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Title: NITROGEN OVER USE, UNDER USE, AND EFFICIENCY

Author
item Hatfield, Jerry
item Prueger, John

Submitted to: International Crop Science Congress Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 10/1/2004
Publication Date: 10/1/2004
Citation: Hatfield, J.L., Prueger, J.H. 2004. Nitrogen Over Use, Under Use, and Efficiency [CD-ROM]. International Crop Science Congress Proceedings. 4th International Crop Science Congress. Brisbane, Australia.

Interpretive Summary:

Technical Abstract: Nitrate nitrogen (N) in surface and ground water is a world-wide problem that agriculture is being asked to address by developing farming systems that reduce leaching and thus decrease both concentration and load of nitrate in water resources. Applications of fertilizer N have remained relatively constant in Western Europe and the United States for the past 15 years but have increased elsewhere because N is an essential plant nutrient and its application is often a valuable agronomic practice because of the plant response. Leaching occurs because nitrate N is extremely mobile. Increased concentrations in water resources are often attributed to application rates that exceed agronomic needs of crops. Grain production usually increases linearly with applied N, but N use efficiency (NUE) expressed as grain production per unit of N applied, has decreased in all countries. Management of N is difficult because of interactions among soil N mineralization, water availability, and the type of crop grown. We illustrate the interaction between N use and water on yield with detailed maize (Zea mays L.) study from Iowa USA. Yield response to N decreased at fertilizer rates above 116 kg N ha**-1 due to water deficits during grain-filling that reduced both yield and water use efficiency. Increasing N rates decreased yield variation within fields, but did not increase total yield. Management of N within fields can be improved by knowing the soil organic matter content and water holding capacity. Integrating soil water data with N management can increase NUE and decrease negative environmental impact of agriculture.