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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. International Crop Science Congress Proceedings. 4th International Crop Science Congress, September 26 to October 1, 2004. Brisbane, Queensland, Australia. p. 52.

Interpretive Summary: Nitrogen is one of the critical requirements for plant growth; however, there is increasing concern that farmers are not using nitrogen fertilizer as efficiently as possible. This assumption is based on increasing observations of nitrate-nitrogen present in surface water and some ground water supplies. Management of nitrogen is made more complex by the fact that nitrate-nitrogen is extremely mobile in water and moves rapidly with moving water. The demand from the public to reduce nitrate-nitrogen levels in water supplies while increasing food supply around the world creates a tension on future crop production practices. This review is developed to evaluate nitrogen response on corn in central Iowa and showed yield response to nitrogen was affected by the amount of water available to the crop. Producers need to understand that increasing nitrogen use efficiency by crops will depend upon the amount of water available for crop growth and the nitrogen rate. Applying this information can improve crop production in areas that depend upon rainfall for crop growth. This knowledge is helping producers reduce their nitrogen application and decrease nitrate-nitrogen loss from fields into nearby water supplies.

Technical Abstract: Nitrogen is a critical element for plant growth and plant response to added nitrogen (N) has proven to be a valuable agronomic practice. However, N is a complex element and extremely mobile in the environment leading to increases in nitrate concentrations in surface and ground water. These detections are often attributed to application rates to crops that exceed agronomic needs. Nitrate in water is a world-wide problem and agriculture is being asked to develop farming systems that will reduce the leaching of nitrate from fields and decrease both the concentration and load of nitrate in water. Nitrogen fertilizer use in the world continues to increase in developing countries; however, it has remained relatively constant for the past 15 years in developed countries. Management of N in farming systems is difficult because of the interactions between soil mineralization potential, soil water availability, and the type of crop grown. A detailed study has been conducted on corn (Zea mays L.) in Iowa that demonstrates the interactions between soil water, N, and yield. Yield response to N showed a decrease with N rates above 116 kg ha**-1. This response was due to water deficits during grain-filling that reduced yield and water use efficiency. Increasing N rates decreased the yield variation within fields without increasing the yield. Management of N within fields can be improved through an analysis of the soil organic matter content and the soil water holding capacity within. Integrating soil water with N management will increase the efficiency of N use and decrease the environmental impact of agriculture.