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.
|Starting Date||January 1, 1948||Meteorological File - Austin, TX (W13958)|
|Ending Date||December 31, 1983||Meteorological File - Austin, TX (W13958)|
|Pan Evaporation Factor (PFAC)||0.71||PRZM Manual Figure 5.1 (EPA, 1998)|
|Snowmelt Factor (SFAC)||0.50m C- 1||PRZM Manual Table 5.1 (EPA, 1998)|
|Minimum Depth of Evaporation (ANETD)||25.0 cm||PRZM Manual Figure 5.2 (EPA, 1998)|
|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)||0.37||Haan and Barfield, 1978|
|USLE P Factor (USLEP)||1.0||Set according to guidance (EPA, 2001)|
|Field Area (AFIELD)||172 ha||Area of Shipman Reservoir watershed (EPA, 1999)|
|NRCS Hyetograph (IREG)||4||PRZM Manual Figure 5.12 (EPA, 1998)|
|Slope (SLP)||2.5%||Set per QA/QC Guidance (EPA, 2001)|
|Hydraulic Length (HL)||600 m||Shipman Reservoir (EPA, 1999)|
* EI = 100 ft-tons * in/ acre*hr
|Initial Crop (INICRP)||1||Set to one for all crops (EPA, 2001)|
|Initial Surface Condition (ISCOND)||1||Set fallow prior to new crop planting|
|Number of Different Crops (NDC)||1||Set to crops in simulation - generally one|
|Number of Cropping Periods (NCPDS)||36||Set to weather data. Austin, TX (W13958)|
|Maximum rainfall interception storage of crop (CINTCP)||0.25||PRZM, Table 5.4 (EPA, 1998)|
|Maximum Active Root Depth (AMXDR)||90 cm||PRZM Manual, Table 5.9 (EPA, 1998)|
|Maximum Canopy Coverage (COVMAX)||100||QA/QC Guidance (EPA, 2001)|
|Soil Surface Condition After Harvest (ICNAH)||1||Winter cover crop planted in most areas.|
|Date of Crop Emergence
(EMD, EMM, IYREM)
|11/03||Usual Planting and Harvesting Dates (USDA, 1984)|
|Date of Crop Maturity
(MAD, MAM, IYRMAT)
|Date of Crop Harvest
(HAD, HAM, IYRHAR)
|Maximum Dry Weight (WFMAX)||0.0||Set 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)|
|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)||
||NRCS, National Soils Characterization Database (NRCS, 2001) http://soils.usda.gov/survey/nscd/|
|Bulk Density (BD)||
|Initial Water Content (THETO)||
|Compartment Thickness (DPN)||
|Field Capacity (THEFC)||
|Wilting Point (THEWP)||
|Organic Carbon Content (OC)|
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).