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The field used to represent corn production in Texas is located in Milam County in the Texas Claypan region of the state. According to the 1997 Census of Agriculture, Texas is ranked 11th among major producers of corn in the U.S. The crop is generally planted the early Spring (March) and harvested beginning in September. Continuous corn is practice is much of the region. However, rotation with other crops such as soybeans and wheat is also practiced. Most of the corn is planted for feed grain. Planting depth and row spacing (generally 30 inches) follows general practices for the U.S. Conventional tillage dominates management practices, followed by no-tillage. The soil selected to simulate the field is a benchmark soil, Axtell very fine sandy loam. Axtell very fine sandy loam is a fine, semectitic, thermic Udertic Paleustalfs. These soils were cultivated in the past, but are now in pasture. Some areas are farmed to corn, grain sorghum, or small grain. Axtell very fine sandy loam is a very deep, moderately well drained, very slowly permeable soil with slow to rapid runoff depending on slope. These soils formed in slightly acid to alkaline clayey sediments of the Pleistocene Age. They are found on broad, nearly level to strongly sloping stream terraces and terrace remnants about 50 to 300 feet above the present streams. Slopes are generally 0 to 5 percent, but may range up to 12 percent. Axtell very fine sandy loam is a Hydrologic Group D soil.

Table 1.
PRZM 3.12 Climate and Time Parameters for Milam County, Texas - Corn
Starting Date January 1, 1948Meteorological File - Austin, TX (W13958)
Ending Date December 31, 1983Meteorological File - Austin, TX (W13958)
Pan Evaporation Factor (PFAC) 0.71PRZM Manual Figure 5.1 (EPA, 1998)
Snowmelt Factor (SFAC) 0.50m C- 1PRZM Manual Table 5.1 (EPA, 1998)
Minimum Depth of Evaporation (ANETD) 25.0 cmPRZM Manual Figure 5.2 (EPA, 1998)

Table 2.
PRZM 3.12 Erosion and Landscape Parameters for Milam County, Texas - Corn
Method to Calculate Erosion (ERFLAG) 4 (MUSS)PRZM Manual (EPA, 1998)
USLE K Factor (USLEK) 0.31 tons EI-1* 0.31 is consistent with fine sandy loam, as described in official soil description- KJC
USLE LS Factor (USLELS) 0.37Haan and Barfield, 1978
USLE P Factor (USLEP) 1.0Set according to guidance (EPA, 2001)
Field Area (AFIELD) 172 haArea of Shipman Reservoir watershed (EPA, 1999)
NRCS Hyetograph (IREG) 4PRZM Manual Figure 5.12 (EPA, 1998)
Slope (SLP) 2.5%Set per QA/QC Guidance (EPA, 2001)
Hydraulic Length (HL) 600 mShipman Reservoir (EPA, 1999)

* EI = 100 ft-tons * in/ acre*hr

Table 3.
PRZM 3.12 Crop Parameters for Milam County, Texas - Corn
Initial Crop (INICRP) 1Set to one for all crops (EPA, 2001)
Initial Surface Condition (ISCOND) 1Set fallow prior to new crop planting
Number of Different Crops (NDC) 1Set to crops in simulation - generally one
Number of Cropping Periods (NCPDS) 36Set to weather data. Austin, TX (W13958)
Maximum rainfall interception storage of crop (CINTCP) 0.25PRZM, Table 5.4 (EPA, 1998)
Maximum Active Root Depth (AMXDR) 90 cmPRZM Manual, Table 5.9 (EPA, 1998)
Maximum Canopy Coverage (COVMAX) 100QA/QC Guidance (EPA, 2001)
Soil Surface Condition After Harvest (ICNAH) 1Winter cover crop planted in most areas.
Date of Crop Emergence
11/03 Usual Planting and Harvesting Dates (USDA, 1984)
Date of Crop Maturity
Date of Crop Harvest
Maximum Dry Weight (WFMAX) 0.0Set to "0" Not used in simulation
SCS Curve Number (CN) 92, 89, 90 Gleams Manual Table A.3, Fallow = Fallow SR/CT/poor; Cropping and Residue = SR, CT, poor condition (USDA, 1990)
Manning's N Value (MNGN) 0.014 RUSLE Project, J94CGWWC; Corn, grain, conventional tillage, Waco (USDA, 2000)
USLE C Factor (USLEC) 0.132 - 0.562 RUSLE Project; J94CGWWC; Corn, grain, conventional tillage, Waco (USDA, 2000)

Table 4.
PRZM 3.12 Axtell Soil Parameters for Milam County, Texas - Corn
ParameterValue Verification Source
Total Soil Depth (CORED) 100 cm NRCS, National Soils Characterization Database (NRCS, 2001)
Number of Horizons (NHORIZ) 3 (Top horizon split in two)
First, Second, and Third Soil Horizons (HORIZN = 1,2,3)
Horizon Thickness (THKNS)
  • 10 cm (HORIZN = 1,2)
  • 80 cm (HORIZN = 3)
NRCS, National Soils Characterization Database (NRCS, 2001) http://soils.usda.gov/survey/nscd/ Exit EPA Disclaimer
Bulk Density (BD)
  • 1.6 g cm-3 (HORIZN = 1,2)
  • 1.7 g cm-3 (HORIZN = 3)
Initial Water Content (THETO)
  • 0.174 cm3-H2O cm3-soil (HORIZN =1,2)
  • 0.235cm3-H2O cm3-soil (HORIZN =3)
Compartment Thickness (DPN)
  • 0.1 cm (HORIZN = 1)
  • 5.0 cm (HORIZN = 2,3)
Field Capacity (THEFC)
  • 0.174 cm3-H2O cm3-soil (HORIZN = 1,2)
  • 0.235cm3-H2O cm3-soil (HORIZN = 3)
Wilting Point (THEWP)
  • 0.064 cm3-H2O cm3-soil (HORIZN = 1,2)
  • 0.165 cm3-H2O cm3-soil (HORIZN = 3)
Organic Carbon Content (OC)
  • 0.58% (HORIZN = 1,2)
  • 0.29% (HORIZN = 3)

EPA. 1998. 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 3.0. National Exposure Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Athens, GA.

EPA. 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. D.C.

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, Kentucky 40506. pp. 286.

EPA. 2001. 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, Washington, D.C.

USDA. 1984. Usual Planting and Harvesting Dates for U.S. Field Crops, Statistical Reporting Service, U.S. Department of Agriculture, Agriculture Handbook #628, pp.78.

USDA. 1990. Davis, F.M., R.A. Leonard, W.G. Knisel. GLEAMS User Manual, Version 1.8.55. USDA-ARS Southeast Watershed Research Laboratory, Tifton GA. SEWRL-030190FMD.

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).

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