COLVIN, T.S., TAPELA, M., MEEK, D.W., COOK, J.D., BAKER, J., CRUSE, R., KARLEN, D.L. A LOOK BACK AT A LONG TERM TILLAGE EXPERIMENT AND A LOOK FORWARD AT THE POTENTIAL FOR SITE SPECIFIC TILLAGE. TILLAGE CONFERENCE PROCEEDINGS. 2003. CD-ROM. WOOSTER, OH.
Colvin, T.S., Cook, J.D., Pecinovsky, K. Water table level as influenced by tiling method. Iowa State University Northeast Research and Demonstration Farm 2002 Report. Available: http://www.ag.iastate.edu/farms/02reports/ne/watertablelevel.pdf.
COLVIN, T.S., MEEK, D.W., COOK, J.D., BAKER, J.L., CRUSE, R.M. ANALYSIS OF LONG TERM TILLAGE EXPERIMENT RECORD. AMERICAN SOCIETY OF AGRICULTURAL ENGINEERS. 2001. Paper No. 01-AETC-01.