Watson, F.C. (1979) Soil survey for Knox, Monroe, and Shelby Counties, Missouri. United States Department of Agriculture, Soil Conservation Service, U.S. Gov’t Printing Off., 8-20.
 University of Missouri Extension (2009) Farm Land Values for Missouri Counties. University of Missouri. http://extension.missouri.edu/p/g403
 United States Environmental Protection Agency (1992) The National Water Quality Inventory. The 1992 Report to Congress. USEPA, Washington DC.
 Fausey, N.R., Brown, L.C., Belcher, H.W. and Kanwar, R.S. (1995) Drainage and Water Quality in Great Lakes and Cornbelt States. J. Irrig. Drain Eng., 121, 283-288. http://dx.doi.org/10.1061/(ASCE)0733-9437(1995)121:4(283)
 Gilliam, J.W., Baker, J.L. and Reddy, K.R. (1999) Water Quality Effects of Drainage in Humid Regions. In Skaggs, R.W. and Van Schilfgaarde, J., Eds., Agricultural Drainage. Agron. Monogr. 38. ASA, CSSA, and SSSA, Wisconsin, 801-830.
 Burkart, M.R. and James, D.E. (1999) Agricultural-Nitrogen Contributions to Hypoxia in the Gulf of Mexico. Journal of Environmental Quality, 28, 850-859. http://dx.doi.org/10.2134/jeq1999.00472425002800030016x
 United States Environmental Protection Agency (2009) National Primary Drinking Water Regulations. USEPA. http://water.epa.gov/drink/contaminants/upload/mcl-2.pdf
 Sims, J.T., Simard, R.R. and Joern, B.C. (1998) Phosphorus Loss in Agricultural Drainage: Historical Perspective and Current Research. Journal of Environmental Quality, 27, 277-293. http://dx.doi.org/10.2134/jeq1998.00472425002700020006x
 Adviento-Borbe, M.A., Kaye, J.P., Bruns, M.A., McDaniel, M.D., McCoy, M. and Harkcom S. (2010) Soil Greenhouse Gas and Ammonia Emissions in Long-Term Maize-Based Cropping Systems. Soil Science Society of America Journal, 74, 1623-1634. http://dx.doi.org/10.2136/sssaj2009.0446
 Gast, R.G., Nelson, W.W. and Randall, G.W. (1978) Nitrate Accumulation in Soils and Loss in Tile Drainage Following Nitrogen Applications to Continuous Corn. Journal of Environmental Quality, 7, 258-261. http://dx.doi.org/10.2134/jeq1978.00472425000700020021x
 Baker, J.L. and Johnson, H.P. (1981) Nitrate-Nitrogen in Tile Drainage as Affected by Fertilization. Journal of Environmental Quality, 10, 519-522. http://dx.doi.org/10.2134/jeq1981.00472425001000040020x
 Randall, G.W. and Vetsch, J.A. (2005) Nitrate Losses in Subsurface Drainage from a Corn-Soybean Rotation as Affected by Fall and Spring Application of Nitrogen and Nitrapyrin. Journal of Environmental Quality, 34, 590-597. http://dx.doi.org/10.2134/jeq2005.0590
 Drury, C.F., McKenney, D.J., Findlay, W.I. and Gaynor, J.D. (1993) Influence of Tillage and Nitrate Loss in Surface Runoff and Tile Drainage. Soil Science Society of America Journal, 57, 797-802.
 Drury, C.F., Tan, C.S., Rynolds, W.D., Welacky, T.W., Oloya, T.O. and Gaynor, J.D. (2009) Managing Tile Drainage, Subirrigation, and Nitrogen Fertilization to Enhance Crop Yields and Reduce Nitrate Loss. Journal of Environmental Quality, 38, 1193-1204. http://dx.doi.org/10.2134/jeq2008.0036
 Evans, R.O., Skaggs, R.W. and Gilliam, J.W. (1995) Controlled Versus Conventional Drainage Effects on Water Quality. Journal of Irrigation and Drainage Engineering, 121, 271-276. http://dx.doi.org/10.1061/(ASCE)0733-9437(1995)121:4(271)
 Gilliam, J.W., Skaggs, R.W. and Weed, S.B. (1979) Drainage Control to Diminish Nitrate Loss from Agricultural Fields. Journal of Environmental Quality, 8, 137-142. http://dx.doi.org/10.2134/jeq1979.00472425000800010030x
 Evans, R.O., Skaggs, R.W. and Gilliam, J.W. (1990) Management Practice Effects on Water Quality. In: Harris, S.C., Ed., Proceedings of the 1990 National Conference, Irrigation and Drainage Division, ASCE, 182-191.
 Fogiel, A. and Belcher, H.W. (1991) Water Quality Impacts of Watertable Management Systems Annual Report. Dep. Agric. Eng., Michigan State University, Lansing.
 Fujinuma, R., Balster, N.J. and Norman, J.M. (2009) An Improved Model of Nitrogen Release for Surface-Applied Controlled-Release Fertilizer. Soil Science Society of America Journal, 73, 2043-2050.http://dx.doi.org/10.2136/sssaj2009.0085
 Nash, P.R., Nelson, K.A., Motavalli, P.P. and Meinhardt, C.G. (2012) Effects of Polymer-Coated Urea Application Ratios and Dates on Wheat and Subsequent Double-Crop Soybean. Agronomy Journal, 104, 1074-1084. http://dx.doi.org/10.2134/agronj2011.0235
 Nelson, K.A., Motavalli, P.P. and Dudenhoeffer, C.J. (2014) Cropping System Affects Polymer-Coated Urea Release and Corn Yield Response in Claypan Soils. Journal of Agronomy and Crop Science, 200, 54-65. http://dx.doi.org/10.1111/jac.12040
 Noellsch, A.J., Motavalli, P.P., Nelson, K.A. and Kitchen, N.R. (2009) Corn Response to Conventional and Slow-Release Nitrogen Fertilizers Across a Claypan Landscape. Agronomy Journal, 101, 607-614.
 Nelson, K.A. and Motavalli, P.P. (2013) Nitrogen Source, Drainage, and Irrigation Affects Corn Yield Response in a Claypan Soil. Applied Engineering in Agriculture, 29, 875-884. http://dx.doi.org/10.13031/aea.29.9809
 Nash, P.R. (2014) Utilization of Managed Subsurface Drainage Systems to Increase Corn and Forage Yields and Reduce Nitrogen Loss in Poorly-Drained, Upland and Bottomland Soils. Dissertation, University of Missouri, Columbia.
 Nathan, M., Stecker, J. and Sun, Y. (2006) Soil Testing in Missouri: A Guide for Conducting Soil Tests in Missouri. University of Missouri. http://soilplantlab.missouri.edu/soil/ec923.pdf
 Chun, J.A. and Cooke, R.A. (2008) Technical Note: Calibrating Agridrain Water Level Control Structures Using Generalized Weir and Orifice Equations. Applied Engineering in Agriculture, 24, 595-602.http://dx.doi.org/10.13031/2013.25274
 SAS Institute (2013) SAS 9.3. SAS Inst., Cary.
 Hernandez-Ramirez, G., Brouder, S.M., Ruark, M.D. and Turco, R.F. (2011) Nitrate, Phosphate, and Ammonium Loads at Subsurface Drains: Agroecosystems and Nitrogen Management. Journal of Environmental Quality, 40, 1229-1240. http://dx.doi.org/10.2134/jeq2010.0195
 Jaynes, D.B., Colvin, T.S., Karlen, D.L., Cambardella, C.A and Meek, D.W. (2001) Nitrate Loss in Subsurface Drainage as Affected by Nitrogen Fertilizer Rate. Journal of Environmental Quality, 30, 1305-1314.
 Qi, Z., Helmers, M.J., Christianson, R.D. and Pederson, C.H. (2011) Nitrate-Nitrogen Losses through Subsurface Drainage under Various Agricultural Land Covers. Journal of Environmental Quality, 40, 1578-1585.http://dx.doi.org/10.2134/jeq2011.0151