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TECHNICAL REPORTS

Surface Water Quality

Nitrate Losses in Subsurface Drainage from a Corn–Soybean Rotation as Affected by Fall and Spring Application of Nitrogen and Nitrapyrin

University of Minnesota Southern Research and Outreach Center, 35838 120th Street, Waseca, MN 56093-4521

^* Corresponding author (grandall{at}umn.edu)

Received for publication June 4, 2004.

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Substantial amounts of NO₃ from agricultural crop production systems on poorly drained soils can be transported to surface water via subsurface drainage. A field study was conducted from the fall of 1993 through 2000 on a tile-drained Canisteo clay loam soil (fine-loamy, mixed, superactive, calcareous, mesic Typic Endoaquoll) to determine the influence of fall vs. spring application of N and nitrapyrin [NP; 2-chloro-6-(trichloromethyl) pyridine] on NO₃ losses from a corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] rotation. Four anhydrous ammonia treatments (fall N, fall N + NP, spring preplant N, and spring N + NP) were replicated four times and applied at 135 kg N ha^–1 for corn on individual drainage plots. Drainage occurred in all seven years. Seventy-one percent of the annual drainage and 75% of the annual NO₃ loss occurred in April, May, and June. Fifty-four percent of the NO₃ lost in the drainage occurred during the corn phase and 46% during the soybean phase. Annual flow-weighted NO₃–N concentrations for the fall, fall + NP, spring, and spring + NP treatments averaged 14.3, 11.5, 10.7, and 11.3 mg L^–1 during the corn phase but annual NO₃–N concentrations were still 10 mg L^–1 in three of six years for the spring preplant treatment. Averaged across the six rotation cycles, flow-normalized NO₃–N losses ranked in the order: fall N > spring N + NP > fall N + NP > spring N. Under these conditions, NO₃ losses in subsurface drainage from a corn–soybean rotation can be reduced 14% by spring N and 10% by late fall N + NP compared with fall-applied N. Nitrate losses were not appreciably reduced by adding NP to spring preplant N.

Abbreviations: ET, evapotranspiration • NP, nitrapyrin

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
ARTIFICIAL DRAINAGE through subsurface tile lines is a common water management practice in highly productive agricultural areas with poorly drained soils that have seasonally perched water tables or shallow ground water. This management practice increases crop productivity, reduces risk (i.e., poor growth and yield, water logged rooting systems, soil compaction, and trafficability), and improves economic returns to producers, particularly in the north-central region of the United States (Zucker and Brown, 1998). Research has shown that substantial amounts of N, particularly NO₃, can be transported in tile drainage from the landscape to surface waters (David and Gentry, 2000; Fenelon and Moore, 1998; Kladivko et al., 1991). Nitrate concentrations in the Mississippi River are generally greatest in tributaries where artificially drained soils planted to corn and soybean dominate the landscape (Burkart and James, 1999). Nitrate transported in the Mississippi River to the Gulf of Mexico has been linked indirectly to hypoxia off the coast of Louisiana (Rabalais et al., 1996; Turner and Rabalais, 1994).

Monitoring of subsurface tile drainage water can be useful in assessing the impact of agricultural management practices on surface and ground water quality (Baker and Johnson, 1981; Gast et al., 1978; Hallberg et al., 1986; Kanwar et al., 1988; Randall and Goss, 2001). Long-term drainage studies to assess management practices are necessary if accurate estimates of nutrient losses and performance evaluation of the practices are desired, because short-term results obtained under unusually wet or dry conditions could be misleading if used by themselves (Jaynes et al., 1999; Owens et al., 2000; Randall and Iragavarapu, 1995). The fruitfulness of long-term research was also emphasized by Goldstein et al. (1998) when evaluating complex systems integrating several measures to reduce NO₃ pollution in drainage waters from the widespread corn–soybean rotation found in the U.S. Corn Belt. Field studies have shown that the corn–soybean rotation contributes significant losses of NO₃ to subsurface drainage waters (Dinnes et al., 2002; Goldstein et al., 1998; Randall et al., 1997).

Management of N to minimize NO₃ leaching losses in row-crop farming is based on a simple concept—avoid excess NO₃ in the root zone when the soil is vulnerable to leaching by excess rainfall, usually spring and fall (Keeney and Follett, 1991). Spring applications of N are frequently superior to fall application because N loss is less between time of N application and uptake by the crop (Randall and Goss, 2001). However, many U.S. corn growers, especially in the northern part of the Corn Belt, prefer to apply N in the fall because they usually have more time, field conditions are better for application, and the cost of N in the fall is usually less.

To enhance the efficiency of fall-applied N, nitrification inhibitors such as nitrapyrin (e.g., N-Serve) are often added to delay the conversion of ammonium to nitrate (Hoeft, 1984). Nitrapyrin added to spring-applied urea for continuous corn in Ohio reduced NO₃ losses in drainage water from lysimeters (Owens, 1987). Smiciklas and Moore (1999) reported that NO₃–N concentrations in subsurface drainage from six 2-ha drainage parcels were 58% greater for fall-applied N than for the same N rate applied in the spring in Illinois. Nitrate N concentrations were also decreased by 9% with NP compared to without NP. Nitrate N losses in subsurface drainage from an eight-year Minnesota study were reduced 18% when including NP with late fall-applied ammonia compared with not using NP, but spring-applied NP was not examined (Randall et al., 2003).

The objective of this seven-year, subsurface, tile drainage study was to determine the effect of fall and spring applications of anhydrous ammonia with and without NP for corn in rotation with soybean on NO₃ losses from both crops in the rotation.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
A field experiment was conducted on a poorly drained Canisteo clay loam glacial till soil from 1994 through 2000 at the University of Minnesota's Southern Research and Outreach Center in Waseca, MN. The site was located on a 0 to 1% slope, and the Ap horizon contained 5.5% organic matter and had a pH of 7.8. Thirty-six individual subsurface tile drainage plots were installed in 1976. Each plot, measuring 9.1 by 6.1 m, is isolated to a depth of 1.8 m by installing a 12-mil-thick plastic sheeting in a trench around each plot, which was then backfilled. A separate drain outlet consists of a tile line (6.1 m in length) placed 1.2 m deep and located 1.5 m from one end of each plot (spaced to simulate a 15.2-m spacing).

Beginning in 1986, a corn–soybean rotation was started with corn planted on one-half of the experimental area while soybean was planted on the other half. Thirty-two plots (a set of 16 for corn and a set of 16 for soybean) with the most uniform drainage were selected for the study. For drainage purposes, the experimental design consisted of a 4 x 4 Latin square where the rows and columns were based on annual tile discharge from each plot during 1977–1983. Spatially, however, the plots were arranged in a randomized complete-block design with four replications and restricted randomization. Specific information on tile plot arrangement to reduce treatment variability can be found in Randall et al. (2003). In the fall of 1993, four N treatments (fall N, fall N + NP, spring N, and spring N + NP) were then assigned within each row and column to minimize drainage variability among treatments. The N treatments were not re-randomized each year; thus, each treatment for corn occupied the same plots in 1994, 1996, and 1998 for one set of 16 plots and in 1995, 1997, and 1999 for the other set of 16 plots. The fall N, fall N + NP, and spring N treatments were continued on the same plots as in 1987–1993, whereas the spring N + NP treatment replaced the split N treatment (Randall et al., 2003).

Anhydrous ammonia was applied for corn at a rate of 135 kg N ha^–1 for all N treatments. Nitrapyrin (N-Serve; Dow AgroSciences, Indianapolis, IN) was applied at the recommended rate of 0.56 kg a.i. ha^–1. Dates of application ranged from 20 October to 6 November for the fall treatments and 14 April to 11 May for the spring preplant treatments. Soil temperatures at the 15-cm depth on the day of fall application were 10°C in four of six years and averaged between 1.0 and 11.2°C in the 10-d period following application, indicating that soil temperatures were cooling to minimize nitrification in most years. No N fertilizer was applied for the soybean phase. Specific fertilization information and cultural practices used in the establishment and production of the corn and soybean are shown in Randall and Vetsch (2005).

The experiment was conducted under ambient precipitation. Precipitation data collected daily at a site 0.5 km from the drainage site were summarized as monthly and seasonal totals from 1994 through 2000 (Table 1).

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Growing Season Precipitation and Drain Flow
Growing season precipitation (April–October) during the seven-year period was consistent ranging from 599 mm (94% of normal) in 1996 to 756 mm (118% of normal) in 1999 (Table 1). Rainfall was above normal in six of seven years and drainage was plentiful in all years except 1997 (Table 2). Distribution of rainfall within the growing season was highly variable among months, however, which in turn led to considerably different drainage patterns among years (Table 3). There were only two years when significant drainage occurred in the fall. A combination of soil thawing, snow melting, and 69 mm of rainfall in the last week of March 1998 was responsible for more than 80% of the annual drainage occurring in March and April. Thus, drainage was distributed across all months from March through November, except September, in this seven-year study.

View this table: [in this window] [in a new window]   Table 3. Monthly distribution of subsurface tile drainage averaged across the corn and soybean phases of the study from 1994 through 2000.

Because NO₃ losses are greatly influenced by the quantity of drain flow, it was important to determine if annual subsurface drain flow was related to or influenced by the N treatments. Subsurface drain flow was not statistically related (P = 0.10 level) to any of the treatments in any year (Table 2).

Nitrate Nitrogen Concentration in Tile Drainage
Flow-weighted annual NO₃–N concentrations in the tile water for both the corn and soybean phases of the rotation were influenced by the main effect of time of application, but not by the main effect of NP (Table 4). During the corn phase, NO₃–N concentrations were greater for fall-applied N in three of six years (1995, 1998, and 1999) compared with spring-applied N. However, during the soybean phase, NO₃–N concentrations in the drainage water were affected by time of N application in only one of six years. In 1997, NO₃–N concentrations were slightly but significantly greater when N had been applied for corn in the spring of 1996 compared with the fall of 1995. This may have been due to limited drainage in 1996 (87 mm). These results suggest that slightly more spring-applied fertilizer N for corn carried over and was leached into the tiles in 1997 compared with fall-applied N.

Temporal variation of monthly flow-weighted NO₃–N concentrations for the main effects of time of N application and NP across the 1994 through 2000 drainage period are shown in Fig. 1 . Monthly drainage exceeded 9 mm and all tiles were flowing for all months shown. Highest NO₃–N concentrations in the drainage water were found with the fall N treatment for corn in April and May 1998 and in April, May, and June 1999. Other months where fall-applied N gave greater NO₃–N concentrations included April and May 1995 and July 1997 for corn. Nitrate N concentrations were greater for spring-applied N compared with fall N in November 1996 (corn), July and August 1997 (soybean), and June 2000 (soybean). When averaged across application time, NP did not affect average NO₃–N concentration in the drainage for any of the months. Nitrate N concentrations in general tended to be slightly lower during the soybean phase of the rotation compared with the corn phase.

View larger version (25K): [in this window] [in a new window]   Fig. 1. Monthly flow-weighted nitrate N concentration in subsurface tile drainage as affected by time of N application (time) and nitrapyrin (NP) for (a) corn grown in even years (1994, 1996, and 1998) and (b) corn grown in odd years (1995, 1997, and 1999) for six cycles of a corn–soybean rotation. All months shown had drainage exceeding 9 mm. Notations above each monthly data set indicate statistical significance at P = 0.01 (**), 0.05 (*), and 0.10 (). Absence of a notation above a monthly data set indicates no significant difference between the flow-weighted nitrate N concentrations.

Nitrate Nitrogen Losses in Tile Drainage
Annual NO₃–N losses (flux), the product of water flow multiplied by NO₃–N concentration, were affected substantially by growing season precipitation and NO₃–N concentration in the drainage water in both the corn and soybean phases of this study (Table 5). Nitrate N losses from the corn phase ranged from about 5 kg ha^–1 yr^–1 in 1997 to about 50 kg ha^–1 yr^–1 in the wettest year (1999) when averaged across the four N treatments. The same trend, but with slightly lower losses, occurred in the soybean phase. These results dramatically show the strong effect of precipitation even in a seven-year period where drainage occurred each year. The value of long-term studies becomes quite apparent in research where climate plays such a significant role, especially when the findings may affect environmental policy development.

Averaged across treatments, 77 and 73% of the NO₃ lost in the drainage water during this six-year period occurred in April through June for corn and soybean, respectively (data not shown). Fifty-four percent of the total NO₃ lost for the corn–soybean rotation occurred from the corn plots and 46% from the soybean plots (Table 5).

The high NO₃–N concentration for corn in 1999 shown in Table 4 and Fig. 1 and high losses shown in Table 5 illustrate a worst-case scenario for fall-applied N. Anhydrous ammonia was applied on 20 Oct. 1998 when the 15-cm-deep soil temperature was 8.8°C. Soil temperature at 15 cm averaged 11.2°C for the next 10 d, 4.4°C for November, and 5.3°C for the first 10 d in December. The soil did not freeze until 23 December. Soil samples taken vertically through the anhydrous ammonia bands indicated that much of the N had been nitrified to NO₃ by 1 December, especially when NP was not used. From 1 to 13 Apr. 1999 soil temperature averaged 7.6°C and 118 mm of rainfall occurred, resulting in highly saturated conditions leading to denitrification, leaching, and abundant subsurface drainage. Cumulative NO₃–N losses in the drainage beginning on 6 April and continuing through 30 June are shown as a function of time of N application in Fig. 2 . Nitrate N losses spiked as a result of major drainage events around 6–12 April, 12–15 May, 21–23 May, and 11–13 June. Precipitation during each of these events totaled 106, 64, 31, and 52 mm, respectively. The effect of time of N application started to appear on 9 April after about 90 mm of drainage. The spring N treatments were applied on 28 April. By that date, 18 kg NO₃–N ha^–1 had already been lost in the drainage, presumably from mineralization of soil organic matter, soybean residue, and soil N in the profile. About 27 kg NO₃–N ha^–1 was lost in the drainage from the fall-applied N plots by 28 April. By difference, we assume that 9 kg NO₃–N ha^–1 was due to the fall-applied N. At the end of the 1999 drainage period (6 July), NO₃–N losses in the drainage water totaled 62 and 38 kg ha^–1 for the fall and spring N applications, respectively, averaged across NP. Nitrification of the spring-applied anhydrous ammonia and subsequent leaching to the tile drains was not likely until at least early June if we assume about 90 mm of drainage is needed to leach NO₃ from the point of injection (15–18 cm) to the tile depth (1.2 m). Further examination of the four major drainage events (6–12 April, 12–15 May, 21–23 May, and 11–13 June) revealed NO₃ losses averaging 19.4, 11.2, 7.0, and 7.2 kg ha^–1 from the fall-applied treatments and 14.6, 5.4, 3.5, and 3.8 kg ha^–1 from the spring-applied treatments, respectively. These data indicate that only about 25% of the NO₃ lost from the fall plots during the 6–12 April event came from fall-applied N compared with 50% coming from fall-applied N in the two May events and the June event. Thus, it appears that very little of the 38 kg NO₃–N ha^–1 lost in drainage for the year could have come directly from the spring-applied N. Based on this analysis, NO₃ resulting from the soybean phase and the soil organic matter probably accounted for at least 50% of the NO₃ lost in drainage from the fall-applied plots and >90% from the spring-applied plots. Secondarily, from a water quality perspective, use of a nitrification inhibitor under these conditions did not measurably reduce NO₃–N losses in drainage water for either fall or spring N application. The extended warm fall and early warm and wet spring encouraged rapid nitrification of fall-applied ammonia and degradation of the NP before the three-month period where substantial drainage occurred. On the other hand, minimal drainage occurred after spring-applied N had nitrified, limiting the possibility of NP showing any effect on NO₃ losses in drainage water.

View larger version (25K): [in this window] [in a new window]   Fig. 2. Cumulative nitrate N loss in subsurface tile drainage as influenced by precipitation events and time of N application averaged across nitrapyrin (NP) in 1999.

Annual flow-normalized NO₃–N losses expressed on a per-centimeter drainage basis provide an excellent basis on which to combine multiple studies and evaluate management practices across a wide range of climatic environments. Combining the flow-normalized NO₃–N concentrations for the fall N, fall N + NP, and spring N treatments from the six rotation cycles in this study with the four rotation cycles from 1990–1993 period (Randall et al., 2003) gives a 10-cycle (20 crop years) average of 1.41, 1.22, and 1.20 kg NO₃–N ha^–1 cm^–1 for these three N treatments, respectively. Thus, compared with late-fall application of N without NP, NO₃–N losses in the subsurface tile drainage water were reduced by 14 and 15% for fall N + NP or spring N, respectively.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Numerous factors, including annual precipitation and temporal distribution of precipitation, affect subsurface tile drainage losses, their interpretation, and their applicability for widespread adoption to watershed- or basin-size scales. For these reasons, long-term studies with detailed measurements are necessary to smooth year-to-year climatic variability, thereby providing more meaningful information.

This study (six cycles of a corn–soybean rotation, i.e., 12 crop years) conducted across a seven-year period where drainage occurred each year and in each month from March through November, except September, provides information on the hydrologic effects governing losses of NO₃ from four N application strategies for corn grown in rotation with soybean. The primary findings are:

• Seventy-one percent of the annual subsurface drainage occurred in April through June. Because precipitation frequently exceeds evapotranspiration during these months, substantial percolation and drainage occurs, which presents a tremendous challenge for management of fall-applied N. If significant nitrification of fall-applied N occurs either in the fall or in the spring before crop uptake of N or increased ET, losses of NO₃ in drainage water can be large. On the other hand, few drainage events occurred in the fall, resulting in only 10% of the annual drainage lost in October and November.
  
• Seventy-seven and 73% of the NO₃ lost annually to subsurface drainage from corn and soybean, respectively, occurs in April, May, and June. This suggests that fall-applied N for corn and mineralization of soil organic matter and soybean residue, including roots, could contribute greatly to leaching losses in the corn phase of the rotation. During July and August, uptake of N is significant for both crops and ET generally exceeds rainfall, leading to small losses of NO₃. These findings agree with drainage studies reported by Jaynes et al. (1999) and NO₃ accumulations in the Mississippi River reported by Antweiler et al. (1995).
  
• When averaged across all four N treatments, 54% of the NO₃ in the drainage occurred during the corn phase and 46% during the soybean phase. Thus, when evaluating the effect of N management practices for corn on NO₃ losses to subsurface drainage, both the corn and soybean phases need to be included in the analysis.
  
• Annual flow-weighted NO₃–N concentrations for the fall, fall + NP, spring, and spring + NP treatments averaged 14.3, 11.5, 10.7, and 11.3 mg L^–1 during the corn phase and 10.3, 9.5, 10.8, and 11.0 mg L^–1 during the soybean phase, respectively. These data illustrate the difficulty of obtaining NO₃–N concentrations less than the U.S. Public Health drinking water standard even when N best management practices are employed for a corn–soybean rotation on this soil.
  
• Compared with late fall–applied N as anhydrous ammonia, losses of NO₃ in subsurface drainage from a corn–soybean rotation can be reduced by 10% by including NP with late fall–applied ammonia, by 14% with spring preplant–applied ammonia, and by 6% with spring-applied N + NP. These data indicate that adding NP to spring preplant–applied N did not reduce NO₃ losses in subsurface drainage sufficiently on this soil to warrant its use as a spring management strategy.
  

	ACKNOWLEDGMENTS

 
The authors thank the technicians on the soils crew for collecting the data and Deanne Nelson for preparing the manuscript. Partial funding of this research was provided by Dow AgroSciences and is greatly appreciated.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

• Antweiler, R.C., D.A. Goolsby, and H.E. Taylor. 1995. Nutrients in the Mississippi River. p. 73–86. In R.H. Meade (ed.) Contaminants in the Mississippi River, 1987-92. Circ. 1133. Available online at http://water.usgs.gov/pubs/circ/circ1133/ (verified 18 Oct. 2004). USGS, Reston, VA.
• Baker, J.L., and H.P. Johnson. 1981. Nitrate-nitrogen in tile drainage as affected by fertilization. J. Environ. Qual. 10:519–522.[Abstract/Free Full Text]
• Burkart, M.R., and D.E. James. 1999. Agricultural-nitrogen contributions to hypoxia in the Gulf of Mexico. J. Environ. Qual. 28:850–859.[Abstract/Free Full Text]
• David, M.B., and L.E. Gentry. 2000. Anthropogenic inputs of nitrogen and phosphorus and riverine export for Illinois, USA. J. Environ. Qual. 29:494–508.[Abstract/Free Full Text]
• Dinnes, D.L., D.L. Karlen, D.B. Jaynes, T.C. Kaspar, J.L. Hatfield, T.L. Colvin, and C.A. Cambardella. 2002. Nitrogen management strategies to reduce nitrate leaching in tile- drained Midwestern soils. Agron. J. 94:153–171.[Abstract/Free Full Text]
• Fenelon, J.M., and R.C. Moore. 1998. Transport of agrichemicals to ground and surface water in a small central Indiana watershed. J. Environ. Qual. 27:884–894.[Abstract/Free Full Text]
• Gast, R.G., W.W. Nelson, and G.W. Randall. 1978. Nitrate accumulation in soils and loss in tile drainage following nitrogen applications to continuous corn. J. Environ. Qual. 7:258–261.[Abstract/Free Full Text]
• Goldstein, W.A., M. Scully, D.H. Kohl, and G. Shearer. 1998. Impact of agricultural management on nitrate concentrations in drainage waters. Am. J. Alternative Agric. 13:2–7.
• Hallberg, G.R., J.L. Baker, and G.W. Randall. 1986. Utility of tile-line effluent studies to evaluate the impact of agricultural practices on groundwater. p. 298–326. In Proc. Conf. Agricultural Impacts on Groundwater, Omaha, NE. 11–13 Aug. 1986. Natl. Well Water Assoc., Dublin, OH.
• Hoeft, R.G. 1984. Current status of nitrification inhibitor use in U.S. agriculture. p. 561–570. In R.D. Hauck (ed.) Nitrogen in crop production. ASA, CSSA, and SSSA, Madison, WI.
• Jaynes, D.B., J.L. Hatfield, and D.W. Meek. 1999. Water quality in Walnut Creek watershed: Herbicides and nitrate in surface waters. J. Environ. Qual. 28:45–59.[Abstract/Free Full Text]
• Kanwar, R.S., J.L. Baker, and D.G. Baker. 1988. Tillage and split N-fertilization effects on subsurface drainage water quality and crop yields. Trans. ASAE 31:453–460.
• Keeney, D.R., and R.F. Follett. 1991. Managing nitrogen for groundwater quality and farm profitability: Overview and introduction. p. 1–7. In R.F. Follett et al. (ed.) Managing nitrogen for groundwater quality and farm profitability. SSSA, Madison, WI.
• Kladivko, E.J., G.E. Van Scoyoc, E.J. Monke, K.M. Oates, and W. Pask. 1991. Pesticide and nutrient movement into subsurface tile drains on a silt loam soil in Indiana. J. Environ. Qual. 20:264–270.[Abstract/Free Full Text]
• Lucey, K.J., and D.A. Goolsby. 1993. Effect of climatic variations over 11 years on nitrate- nitrogen concentrations in the Raccoon River, Iowa. J. Environ. Qual. 22:38–46.[Abstract/Free Full Text]
• Owens, L.B. 1987. Nitrate leaching losses from monolith lysimeters as influenced by nitrapyrin. J. Environ. Qual. 16:34–38.[Abstract/Free Full Text]
• Owens, L.B., R.W. Malone, M.J. Shipitalo, W.M. Edwards, and J.V. Bonta. 2000. Lysimeter study of nitrate leaching from a corn-soybean rotation. J. Environ. Qual. 29:467–474.[Abstract/Free Full Text]
• Rabalais, N.N., R.E. Turner, D. Justic, Q. Dortch, W.J. Wiseman, Jr., and B.K. Sen Gupta. 1996. Nutrient changes in the Mississippi River and system responses on the adjacent continental shelf. Estuaries 19:386–407.[ISI]
• Randall, G.W. 1998. Implications of dry and wet cycles on nitrate loss to subsurface tile drainage. p. 53–60. In L.C. Brown (ed.) Drainage in the 21st century: Food production and the environment. Proc. 7th Annual Drainage Symp., Orlando, FL. 8–10 Mar. 1998. Am. Soc. of Agric. Eng., St. Joseph, MI.
• Randall, G.W., and M.J. Goss. 2001. Nitrate losses to surface water through subsurface tile drainage. p. 95–122. In R.F. Follett and J.L. Hatfield (ed.) Nitrogen in the environment: Sources, problems, and management. Elsevier Sci., Amsterdam.
• Randall, G.W., D.R. Huggins, M.P. Russelle, D.J. Fuchs, W.W. Nelson, and J.L. Anderson. 1997. Nitrate losses through subsurface tile drainage in CRP, alfalfa, and row crop systems. J. Environ. Qual. 26:1240–1247.[Abstract/Free Full Text]
• Randall, G.W., and T.K. Iragavarapu. 1995. Impact of long-term tillage systems for continuous corn on nitrate leaching to tile drainage. J. Environ. Qual. 24:360–366.[Abstract/Free Full Text]
• Randall, G.W., and J.A. Vetsch. 2005. Corn production on a subsurface-drained Mollisol as affected by fall versus spring application of nitrogen and nitrapyrin. Agron. J. 97:472–478.[Abstract/Free Full Text]
• Randall, G.W., J.A. Vetsch, and J.R. Huffman. 2003. Nitrate losses in subsurface drainage from a corn-soybean rotation as affected by time of nitrogen application and use of nitrapyrin. J. Environ. Qual. 32:1764–1772.[Abstract/Free Full Text]
• Rehm, G., M. Schmitt, G. Randall, J. Lamb, and R. Eliason. 2000. Fertilizing corn in Minnesota. FO-3790. Univ. of Minnesota Ext. Serv., St. Paul.
• SAS Institute. 1988. SAS/STAT user's guide. Release 6.08 ed. SAS Inst., Cary, NC.
• Smiciklas, K.D., and A.S. Moore. 1999. Fertilizer nitrogen management to optimize water quality. p. 117–124. In R.G. Hoeft (ed.) Illinois Fertilizer Conf. Proc., Peoria, IL. 25–27 Jan. 1999. Also available online at http://frec.cropsci.uiuc.edu/1999/report10/ (verified 18 Oct. 2004). Univ. of Illinois, Urbana-Champaign.
• Turner, R.E., and N.N. Rabalais. 1994. Coastal eutrophication near the Mississippi River delta. Nature (London) 368:619–621.[ISI]
• Zucker, L.A., and L.C. Brown (ed.) 1998. Agricultural drainage: Water quality impacts and subsurface drainage studies in the Midwest. Bull. 871. Ohio State Univ. Ext., Columbus.

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