**Nebraska Corn**

The Nebraska corn scenario was developed to represent an environment in
which field corn is grown in an area where rainfall is high and soils
are more vulnerable to runoff than most places in the state. Based on
the 2002 USDA National Agricultural Statistics Summary, Nebraska has the
third highest acreage of corn in the nation, with 7,344,715 acres (USDA,
2005), representing 10.8% of the corn acreage in the United States.
Besides field corn, two other crops are in the species of *Zea mays:*
popcorn and sweet corn. However, this scenario is not intended to be
used for either of these two other forms of corn as they have different
cultural practices and tend to be more prominent in other parts of the
country than the Midwest.

While irrigation extends corn culture west across Nebraska along the
Platte River and its tributaries, unirrigated corn is predominantly
grown along the eastern edge of the state. In general, occurrence of
pesticides in surface waters from use on irrigated corn fields is less
than in areas which rely on natural rainfall. The two top counties in
unirrigated acreage are just west of Omaha; Saunders and Lancaster.
Since Omaha also has the most annual rainfall of the candidate weather
stations (Table 1) and close to the highest average June precipitation,
it was selected as the weather station for the scenario. The top
unirrigated corn acreage county, Saunders, was selected as the location
for the Nebraska corn scenario as it is due west of Omaha about 20 mi.
There are 127,150 acres of unirrigated corn in Saunders County and a
total of 180, 288 acres of corn (USDA, 2005). Saunders ranks third in
corn acreage overall, behind York and Hamilton Counties.

  ---------------- ------------------ ------------------- ----------------
  **Table 1.**                                            
  Candidate                                               
  Weather Stations                                        
  in Nebraska for                                         
  the NE Corn                                             
  Scenario.                                               

  Station ID       Location           Annual Average      June Average
                                      Precipitation       Precipitation

  W14935           Grand Island, NE   25.9 in             3.7 in

  W14941           Norfolk, NE        26.7 in             4.3 in

  W24023           North Platte, NE   19.9 in             3.2 in

  W24028           Scotts Bluff, NE   16.3 in             2.6 in

  **W94918**       **Omaha, NE**      **30.2 in**         **4.0 in**
  ---------------- ------------------ ------------------- ----------------

The site for this scenario is in MLRA M106, the Kansas and Nebraska
Loess Drift Hills. This area, which is located in the Platte River
watershed of the Missouri Basin, is almost entirely dissected till
plains. Soils in this area have dominantly formed in till, alluvium, or
colluvium (USDA, 2006). Corn, soybeans, sorghum, and wheat are the
dominant crops, but 22% of the land is grasslands

The soil selected for the scenario is the Filbert silt loam, which is
classified as a fine, smectitic, mesic Vertic Argialbolls and is in
Hydrologic Group D. It is not a benchmark soil, but no benchmark soils
that are used extensively for corn agriculture in C & D Hydrologic
Groups occur in the county. Ten percent of the soils in Saunders County
are in Group D, and Filbert soil is moderately extensive itself covering
4.5% of the land area in the county. Because D soils are somewhat
extensive in the county and in order to be protective of these more
vulnerable sites, a D soil was chosen to represent the county.

+-----------------+----------+-----------------------------------------+
| **Table 2**.    |          |                                         |
| PRZM 3.12.2     |          |                                         |
| Climate and     |          |                                         |
| Time Parameters |          |                                         |
| for Saunders    |          |                                         |
| County, NE Corn |          |                                         |
| Scenario.       |          |                                         |
+-----------------+----------+-----------------------------------------+
| Parameter       | Value    | Source/Comments                         |
+-----------------+----------+-----------------------------------------+
| Starting Date   | Jan. 1,  | Meteorological File from Omaha, NE      |
|                 | 1961     | (W94918)                                |
+-----------------+----------+-----------------------------------------+
| Ending Date     | Dec. 31, | Meteorological File from Omaha, NE      |
|                 | 1990     | (W94918)                                |
+-----------------+----------+-----------------------------------------+
| Pan Evaporation | 0.71     | PRZM Manual Figure 5.1 (USEPA, 2006)    |
| Factor (PFAC)   |          |                                         |
+-----------------+----------+-----------------------------------------+
| Snowmelt Factor | 0.36 cm  | Number range CHAPTER Maximum value of   |
| (SFAC)          | °C^-1^   | minimum range of PRZM Manual Table 5.1  |
|                 |          | (USEPA, 2006)                           |
+-----------------+----------+-----------------------------------------+
| Minimum Depth   | 17.5 cm  | PRZM Manual (USEPA, 2006) Average of    |
| of              |          | 15-20 cm                                |
|                 |          |                                         |
| Evaporation     |          |                                         |
| (ANETD)         |          |                                         |
+-----------------+----------+-----------------------------------------+
| Pan Factor Flag | 0        | Pan Factor Flag set to read from        |
| (IPEIND)        |          | weather data as per guidance (USEPA,    |
|                 |          | 2004)                                   |
+-----------------+----------+-----------------------------------------+

+-----------------+----------+-----------------------------------------+
| **Table 3.**    |          |                                         |
| PRZM 3.12.2     |          |                                         |
| Erosion and     |          |                                         |
| Landscape       |          |                                         |
| Parameters for  |          |                                         |
| Saunders        |          |                                         |
| County, NE Corn |          |                                         |
| Scenario.       |          |                                         |
+=================+==========+=========================================+
| Parameter       | Value    | Source/Comments                         |
+-----------------+----------+-----------------------------------------+
| Method to       | 4 (MUSS) | PRZM Manual (USEPA, 2006)               |
| Calculate       |          |                                         |
| Erosion         |          |                                         |
| (ERFLAG)        |          |                                         |
+-----------------+----------+-----------------------------------------+
| USLE K Factor   | 0.37     | USDA NRCS Soil Data Mart                |
| (USLEK)         | tons     | (http://soildatamart.nrcs.usda.gov/)    |
|                 | EI^-1\*^ |                                         |
+-----------------+----------+-----------------------------------------+
| USLE LS Factor  | 0.38     | Value listed for 2.6% slope at 400 feet |
| (USLELS)        |          | using equation in Hann and Barfield     |
|                 |          | (1978)                                  |
+-----------------+----------+-----------------------------------------+
| USLE P Factor   | 0.5      | 2.6% slope row crop with contouring     |
| (USLEP)         |          | PRZM Manual; Table 5.6 (USEPA, 2006)    |
+-----------------+----------+-----------------------------------------+
| Field Area      | 172 ha   | Area of Shipman Reservoir watershed     |
| (AFIELD)        |          | (EPA, 1999)                             |
+-----------------+----------+-----------------------------------------+
| NRCS Hyetograph | 3        | PRZM Manual, Figure 5.8 (USEPA, 2006)   |
| (IREG)          |          |                                         |
|                 |          | Type II, IREG=3                         |
+-----------------+----------+-----------------------------------------+
| Slope (SLP)     | 2.6%     | Acreage-weighted mean value for Filbert |
|                 |          | silt loam                               |
+-----------------+----------+-----------------------------------------+
| Hydraulic       | 600 m    | Shipman Reservoir (USEPA, 1999)         |
| Length (HL)     |          |                                         |
+-----------------+----------+-----------------------------------------+
| Irrigation Flag | 0        | Irrigation off                          |
| (IRFLAG)        |          |                                         |
+-----------------+----------+-----------------------------------------+
| \* EI = 100     |          |                                         |
| ft-tons \* in/  |          |                                         |
| acre\*hr        |          |                                         |
+-----------------+----------+-----------------------------------------+

+-----------------+----------+-----------------------------------------+
| **Table 4.**    |          |                                         |
| PRZM 3.12.2     |          |                                         |
| Crop Parameters |          |                                         |
| for Saunders    |          |                                         |
| County, NE Corn |          |                                         |
| Scenario.       |          |                                         |
+=================+==========+=========================================+
| Parameter       | Value    | Source/Comments                         |
+-----------------+----------+-----------------------------------------+
| Initial Crop    | 1        | Set to 1 for all crops (USEPA, 2004).   |
| (INICRP)        |          |                                         |
+-----------------+----------+-----------------------------------------+
| Initial Surface | 1        | 1= fallow; default parameter is ignored |
| Condition       |          | as ERFLAG \> 0.                         |
|                 |          |                                         |
| (ISCOND)        |          |                                         |
+-----------------+----------+-----------------------------------------+
| Number of       | 1        | Set to number of crops in simulation.   |
| Different Crops |          |                                         |
| (NDC)           |          |                                         |
+-----------------+----------+-----------------------------------------+
| Number of       | 30       | Set to weather data in meteorological   |
| Cropping        |          | file: Omaha, NE (W94918).               |
| Periods (NCPDS) |          |                                         |
+-----------------+----------+-----------------------------------------+
| Maximum         | 0.25     | Low end of corn heavy canopy; PRZM      |
| rainfall        |          | Table 5-4. (USEPA, 2006)                |
| interception    |          |                                         |
| storage of crop |          |                                         |
| (CINTCP)        |          |                                         |
+-----------------+----------+-----------------------------------------+
| Maximum Active  | 90 cm    | Middle of range for corn, Table 5.9     |
| Root Depth      |          | (USEPA, 2006)                           |
| (AMXDR)         |          |                                         |
+-----------------+----------+-----------------------------------------+
| Maximum Canopy  | 100      | Set to 100 for row crops, as per        |
| Coverage        |          | guidance (USEPA, 2004)                  |
| (COVMAX)        |          |                                         |
+-----------------+----------+-----------------------------------------+
| Soil Surface    | 3        | 3 = residue, as according to guidance.  |
| Condition After |          | (USEPA, 2004)                           |
| Harvest (ICNAH) |          |                                         |
+-----------------+----------+-----------------------------------------+
| Date of Crop    | 25/05/61 | Consistent with RUSLE dates (USDA,      |
| Emergence       |          | 2000); G87CGBSM; 15 days from planting  |
|                 |          | to emergence                            |
| (EMD, EMM,      |          |                                         |
| IYREM)          |          |                                         |
+-----------------+----------+-----------------------------------------+
| Date of Crop    | 24/07/61 | 60 days after emergence                 |
| Maturity        |          |                                         |
|                 |          |                                         |
| (MAD, MAM,      |          |                                         |
| IYRMAT)         |          |                                         |
+-----------------+----------+-----------------------------------------+
| Date of Crop    | 20/10/61 | Consistent with RUSLE dates (USDA       |
| Harvest (HAD,   |          | 2000); G87CGBSM                         |
| HAM, IYRHAR)    |          |                                         |
+-----------------+----------+-----------------------------------------+
| Maximum Dry     | 0.0      | Not used in scenario                    |
| Weight (WFMAX)  |          |                                         |
+-----------------+----------+-----------------------------------------+
| Maximum Crop    | 300 cm   | Upper end for corn from PRZM Manual     |
| Height (HTMAX)  |          | Table 5.16 (USEPA, 2006)                |
+-----------------+----------+-----------------------------------------+
| SCS Curve       | 94, 88,  | PRZM Table 5.10, D Soil, fallow, and    |
| Number (CN)     | 94       | row crop, contoured, poor condition     |
|                 |          | (USEPA, 2006)                           |
+-----------------+----------+-----------------------------------------+
| Manning's N     | 0.014    | RUSLE Project; G87CGBSM; corn for       |
| Value (MNGN)    |          | grain, Lincoln weather station; mulch   |
|                 |          | tillage (USDA, 2000).                   |
+-----------------+----------+-----------------------------------------+
| USLE C Factor   | 0.0      | RUSLE Project; G87CGBSM; corn for       |
| (USLEC)         | 39-0.501 | grain, Lincoln weather station; mulch   |
|                 |          | tillage (USDA, 2000).                   |
+-----------------+----------+-----------------------------------------+

+----------------------+-------------------+--------------------------+
| **Table 5.** PRZM    |                   |                          |
| 3.12 Filbert silt    |                   |                          |
| loam Soil Parameters |                   |                          |
| for Saunders County, |                   |                          |
| NE.                  |                   |                          |
+----------------------+-------------------+--------------------------+
| Parameter            | Value             | Source/Comments          |
+----------------------+-------------------+--------------------------+
| Total Soil Depth     | 158 cm            | NRCS Soil Data Mart      |
| (CORED)              |                   | (SDM)                    |
|                      |                   | (http://soi              |
|                      |                   | ldatamart.nrcs.usda.gov) |
+----------------------+-------------------+--------------------------+
| Number of Horizons   | 4                 | NRCS Soil Data Mart      |
| (NHORIZ)             |                   | (SDM)                    |
+----------------------+-------------------+--------------------------+
| Horizon Thickness    | 10 cm (HORIZN =   | NRCS Soil Data Mart      |
| (THKNS)              | 1)                | (SDM). The top horizon   |
|                      |                   | was split into two       |
|                      | 8 cm (HORIZN = 2) | horizons as per PRZM     |
|                      |                   | Scenario Guidance        |
|                      | 20 cm (HORIZN =   | (USEPA, 2004).           |
|                      | 3)                |                          |
|                      |                   |                          |
|                      | 120 cm (HORIZN =  |                          |
|                      | 4)                |                          |
+----------------------+-------------------+--------------------------+
| Bulk Density (BD)    | 1.3 g/cm^3^       | NRCS Soil Data Mart      |
|                      | (HORIZN = 1)      | (SDM)                    |
|                      |                   | ([                       |
|                      | 1.3 g/cm^3^       | http://soildatamart.nrcs |
|                      | (HORIZN = 2)      | .usda.gov](http://soilda |
|                      |                   | tamart.nrcs.usda.gov/)). |
|                      | 1.3 g/cm^3^       | Midpoint of the reported |
|                      | (HORIZN = 3)      | range; PRZM Scenario     |
|                      |                   | Guidance (EPA, 2004).    |
|                      | 1.15 g/cm^3^      |                          |
|                      | (HORIZN = 4)      |                          |
+----------------------+-------------------+--------------------------+
| Initial Water        | 0.386 cm^3^/cm^3^ | NRCS Soil Data Mart      |
| Content (THETO)      | (HORIZN =1)       | (SDM); values are mean   |
|                      |                   | available water plus the |
|                      | 0.386 cm^3^/cm^3^ | wilting point water      |
|                      | (HORIZN =2)       | content of Filbert silt  |
|                      |                   | loam soils.              |
|                      | 0.345 cm^3^/cm^3^ |                          |
|                      | (HORIZN = 3)      |                          |
|                      |                   |                          |
|                      | 0.35 cm^3^/cm^3^  |                          |
|                      | (HORIZN = 4)      |                          |
+----------------------+-------------------+--------------------------+
| Compartment          | 0.1 cm (HORIZN =  | NRCS Soil Data Mart      |
| Thickness (DPN)      | 1)                | (SDM)                    |
|                      |                   | ([                       |
|                      | 2 cm (HORIZN = 2) | http://soildatamart.nrcs |
|                      |                   | .usda.gov](http://soilda |
|                      | 4 cm (HORIZN = 3) | tamart.nrcs.usda.gov/)); |
|                      |                   | PRZM Scenario Guidance   |
|                      | 4 cm (HORIZN = 4) | (USEPA, 2004).           |
+----------------------+-------------------+--------------------------+
| Field Capacity       | 0.386 cm^3^/cm^3^ | NRCS Soil Data Mart      |
| (THEFC)              | (HORIZN =1)       | (SDM); values are mean   |
|                      |                   | available water plus the |
|                      | 0.386 cm^3^/cm^3^ | wilting point water      |
|                      | (HORIZN =2)       | content of Filbert silt  |
|                      |                   | loam soils.              |
|                      | 0.345 cm^3^/cm^3^ |                          |
|                      | (HORIZN = 3)      |                          |
|                      |                   |                          |
|                      | 0.35 cm^3^/cm^3^  |                          |
|                      | (HORIZN = 4)      |                          |
+----------------------+-------------------+--------------------------+
| Wilting Point        | 0.156 cm^3^/cm^3^ | Estimated using Table    |
| (THEWP)              | (HORIZN =1)       | 5.23 in PRZM 3.2 manual  |
|                      |                   | with NRCS Soil Data Mart |
|                      | 0.156 cm^3^/cm^3^ | Data for Filbert silt    |
|                      | (HORIZN =2)       | loam soil.               |
|                      |                   |                          |
|                      | 0.115 cm^3^/cm^3^ |                          |
|                      | (HORIZN = 3)      |                          |
|                      |                   |                          |
|                      | 0.230 cm^3^/cm^3^ |                          |
|                      | (HORIZN = 4)      |                          |
+----------------------+-------------------+--------------------------+
| Organic Carbon       | 1.740% (HORIZN =  | NRCS SDM; values for     |
| Content (OC)         | 1)                | horizons 1 to 3 = mean   |
|                      |                   | %OM / 1.724. PRZM        |
|                      | 1.740% (HORIZN =  | Scenario Guidance        |
|                      | 2)                | (USEPA, 2004).           |
|                      |                   |                          |
|                      | 0.435% (HORIZN =  |                          |
|                      | 3)                |                          |
|                      |                   |                          |
|                      | 0.435% (HORIZN =  |                          |
|                      | 4)                |                          |
+----------------------+-------------------+--------------------------+

**References**

Haan, C.T., and B.J. Barfield. 1978. Hydrology and Sedimentology of
Surface Mined Lands. Office of Continuing Education and Extension,
College of Engineering, University of Kentucky, Lexington KY 40506. pp
286.

USDA. 2000. Revised Universal Soil Loss Equation (RUSLE) EPA Pesticide
Project. U.S. Department of Agriculture, National Resources Conservation
Service (NRCS) and Agricultural Research Service (ARS).

USDA. 2005. 2002 Census of Agriculture. U.S. Department of Agriculture,
National Agricultural Statistics Service (NASS). Online at:
<http://www.nass.usda.gov/index.asp>.

USDA. 2003. Official Series Description -- Filbert Series. U.S.
Department of Agriculture, Natural Resources Conservation Service
(NRCS). Dec. 2006. Online at:
<http://ortho.ftw.nrcs.usda.gov/osd/dat/F/FILBERT.html>

USEPA. 1999. Jones, R.D., J. Breithaupt, J. Carleton, L. Libelo, J. Lin,
R. Matzner, and R. Parker. *Guidance for Use of the Index Reservoir in
Drinking Water Exposure Assessments*. Environmental Fate and Effects
Division, Office of Pesticide Programs, U.S. Environmental Protection
Agency, Washington, DC.

USEPA. 2004. Abel, S.A. *Procedure for Conducting Quality Assurance and
Quality Control of Existing and New PRZM Field and Orchard Crop Standard
Scenarios.* Environmental Fate and Effects Division, Office of Pesticide
Programs, U.S. Environmental Protection Agency.

USEPA. 2006. Carsel, R.F., J.C. Imhoff, P.R. Hummel, J.M. Cheplick, and
A.S. Donigian, Jr. *PRZM-3, A Model for Predicting Pesticide and
Nitrogen Fate in the Crop Root and Unsaturated Soil Zones: Users Manual
for Release 3.12.2.* National Exposure Research Laboratory, Office of
Research and Development, U.S. Environmental Protection Agency, Athens,
GA.