Sunday, November 12, 2006

Water Management: A Key to Reduce Nitrogen Losses.

E. J. Sadler, USDA-ARS CS&WQRU, Columbia, MO 65203, Walter Bausch, USDA-ARS Water Mngmnt Research, 2150 Centre Ave, Bldg D Ste 320, Fort Collins, CO 80526, Norman Fausey, USDA/ARS, 590 Woody Hayes Drive Room 234, Columbus, OH 43210, United States of America, and R.B. Ferguson, Univ of Nebraska, Dept of Agronomy & Horticulture, Lincoln, NE 68583-0724.

Improving yield per unit water applied has probably always been the goal of irrigators. This ratio of yield per unit water was some 40 years ago named water use efficiency (WUE). This emphasized obtaining the maximum yield for a given irrigation amount, often by increasing fertilizer applications, usually of nitrogen (N). The implications of this approach were examined in case studies. The South and Central Platte River valley experiences showed elevated groundwater nitrate-N levels from continuous irrigated, intensively managed maize. The US Corn Belt illustrated that intensive management of maize under rainfed conditions can also cause losses of nitrate-N. A case study in the Southeast Atlantic Coastal Plain documented spatial variation in both WUE and N use efficiency.  Examination of the water and N balances shows points of interactions where mobile soluble N species can migrate with moving water, or relatively less mobile species can transform to more mobile species because of the prevailing water content. Results from these case studies lead to a conclusion that simultaneous optimization of both inputs will be required for economically and environmentally sustainable agriculture.