Tom Doerge. Soils Specialist, Department of Soil and Water Science.
Ph.D., Oregon State University. Development, validation and improvement
of nitrogen and water management practices designed to reduce leaching losses
of nitrate below the root zone of irrigated croplands, thereby minimizing
degradation of groundwater quality.
The appropriate use of nitrogen fertilizers greatly increases agricultural
productivity and lowers the unit cost of farm commodities. However, overuse
can degrade the environment if nitrate contaminated waters from farm lands
migrate into streams or aquifers. I am coordinating a research and demonstration
program designed to develop, validate, and disseminate state-of-the art
Best Management Practices (BMPs) for nitrogen fertilizer use, which will
enable Arizona growers to produce crops with maximum profitability, while
also safeguarding water resources from nitrate contamination. 15N materials
and other tracers are used to document the fate of nitrogen in irrigated
cotton and wheat cropping systems receiving deficient, optimum and excessive
levels of fertilization.
Additional research involves the development of BMP's for high-value crops
such as broccoli, cauliflower, leaf lettuce, greens and spinach. In this
research, deficient, optimum and excessive amounts of nitrogen are applied
to commercially important cultivars, using a drip irrigation system to document
the response of these crops to different nitrogen supplies, and then develop
suitable diagnostic plant tissue test procedures to monitor crop nitrogen
status throughout the growing season. In addition, this information will
then ben incorporated into a computerized decision aid which can monitor
the fertilizer needs of all major crops grown in Arizona, using detailed
crop growth models and plant tissue analysis techniques.
I have completed a reference book on current BMP techniques which will serve
as the basis for the state's newly mandated continuing educational program
for agricultural use of nitrogen fertilizers. This book is also a model
for similar reference materials on other regulated activities, such as confined
animal feeding.
Knowles, T.C., Doerge, T.A., and M.J. Ottman. 1991. Improved nitrogen management
in irrigated durum wheat using stem nitrate analysis: I. Nitrate uptake
dynamics. Agron. J. 83:346-352.
Knowles, T.C., Doerge, T.A., and M.J. Ottman. 1991. Improved nitrogen management
in irrigated durum wheat using stem nitrate analysis: II. Interpretation
of nitrate-nitrogen concentrations. Agron. J. 83:353-356.
Doerge, T.A., Roth, R.L., and B.R. Gardner. 1991. Nitrogen fertilizer management
in Arizona. Cooperative Extension, College of Agriculture, The University
of Arizona Report No. 191025. 87 pages.
Silvertooth, J.C., J.E. Watson, J.E. Malcuit and T.A. Doerge. 1992. Bromide
and nitrate movement in an irrigated cotton production system. Soil Sci.
Soc. Amer. J. 56:548-555.
Pier, J.W. and T.A. Doerge. Nitrogen and water interactions in trickle irrigated
watermelons. 1995. Soil Sci. Soc. Amer. J. 59:145-150.
Pier, J.W. and T.A. Doerge. Optimizing water and nitrogen inputs for trickle
irrigated watermelon. 1995. J. of Environ. Qual. 24:79-86.
Pritchard, K.H., T.A. Doerge and T.L. Thompson. Evaluation of in-season
nitrogen tissue tests for drip irrigated leaf and romaine lettuce. Commun.
Soil Sci. Plant Anal. 26:237-258.
Thompson, T.L. and T.A. Doerge. 1996. Nitrogen and water interactions in
subsurface trickle-irrigated leaf lettuce: I. Plant response. Soil Sci.
Soc. Amer. J. 60:000-000.
Thompson, T.L. and T.A. Doerge. 1996. Nitrogen and water interactions in
subsurface trickle-irrigated leaf lettuce: II. Agronomic, economic and environmental
outcomes. Soil Sci. Soc. Amer. J. 60:000-000.