Typical N fertilizer management for corn production

inventory (USEPA, 1992) notes that in the rivers stud- in the subhumid Midwest currently consists of a single

ied, 72% of the water quality problems were attributed preplant application, usually in autumn before the year

to agriculture. Plant nutrients have been identified as that corn is grown. This practice was promoted by agsurface-water contaminants throughout the Midwest (Ba- ricultural experts because the potential for soil compacker, 1988; Thurman et al., 1992; USEPA, 1992; Goolsby tion following harvest is generally less, labor is often

and Battaglin, 1993). Nitrate N concentrations in excess more available, weather and soil conditions are generof 10 mg L1 in drinking water may pose risks to humans ally more favorable, and fertilizer prices are frequently

and livestock (USDA, 1991; Tyson et al., 1992) and lower than in the spring. However, fall application

have cost some communities millions of dollars for their places the applied N in the soil several months before

removal or to provide alternate drinking water sources. the crop needs it, and thus increases the potential for

For example, Des Moines, IA alone has spent in excess of leaching or other losses. Sanchez and Blackmer (1988)

$4.8 million for NO3 removal from drinking waters be- reported that 49 to 64% of the fall-applied fertilizer N

tween 1991 and 1999 (G. Benjamin, unpublished data, was lost from the upper 1.5 m of the soil profile through

2000). pathways other than plant uptake.

Nitrogen loadings into the Mississippi River and its Changing the timing of a single preplant fertilizer

tributaries have also been identified as a potential cause application from fall to spring could significantly defor degradation of freshwater and marine ecosystems. crease N loss and increase fertilizer use efficiency. This

Elevated N concentrations have altered natural aquatic was demonstrated for southern Minnesota (Randall et

floral and faunal population dynamics, exacerbated oc- al., 1992; Randall, 1997) where spring application incurrences of hypoxia and anoxia, and sped the process creased N use efficiency by more than 20% compared

of eutrophication in the Gulf of Mexico (Alexander et with fall N application. In addition, annual NO3 losses

al., 1995; Rabalais et al., 1996). Turner and Rabalais from tile drainage were reduced by an average of 36%.

(1991) reported that increased levels of NO3 in the Mis- Despite the opportunities for increased nutrient use effisissippi River have paralleled increased use of commer- ciency and decreased loss of N through drainage waters,

cial fertilizer throughout the river basin and increased many farmers continue fall fertilizer applications to minseverity of hypoxic events in the Gulf of Mexico since imize real and perceived risk. Spring rainfall patterns

the 1950s. Alexander et al. (1995) estimated that drain- can result in very wet soils and prevent or delay N

age from the Upper and Central Mississippi Basins (in- fertilizer applications. This risk is very real because there

cluding portions of Minnesota, Wisconsin, Iowa, Mis- are few options in most rainfed farming operations to

souri, and Illinois) accounts for 39% of the N delivered compensate the farmer for yield losses and reduced

to the Gulf. This is the largest estimated source fraction income associated with an inadequate N supply. Thereamong the Mississippi River’s various drainage basins. fore, to achieve significant farmer adoption of N management practices other than fall fertilization, concepts

STRATEGIES FOR IMPROVED NITROGEN such as insurance policies against N deficiencies are

MANAGEMENT needed along with more flexible and efficient application methods. Timing of Application and Nitrogen Rates Power et al. (2000) reported that midwestern fields

Many attempts to reduce NO3 concentrations in shal- frequently have a high degree of variability in soil NO3

low ground-water draining to tiles have focused on tim- content from site to site within a single field. They stated

ing and N application rate. Randall (1997) stated that that “. . . soils are seldom uniform throughout a field,

“. . . fertilizer N management, particularly rate and time so applying sufficient fertilizer N to assure high yields

of application, plays a dominant role in the loss of nitrate for more productive areas of the field often results in

to surface waters.” The challenge is to manipulate N over-fertilization of the less productive areas. This may

availability before, during, and after peak crop demand. lead to greater nitrate leaching, particularly in those

Nitrogen molecules are susceptible to leaching, denitri- areas of the field that are more susceptible to leaching.”

fication, volatilization, and immobilization processes Kranz and Kanwar (1995) estimated that within a given

within the soil environment. The risk of N losses due field, 70% of the NO3 leached typically comes from
DINNES ET AL.: STRATEGIES TO REDUCE NITRATE LEACHING IN MIDWESTERN SOILS 157

30% of its area. To be effective, variable-rate technology must accurately identify within-field spatial and

temporal variability and reliably interpret these patterns

of variability (Sawyer, 1994). If this is accomplished, a

reliable variable-rate or site-specific N fertilizer application program could reduce application on areas requiring little to no additional N to optimize yield (Dinnes

et al., 1998) and could limit application on areas sensitive

to leaching and surface runoff (Larson and Robert,

1991). Methodologies to accurately assess within-field

spatial and temporal variability for subsequent N application, however, have yet to be fully developed.

Most conventional methods of N fertilizer recommendation were developed on a state or regional scale, so

it is questionable whether these methods can reasonably Fig. 3. General seasonal patterns for precipitation, N uptake rate by be used for variable-rate N management that attempts a corn crop, cropping system water use, and periods potentially to account for within-field spatial and temporal variabil- favorable for NO3 leaching from midwestern corn production

ity (Hergert et al., 1997). Several research studies have (adapted from Fig. 4 of Power et al., 1998).

found large differences in crop yield and crop N response within individual fields (Ferguson et al., 1995; to slow NO3 accumulation include use of nitrification

Kitchen et al., 1995; Vetch et al., 1995), confirming the inhibitors (Kidwaro and Kephart, 1998) or temporary

need for reliable methods to generate site-specific N immobilization by cycling N through cover crops (Doran

recommendations (Hergert et al., 1997). and Smith, 1991; Staver and Brinsfield, 1998; Wagger

Pierce and Nowak (1999) discussed three basic man- et al., 1998). Minimizing NO3 accumulation until the

agement approaches currently being tested for variable- primary crop is actively growing can generally reduce

rate N application. The first involves determining plant- leaching loss because, by that time, plant water use will

available N levels from field grid sampling and interpre- generally exceed available precipitation (Hatfield et al.,

ting N rates based on current recommendation methods 1998; Power et al., 1998).

(i.e., a N balance equation). The second approach bases Monitoring N mineralization to better match the reN rates on observed crop N responses using replicated quired amount of available N with crop needs is one

strips with varying N rates across the landscape. The strategy for reducing NO3 leaching potential. To accomthird approach involves determining crop N status by plish this task, several versions of a presidedress soil

monitoring (i.e., light reflectance or chlorophyll con- nitrate test (PSNT) (Magdoff et al., 1984; Fox et al.,

tent). Usually this intervention-type approach uses a 1989; Magdoff et al., 1990) or modifications such as the

portion of the crop that is well fertilized as a standard late-spring nitrate test (LSNT) (Blackmer et al., 1997)

for comparison. The best approach for a particular field, have been developed. These tests generally involve sambe it conventional or site-specific, will depend on the pling the soil approximately 6 wk after planting. The

amount of spatial and temporal N variability (Pierce philosophy behind the tests is that by late spring, the net

and Nowak, 1999). Pan et al. (1997) reported that tem- effects of mineralization, leaching, and other potential

poral N variability could frequently exceed spatial vari- losses that may have occurred since the last crop was

ability. While highly predictable spatial variability may harvested can be accurately assessed. Soil test results

be amenable to multiple approaches of site-specific N can then be used to determine the appropriate amount

management, strong temporal variability is much more of additional N fertilizer to apply.

difficult to manage (Pierce and Nowak, 1999). In this Plot-scale studies using PSNT or LSNT strategies to

case, Pierce and Nowak (1999) concluded that an inter- determine fertilizer N rates have generally shown reductions in measured or potential NO3 vention strategy would be the most appropriate option. leaching. In Iowa,

these procedures resulted in fertilizer N applications

ranging from 50 to 168 kg N ha1 and significantly re- Crediting Nitrogen Mineralization duced NO3 loss to subsurface drainage tiles compared

Nitrate, as an end product of mineralization and sub- with single preplant applications of only 112 kg N ha1

sequent nitrification of SOM, manure, crop residue, or (Kanwar et al., 1996). A study in Vermont (Durieux et

previously applied fertilizer N that has cycled through al., 1995) also reduced leaching potential compared with

soil organic N pools, can make significant contributions a yield-goal N management strategy. In this 3-yr study,

toward meeting crop N requirements (Oberle and the PSNT–LSNT N management program resulted in

Keeney, 1990; Kanwar et al., 1996). However, to ensure fertilization rates of 112, 123, and 123 kg N ha1 and

NO3 is used efficiently, it is important to quantify the corresponding residual soil NO3 levels in the upper 1.2

amount being produced and, where possible, minimize m of the soil profile of 87, 68, and 44 kg N ha1 in the

its accumulation during noncropping periods. This strat- fall. In contrast, the yield-goal management program

egy is important when crop uptake is minimal or nonex- required 168 kg N ha1 and resulted in residual soil NO3

istent because much of the NO3 produced during those levels in the upper 1.2 m of the soil of 138, 160, and 156

kg N ha1 periods is susceptible to leaching (Fig. 3). Strategies , respectively. These plot-scale results suggest
158 AGRONOMY JOURNAL, VOL. 94, JANUARY–FEBRUARY 2002

that the PSNT–LSNT approach for N management has Hanna et al. (1999) measured anhydrous NH3 distrithe potential for avoiding excess N application com- bution for several manifold designs during field applicapared with yield-goal approaches (Magdoff, 1991; Du- tion at three flow rates (56, 112, and 168 kg N ha1 ).

rieux et al., 1995; Kanwar et al., 1996; Randall, 1997; This experiment accounted for dynamic vibration of the

Karlen et al., 1998). However, while designed to provide applicator’s distribution system, which can affect the

an optimum N fertilizer rate at an appropriate time to anhydrous NH3 vapor–liquid phase separation within

improve crop N use efficiency, the impacts on water the manifold. They found that a Vertical Dam maniquality and risk to the farmer for adopting this approach fold had less variability than a conventional manifold

have been poorly quantified at the whole-field scale and at the 56 kg N ha1 rate. At the two higher N rates,

have only begun to be evaluated at the watershed scale. they detected little difference in variability between the

A regional study (Bundy et al., 1999) determined that two designs. When examining flow rates by manifold

the PSNT–LSNT program at the watershed scale failed outlet location in relation to incoming flow, Hanna et

to identify some field sites where a yield response to N al. (1999) found that the highest flow rates came from

fertilizer was not achieved. Their follow-up investiga- outlet ports located directly across from the incoming

tion found that such errors were reduced by increasing flow port. Next highest flow rates came from outlet

the soil-sampling depth from 30 to 60 cm (Bundy et al., ports near the incoming flow port. They theorized that

1999). The end-of-season basal stalk NO3 test (Blackmer this was due to flow reflected from the opposite side of

and Mallarino, 1997) has also been used to verify the the manifold chamber. The least amount of flow came

accuracy of the PSNT–LSNT program. Stalk NO3 con- from outlet ports located on both sides perpendicular

centrations are categorized into four groups: low (250 to the incoming flow path. The conventional manifold

mg kg1 NO3 ), marginal (250–700 mg kg1 NO3 ), opti- exhibited these traits to a stronger degree than alternamal (700–2000 mg kg tive designs, but all manifolds showed similar patterns. 1 NO3 ), and excess (2000 mg

kg1 NO3 ). Although the information does not assist in Liquid N fertilizer applicators tend to have less variacorrecting in-season deficiencies, it is useful for guiding tion in fertilizer distribution across all outlets along the

future operations to improve N use efficiency. This test implements’ toolbars than conventional anhydrous NH3

is helpful in assessing the performance of any N man- applicators. Recently, liquid N fertilizer applicators

agement program for corn production (Magdoff, 1991; have become even more accurate with the use of hydrauBlackmer and Mallarino, 1997). lic flow rate control devices. With careful installation

and calibration, applied rates can easily be within 1 to 4% Fertilizer Application Equipment of the target rate (Dinnes et al., unpublished data, 2000).

When measuring the efficiency of any system, the Some recent innovations in the design and function

of N fertilizer application equipment have focused on variation or error of each step is additive. Therefore, strategies to limit N losses from leaching, volatilization, the overall efficiency is only as good as the summed

margins of error for each step. For site-specific N man- and runoff. One, a localized compaction and doming

(LCD) applicator (Ressler et al., 1997), was developed agement, attempting to apply variable N rates will do to alter soil physical properties immediately above the little to improve overall N fertilizer use efficiency if the soil volume where knife-injected liquid N fertilizer was application equipment has a high degree of error. This placed. A compacted zone with a higher bulk density problem was confronted in studies examining the per- is created above the injection zone so that water infil- formance of conventional anhydrous NH3 manifolds.

Weber et al. (1993) found appreciable degrees of error tration through that area would be reduced compared

with a conventional knife-injection applicator. When over entire fields, and other investigators documented compared with either conventional knife or broadcast large degrees of error across the individual outlets of methods of N application, the LCD design reduced the the equipments’ manifolds (Reichenberger, 1994; Fee, amount of NO3 leaching following an intense rainfall 1997; Schrock et al., 1999).

Research efforts have concentrated on evaluating that occurred soon after fertilizer application (Ressler

new technology to reduce equipment application error. et al., 1998).

Boyd et al. (2000) conducted an evaluation of anhydrous Another application technique developed to imNH prove N management was the point injector, which un- 3 manifolds under field conditions at two target application rates (84 and 168 kg N ha1 ). Several anhy- der no-till conditions, was demonstrated to have the

drous NH potential to reduce NH3 volatilization and N immobili- 3 manifold entry methods were used for conventional manifolds, and although each method had zation at the surface without destroying surface residues

differing coefficients of variation at both N rates, all or adversely affecting corn yield (Baker et al., 1985). In

had similar trends, with greater coefficients of variation Minnesota (Randall et al., 1997b), point injection of

at 84 kg N ha1 (12–80%) than at 168 kg N ha1 (10– urea ammonium nitrate resulted in greater corn grain

66%). Alternative manifold designs typically performed yield and total N uptake compared with surface-broadbetter than conventional manifolds at both rates, with cast or banded urea ammonium nitrate in a ridge tillage

less variability at the high rate. Rotaflow and small- system. Additional agricultural drainage studies in Iowa

housing Vertical Dam manifolds produced the least from 1995 through 1997 (Iowa Dep. of Agric. and Land

amount of variability across all outlets at both the low Stewardship, 1997) showed that both LCD and point

and high N rates. A John Blue FD-1200 manifold had injection methods consistently reduced NO3 concentraa low variability at the higher rate. tions in tile drainage water compared with conventional
DINNES ET AL.: STRATEGIES TO REDUCE NITRATE LEACHING IN MIDWESTERN SOILS 159

knife-injection methods. In addition to having the lowest 1988). The variable results with nitrapyrin use are probNO3 concentrations in the drainage water, the LCD ap- ably due to differences among factors affecting the miplication method also resulted in the highest corn grain crobial process of nitrification (e.g., climate and soil

yield. type). Further research should focus on quantifying

those factors to determine when and where the use of

Nitrification Inhibitors nitrapyrin will be most beneficial.

Nitrification inhibitors for N fertilizers have met with Chlorophyll Monitoring varying success, generally depending on soil type and

weather pattern under which they were used. These Other methods of monitoring N availability for corn

inhibitors function by limiting the activity and popula- have also been used to guide in-season fertilizer application of Nitrosomonas bacteria that convert NH4 to NO2. tions. In some studies, chlorophyll measurements have

The primary use for nitrification inhibitors in the Upper been shown to correlate well with N concentrations in

Midwest is to slow the conversion of fall-applied anhy- the plant tissue and to have the ability to predict grain

drous NH yield (Wood et al., 1992; Siambi et al., 1999). In Pennsyl- 3 fertilizer to the more leachable NO3 form,

thus potentially reducing N fertilizer losses before peak vania, Piekielek and Fox (1992) showed that the chloroN demand by subsequent corn crops. phyll meter measures were as accurate as several soil

An 8-yr project in Ohio (Stehouwer and Johnson, N availability tests (NO3 concentration of the surface

1990) examined different application timings with and 20 cm of soil at planting, ultraviolet absorbance at 200

without a nitrification inhibitor. The results showed that nm of a 0.01 M NaHCO3 extract of the surface 20 cm

at similar N rates, spring preplant application of urea of soil at planting, and PSNT) in identifying N responsive and nonresponsive sites. However, the chlorophyll [(NH2 )2CO] or anhydrous NH3 produced higher yields meter did not correlate well enough with soil N-supply- than fall applications. Addition of nitrapyrin [2-chloro- ing capacity (in-season mineralization) to accurately 6-(trichloromethyl)-pyridine] as a nitrification inhibitor

with spring-applied N had no effect on grain yield but make N sidedress recommendations. Chlorophyll meter

in combination with a sufficiency index was very success- did increase yields associated with fall N applications. ful as an in-season N management strategy for irrigated Similarly, in Minnesota, Randall et al. (1992) found that corn in Nebraska (Varvel et al., 1997a). The chlorophyll corn yield and N use efficiency were lowest with fall N meter identified when additional N fertilizer was re- applications without nitrapyrin, highest with spring N quired, but it did not estimate the amount needed. A applications, and intermediate with fall N plus nitra- sufficiency index was calculated [(treatment/well-fertil- pyrin. They reported N use efficiency of fall-applied N ized control) 100], and in-season N fertilizer applica- fertilizer was 16%, whereas with nitrapyrin, it improved tions were made when index values were below 95%. to 26%. Spring applications, with or without nitrapyrin, Their N adjustment was to hand-apply 30 kg N ha1

had fertilizer N use efficiencies ranging from 42 to 48%. and water it within 24 h of when the chlorophyll meter The highest NO3 losses associated with corn production measurements were taken and the sufficiency index fell occurred with fall N applications, with or without ni- below 95%. trapyrin. Currently, it is unlikely that chlorophyll meter data The economics of nitrapyrin use have shown mixed alone will be sufficient to guide N fertilizer applications results. In a 7-yr study by Christensen and Huffman in subhumid regions. Factors other than N availability (1992), nitrapyrin in spring-applied N fertilizer signifi- affect leaf chlorophyll content and can confound chloro- cantly increased corn grain yield, with the increase more phyll meter data, thus limiting its applicability as a N than compensating for the added cost of the nitrapyrin. test (Piekielek and Fox, 1992). Piekielek and Fox (1992) In Minnesota, 7-yr averages of corn fertilized with 150 pointed out that leaf chlorophyll content could be af- kg N ha1 showed that yield was increased 5% by fall- fected by any of the following: plant leaf chlorosis due applied N with nitrapyrin, 5% by spring preplant N, to nutrient deficiencies other than N (i.e., K and Mg), and 10% by split-applied N (40% preplant and 60% disease, insect damage, cold temperatures, too high or sidedressed at V8 corn growth stage) compared with too low plant populations on soils with marginal N avail- fall-applied N without nitrapyrin (G.W. Randall, per- ability, and recent N fertilizer application. These authors sonal communication, 2000). Economic returns for the also stated that for soils with large organic N pools in 7-yr study were split-applied N ($239.40 ha1 yr1 )  areas of highly variable weather conditions, any test that spring preplant N ($210.90 ha1 yr1 )  fall-applied N measures plant N content at the six-leaf stage will not with nitrapyrin ($192.40 ha1 yr1 )  fall-applied N always be indicative of soil N availability for the remain- without nitrapyrin ($166.70 ha1 yr1 ). Although the der of the growing season nor always relate to final yield.

nitrapyrin treatment did not result in an economic ad- Excess soil water content is another major factor in

vantage for the spring and split N application treat- subhumid regions with high organic matter soils that can

ments, the results indicate that for farmers who continue confound developing relationships between chlorophyll

to fall-apply N, there is a positive economic return for meter data and plant N status. In the Upper Midwest,

using nitrapyrin. However, a number of other studies poorly drained prairie potholes comprise an appreciable

have found no significant yield effect nor economic ad- amount of the total cropland area. Even with surface

vantage with the use of nitrapyrin (Hendrickson et al., inlets to subsurface tile drainage lines, these areas often

1978; Touchton et al., 1979; Blackmer and Sanchez, have periods during spring and early summer when wa-
160 AGRONOMY JOURNAL, VOL. 94, JANUARY–FEBRUARY 2002

ter is ponded on the surface. Under such conditions, though the amount of reduction can be minimal, demany plant species often become chlorotic because of pending on climatic conditions (Randall et al., 1997a).

aeration stress rather than insufficient plant-available With soybean, the leaching potential is reduced most N (Hocking et al., 1987). Lizaso and Ritchie (1997) when it is between growth stages V4 and R5, but leach- reported a three to seven times greater rate of senes- ing can be quite high during the early spring if large cence and loss of green leaf area in corn under ponded quantities of residual NO3 remain following the corn conditions compared with a control at the 12-leaf stage. crop. Significant NO3 leaching can also occur following Undoubtedly, denitrification and leaching can deplete soybean (Randall et al., 1992; Baker and Melvin, 1994; NO3 when water is ponded on these areas, but most of Kanwar et al., 1996; Jaynes et al., 1999), especially if the pothole soils contain very high levels of organic significant mineralization occurs when soils are not fro- N, which can become available to the plant through zen during the late fall, winter, or early spring. mineralization later in the growing season (Cambardella Including perennial legume or nonlegume crops in et al., 1994). This situation has been observed in the rotations has also been shown to decrease NO3 losses. preliminary results from our watershed-scale N manage- In Iowa, Baker and Melvin (1994) documented much ment research project (Walnut Creek N Initiative) lower NO3–N concentrations beneath alfalfa than for where the prairie pothole soils have been unresponsive corn or soybean. Also, in Minnesota, Randall et al. to additional N fertilizer (Dinnes et al., 1998) despite (1997a) measured NO3–N concentrations in drainage having lower corn leaf chlorophyll levels when mea- water from alfalfa fields and Conservation Reserve Pro- sured at V9 to V12 growth stages (Dinnes et al., unpub- gram (CRP) lands cropped to a mixture of alfalfa and lished data, 2000). It also suggests that one reason for the perennial grasses and found they were 37 and 35 times success of the chlorophyll meter method under irrigated

conditions is the absence of chlorosis from excess soil lower than in drainage water from corn and soybean

water and the fact that the soils are generally well fields, respectively. They attributed the differences to

drained and have relatively low SOM levels. longer growing seasons and greater annual evapotransInsufficient soil water content can also confound in- piration in fields with perennials because both of these

terpretation of chlorophyll meter measurements. processes contribute to greater N uptake and less drainLeaves under water stress can have changes in the red age than in fields with only annual crops. Differences

and near-infrared (NIR) reflectances and because the in fertilizer management between annual and perennial

chlorophyll meter computes the reading as the ratio of cropping systems also impact their relative NO3–

red/NIR, deviations away from normal will affect this leaching potentials. Typically, perennial cropping sysratio in the absence of N stress. Red and NIR reflec- tems receive less tillage and N fertilizer than do annual tances change with age of the leaf, with the greater cropping systems. change in the NIR (Gausman et al., 1970). Observations Factors contributing to differences in NO3–leaching of leaf reflectance from corn grown under N and water potential for various crop rotations extend beyond fertil- stress showed that NIR was more affected by water izer practices. Interactions between hydrology and till- stress (Hatfield and Prueger, unpublished data, 2000). age are very important because any residual NO3 that

Changes in leaf reflectance with water stress have been accumulates in the soil profile, whether from N fertilizer known for several years, as shown by Thomas et al. or microbial processes, can be leached if it is not assimi- (1971), who found leaf water content could be estimated lated by microbes decomposing crop residue or taken through reflectance measurements. Chlorophyll meter up by another plant. When a crop such as alfalfa depletes readings can be affected by leaf water status, but the profile water content and the amount of precipitation change induced would predict lower N requirements is not sufficient to fully recharge the profile, the leaching because the meter readings would increase under long- potential will be minimal and very little water will be term water stress. moving into subsurface drainage lines. Differences in The chlorophyll meter has been successfully used in residue and root decomposition relationships, as well conjunction with the end-of-season basal corn stalk NO3 as soil–plant–water dynamics (i.e., soil water extraction test (Blackmer and Mallarino, 1997) to guide and im- capacity), among various plant species also influence prove future soil sampling for site-specific N fertilizer the leaching potential (Baker and Melvin, 1994; Randall recommendations for irrigated corn (Varvel et al.,

1997b). By combining both monitoring techniques, field et al., 1997a; Malpassi et al., 2000). The rate of N cycling

areas with different soil N pools and N mineralization is important because although N-fixing legumes can repotential can be identified and sampled separately. The lease large quantities of N to soils over time, organic N

PSNT–LSNT program or any future soil tests developed derived from plant and microbial residues is not as rapto better predict N mineralization potentials could then idly available to plants as inorganic N provided by most

be used to determine optimum fertilizer N rates for commercial fertilizers. Additionally, the gradual release

those areas. This approach could assist in creating a of organic N is often better synchronized with subsereliable variable N rate protocol for areas where field- quent plant needs and microbial population dynamics scale variability in soil N content is very high (Cambar- than point-in-time applications of N fertilizers. The large della et al., 1994). flush of available N following an inorganic fertilizer

N application can often supply more N than can be Diversified Crop Rotations assimilated by plants and microbes. When this pool is

Changing from continuous corn to a corn–soybean nitrified, large amounts of NO3 are susceptible to leachrotation has been shown to reduce NO3 leaching al- ing and can potentially contaminate surface and ground
DINNES ET AL.: STRATEGIES TO REDUCE NITRATE LEACHING IN MIDWESTERN SOILS 161

water resources. These processes are not limited to row Tillage Impact on Nitrogen Cycling

crop areas because research also suggests that if exces- Although tillage affects N cycling within soils, mid- sive N is applied to either annual or perennial forage western farmers generally do not intentionally use till- crops, water quality can be degraded by a resultant in- age to manage N. In more arid regions of the USA crease in soil NO3 concentrations (Anderson et al., 1997). where fallow was traditionally used every second or

third year, increased N availability following the fallow Cover Crops period was often more important than the perceived

Cover crops have been shown to reduce the potential water conservation associated with that soil management practice (Haas et al., 1974). Tillage alters the soil for NO3 leaching from farm fields (Magdoff, 1991;

Staver and Brinsfield, 1998) by mimicking natural eco- environment by aerating the zone of disturbance and

increasing the availability of O2 to soil microorganisms. systems such as prairies where some plant species are

growing whenever the ground is not frozen. They func- This favors different microbial species, populations, and

processes than a nontilled soil (Doran, 1987). The net tion by accumulating the inorganic soil N between maincrop seasons and holding it in an organic form, thus result of tillage is increased aerobic microbial activity,

preventing it from leaching (Magdoff, 1991; Staver and leading to elevated oxidation of SOM and mineralizaBrinsfield, 1998). The N is subsequently released to the tion of soil N (Randall et al., 1997a). This N mineralizanext crop as the cover crop residue decomposes. Cover tion response, often associated with preplant tillage, is

crops also protect against soil erosion (Dabney, 1998; also a benefit associated with using cultivation for weed

Kaspar et al., 2001), increase SOM (Reicosky and For- control during the growing season.

cella, 1998), and suppress weed growth (Buhler et al., Depending on tillage to release N for crop production

1998; Lal et al., 1991). is generally not a wise soil management practice. From

Desirable attributes for midwestern cover crops in- a soil quality perspective, it reduces the benefits of SOM

clude the ability to establish rapidly under less-than- such as cation exchange capacity, soil structure, and

ideal conditions, grow vigorously despite cool tempera- water retention capacity merely for the release of planttures and decreasing daylength, and not inhibit the available N. It also exposes the soil surface to wind and

growth of subsequent row crops. The biggest problem water forces, thus increasing the potential for increased

facing cover crops in this region is the short and gener- erosion (Reicosky et al., 1995). Furthermore, depending

ally cool growing season between harvest and planting on seasonal weather patterns, temperature, and rainfall,

of the subsequent row crop. In studies reviewed by Mei- tillage during autumn or early spring can cause N minersinger et al. (1991), cover crops reduced both the mass alization too early and increase the potential for NO3

of N leached and NO leaching before subsequent crops have an opportunity 3 concentration of leachate 20 to

80% compared with no cover crop control. They also to assimilate the N provided by these processes.

determined that grasses and brassicas were two to three Effects of tillage on N management have been demontimes more effective than legumes in reducing NO strated in studies comparing no-till with conventional 3

leaching. Rye (Secale cereale L.) has been used success- tillage at several midwestern locations. In a long-term

fully as a cover crop in the northern Corn and Soybean Minnesota study (Randall and Iragavarapu, 1995), reBelt. But because rye overwinters, it must be killed or sidual soil NO3 contents in the 0- to 1.5-m soil profile

it can reduce the yield of subsequent corn crops by using were significantly higher with conventional tillage than

too much water in the spring or immobilizing soil N no-till for 5 out of 11 yr and were not significantly

(Munawar et al., 1990; Karlen and Doran, 1991; Tollen- different for the other 6 yr. Average flow-weighted

NO3–N concentrations were 13.4 and 12.0 mg L1 aar et al., 1993; Johnson et al., 1998). Other evidence for

suggests that the corn yield depression caused by the conventional and no-till corn production treatments, rerye cover crop may be due to allelochemicals (Tollenaar spectively. Furthermore, while the no-till treatment had

et al., 1993). Further research may identify rye geno- 12% greater subsurface drainage flow than the conventional treatment, NO3 types that do not release these compounds. Oat has losses were marginally greater

been demonstrated to be an effective cover crop for (about 5%) with conventional tillage. Although insignifthis region because seed is easy to obtain and inexpen- icant, these results suggest a minimal trend toward

greater NO3 sive, fall growth is more vigorous than rye, and it winter- losses with conventional tillage in this study.

The authors concluded that NO3 kills, thus eliminating the need for herbicide or tillage losses through tile

in spring (Johnson et al., 1998). drainage depend more on growing-season precipitation

Other plant species, including legumes, cereals, than on tillage. Recently, Randall and Mulla (2001)

concluded that NO3 grasses, and brassicas, have been evaluated and used as losses from agricultural fields are

cover crops, but these species have generally not been minimally affected by differences in tillage systems comsuccessful as true cover crops in the northern Corn and pared with N management practices.

In Iowa, Kanwar et al. (1993) monitored NO3 Soybean Belt. One exception was a study done in Wis- leaching

consin where hairy vetch (Vicia villosa Roth) and red beneath both continuous corn and corn–soybean rotaclover grown in an oat–corn rotation showed a favorable tions managed using moldboard plowing, chisel plowing,

economic comparison with continuous corn fertilized ridge tillage, and no-tillage practices. The 3-yr average

with 180 kg N ha NO3–N concentration in drainage water from continu- 1 commercial N fertilizer (Stute and

Posner, 1995). ous corn plots receiving moldboard tillage was signifi-
162 AGRONOMY JOURNAL, VOL. 94, JANUARY–FEBRUARY 2002

cantly greater (35.8 mg L1 ) than for either no-till or Disturbance of plant residue through tillage can sigridge tillage treatments (22.2 and 21.8 mg L nificantly increase the decomposition rates (Douglas et 1

, respectively). Similar trends were observed for the corn–soy- al., 1980; Doran, 1987; Holland and Coleman, 1987; Aubean rotation where the 3-yr average NO3–N concentra- lakh et al., 1991). Additionally, root residues may retions in drainage water were 19.0, 13.4, and 13.9 mg spond differently to tillage or disturbance than shoot

L residues. For example, Martin (1989) observed that de- 1 for moldboard plow, no-tillage, and ridge tillage

treatments, respectively. However, due to a higher vol- composition of root residues was more rapid and more

ume of water moving through the soil with no-till and complete when they were left undisturbed in the soil

chisel plow, the 3-yr average NO3–N losses in subsurface than when air-dried roots were mixed with moist or airdrain flow were greater with no-till and chisel plow dried soil.

systems (61.2 and 64.3 kg ha1

, respectively) than with Even in the absence of disturbance, decomposition

moldboard plow (45.8 kg ha rates of root and shoot residue may differ. In a labora- 1 ) under continuous corn.

Nitrate N load losses by tillage method for the corn– tory simulated no-till experiment, Gale and Cambardesoybean rotation produced trends that differed from lla (2000) found that 75% of the new C inputs into soil

those of continuous corn. Under the corn–soybean rota- after 1 yr of decomposition were root derived and 25%

tion, greatest NO were shoot derived. They concluded that accrual of soil 3–N losses were observed with chisel

plow (32.1 kg ha1 ), followed by moldboard plow (27.5 organic C associated with no-till is primarily due to the

kg ha greater retention of root-derived C in the soil. 1 ), no-till (23.9 kg ha1 ), and ridge tillage (23.7

kg ha1 ). These results led Weed and Kanwar (1996)

to conclude that despite having an influence on N miner- NITROGEN REMOVAL STRATEGIES

alization, tillage had less impact than crop rotation. If agricultural management of N by all in-field means

Plant Residue Management (e.g., crop rotations, cover crops, fertilizer application

best management practices, and tillage) cannot satisfac- Management of plant residues is directly related to torily reduce NO3 concentrations, alternative strategies tillage and affects N cycling in soils because plant tissue may be needed to remove NO3 from subsurface drain- is a primary source and sink for C and N. Normally, age, shallow ground water, and/or surface water. Nu- when plant residues with C/N ratios greater than ap- merous methods for removing NO3 from water have proximately 20:1 are added to the soil, available N is been identified. These include ion exchange, biological immobilized during the first few weeks of decomposi- denitrification and assimilation, chemical denitrifica- tion (Sinha et al., 1977; Doran and Smith, 1991; Somda tion, reverse osmosis, electrodialysis, and catalytic deni- et al., 1991; Green and Blackmer, 1995). Green et al. trification (Kapoor and Viraraghavan, 1997). Of these, (1995) observed that incorporation of corn stover into only biological denitrification and assimilation seem soil resulted in rapid immobilization of all available suitable and adaptable for removing NO3 from subsur- inorganic N during the decomposition period. This oc- face drainage in agricultural fields and watersheds. Mul- curred because the microbial population decomposing tiple basic strategies that rely on biological denitrifica- the plant residue had increased its biomass in response tion and/or assimilation as either primary or secondary to the C source. If such immobilization occurs when mechanisms for reducing NO3 concentrations in shallow plants need N for growth and development, the avail- subsurface waters have been and continue to be re- ability of NO3 for the plants may be reduced. When this searched. Several are discussed below. involves the primary crop, the immobilization process

can have a negative economic impact by ultimately lim- Buffers iting yield. Eventually, as residue decomposition proceeds, the C/N ratio will begin to approach that of SOM Research on effects of riparian buffers on shallow

(≈10:1 or 12:1), microbial biomass will decrease, and N ground-water quality has been conducted in many areas

from plant residues that was incorporated in the micro- across the USA and overseas. A consistent conclusion

bial biomass will once again be released into the soil. of research projects on riparian buffers is that the buffers

However, if temperature, water content, or other factors decrease the NO3 concentration of the shallow ground

slow the residue decomposition process, N may not be water flowing through them, in many cases to a dramatic

released from the plant residue or microbial biomass degree, ranging from 48 to 100% (Peterjohn and Correll,

until the primary crop has matured and stopped assimi- 1983; Lowrance et al., 1984; Jacobs and Gilliam, 1985;

lating N. This was hypothesized by Varvel and Peterson Haycock and Pinay, 1993; Jordan et al., 1993; Hubbard

(1990) as a factor affecting continuous corn production and Lowrance, 1997; Verchot et al., 1997; Snyder et al.,

when they estimated that 80% of the applied fertilizer 1998; Addy et al., 1999; Rickerl et al., 2000; Spruill,

N was still immobilized in crop residues, SOM, and 2000). However, there are differences among these studmicrobial biomass at the end of the growing season. ies as to the reported primary mechanisms responsible

This emphasizes the importance of understanding all of for these reductions.

the factors affecting plant residue decomposition and One potential contributing factor to reduced NO3

how they might be manipulated to reduce the potential concentrations in shallow ground water is dilution. Prefor NO3 leaching without decreasing availability of N cipitation that infiltrates in the buffer area can contain

to the primary crop or adversely affecting the soil C low NO3 concentrations compared with the shallow

and N pools. ground water originating from the adjacent cropland.
DINNES ET AL.: STRATEGIES TO REDUCE NITRATE LEACHING IN MIDWESTERN SOILS 163

Most studies have reported insignificant effects of dilu- Although riparian buffers have repeatedly been

tion on the observed NO3 concentration reductions, but proven very effective at removing NO3 from shallow

there have been a couple of exceptions. In a study of ground water, any field tile drainage line that passes

various riparian forest management techniques on NO3 through a buffer and empties directly into a surface

reduction in the Georgia coastal plain, Hubbard and water stream will bypass all NO3 remediation benefits

Lowrance (1997) found that dilution did play a role in of a riparian buffer. In order to utilize riparian buffer

reducing NO3 concentration of the shallow ground water technology in tile-drained areas, alterations would be

from a clear-cutting management treatment. Spruill required. One option would be to terminate tile lines

(2000) found a 95% reduction in NO3 concentration of before entering a buffer zone. The tile flow would then

young ground water in riparian buffer areas and esti- seep through the buffer to the stream. Though effective,

mated that 30 to 35% of the reduction was due to dilu- this strategy would severely limit the drainage capacity

tion effects. The remaining 65 to 70% reduction of NO3 of the tile. A more appropriate option may be to disconcentration was attributed to other processes. charge the tile effluent to a wetland retention area adjaVegetative assimilation is one potential biological fate cent to the riparian buffer to treat the tile drainage

of NO3 in shallow ground water as it passes through a before it enters the stream.

riparian buffer. Forest trees, and the grass strips that

are frequently placed between the trees and cropland, Wetlands

do assimilate NO3 from the shallow ground water. It is

the degree to which each vegetative group assimilates Natural and constructed wetlands have been used

NO successfully as biological treatment systems for NO3 re- 3 that varies among the research studies. Lowrance moval (Gersberg et al., 1983; Crumpton et al., 1995; (1992) measured a seven- to ninefold decrease in the Romero et al., 1999). Eriksson and Weisner (1997) con- shallow ground water NO3 and NO3/Cl ratio within the

first 10 m of riparian forest buffer. He attributed this firmed that epiphytic biofilms on submerged vegetation

could remove NO3 by denitrification. In a laboratory change in NO3 concentration primarily to forest vegeta- wetland microcosm experiment, Ingersoll and Baker tion assimilation because the denitrification potentials

of the soils at the typical depths of the water table were (1998) determined NO3 removal efficiencies at two temperatures (28 and 35C), varying hydraulic-loading rates too limited to account for the dramatic losses of NO3. (5–20 cm d1 ) and C additions (1–6 g wk1 Hubbard and Lowrance (1997) also determined that dried plant

residue) with NO3–contaminated water (30 mg L1 vegetative assimilation was a significant sink of shallow

subsurface-flow NO3. They reported that a grass buffer NO3–N). They measured NO3 removal efficiencies from

assimilated some of the NO 8% to 95%, which decreased with increasing hydrau- 3 but that a downslope ripar- lic-loading rates and increased with increasing C addi- ian forest was more efficient at assimilating NO3 from

shallow ground water. Other studies (Jacobs and Gil- tion rates. Nitrate removal efficiencies increased as the

liam, 1985; Verchot et al., 1997; Addy et al., 1999) re- C/N ratio increased to 5:1, and at C/N ratios  5:1, NO3

ported that vegetative assimilation did not play a signifi- loss was nearly complete. One conclusion was that the

cant role in reducing NO denitrification rate constant directly depended on the 3 concentration of shallow

ground water. In these reports, denitrification was iden- C addition rate. Therefore, the authors suggested that

tified as the main loss mechanism. a wetland could become more efficient at NO3 removal

Riparian buffers adjacent to cropland and placed in if its plant growth were to be increased or if the plants

wet soils can provide several of the environmental fac- were cut and the residue was left in place.

tors that are essential to drive the processes of denitrifi- Crumpton et al. (1995) studied the efficacy of wetcation. Riparian buffers can supply the C required by lands for removing NO3 by assimilation and denitrificathe denitrifying bacteria, helping to fuel a biologically tion. They estimated that NO3 draining from approxiactive zone within the soil profile. Denitrification rates mately 100 ha of land producing corn could potentially

have been found to be much greater within riparian be removed by a 1-ha wetland. However, given an apbuffers placed in soils with high water tables and organic proximate 100:1 ratio of cropland to wetland area sugC than in well-drained soils that are more aerobic (Ja- gested by Crumpton et al. (1995), such a wetland may

cobs and Gilliam, 1985; Ambus and Lowrance, 1991; not provide sufficient residence time to remove an apGold and Groffman, 1995; Addy et al., 1999). preciable amount of NO3 from drainage water during

An additional factor that influences denitrification is high rainfall events, which are typical for the Midwest

the residence time of the shallow ground water as it during spring and early summer. Xue et al. (1999) came

passes through the soil. Areas where flow of shallow to similar conclusions in their study of the denitrification

ground water is relatively slow are the most effective capacity of three wetlands in Illinois. Mean monthly

at removing NO3 because of increased residence time NO3–loading rates to the wetlands were highly variable

in anaerobic and biologically active zones (Lowrance et (4–451 kg N) due to a wide range in amounts of monthly

al., 2000). Snyder et al. (1998) observed the smallest precipitation. The ratios of denitrification capacity and

degree of NO3 reduction in a riparian buffer where the mean NO3 load ranged from 19 to 59% for the three

terrain was steep and ground water flow was rapid. They wetlands, with an average of 33%. The authors estifound the greatest NO3 reductions in wet soils where mated that for months of low inputs, almost all of the

the topographic gradient was very low and ground water NO3 could be denitrified, but for months of high inputs,

movement was low. only a small percentage would be removed. A conclu-
164 AGRONOMY JOURNAL, VOL. 94, JANUARY–FEBRUARY 2002

sion from their studies was, “The ultimate wetland deni- change the level of the drainage line outlet, or both.

trifying efficiency depends on both wetland capacity and Such drainage control studies have used one or more

the water residence time in each wetland.” of three basic strategies to reduce NO3 contamination of

surface waters. One strategy is to increase the anaerobic

Bioreactors volume of the soil profile to enhance denitrification. A

second is to decrease the amount of drainage water Substantial research has been done on designing bior- exiting the artificial drainage system. The third is to eactors for denitrification (McCleaf and Schroeder, decrease the depth of the soil profile through which 1995; Reising and Schroeder, 1996; Shanableh et al., water infiltrates to reduce the leaching potential of soil 1997). Most designs require a supplemental C source NO3. All three of these strategies can be accomplished such as sucrose (Sison et al., 1995), ethanol [C2H5OH] by creating a shallower depth to the water table than or acetic acid [C2H4O2] (Constantin and Fick, 1997), or exists with conventional, uncontrolled artificial drain- methane [CH4] (Thalasso et al., 1997) to be effective. age designs. They also require a high level of management for in- In Indiana, Kladivko et al. (1999) conducted a subsur- field or edge-of-field treatment of subsurface drainage face drain-spacing study where they installed drain lines water. Solid C sources have also been tested and would at spacings of 5, 10, and 20 m, all at an average depth appear to be more amenable to field application. Volok- of 0.75 m. They found a consistent trend of greater loads ita et al. (1996) used shredded newspaper as a C source of NO3 removed with increasingly narrow drain line in laboratory columns to obtain N removal rates ranging spacing during the 3 yr of study. Skaggs and Chescheir from 0.056 to 0.875 mg N g1 newspaper d1

. Blowes (1999) ran a simulation model for drain depths of 0.75 et al. (1994) used a fixed-bed bioreactor filled with a and 1.5 m and varied spacing for corn production on a compost mixture of sand, tree bark, wood chips, and sandy loam soil near Plymouth, NC. Their predictions leaves to treat drainage water from a farm field. Over showed that NO3 losses could be reduced by a factor a year, a 200-L bioreactor was able to remove nearly of more than 2.5 by placing drainage lines relatively all NO3 from a 10 to 60 L d1 discharge of field drainage shallow and close together. These predicted results are water containing 3 to 6 mg L1 NO3–N. Neither study contrary to spacing effects reported by Kladivko et al. differentiated between assimilation and denitrification (1999), which may likely be due to the differing climates as the NO3 loss mechanism. and soils of Indiana and North Carolina. Robertson and Cherry (1995) demonstrated the NO3 Jacinthe et al. (1999) used soil columns with added removal potential of a bioreactor constructed in situ. NO3–N fertilizer (2.11 g column1 KNO3–N ) to simulate They filled a 0.6-m-wide trench that extended 0.75 m two water table management (WTM) techniques. The below a shallow water table with sand containing 20% first WTM treatment (WTM1) had a static water table (v/v) coarse sawdust and measured the concentration maintained at 0.5 m below the soil surface for 92 d, after of NO3 in ground water before and after flowing through which the water table was raised to 0.1 m below the soil the mixture. Very high NO3–N concentrations (57–62 surface for the next 18 d. The other WTM treatment mg L1 ) were reduced to much lower concentrations (WTM2) simulated a dynamic water table where the (2–25 mg L1 ) in ground water passing laterally through water table was held at 0.5 m below the soil surface for the bioreactor. They attributed the removal of NO3 to 7 d and raised to 0.1 m for the next 4 d. The water table heterotrophic denitrification, with the sawdust serving was then lowered gradually to the 0.7-m depth, held as a labile C source, and estimated that this denitrifica- there for the following 4 d, and then raised back to 0.5 tion wall would have an effective lifetime of 20 to 200 m and maintained at that level for the next 43 d. Before yr. However, they offered only indirect evidence that termination of the experiment, the researchers raised denitrification was the primary removal mechanism, cit- the water table back to the 0.1-m depth below the soil ing only reduced O2 and SO4 concentrations in water surface, holding it at that level for another 18 d. The passing through the wall. In a similar study with a con- WTM1 treatment removed 9 to 14% of the added structed denitrification wall, Schipper and Vojvodic-Vu- NO3–N during the 130-d simulation. The WTM2 treat- kovic (1998) found NO3–N concentrations to be reduced ment removed 24 to 43% of the added NO3–N, and the from between 5 and 16 mg L1 to 2 mg L1 in shallow researchers detected a faster rate of NO3 removal when ground water passing through a wall. They attributed the water table was perched near the soil surface. Their the NO3 removal to denitrification and reported that conclusion was that NO3 removal can be stimulated and denitrifying enzyme activity reached a plateau of 906 enhanced by raising a water table into the upper soil ng g1 h1 after 6 mo of operation. Placing C source profile layers, but the need for doing so during time denitrification walls around or near tile lines may help periods conducive for denitrification—coinciding with reduce NO3–N concentrations of shallow ground water a summer annual crop’s growing season—could limit before it enters the tiles and discharges into surface application of WTM practices due to possible damage waters. to the crop.

An Iowa research project examined NO3 transport in Drainage Control Strategies shallow ground water under two different WTM

Other investigations have focused on methods to ma- schemes (Kalita and Kanwar, 1993). One scheme mainnipulate water table depth by altering the conventional tained water table depths at 0.2, 0.3, 0.6, 0.9, and 1.1 m

designs of artificial drainage lines, using structures to for time periods of 53 to 96 d after planting of corn for
DINNES ET AL.: STRATEGIES TO REDUCE NITRATE LEACHING IN MIDWESTERN SOILS 165

1989 and 1990 and 45 to 97 d after planting in 1991. increased management time may make drainage control

Samples of shallow ground water were taken from pi- impractical on landscapes of steeper slope (Skaggs and

ezometers installed at depths of 1.2, 1.8, and 2.4 m for Chescheir, 1999).

each water table depth treatment. In general, there was

a trend of increasing NO3–N concentrations in ground FUTURE RESEARCH NEEDS

water with increasing depth to the water table. The Several methods for improving N management and 1.2-m piezometer yielded average NO3–N concentrareducing NO3 contamination of water resources have tions varying from 7 to 2.5, 14.7 to 8.2, and 20.3 to 17

mg L1 previously been proposed by others (Kanwar et al., 1996; under shallow, medium, and deep water table Randall, 1997). Among them are recommendations for depths, respectively. The second WTM scheme had wa- (i) better use of soil tests to properly credit N sources ter tables maintained at 0.3, 0.6, and 0.9 m from 50 to other than commercial N fertilizers, (ii) abandoning tile 53 d after planting to the time of harvest during the 3- and surface drainage systems, (iii) installing constructed yr study. Piezometers were again located at the 1.2-, wetlands or denitrifying ponds, (iv) implementing crop 1.8-, and 2.4-m depths. The researchers found a trend rotations that include perennial and cover crops, (v) of decreasing NO3 concentrations in ground water with improving the timing of N fertilizer application, and (vi) time during the growing season at all three sampling applying the proper rate of N fertilizer. The remainder depths, with the lowest average NO3 concentrations obof this review will focus on our perspectives of these served under the 0.3-m water table depth. Corn grain suggestions and on some potential new directions for yields were negatively affected by increasingly higher

water table levels at both sites for each year of the research and development.

project. The researchers concluded that ground water Improved Monitoring of Soil Nitrogen for Split NO3 concentrations could be reduced by maintaining Nitrogen Application Programs shallow water table depths and that the 0.3-m water

table depth would provide the most beneficial water The logistics and time required for soil sampling and

quality results. However, maintaining a water table at analysis in relation to the window of opportunity for

such a shallow depth would restrict the ability to pro- fertilizer application has prevented widespread adopduce high corn grain yields. tion of the PSNT–LSNT N management approach. A

Fisher et al. (1999) compared a subirrigation with test is needed that can be performed earlier in the season

controlled drainage (SI–CD) treatment with a subsur- and that relies on real-time meteorological and soil data

face drainage treatment with no drainage control in a to predict plant-available soil N status in late spring.

field-plot scale corn–soybean production system. The This would allow for more timely soil sampling and

SI–CD treatment had a water table maintained at 0.4 m. would increase the window of opportunity for N applicaThe authors found that mean soil NO3 concentrations tion. One approach to developing a model to predict

were not affected by the SI–CD treatment at the 0- to soil N mineralization from soil and meteorological data

15- and 15- to 30-cm depths, but at the 30- to 75-cm is to use soil respiration measurements as a surrogate

depth, the SI–CD treatment reduced the 2-yr mean soil for measurements of soil N mineralization (Parkin et

NO3 concentration by 46% compared with the subsur- al., 1996). Because soil N mineralization is the direct

face drainage treatment. Compared with the subsurface result of microbial activity, measurements of soil respidrainage treatment, the SI–CD treatment increased av- ration without actively growing plants present are an

erage corn N uptake by 13% and yield by 19% and integrated measure of soil microbial activity and are

increased average soybean N uptake by 62% and yield likely correlated with soil N mineralization. The advanby 64%. The researchers concluded that proper imple- tage of using soil respiration measures as a surrogate

mentation of a SI–CD management system could stabi- for soil N mineralization measurements is that soil respilize crop yield and N use efficiency and significantly ration can be measured almost continuously, responds

reduce soil NO3 concentrations deeper in the soil profile quickly to changes in meteorological conditions, and

compared with subsurface drainage management, re- can be used to determine cumulative activity of microorsulting in an overall reduction in NO3 leaching. ganisms over very short or very long time periods. This

Although drainage control methods have shown posi- approach should be more amenable to determining the

tive results in reducing NO3 loading to surface waters effect of meteorological conditions on soil N mineralizafrom tile drainage, these technologies currently have tion than direct measurements of changes in soil NO3

substantial limitations. Drainage control is typically lim- concentrations, which must be taken at discrete points

ited to landscapes with 1% slope or less due to the in time. Coupling respiration measurements with meteocosts of drainage control structures (Evans et al., 1992; rological data and estimates of soil water movement

Shirmohammadi et al., 1992; Skaggs and Chescheir, should allow the prediction of soil NO3 accumulation.

1999). At a 1% slope, there would be a 1-m depth to A model that predicts N mineralization based on temwater table difference from the height of the drainage perature (growing degree days) has been developed

control structure to an upslope point 100 m along the (Honeycutt et al., 1988). However, application of the

drainage path. This may necessitate the need for multi- model requires a calibration procedure for the soil of

ple drainage control structures, even within a moder- interest. This calibration involves lengthy incubations of

ately sized field of 32 ha, to maintain a uniform water soil samples (30 to 60 d) to determine N mineralization

table depth. Even if structure costs were reduced, the potential, and thus precludes widespread adoption and
166 AGRONOMY JOURNAL, VOL. 94, JANUARY–FEBRUARY 2002

use. However, N mineralization potential is often not tion practices in the northern Corn and Soybean Belt.

fully realized due to variations in climatic conditions. Cultural and plant-breeding research is needed to imSoil respiration measurements may be a means of in prove the compatibility of cover crops with current cropsitu calibration. Improving our understanding of N im- ping systems. For example, rye cover crops grow well

mobilization and nitrification processes in soils and N in the northern Corn and Soybean Belt, but rye genoassimilation processes in plants would also facilitate de- types that do not reduce corn yields need to be found

velopment of predictive models based on interactions or developed. A better understanding of the timing of

between local soils and weather patterns, and thus re- cover crop N release from shoot and root residues as

duce or eliminate the need for PSNT–LSNT sampling well as their interactions with tillage and surface condiand soil analyses. tions is needed. Agronomic research focusing on improved establishment of cover crops, reduced manageVariable-Rate Nitrogen Application Models ment costs, and decreased negative impacts on

and Methodologies subsequent row crops is also needed. Achievements in

these areas may be especially important as N manage- Pierce and Nowak (1999) state that, “There appear ment tools for both conventional and organic produc- to be no standards regarding the underlying agronomic tion systems. principles that should be guiding the development and

application of precision agriculture.” At this time, there Developing Perennial Cash-Cropping Systems appears to have been little advancement in regard to

this problem, which indicates that much research is Based on the native prairie model, incorporation of

needed in this area if precision farming techniques are more perennial crops into midwestern crop rotations

to become adopted and successfully practiced by farm- could greatly reduce the amount of NO3 that leaches

ers. The nature and predictability of spatial and tempo- into subsurface drainage lines. However, farmers and

ral variability within farm fields, at least at the local landowners will not adopt these crops until they have

level, need to be identified to guide farmers as to which been proven to maintain or improve net economic reprecision farming techniques may improve their profit- turns. Research is desperately lacking in this area deability and protect the environment. spite evidence that native prairies, forage crops, and

Improvements in long-range weather prediction mod- Conservation Reserve Program land can substantially

els and incorporation of soil drainage and organic mat- improve the quality of subsurface drainage water.

ter decomposition modules for various soil types are Public funding and use of government resources are

needed to create more reliable guidelines for variable- vital to this area of research because currently there is

rate N management. Remote-sensing technologies that very little economic incentive for private industry or

replace chlorophyll meters may play an integral role in commodity groups to support such efforts. Developestablishing variable-rate strategies, but further re- ment of alternative cropping strategies, however, would

search is needed to refine the technologies and their be of very great benefit to the environment, farmers,

application for agricultural processes. To be effective, and rural communities. Adoption of alternative and/or

remote sensing must be able to correctly differentiate perennial crops could reduce farmer reliance on contincrop areas that are N deficient due to low soil N from uous corn and corn–soybean rotations, offer an opportuall other conditions that may lead to chlorosis in plants, nity for improved environmental quality, bolster prices

such as water-saturated soils, Mg and K deficiencies, or of current commodities by reducing their overproducdisease and insect infestations. Currently, it remains to tion, and reduce government spending on farm support

be seen whether sensing across multiple wavelengths and emergency relief programs.

(hyperspectral remote sensing) can separate these fac- Aside from the current social and environmental contors and correctly identify those areas where soils are N cerns of genetic modification, this recent technology

deficient. If these areas cannot be accurately identified, could serve to vastly accelerate the development of both

simply using remote sensing to determine variable rates more suitable cover crops and perennial cash crops.

of N application is no guarantee against overapplication Genetic modification could enhance nutrient contents

and, thus, an increased potential for NO3 leaching and of perennial crops or add pharmaceutical traits, making

contamination of water resources. them more valuable commodities. Also, genetic modifiIf these challenges are met by science and technology cation could improve other traits of perennial and cover

in developing reliable variable-rate application method- crops that would make it easier for farmers to incorpoologies, they should play a significant role in improving rate them into their operations.

water quality, protecting the environment, and improving crop production efficiencies. Whether farmer eco- Nitrate Removal Strategies

nomics are improved will depend on how much it will If field-based N management fails to provide ade- cost the farmer to adopt and learn the new method- quate protection against NO3 contamination of subsur- ologies. face drainage water, alternative strategies will have to

be developed for treating the water before it enters Cover Crop Options and Management Strategies surface waters. Unless subsurface drainage lines are

Presently, there are no cover crop species or geno- blocked or cut, riparian buffers will not provide the

types that integrate well with corn and soybean produc- protection needed because these drains often bypass
DINNES ET AL.: STRATEGIES TO REDUCE NITRATE LEACHING IN MIDWESTERN SOILS 167

buffer areas and discharge directly into streams. Re- 5–6 Dec. 1995. USEPA Publ. 855R97001. USEPA Natl. Cent. for

Environ. Publ. and Inf., Washington, DC. search will be needed to address a variety of limitations Ambus, P., and R. Lowrance. 1991. Comparison of denitrification in for wetlands, buffers, and bioreactors, including resi- two riparian soils. Soil Sci. Soc. Am. J. 55:994–997.

dence time for remediation and assimilation, available Anderson, I.C., D.R. Buxton, D.L. Karlen, and C.A. Cambardella.

C sources, land area limitations, and costs of implemen- 1997. Cropping system effects on nitrogen removal, soil nitrogen,

aggregate stability, and subsequent corn yield. Agron. J. 89:881– tation. Also, because the predominant types of limita- 886. tions will differ geographically, a suite of options will Aulakh, M.S., J.W. Doran, D.T. Walters, A.R. Mosier, and D.D. need to be developed rather than a single solution. Francis. 1991. Crop residue type and placement effects on denitrifiResearch on drainage control or WTM strategies has cation and mineralization. Soil Sci. Soc. Am. J. 55:1020–1025.

produced some favorable water quality and crop yield Baker, D.B. 1988. Sediment, nutrient, and pesticide transport in selected lower Great Lakes tributaries. EPA–905/4-88-001. USEPA, results. The most promising appears to be systems that Chicago, IL. allow for dynamic control of the water table during the Baker, J.L. K.L. Campbell, H.P. Johnson, and J.J. Hanway. 1975.

growing season to change the drainage level in response Nitrate, phosphorus, and sulfate in subsurface drainage water. J.

to precipitation events. However, these technologies are Environ. Qual. 4:406–412.

Baker, J.L., T.S. Colvin, S.J. Marley, and M. Dawelbeit. 1985. Im- economically limited at this time to lands with little to proved fertilizer management with a point-injector applicator. In no slope. Future research in this area needs to examine Proc. 1985 Winter Meetings of the Am. Soc. of Agric. Eng., Chi- designs that are low cost and will allow for easy retrofit- cago, IL. 17–20 Dec. 1985. Am. Soc. of Agric. Eng., St. Joseph, MI.

ting of existing field tile drainage lines. Baker, J.L., and H.P. Johnson. 1981. Nitrate-nitrogen in tile drainage

as affected by fertilization. J. Environ. Qual. 10:519–522.

Baker, J.L., and S.W. Melvin. 1994. Chemical management, status, SUMMARY AND CONCLUSIONS and findings. p. 27–60. In Agricultural drainage well research and

demonstration project—annual report and project summary. Iowa The most desirable outcome associated with research Dep. of Agric. and Land Stewardship, Des Moines, IA. and technology development to minimize NO3 contami- Benoit, G.R. 1973. Effect of agricultural management of wet sloping

nation of water resources throughout the Midwest is a soil on nitrate and phosphorus in surface and subsurface water.

better public recognition that several different manage- Water Resour. Res. 9:1296–1303.

ment practices will be required to ensure that surface Bergstro ̈ m, L. 1987. Nitrate leaching and drainage from annual and

perennial crops in tile-drained plots and lysimeters. J. Environ. and ground water resources achieve a quality acceptable Qual. 16:11–18. to society as a whole. The problem is not solely caused Bijeriego, M., R.D. Hauck, and R.A. Olson. 1979. Uptake, translocation and utilization of by N fertilizer management nor any other single factor 15N-depleted fertilizer in irrigated corn. Soil

but is a combination of the soil management practices Sci. Soc. Am. J. 43:528–533.

Blackmer, A.M., and A.P. Mallarino. 1997. Cornstalk testing to evalu- and inherent physical, chemical, and biological charac- ate nitrogen management. PM-1584. Iowa State Coop. Ext., Iowa teristics of the soil. State Univ., Ames.

Several current and potential N management prac- Blackmer, A.M., and C.A. Sanchez. 1988. Response of corn to nitrotices are being evaluated and used to reduce the NO gen-15-labeled anhydrous ammonia with and without nitrapyrin in 3 Iowa. Agron. J. 80:95–102. loading of subsurface drainage water, ground water, and Blackmer, A.M., R.D. Voss, and A.P. Mallarino. 1997. Nitrogen fertil- surface water resources. Based on current experiences, izer recommendations for corn in Iowa. PM-1714. Iowa State Coop. a combination of two or more management practices Ext., Iowa State Univ., Ames.

may work in harmony to reduce NO Blowes, D.W., W.D. Robertson, C.J. Ptacek, and C. Merkley. 1994. 3 loss to field drainRemoval of agricultural nitrate from tile-drainage effluent water age, and thus make implementation of the practices using in-line bioreactors. J. Contam. Hydrol. 15:207–221. more cost effective. One example would be to establish Boyd, P.M., H.M. Hanna, J.L. Baker, M. White, and T.S. Colvin. 2000. a perennial cash crop that could also function as a tile Field evaluation of anhydrous ammonia distribution manifolds.

drainage line biofilter by growing the crop directly ASAE Paper 001140. 2000 ASAE Int. Meet., Milwaukee, WI. Am.

above subsurface drainage lines. The perennial crop Soc. of Agric. Eng., St. Joseph, MI.

Buhler, D.D., K. Kohler, and M.S. Foster. 1998. Spring-seeded may be able to remove NO3 from the water as it flows smother plants for weed control in corn and soybean. J. Soil Water toward the drainage lines. An income-producing bio- Conserv. 53:272–275.

filter such as this would reduce the farmer’s costs for Buhler, D.D., G.W. Randall, W.C. Koskinen, and D.L. Wyse. 1993.

achieving compliance and accelerate adoption of man- Atrazine and alachlor losses from subsurface tile drainage of a clay

loam soil. J. Environ. Qual. 22:583–588. agement practices that more effectively mitigate NO3 Bundy, L.G., D.T. Walters, and A.E. Olness. 1999. Evaluation of soil contamination of water resources. nitrate tests for predicting corn nitrogen response in the north

central region. North Central Regional Res. Publ. 342. Wisconsin

ACKNOWLEDGMENTS Agric. Exp. Stn., Madison.

Cambardella, C.A., T.B. Moorman, D.B. Jaynes, T.B. Parkin, and D.L. The authors thank Dr. Gyles Randall, Jim Schepers, and Karlen. 1999. Water quality in Walnut Creek watershed: Nitrate

Dean Martens for their helpful comments and advice for nitrogen in soils, subsurface drainage water and shallow groundwathis review. ter. J. Environ. Qual. 28:25–34.

Cambardella, C.A., T.B. Moorman, J.M. Novak, T.B. Parkin, D.L.

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LETTER FROM THE EDITOR

As of 1 Jan. 2002, I succeeded Dr. Ken Barbarick as Editor scripts assigned to them. Manuscript Tracker will be a major

of Agronomy Journal (AJ). During the 6 yr that Dr. Barbarick change in how we review and handle manuscripts, and we

was Editor, AJ experienced many significant changes, possibly anxiously anticipate this exciting, new development. We

more so than at any time in the history of the journal. Dr. readily see how valuable this software will be to our authors

Barbarick’s excellent leadership during this unprecedented and editors. We do, however, anticipate a startup phase with

period of change is noteworthy. These changes were necessary Manuscript Tracker, and we ask for your indulgence during

to address current demands and to prepare for anticipated this time.

needs. As I begin as Editor of AJ, I welcome your questions and

While AJ has experienced many changes in recent years, comments about how we can better serve our authors and

more changes are on the horizon. Sometime this year, we readers. You may communicate with me by telephone, inexpect to begin using Manuscript Tracker. This web-based ternet, or letter, whichever is most convenient for you.

software will allow authors, editors, and headquarters staff to We encourage authors to submit manuscripts electronically.

access and input information appropriate to their responsibilit- International authors are well served with electronic submisies. With the use of Manuscript Tracker, manuscripts will be sions by the savings they obtain in time and mailing costs.

submitted and moved electronically through the steps of the Authors who wish to submit manuscripts electronically should

review process. This will greatly speed the transfer of manu- continue to send them to Dr. Robert Lascano at r-lascano@

scripts from one person to another. Ultimately, everything tamu.edu.

else staying the same, the use of Manuscript Tracker will As of January 2002, paper-copy manuscripts should be subreduce the time it takes for manuscripts to go from submission mitted to me at the address below.

to publication. Obviously, Manuscript Tracker does not have

any control over manuscripts during the time when authors Dr. Calvin H. Pearson

are making revisions on their papers. Typically, the longest Editor, Agronomy Journal

time spent in the review and publication process is when au- Colorado State University

thors are revising their manuscripts. Agricultural Experiment Station

Manuscript Tracker will give authors new freedom in that Western Colorado Research Center–Fruita

they can follow the review of their manuscripts using the 1910 L Road, Fruita, CO 801521

internet and they can check on the status of their manuscripts Phone: 970-858-3629

whenever they want. Editors will also be able to conveniently Fax: 970-858-0461

enter and maintain up-to-date review information for manu- Email: calvin.pearson@colostate.edu