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The field used to represent cotton production in Texas is located in Milam County, although cotton is grown throughout Texas. According to the 1997 Census of Agriculture, Texas ranked 1st among the major cotton producing states in the U.S. with more than 5 million acres in production. Most cotton is grown in the High Plains (67%) and Rolling Plains (20%) regions of the state. Cotton is planted in the late winter/early Spring (February and March) in the Lower Rio Grande region and progresses into June in the southern High Plains. Cotton is planted by the "skip-row" or "ultra-narrow row" method. Skip row refers to the technique where every third row is "skipped" to permit the crop to take advantage of soil moisture in semi-arid regions. Ultra-narrow row (UNR) cotton is spaced at 20 inches apart which tends to increase yields and efficiency of productions systems. Both systems require the use of irrigation. Fifty percent of cotton production in the High Plains is irrigated and less than ten percent in the Rolling Plains is irrigated. Furrow irrigation is the most common in the Lower Rio Grande and sprinkler systems are most common in the High Plains. Low Energy Precision Application center pivot irrigation is beginning to make inroad in the area because of its lower pressure requirements, lower evaporation losses and water savings. Row spacing is generally 38-inches with 3-4 plants per foot row in all but UNR cotton. Row canopies tend to be very close to 100 percent, while the canopy between rows is much less. All cotton is defoliated prior to harvesting. Conventional tillage is the dominant practice. The soil selected to simulate the field is a Crockett fine sandy loam. Crockett fine sandy loam is a fine, smectitic, thermic Udertic Paleustalfs. The series is mainly used to grow cotton, grain sorghum, and small grains, but more than half the acreage is now in pasture. Crockett fine sandy loam is a deep, moderately well drained, very slowly permeable soil with low to very high runoff depending on slope. These soils formed in residuum derived from weathered alkaline marine clays, sandy clays, or shale, interbedded with sandier materials mainly of Cretaceous age. They are located on broad nearly level to moderately sloping uplands. Slopes are generally between 1 to 5 percent, but may range from 0 to 10 percent. The series is extensive in MLRA 86, 87A, and 87B. Crockett fine sandy loam is a Hydrologic Group C soil.

Table 1.
PRZM 3.12 Climate and Time Parameters for the Milam, County - Cotton
Starting Date January 1, 1950Meteorological File - Austin, TX (W13958)
Ending Date December 31, 1983Meteorological File - Austin, TX (W13958)
Pan Evaporation Factor (PFAC) 0.7PRZM Manual Figure 5.1 (EPA, 1998)
Snowmelt Factor (SFAC) 0.3 cm 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 - Cotton
Method to Calculate Erosion (ERFLAG) 4 (MUSS)PRZM Manual (EPA, 1998)
USLE K Factor (USLEK) 0.3 tons EI-1*FARM Manual, Table 3.1 (EPA, 1985)
USLE LS Factor (USLELS) 0.365Haan and Barfield, 1978
USLE P Factor (USLEP) 1.00PRZM Manual (EPA, 1998)
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%Selected according to 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 - Cotton
Initial Crop (INICRP) 1Set to one for all crops (EPA, 2001)
Initial Surface Condition (ISCOND) 1Set to default for fallow surface prior to 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) 0.2 PRZM Table 5.4 (EPA, 1998)
Maximum Active Root Depth (AMXDR) 60 cmPRZM Input Collator, PIC (Burns, 1992); PRZM Table 5.9 (EPA, 1998)
Maximum Canopy Coverage (COVMAX) 100PRZM Input Collator, PIC (Burns, 1992) Per QA/QC Guidance (EPA, 2001)
Soil Surface Condition After Harvest (ICNAH) 3Residues left on field until following year or cover crop is planted.
Date of Crop Emergence
25/04 Personal communication with Cullen "Dusty" Tittle, Milam Co. Extension Agent. Maturation and harvest close together because the plants are desiccated anywhere from late Aug through Sept.
Date of Crop Maturity
Date of Crop Harvest
Maximum Dry Weight (WFMAX) 0.0Set to "0" Not used in simulation
SCS Curve Number (CN) 89, 86, 87 Gleams Manual Table; Fallow = Fallow SR/CT/poor; Cropping and Residue = Row Crop SR/CT/poor (USDA, 1990)
Manning's N Value (MNGN) 0.023RUSLE Project, J94CTCTN; Cotton, no-tillage, Waco TX (USDA, 2000)
USLE C Factor (USLEC) 0.111 - 0.365 RUSLE Project; J94CTCTN; Cotton, no-tillage, Waco TX (USDA, 2000)

Table 4.
PRZM 3.12 Axtell Soil Parameters for Milam, County - Cotton
ParameterValue Verification Source
Total Soil Depth (CORED) 100 cm PIC (Burns, 1992) Confirmed with: 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)
  • 10 cm (HORIZN = 2)
  • 80 cm (HORIZN = 3)
PIC (Burns, 1992) Confirmed with: 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)
  • 0.170 cm3-H2O cm3-soil (HORIZN =1, 2)
  • 0.247 cm3-H2O cm3-soil (HORIZN =3)
Compartment Thickness (DPN)
  • 0.1 cm (HORIZN = 1)
  • 1 cm (HORIZN = 2)
  • 5 cm (HORIZN = 3)
Field Capacity (THEFC)
  • 0.170 cm3-H2O cm3-soil (HORIZN = 1, 2)
  • 0.247 cm3-H2O cm3-soil (HORIZN = 3)
Wilting Point (THEWP)
  • 0.06 cm3-H2O cm3-soil (HORIZN = 1,2)
  • 0.127 cm3-H2O cm3-soil (HORIZN = 3)
Organic Carbon Content (OC)
  • 1.16% (HORIZN = 1,2)
  • 0.29% (HORIZN = 3)

Burns. 1992. Burns, L.A., (Coordinator), B.W. Allen, Jr., M.C. Barber, S.L. Bird, J.M. Cheplick, M.J. Fendley, D.R. Hartel, C.A. Kittner, F.L. Mayer, Jr., L.A. Suarez, and S.E. Wooten. Pesticide and Industrial Chemical Risk Analysis and Hazard Assessment, Version 3.0. (PIRANHA) Environmental Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Athens, GA. 1992.

EPA. 1985. Field Agricultural Runoff Monitoring (FARM) Manual, (EPA/600/3-85/043) Environmental Research Laboratory, U.S. Environmental Protection Agency, Athens, GA.

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. 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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