ABSTRACT: The effectiveness of nitrogen tillage systems in reducing the movement of nitrate in surface and sub-surface flow in the Little Vermilion River watershed is presented. Nitrate in sub-surface tile flow have been monitored for four years from fields with various tillage and cropping management practices. Water samples have also been obtained along the mainstreams of the watershed. Concentrations of nitrate differed little among specific sampling locations along the river, but they definitely followed a seasonal cycle. Nitrate concentrations from the tile drains varied considerably between fields depending upon the cropping management systems used, primarily based on the level of nitrogen fertilizer applied. The effect of the application of large amounts of nitrogen fertilizer, particularly as a pre-plant operation, is clearly shown in the nitrate-N concentrations from tile drains. The pre-plant anhydrous-N application systems with average nitrogen application of 110 kg/ha/yr. had a mean concentration of nitrate-N of 15.5 mg/L while the side-dress and manure application systems with average nitrogen application of 97 kg/ha/yr. had a mean concentration of nitrate-N of 9.4 mg/L. The mean concentration of nitrate-N from a permanent meadow field was 1.0 mg/L. Nitrate-N losses from cropped fields have ranged from 13 to 35 kg/ha/yr. depending upon the management system. Losses from the grassed system was 2.8 kg/ha/yr. and in the most upstream river station was 12 kg/ha/yr. of nitrate-N.

KEY TERMS: Nitrate, Cropping Systems, Water Quality

The overall goal of the Little Vermilion River Agricultural Nonpoint Source Hydrologic Unit Area Project is to reduce the levels of nitrate and pesticides entering Georgetown Lake. To accomplish this goal, the Cooperative Extension Service (CES), Soil Conservation Service (SCS), and Agricultural Stabilization and Conservation Service (ASCS) are encouraging the adoption of integrated crop management (ICM) practices throughout the watershed. Besides helping improve the quality of water in the lake, these practices should also help maintain good water quality in aquifers that serve private wells.

The objective of this research is to determine if selected management practices can eliminate, reduce, or retard the movement of nitrate to ground water and streams. Studies are being conducted in the Little Vermilion River Watershed on several fields that have various practices, including fertilizer and pesticide management systems, buffer strips and wetlands.

The Little Vermilion River Agricultural Nonpoint Source Hydrologic Unit Area is located in East Central Illinois and includes 48,900 hectares in parts of Vermilion, Champaign, and Edgar counties. River water quality and sub-surface drain tile flow and water quality, as well as other practices, have been monitored in the watershed.

Seven sampling points were established along the Little Vermilion River, including Georgetown Lake. Water samples were collected at intervals following rainfall events and during baseflow. Water was analyzed for nitrate and nine pesticides.

Eight small sub-surface drainage systems were selected that have the exact extent of drainage known. Seven of the sites are in corn-soybean production in various combinations, while an eighth site is permanent meadow. Tillage practices represented by the seven sites under production include no-till, reduced tillage and conventional tillage. Nitrogen applications for the seven sites are listed in Table 1.

Table 1. Annual and Mean Nitrogen Applications, kg/ha.
 

		Crop Year*				Annual Rotation
	Site	1991-92	1992-93	1993-94	1994-95		Mean
Pre-Plant	Reduced-Till Corn-Beans	0	220	0	224		111
Application	Reduced-Till Beans-Corn	264	26	237	24		138
	Seed Corn	207	0	186	0		98
	White Corn	190	0	174	0		91
	Mean	165	62	149	62		110
Side Dress	Conventional-Till Beans-Corn	219	0	206	0	106
or Manure	No-Till Corn-Beans	0	155	0	183	85
	Corn Silage	125	137	31	125	100**
	Mean	110**	97	79	106	97

 

* Crop year is defined from harvest to harvest.

** The 1991-92 nitrogen application for Corn Silage is not included in the annual rotation mean because that site has a three year rotation period.

 

Three more drainage monitoring sites are located where soils are predominately Flanagan silt loam and Drummer silty clay loam soils. One site, designated Seed Corn, has a 6.8 ha sub-surface drainage system where high-nitrogen reduced tillage seed corn management is alternated with soybeans. The second site is an 8.4 ha sub-surface drainage system under a corn-soybean reduced tillage management system where white food grade corn is raised; thus, the name White Corn for this site. The third site is a 20.5 ha sub-surface drainage system under a corn-soybean conventional tillage management system, and is named C-Till Beans-Corn. The Seed Corn field and White Corn were tilled using only discs and field cultivators, and received means of 98 and 91 kg/ha/yr. nitrogen, respectively in pre-plant applications during the four years of cropping record. The C-Till Beans-Corn field is moldboard plowed after corn production with a field cultivator used as the secondary tillage tool; this field received a mean of 106 kg/ha/yr. nitrogen, with most of that in a side-dress application after corn planting.

At another location where soils are predominately Sabina and Xenia silt loams, a 7.5 ha sub-surface drainage system is under no-till row crop management. This field is named No-Till Corn-Beans because the cropping pattern is alternately corn and soybeans. This field receives no tillage except the planting tool. The mean of 85 kg/ha/yr. nitrogen over the four crop years was predominately a side-dress application. A second 6.9 ha sub-surface drainage system outlets from a field in permanent grass, and is named Grass.

One drainage monitoring site where soils are predominately Birkbeck and Sabina silt loam soils, designated Corn Silage, is a 10.9 ha sub-surface drainage system under soybean-corn-corn reduced tillage management. The second year corn was harvested as silage and the only fertilization over the last four years was cattle manure at the rate of 45 Mg/ha during the winter prior to corn, which was estimated to contain a mean of 100 kg/ha/yr. available nitrogen for the three year crop rotation.

Sub-surface drainage (tile) flow was sampled bi-weekly and additional samples were taken during increased flow following major rainfall events. These samples were analyzed for nitrate as well as pesticides. The sub-surface outflow depth was monitored continuously with a flume and stage recorder. Records of agrichemical application to and tillage on the monitored fields are maintained. Soil sampling was performed to provide background and periodic concentration of agrichemicals in the field soil.

Nearly five years of water quality monitoring give evidence of seasonal variation in concentration of nitrate at the river stations. Impacts of local agricultural practice and season are observed in the four years of data from the sub-surface drainage systems.

A seasonal fluctuation of nitrate-N concentrations are shown in Figure 1 for five river and one lake sampling stations. During April, May, and June, 1991, all water samples contained nitrate-N at concentrations exceeding the US EPA Maximum Contaminant Level (MCL) of 10 mg/L NO3-N. By July, 1991, however, nitrate dropped below the MCL. Nitrate levels rose somewhat during November and December and returned to greater than 10 mg/L during March through April, 1992. Nitrate-N concentrations again dropped at most locations, and were generally below the MCL at all locations except the most upstream station (30 km above dam) until February, 1993, except for a rise in July, 1992, at most stations. The February, 1993, rise to slightly above and below 10 mg/L at the station 30 km above the dam through May, 1993, was less than the peak amounts the previous two years. In July, 1993, nitrate-N concentrations again decreased below the MCL and remained low until May, 1994, except for a large concentration at the location immediately upstream from the lake. Nitrate-N concentrations were very low in the late part of 1994 when flow in the river nearly ceased. However, once again in the spring and early summer of 1995 nitrate-N concentrations again were above the MCL. Nitrate-N concentrations were again low the latter part of 1995 when river flow was very low.

Figure 1. Nitrate-N concentrations at Little Vermilion River locations and in Georgetown Lake.

Results of the nitrate concentrations for the eight tile monitoring stations are presented in Figure 2. Nitrate-N concentrations were above the MCL at all but a few sampling times from the Reduced Till (R-Till), Seed Corn and White Corn locations. Nitrate-N concentrations were generally slightly above and below the MCL from the Conventional Till (C-Till), No-till, and Corn Silage locations. However, nitrate-N concentrations from the corn silage location were quite large in early 1995. Nitrate-N concentrations from the Continuous Meadow location averaged 1.0 mg/L NO3-N for the period of record. As expected, the seasonal pattern of nitrate-N concentrations from the tile stations is similar to, but less pronounced than that found in the river (Figure 1); after all, the tile systems supply the river flow. However, it is well to note that the scales of nitrate-N concentration of Figures 1 and 2 are quite
 

Figure 2. Nitrate-N concentrations at eight tile monitoring sites.

different, with the concentrations in the river about half that of the maximum tile outlets. Either dilution by other low nitrate flows or denitrification or both are occurring.

The amount of fertilization, as well as the method and timing of nitrogen application affects the nitrate-N concentrations from field tile. The greatest concentrations are from R-Till Corn-Beans, R-Till Beans-Corn, Seed Corn and White Corn fields where pre-plant broadcast fertilization at somewhat greater nitrogen amounts are applied (Table 1). These four cropping systems received the amount of nitrogen fertilizer for each crop year of record as shown in Table 1. The average nitrogen applied to these four systems was 165 kg/ha in 1991-92, 62 kg/ha in 1992-93, 149 kg/ha in 1993-94, and 62 kg/ha in 1994-95; for an overall average of 110 kg/ha/yr.

The lesser concentrations of NO3-N in the tile discharge come from the C-Till Beans-Corn and No-Till Corn-Beans fields where side dress application of nitrogen to corn was used, and the Corn Silage field where cattle manure was the only source of nitrogen (Table 1). The average nitrogen applied to these three systems was 110 kg/ha in 1991-92, 97 kg/ha in 1992-93, 79 kg/ha in 1993-94, and 106 kg/ha in 1994-95; for an overall average of 97 kg/ha/yr.

The average nitrate-N concentrations and standard deviation in the tile flow for the periods of record are shown in Table 2. The R-Till Corn-Beans, R-Till Beans-Corn, Seed Corn, and White Corn management systems produced average nitrate-N concentrations of 15.0 mg/L, 14.8 mg/L, 16.5 mg/L,

Table 2. Mean and Standard Deviation Nitrate-N Concentrations in Tile Outflows.
 

		NO3-N, mg/L
Management System	Period of Observation	Mean	Standard Deviation
R-Till Corn-Beans	12/91 - 12/95	15.0	6.1
R-Till Beans-Corn	2/92 - 12/95	14.8	4.5
Seed Corn	9/92 - 12/95	16.5	4.3
White Corn	4/94 - 12/95	15.6	5.7
Pre-Plant Application Mean		15.5
C-Till Beans-Corn	11/92 - 12/95	9.6	3.6
No-Till Corn-Beans	10/91 - 12/95	7.3	2.8
Corn Silage	8/93 - 612/95	11.2	4.8
Side-Dress or Manure Mean		9.4
Grass	10/91 - 12/95	1.0	1.1

and 15.6 mg/L, respectively, for the period of observation (Table 2). The mean concentration for this management group is 15.5 mg/L. The average nitrate-N concentrations for the C-Till Beans-Corn, No-Till Corn-Beans and the Corn Silage management systems were 9.6 mg/L, 7.3 mg/L, and 11.2 mg/L, respectively. The mean concentration for this management group is 9.4 mg/L which is significantly different than the 15.5 mg/L mean of the other management group. The lesser concentrations were from fields where nitrogen was usually applied to corn as a side dress application one month after planting when the corn can immediately utilize the nitrogen and where fertilization was animal manure that is a combination of readily-available and slow-release nitrogen. The pre-plant application treatment means are significantly different from the side-dress and manure application treatment means with an overall difference between the treatments of 6.1 mg/L nitrate - N.

Total nitrate-N lost at each monitoring station may be computed from the continuous flow records and nitrate-N concentrations from the water samples. The results of that analysis is illustrated in Figure 3. Nitrate-N lost from the Pre-plant application systems are from 25 to 35 kg/ha/yr., while the side-dress and manure application systems lost 10 to 20 kg/ha/yr. Only 2.8 kg/ha/yr. of nitrate-N is lost from the Grass system. The nitrate-N flowing in the river at the most upstream station (County Line) is 12 kg/ha/yr.

Figure 3. Nitrate-N lost at each of the tile monitoring stations and at the upstream most river station.

The objective of this study was to evaluate the effectiveness of tillage and cropping management systems in reducing the movement of nitrate in surface and sub-surface flow. Nitrate in sub-surface tile flow have been monitored for four years from fields with various tillage and cropping management practices. Samples have also been obtained along the mainstream of the watershed for nearly five years.

Concentrations of nitrate differed little among specific sampling locations along the river, but they definitely followed a seasonal cycle. Nitrate concentrations from tile drains varied considerably between fields depending upon the cropping management systems used, with concentrations varying seasonally as in the river.

The effect of the application of broadcast, pre-plant nitrogen fertilizer is clearly shown in the nitrate-N concentrations from tile drains. The pre-plant anhydrous-N application systems with average nitrogen application of 110 kg/ha/yr. had a mean concentration of nitrate-N of 15.5 mg/L while the side-dress and manure application systems with average nitrogen application of 97 kg/ha/yr. had a mean concentration of nitrate-N of 9.4 mg/L. The mean concentration of nitrate-N from a permanent meadow field was 1.0 mg/L.

Nitrate-N losses from cropped fields have ranged from 13 to 35 kg/ha/yr. depending upon the management system. Losses from the grassed system was 2.8 kg/ha/yr. and in the most upstream river station was 12 kg/ha/yr. of nitrate-N.

Contribution of the Illinois Agricultural Experiment Station, University of Illinois at Urbana-Champaign as a part of Project 10-309 and Southern Regional Research Project S-218. Supported in part with funds from the Little Vermilion River Hydrologic Unit Area Project and by the Illinois Groundwater Consortium (SIUC 92-04). We also wish to acknowledge the assistance of the Champaign County Soil and Water Conservation District that sponsored the installation of the County Line gaging station.

The authors wish to thank Steve Maddock for his installation efforts and continued vigilance over equipment; Mary Ann Hoeffligger, formerly Resource Conservationist, SCS, USDA, Danville, IL, for her data collection assistance and Duane Kimme, Extension Assistant, for his laboratory analyses.