The field used to represent sorghum 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 2nd among major producers of sorghum in the U.S. The crop is generally planted under both dry land and irrigation conditions in the Spring (May), but may extend into July, and harvested beginning in September. Continuous sorghum is practice is much of the region. Row spacing is generally 30 inches for planted systems or in narrow rows of 15 inches in drilled systems. Conservation tillage practices are emphasize for erosion control and include reduced-till, mulch-till, ecofallow, strip-till, ridge-till, zero-till, and no-till. 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)||0.36m 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)||0.43 tons EI-1*||GLEAMS Manual; Representative Soils USDA (1990)|
|USLE LS Factor (USLELS)||0.402||GLEAMS Manual; Representative Soils USDA (1990)|
|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)||0.1||PRZM, Table 5.4 (EPA, 1998)|
|Maximum Active Root Depth (AMXDR)||22 cm||PRZM Manual, Table 5.9 (EPA, 1998)|
|Maximum Canopy Coverage (COVMAX)||85||PRZM Input Collator, PIC (Burns, 1992)|
|Soil Surface Condition After Harvest (ICNAH)||1||Default (EPA, 2001)|
|Date of Crop Emergence
(EMD, EMM, IYREM)
|11/05||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, 86,87||Gleams Manual Table A.3,Fallow SR/CT/poor; Cropping and Residue = small grain, SR/CT, poor condition (USDA, 1990)|
|Manning's N Value (MNGN)||0.014||RUSLE Project, J94SGSGC; Sorghum grain, conventional tillage, Waco TX (USDA, 2000)|
|USLE C Factor (USLEC)||0.050 - 0.704||RUSLE Project; J94SGSGC; Sorghum grain, conventional tillage, Waco TX (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.
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.
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.
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).