The Agricultural Policy/Environmental eXtender (APEX) model: An emerging tool for landscape and watershed environmental analyses

Transactions of the ASABE

Volumn 53, Issue 3, 2010, Pages 711-740

  Gassman, P W ^a   Williams, J R ^b   Wang, X ^b   Saleh, A ^c   Osei, E ^c   Hauck, L M ^c   Izaurralde, R C ^d   Flowers, J D ^e  

^a IOWA STATE UNIVERSITY   (United States)

^b BLACKLAND RESEARCH AND EXTENSION CENTER   (United States)

^c Tarleton State University   (Canada)

^d UNIVERSITY OF MARYLAND   (United States)

^e JACOBS ENGINEERING   (United States)

Author keywords

APEX; Best management practices; Conservation practices; Farm and watershed simulations; Soil carbon; Water quality

Indexed keywords

AGRICULTURAL LANDSCAPES; APEX; BEST MANAGEMENT PRACTICES; BUFFER STRIP; CROP FIELDS; CROPPING SYSTEMS; DYNAMIC TOOLS; ENVIRONMENTAL ANALYSIS; GRASSED WATERWAYS; LAND APPLICATIONS; LAND MANAGEMENTS; LAND-USE SCENARIO; LIVESTOCK MANURE; MANAGEMENT PRACTICES; MANAGEMENT SCENARIOS; PILOT PROJECTS; POLLUTANT LOSS; REGIONAL SCALE; RESEARCH NEEDS; SIMULATION STUDIES; SMALL WATERSHEDS; SOIL CARBON; VALIDATION RESULTS; WASTE STORAGE PONDS; WATERSHED SIMULATION;

FARMS; LAND USE; LANDFORMS; MANURES; SOIL CONSERVATION; SOILS; WATER POLLUTION; WATER QUALITY; WATERSHEDS;

WASTE MANAGEMENT;

AGRI-ENVIRONMENTAL POLICY; AGRICULTURAL LAND; ALTERNATIVE AGRICULTURE; BEST MANAGEMENT PRACTICE; BUFFER ZONE; CONSERVATION MANAGEMENT; ENVIRONMENTAL IMPACT; FARMING SYSTEM; GIS; LAND MANAGEMENT; LAND USE; LIVESTOCK FARMING; MANURE; SOIL CARBON; WATER MANAGEMENT; WATER QUALITY; WATERSHED;

EID: 77954125860     PISSN: 21510032     EISSN: None     Source Type: Journal    
DOI: None     Document Type: Review

References (128)

1. Arnold, J. G., and N. Fohrer. 2005. SWAT2000: Current capabilities and research opportunities in applied watershed modeling. Hydrol. Proc. 19(3):563-572.
2. Arnold, J. G., R. Srinivasan, R. S. Muttiah, and J. R. Williams. 1998. Large-area modeling and assessment: Part I. Model development. J. American Water Resour. Assoc. 34(1):73-89. (Pubitemid 28190080)
3. Azevedo, J. C., J. R. Williams, M. G. Messina, and R. F. Fisher. 2005a. Impacts of the sustainable forestry initiative landscape level measures on hydrological processes. Water Resour. Mgmt. 19(2):95-110.
4. Azevedo, J. C., X. B. Wu, M. G. Messina, and R. F. Fisher. 2005b. Assessment of sustainability in intensively managed forested landscapes: A case study in eastern Texas. Soc. American Foresters 51(4):321-333.
5. Azevedo, J. C., X. B. Wu, M. G. Messina, J. R. Williams, and R. F. Fisher. 2008. The role of the sustainable forestry initiative in forest landscape changes in Texas, USA. In Patterns and Processes in Forest Landscapes, 273-295. R. Lafortezza, J. Chen, G. Sanesi, T. R. Crow, eds. Berlin, Germany: Springer Verlag.
6. Bagnold, R. A. 1977. Bed-load transport by natural rivers. Water Resour. Research 13(2):303-312.
7. Baier, W., and G. W. Robertson. 1965. Estimation of latent evaporation from simple weather observations. Canadian J. Plant Sci. 45: 276-284.
8. Borah, D. K., J. G. Arnold, M. Bera, E. C. Krug, and X. Liang. 2007. Storm event and continuous hydrologic modeling for comprehensive and efficient watershed simulations. J. Hydrol. Eng. 12(6):605-616.
9. BREC. 1999. APEX User's Guide and Technical Documentation. Version 8190. Temple, Tex.: Texas A&M University, Texas Agricultural Experiment Station, Blackland Research and Extension Center.
10. Cambardella, C. A., T. B. Moorman, S. S. Andrews, and D. L. Karlen. 2004. Watershed-scale assessment of soil quality in the loess hills of southwest Iowa. Soil Tillage Res. 78(2):237-247.
11. CARD. 2010. CARD interactive software programs. Ames, Iowa: Iowa State University, Center for Agricultural and Rural Development. Available at: www.card.iastate.edu/environment/interactive-programs.aspx. Accessed 1 May 2010.
12. Cerri, C. E. P., K. Paustian, M. Bernoux, R. L. Victoria, J. M. Melillos, and C. C. Cerri. 2004. Modeling changes in soil organic matter in Amazon forest to pasture conversion with the Century model. Global Change Biol. 10(5):815-832.
13. Chung, S. W., P. W. Gassman, D. R. Huggins, and G. W. Randall. 2001. Evaluation of EPIC for tile flow and tile nitrate losses from three Minnesota cropping systems. J. Environ. Qual. 30(3):822-830.
14. Chung, S. W., P. W. Gassman, R. Gu, and R. S. Kanwar. 2002. Evaluation of EPIC for assessing tile flow and nitrogen losses for alternative agricultural management systems. Trans. ASAE 45(4):1135-1146.
15. Di Luzio, M., R. Srinivasan, and J. G. Arnold. 2004. A GIS-coupled hydrological model system for the watershed assessment of agricultural nonpoint and point sources of pollution. Trans. GIS 8(1):113-136.
16. Duriancik, L. F., D. Bucks, J. P. Dobrowski, T. Drewes, S. D. Eckles, L. Jolley, R. L. Kellogg, D. Lund, J. R. Makuch, M. P. O'Neill, C. A. Rewa, M. R. Walbridge, R. Parry, and M. A. Weltz. 2008. The first five years of the Conservation Effects Assessment Project. J. Soil Water Conserv. 63(6):185A-197A.
17. EAWAG. 2009. SWAT-CUP. Dübendorf, Switzerland: Swiss Federal Institute of Aquatic Science and Technology. Available at: www.eawag.ch/ organisation/abteilungen/siam/software/swat/index-EN.
18. Eckhardt, K., and U. Ulbrich. 2003. Potential impacts of climate change on groundwater recharge and streamflow in a central European low mountain range. J. Hydrol. 284 (1-4) : 244-252.
19. FAPRI-UMC. 2007. Estimating water quality, air quality, and soil carbon benefits of the Conservation Reserve Program.
20. FAPRI-UMC Report 01-07. Columbia, Mo.: University of Missouri, Food and Agricultural Policy Research Institute. Available at: www.fapri.missouri.edu/ outreach/publications/2007/FAPRI-UMC-Report-01-07.pdf. Accessed 5 June 2009.
21. FAPRI-UMC. 2008. Evaluating economic and environmental benefits of soil and water conservation measures applied in Missouri. FAPRI-MU Report 31-07. Columbia, Mo.: University of Missouri, Food and Agricultural Policy Research Institute. Available at: www.fapri.missouri.edu/outreach/publications/2007/ FAPRI-MU-Report-31-07.pdf. Accessed 5 June 2009.
22. Flowers, J. D., J. R. Williams, and L. M. Hauck. 1996. Livestock and the environment: A national pilot project. NPP integrated modeling system: Calibration of the APEX model for dairy waste application fields in Erath County, Texas. TIAER Report No. PR9607. Stephenville, Tex.: Tarleton State University, Texas Institute for Applied Environmental Research. Available at: http://tiaer.tarleton.edu/pdf/PR9607.pdf. Accessed 2 February 2010.
23. Flowers, J., E. Osei, L. Hauck, P. Gassman, and A. McFarland. 1998. Livestock and the environment: A national pilot project: Manure nutrient application rates and other assumptions underlying APEX runs. TIAER Information Bulletin 9803. Stephenville, Tex.: Tarleton State University, Texas Institute for Applied Environmental Research.
24. Gassman, P. W. 1997. The national pilot program integrated modeling system: Environmental baseline assumptions and results for the APEX model (Livestock Series Report 9). Staff Report 97-SR 85. Ames, Iowa: Iowa State University, Center for Agricultural and Rural Development. Available at: www.card. iastate.edu/publications/synopsis.aspx?id=205. Accessed 2 February 2010.
25. Gassman, P. W., and L. Hauck. 1996. The environmental component of the national pilot program integrated modeling system (Livestock Series Report 8). Staff Report 96-SR 84. Ames, Iowa: Iowa State University, Center for Agricultural and Rural Development. Available at: www.card.iastate.edu/ publications/synopsis.aspx?id=172. Accessed 2 February 2010.
26. Gassman, P. W., J. Abraham, L. Hauck, A. Saleh, and K. Keplinger. 2001. Simulation of nutrient losses from chicken litter applications in east central Texas with APEX and SWAT. ASAE Paper No. 012004. Presented at the 2001 ASAE Annual International Meeting. St. Joseph, Mich.: ASAE.
27. Gassman, P. W., E. Osei, A. Saleh, and L. M. Hauck. 2002. Application of an environmental and economic modeling system for watershed assessments. J. American Water Resour. Assoc. 38(2):423-438.
28. Gassman, P. W., A. Saleh, E. Osei, J. Abraham, and J. Rodecap. 2003. Environmental and economic impacts of alternative management scenarios for the Mineral Creek watershed. In Proc. Total Maximum Daily Load (TMDL) Environmental Regulations II, 323-331. St. Joseph, Mich.: ASAE.
29. Gassman, P. W., J. R. Williams, V. W. Benson, R. C. Izaurralde, L. Hauck, C. A. Jones, J. D. Atwood, J. Kiniry, and J. D. Flowers. 2005. Historical development and applications of the EPIC and APEX models. Working Paper 05-WP 397. Ames, Iowa: Iowa State University, Center for Agricultural and Rural Development. Available at: www.card.iastate.edu/publications/synopsis.aspx?id= 763. Accessed 5 June 2009.
30. Gassman, P. W., E. Osei, A. Saleh, J. Rodecap, S. Norvell, and J. R. Williams. 2006. Alternative practices for sediment and nutrient loss control on livestock farms. Agric. Ecosys. and Environ. 117 (2-3) : 135-144.
31. Gassman, P. W., M. Reyes, C. H. Green, and J. G. Arnold. 2007. The Soil and Water Assessment Tool: Historical development, applications, and future directions. Trans. ASABE 50(4):1211-1250.
32. Godwin, D. C., C. A. Jones, J. T. Ritchie, P. L. G. Vlek, and L. G. Youngdahl. 1984. The water and nitrogen components of the CERES models. In Proc. Intl. Symp. on Minimum Data Sets for Agrotechnology Transfer, 95-100. Patancheru, India: International Crops Research Institute for the Semi-Arid Tropics.
33. Green, W. H., and G. A. Ampt. 1911. Studies on soil physics:1. Flow of air and water through soils. J. Agric. Sci. 4: 1-24.
34. Hargreaves, G. H., and Z. A. Samani. 1985. Reference crop evapotranspiration from temperature. Applied Eng. in Agric. 1(2):96-99.
35. Harman, W. L., E. Wang, and J. R. Williams. 2004. Reducing atrazine losses: Water quality implications of alternative runoff control practices. J. Environ. Qual. 33(1):7-12.
36. Intarapapong, W., and D. Hite. 2003. Watershed-level policies to implement best management practices under environmental risk. Paper presented at the Southern Agricultural Economics Association Annual Meeting. Available at: http://purl.umn.edu/35007. Accessed 2 February 2010.
37. Intarapapong, W., D. Hite, and A. Renck. 2002. Environmental risk assessment under environmental standard and safety-first constraints. Paper presented at the Western Agricultural Economics Association Annual Meeting. Available at: http://purl.umn.edu/36673. Accessed 2 February 2010.
38. Izaurralde, R. C., J. R. Williams, W. B. McGill, N. J. Rosenberg, and M. C. Quiroga Jakas. 2006. Simulating soil C dynamics with EPIC: Model description and testing against long-term data. Ecol. Model. 192 (3-4) : 362-384.
39. Jones, C. A., C. V. Cole, A. N. Sharpley, and J. R. Williams. 1984. A simplified soil and plant phosphorus model: I. Documentation. SSSA J. 48(4):800-805.
40. Jones, R., L. Frarey, A. Bouzaher, S. Johnson, and S. Neibergs. 1993. Livestock and the environment: A national pilot project: Detailed problem statement. Stephenville, Texas: Tarleton State University, Texas Institute for Applied Environmental Research. Available at: http://tiaer.tarleton.edu/pdf/ PR9304.pdf. Accessed 22 December 2009.
41. Kannan, N., C. Santhi, J. R. Williams, and J. G. Arnold. 2008. Development of a continuous soil moisture accounting procedure for curve number methodology and its behaviour with different evapotranspiration methods. Hydrol. Proc. 22(13):2114-2121.
42. Keith, G., S. Norvell, R. Jones, C. Maguire, E. Osei, A. Saleh, P. Gassman, and J. Rodecap. 2000. Livestock and the environment: A national pilot project: CEEOT-LP modeling for the Upper Maquoketa River watershed, Iowa: Final report. TIAER Report No. PR003. Stephenville, Tex.: Tarleton State University, Texas Institute for Applied Environmental Research. Available at: http://tiaer.tarleton.edu/pdf/PR0003.pdf. Accessed 2 February 2010.
43. Kiniry, J. R., J. R. Williams, P. W. Gassman, and P. Debaeke. 1992. A general, process-oriented model for two competing plant species. Trans. ASAE 35(3):801-810.
44. Knisel, W. G. 1980. CREAMS: A field-scale model for chemicals, runoff, and erosion from agricultural management systems. Conservation Research Report No. 26. Washington, D. C.: USDA National Resources Conservation Service.
45. Krause, P., D. P. Boyle, and F. Bäse. 2005. Comparison of different efficiency criteria for hydrological model assessment. Adv. Geosci. 5: 89-97.
46. Lemunyon, J. L., and R. L. Kellogg. 2008. Assessment of conservation benefits derived from conservation practices in the United States. In Proc. 21st Century Watershed Technology Conf.: Improving Water Quality and Environment. E. W. Tollner and A. Saleh, eds. St. Joseph, Mich.: ASABE.
47. Long, S. P., E. A. Ainsworth, A. D. B. Leakey, J. Nösberger, and D. R. Ott. 2006. Food for thought: Lower-than-expected crop yield stimulation with rising CO2 concentrations. Science 312(5782):1918-1921.
48. Magre, M., J. R. Williams, W. L. Harman, T. Gerik, J. Greiner, L. Francis, E. Steglich, and A. Meinardus. 2006. WinAPEX Users Guide. Version 1.0. Temple, Tex.: Texas A&M University, Texas Agricultural Experiment Station, Blackland Research and Extension Center. Available at: http://winapex.brc.tamus. edu/downloads/user-manuals.aspx. Accessed 5 June 2009.
49. McElroy, A. D., S. Y. Chiu, J. W. Nebgen, A. Aleti, and F. W. Bennett. 1976. Loading functions for assessment of water pollution from nonpoint sources. EPA 600/2-76-151. Washington, D. C.: U. S. Environmental Protection Agency.
50. McNitt, J., and R. Jones. 1999. Livestock and the environment: Precedents for runoff policy. Stephenville, Tex.: Tarleton State University, Texas Institute for Applied Environmental Research.
51. Monteith, J. L. 1965. Evaporation and environment. Symp. Soc. Exp. Biol. 19: 205-234.
52. Moriasi, D. N., J. G. Arnold, M. W. Van Liew, R. L. Binger, R. D. Harmel, and T. Veith. 2007. Model evaluation guidelines for systematic quantification of accuracy in watershed simulations. Trans. ASABE 50(3):885-900.
53. Mudgal, A., C. Baffaut, S. H. Anderson, E. J. Sadler, and A. L. Thompson. 2010. APEX model assessment of variable landscapes on runoff and dissolved herbicides. Trans. ASABE 53 (4) (accepted).
54. Nash, J. E., and J. V. Sutcliffe. 1970. River flow forecasting through conceptual models: Part I. A discussion of principles. J. Hydrol. 10(3):282-290.
55. Neitsch, S. 1998. Environmental impacts of dairy operations in the Lake Fork Reservoir watershed: SWAT baseline modeling results. Temple, Tex.: Texas A&M University, Texas Agricultural Experiment Station, Blackland Research and Extension Center.
56. Nicks, A. D. 1974. Stochastic generation of the occurrence, pattern, and location of maximum amount of daily rainfall. Misc. Publ. No. 1275. In Proc. Symp. on Statistical Hydrology, 154-171. Washington, D. C.: USDA.
57. Nicks, A. D., L. J. Lane, and G. A. Gander. 1995. Chapter 2. Weather generator. In USDA Water Erosion Prediction Project: Hillslope Profile and Watershed Model Documentation. D. C. Flanagan and M. A. Nearing, eds. NSERL Report No. 10. West Lafayette, Ind.: USDA-ARS National Soil Erosion Research Laboratory. Available at: www.ars.usda.gov/Research/docs.htm?docid=18073. Accessed 22 December 2009.
58. Olivera, F., M. Valenzuela, R. Srinivasan, J. Choi, H. Cho, S. Koka, and A. Agrawal. 2006. ArcGIS-SWAT: A geodata model and GIS interface for SWAT. J. American Water Resour. Assoc. 42(2):295-309.
59. Onstad, C. A., and G. R. Foster. 1975. Erosion modeling on a watershed. Trans. ASAE 18(2):288-292.
60. Osei, E., P. W. Gassman, R. Jones, S. Pratt, L. Hauck, L. Beran, W. Rosenthal, and J. R. Williams. 2000a. Economic and environmental impacts of alternative practices on dairy farms in an agricultural watershed. J. Soil and Water Conserv. 55(4):466-472.
61. Osei, E., P. Gassman, and A. Saleh. 2000b. Livestock and the environment: A national pilot project: Economic and environmental modeling using CEEOT. TIAER Report No. PR0002. Stephenville, Tex.: Tarleton State University, Texas Institute for Applied Environmental Research. Available at: http://tiaer. tarleton.edu/pdf/PR0002.pdf. Accessed 2 February 2010.
62. Osei, E., P. Gassman, and A. Saleh. 2000c. Livestock and the environment: A national pilot project: Upper Maquoketa River watershed, Iowa, modeling assumptions. TIAER Report No. RR0001. Stephenville, Tex.: Tarleton State University, Texas Institute for Applied Environmental Research. Available at: http://tiaer.tarleton.edu/pdf/RR0001.pdf. Accessed 2 February 2010.
63. Osei, E., P. W. Gassman, L. M. Hauck, R. Jones, L. Beran, P. T. Dyke, D. W. Goss, J. D. Flowers, and A. M. S. McFarland. 2003a. Economic costs and environmental benefits of manure incorporation on dairy waste application fields. J. Environ. Mgmt. 68(1):1-11.
64. Osei, E., P. W. Gassman, L. M. Hauck, S. Neitsch, R. D. Jones, J. McNitt, and H. Jones. 2003b. Economic and environmental impacts of pasture nutrient management. J. Range Mgmt. 56(3):218-226.
65. Osei, E., B. Du, A. Bekele, L. Hauck, A. Saleh, and A. Tanter. 2004. CEEOT-MMS: A macro modeling system for environmental assessment. TIAER Report No. TR0409. Stephenville, Tex.: Tarleton State University, Texas Institute for Applied Environmental Research. Available at: http://tiaer.tarleton.edu/pdf/ TR0303.pdf. Accessed 2 February 2010.
66. Osei, E., B. Du, and L. M. Hauck. 2007. Impacts of changing herd sizes on the effects of manure application rates. In Proc. 4th Conf.: Watershed Management to Meet Water Quality Standards and TMDLs, 59-66. A. McFarland and A. Saleh, eds. St. Joseph, Mich.: ASABE.
67. Osei, E., B. Du, A. Bekele, L. Hauck, A. Saleh, and A. Tanter. 2008a. Impacts of alternative manure application rates on Texas animal feeding operations: A macro-level analysis. J. American Water Resour. Assoc. 44(3):1-15.
68. Osei, E., B. Du, L. M. Hauck, A. Saleh, and A. Tanter. 2008b. Macro-level analysis of CNMPs in the Ohio River basin. In Proc. 21st Century Watershed Technology Conf.: Improving Water Quality and Environment. E. W. Tollner and A. Saleh, eds. St. Joseph, Mich.: ASABE.
69. Osei, E. L. Hauck, R. Jones, C. Ogg, and K. Keplinger. 2008c. Livestock and the environment: Lessons from a national pilot project. TIAER Report No. PR0801. Stephenville, Tex.: Tarleton State University, Texas Institute for Applied Environmental Research. Available at: http://tiaer.tarleton.edu/pdf/ PR0801.pdf. Accessed 22 December 2009.
70. Parton, W. J., D. S. Schimel, C. V. Cole, and D. S. Ojima. 1987. Analysis of factors controlling soil organic matter levels in Great Plains grasslands. SSSA J. 51(5):1173-1179.
71. Peabody, P. J. 2005. Agricultural cost of maintaining playa lake hydroperiod to preserve playa lake ecosystems in the Texas High Plains. MS thesis. Lubbock, Tex.: Texas Tech University, Department of Agriculture and Applied Economics. Available at: http://repositories.tdl.org/tdl/handle/2346/ 1275?show=full. Accessed 14 May 2009.
72. Paudel, K. P., D. Hite, W. Intarapapong, and D. Susanto. 2003. A watershed-based economic model of alternative management practices in southern agricultural systems. J. Agric. Applied Econ. 35(2):381-389.
73. Penman, H. L. 1948. Natural evaporation from open water, bare soil, and grass. Proc. Royal Soc. London A 193(1032):120-145.
74. Potter, K. N., J. R. Williams, F. J. Larney, and M. S. Bullock. 1998. Evaluation of EPIC's wind erosion submodel using data from southern Alberta. Canadian J. Soil Sci. 78(3):485-492.
75. Potter, S., S. Wang, and A. King. 2009. Modeling structural conservation practices: Cropland component of the National Conservation Effects Assessment Project. Temple, Tex.: Texas A&M University, Texas Agricultural Experiment Station, Blackland Research and Extension Center. Available at: www.nrcs.usda.gov/technical/NRI/ceap/umrbdocumentation/. Accessed 1 February 2010.
76. Pratt, S., R. Jones, and C. A. Jones. 1997. Livestock and the environment: Expanding the focus: Policy options: CEEOT-LP. TIAER Report No. PR9603. Stephenville, Tex.: Tarleton State University, Texas Institute for Applied Environmental Research.
77. Priestley, C. H. B., and R. J. Taylor. 1972. On the assessment of surface heat flux and evaporation using large-scale parameters. Monthly Weather Rev. 100(2):81-92.
78. Qiu, Z., T. Prato, L. Godsey, and V. Benson. 2002. Integrated assessment of uses of woody draws in agricultural landscapes. J. American Water Resour. Assoc. 38(5):1255-1269.
79. Reddy, K. R., R. Khaleel, M. R. Overcash, and P. W. Westerman. 1979. A nonpoint-source model for land areas receiving animal wastes: II. Ammonia volatilization. Trans. ASAE 22(6):1398-1404.
80. Renard, K. G., G. R. Foster, G. A. Weesies, D. K. McCool, and D. C. Yoder. 1997. Predicting soil erosion by water: A guide to conservation planning with the Revised Universal Soil Loss Equation (RUSLE). Agriculture Handbook No. 703. Washington, D. C.: USDA Agricultural Research Service.
81. Reungsang, P., R. S. Kanwar, M. Jha, P. W. Gassman, K. Ahmad, and A. Saleh. 2007. Calibration and validation of SWAT for the Upper Maquoketa River watershed. Intl. Agric. Eng. J. 169 (1-2) : 35-48.
82. Richardson, C. W. 1981. Stochastic simulation of daily precipitation, temperature, and solar radiation. Water Resour. Res. 17(1):182-190.
83. Ritchie, J. T. 1972. Model for predicting evaporation from a row crop with incomplete cover. Water Resour. Res. 8(5):1204-1213.
84. Saleh, A., and O. Gallego. 2007. Application of SWAT and APEX using the SWAPP (SWAT-APEX) program for the Upper North Bosque River watershed in Texas. Trans. ASABE 50(4):1177-1187.
85. Saleh, A., J. G. Arnold, P. W. Gassman, L. M. Hauck, W. D. Rosenthal, J. R. Williams, and A. M. S. McFarland. 2000. Application of SWAT for the Upper North Bosque River watershed. Trans. ASAE 45(3):1077-1087.
86. Saleh, A., P. W. Gassman, J. Abraham, and J. Rodecap. 2003. Application of SWAT and APEX models for Upper Maquoketa River watershed in northeast Iowa. ASAE Paper No. 032063. Presented at the 2003 ASAE Annual International Meeting. St. Joseph, Mich.: ASAE.
87. Saleh, A., J. R. Williams, J. C. Wood, L. M. Hauck, and W. H. Blackburn. 2004. Application of APEX for forestry. Trans. ASAE 47(3):751-765.
88. Saleh, A., E. Osei, and O. Gallego. 2008. Use of CEEOT-SWAPP modeling system for targeting and evaluating environmental pollutants. In Proc. 21st Century Watershed Technology Conf.: Improving Water Quality and Environment. E. W. Tollner and A. Saleh, eds. St. Joseph, Mich.: ASABE.
89. Seligman, N. G., and H. van Keulen. 1981. PAPRAN: A simulation model of annual pasture production limited by rainfall and nitrogen. In Proc. Workshop: Simulation of Nitrogen Behaviour of Soil-Plant Systems, 192-221. M. J. Frissel and J. A. van Veen, eds. Wageningen, The Netherlands: Centre for Agricultural Publishing and Documentation.
90. Skaggs, R. W. 2007. Criteria for calculating drain spacing and depth. Trans. ASABE 50(5):1657-1662.
91. Srivastava, P., K. W. Migliaccio, and J. im nek. 2007. Landscape models for simulating water quality at point, field, and watershed scales. Trans. ASABE 50(5):1683-1693.
92. Steglich, E. M., and J. R. Williams. 2008. Agricultural Policy/Environmental Extender Model: User's Manual. Version 0604 DOS and WINAPEX interface. BREC Report 2008-16.
93. Temple, Tex.: Texas A&M University, Texas AgriLIFE Research, Blackland Research and Extension Center. Available at: http://epicapex.brc. tamus.edu/downloads/user-manuals.aspx. Accessed 31 January 2010.
94. Tubiello, F. N., J. S. Amthor, K. J. Boote, M. Donatelli, W. Easterling, G. Fischer, R. M. Gifford. M. Howden, J. Reilly, and C. Rosenzweig. 2007. Crop response to elevated CO2 and world food supply: A comment on "Food for Thought..." by Long et al., Science 312: 1918-1921
95. European J. Agron. 26(3):215-223.
96. Tuppad, P., M. F. Winchall, X. Wang, R. Srinivasan, and J. R. Williams. 2009. ARCAPEX: ARCGIS interface for Agricultural Policy Environmental Extender (APEX) hydrology/water quality model. Intl. Agric. Eng. J. 18 (1-2) : 59-71.
97. USDA-ARS. 2005. Revised Universal Soil Loss Equation 2: Overview of RUSLE2. Oxford, Miss.: USDA-ARS National Sedimentation Laboratory, Watershed Research Physical Processes Unit. Available at: www.ars.usda.gov/Research/docs. htm?docid=6010. Accessed 2 February 2010.
98. USDA-NRCS. 1986. Urban hydrology for small watersheds. Technical Release 55. Washington, D. C.: USDA National Resource Conservation Service. Available at: www.hydrocad.net/pdf/TR-55%20Manual.pdf. Accessed 31 January 2010.
99. USDA-NRCS. 2004. Chapter 10: Estimation of direct runoff from storm rainfall. In NRCS National Engineering Handbook, Part 630: Hydrology, 10.1-10.22. Washington, D. C.: USDA National Resource Conservation Service. Available at: http://directives.sc.egov. usda.gov/viewerFS.aspx?hid=21422. Accessed 5 June 2009.
100. USDA-NRCS. 2009a. Conservation Effects Assessment Project (CEAP). Washington, D. C.: USDA National Resources Conservation Service. Available at: www.nrcs.usda.gov/technical/NRI/ceap/.
101. USDA-NRCS. 2009b. National Resource Inventory: A statistical survey of land use and natural resource conditions and trends on U. S. non-federal lands. Washington, D. C.: USDA National Resources Conservation Service. Available at: www.nrcs.usda.gov/technical/NRI/.
102. USDA-NRCS. 2010. Assessment of the effects of conservation practices on cultivated cropland in the Upper Mississippi River basin. Washington, D. C.: USDA Natural Resources Conservation Service. Available at: www.nrcs.usda.gov/ technical/nri/ceap/cropland.html.
103. Wang, E., W. L. Harman, M. Magre, J. R. Williams and J. M. Sweeten. 2002. Profitability and nutrient losses of alternative manure application strategies with conservation tillage. J. Soil and Water Conserv. 57(4):221-228.
104. Wang, E., C. Xin, J. R. Williams, and C. Xu. 2006a. Predicting soil erosion for alternative land uses. J. Environ. Qual. 35(2):459-467.
105. Wang, X., S. R. Potter, J. R. Williams, J. D. Atwood, and T. Pitts. 2006b. Sensitivity analysis of APEX for national assessment. Trans. ASABE 49(3):679-688.
106. Wang, X., A. Saleh, M. W. McBroom, J. R. Williams, and L. Yin. 2007. Test of APEX for nine forested watersheds in east Texas. J. Environ. Qual. 36(4):983-995.
107. Wang, X., P. W. Gassman, J. R. Williams, S. Potter, and A. R. Kemanian. 2008a. Modeling the impacts of soil management practices on runoff, sediment yield, maize productivity, and soil organic carbon using APEX. Soil Tillage Res. 101 (1-2) : 78-88.
108. Wang, X., S. Shang, and W. Yang. 2008b. Simulation of an agricultural watershed using an improved curve number method in SWAT. Trans. ASABE 51(4):1323-1339.
109. Wang, X., D. W. Hoffman, J. E. Wolfe, J. R. Williams, and W. E. Fox. 2009. Modeling the effectiveness of conservation practices at Shoal Creek watershed, Texas, using APEX. Trans. ASABE 52(4):1181-1192.
110. White, E. D., G. W. Feyereisen, T. L. Veith, and D. D. Bosch. 2008. Improving daily water yield estimates in the Little River watershed: SWAT adjustments. Trans. ASABE 52(1):69-79.
111. Williams, J. R. 1975. Sediment yield prediction with universal equation using runoff energy factor. ARS-S-40. Washington, D. C.: USDA Agricultural Research Service.
112. Williams, J. R. 1990. The erosion productivity impact calculator (EPIC) model: A case history. Phil. Trans. Royal Soc. London 329(1255):421-428.
113. Williams, J. R. 1995. The EPIC model. In Computer Models of Watershed Hydrology, 909-1000. V. P. Singh, ed. Highlands Ranch, Colo.: Water Resources Publications.
114. Williams, J. R., and R. W. Hann. 1978. Optimal operation of large agricultural watersheds with water quality constraints. Tech. Report No. 96. College Station, Tex.: Texas A&M University, Texas Water Resources Institute.
115. Williams, J. R., and R. C. Izaurralde. 2005. The APEX model. BREC Report No. 2005-02. Temple, Tex.: Texas A&M University, Texas Agricultural Experiment Station, Blackland Research and Extension Center.
116. Williams, J. R., and R. C. Izaurralde. 2006. The APEX model. In Watershed Models, 437-482. V. P. Singh and D. K. Frevert, eds. Boca Raton, Fla.: CRC Press.
117. Williams, J. R., C. A. Jones, and P. T. Dyke. 1984. A modeling approach to determining the relationship between erosion and soil productivity. Trans. ASAE 27(1):129-144.
118. Williams, J. R., C. A. Jones, J. R. Kiniry, and D. A. Spanel. 1989. The EPIC crop growth model. Trans. ASAE 32(2):497-511.
119. Williams, J. R., C. A. Jones, P. W. Gassman, and L. M. Hauck. 1995. Simulation of animal waste management with APEX. In Innovations and New Horizons in Livestock and Poultry Manure Management, 22-26. J. McFarland, ed. Austin, Tex.: Texas A&M University, Texas Agricultural Extension Service.
120. Williams, J. R., J. G. Arnold, and R. Srinivasan. 2000. The APEX model. BREC Report No. 00-06. Temple, Tex.: Texas A&M University, Texas Agricultural Experiment Station, Blackland Research and Extension Center.
121. Williams, J. R., E. Wang, A. Meinardus, and W. L. Harman. 2003. APEX Users Guide. Version 1310. Temple, Tex.: Texas A&M University, Texas Agricultural Experiment Station, Blackland Research and Extension Center.
122. Williams, J. R., W. L. Harman, M. Magre, U. Kizil, J. A. Lindley, G. Padmanabhan, and E. Wang. 2006a. APEX feedlot water quality simulation. Trans. ASAE 49(1):61-73.
123. Williams, J. R., E. Wang, A. Meinardus, W. L. Harman, M. Siemers, and J. D. Atwood. 2006b. APEX Users Guide. Version 2110. Temple, Tex.: Texas A&M University, Texas Agricultural Experiment Station, Blackland Research and Extension Center.
124. Williams, J. R., J. G. Arnold, J. R. Kiniry, P. W. Gassman, and C. H. Green. 2008a. History of model development at Temple, Texas. Hydrol. Sci. J. 53(5):948-960.
125. Williams, J. R., R. C. Izaurralde, and E. M. Steglich. 2008b. Agricultural Policy/Environmental Extender model: Theoretical Documentation. Version 0604. BREC Report 2008-17. Temple, Tex.: Texas A&M University, Texas AgriLIFE Research, Blackland Research and Extension Center. Available at: http://epicapex.brc.tamus.edu/downloads/user-manuals.aspx. Accessed 31 January 2010.
126. Willis, D. B. 2008. Cost-effectiveness of on-farm conservation practices to protect playa lake hydroperiod in the Texas High Plains. Paper presented at the Southern Agricultural Economics Association Annual Meeting. Available at: http://purl.umn.edu/6753. Accessed 2 February 2010.
127. Wischmeier, W. H., and D. D. Smith. 1978. Predicting rainfall erosion losses: A guide to conservation planning. Agric. Handbook No. 537. Washington, D. C.: USDA. Available at: http://naldr.nal.usda.gov. Accessed 2 February 2010.
128. Yin, L., X. Wang, J. Pan, and P. W. Gassman. 2009. Evaluation of APEX for daily runoff and sediment yield from three plots in the Upland Huaihe River watershed, China. Trans. ASABE 52(6):1833-1845.