The Effect of Multi-Year Reduced Nitrogen Application Rates On Corn Grain Yield in Continuous Corn and Corn / Soybean Rotations.

Nitrogen (N) fertilizer prices have skyrocketed in recent years, adding significantly to the cost of producing corn. To help lower N input costs for its customers, Pioneer Hi-Bred is developing corn hybrids with improved Nitrogen Use Efficiency (NUE). Specifically, Pioneer’s goals are to develop hybrids that maintain yield but utilize 30% less N or yield significantly more with the same N rate.  The objective of this ongoing study is to determine the time it takes for reduced N rates to significantly lower corn grain yields.  This study is conducted under both continuous corn and corn / soybean rotation over multiple years and locations.  Long term reduced nitrogen field plots have been set up at Johnston, Iowa (3 years of data), Mankato, Minnesota (2 years of data), Windfall, Indiana (2 years of data), Champaign, Illinois (2 years of data), and York Nebraska (1 year of data).  Nitrogen treatments are standardized to five rates as a percentage of University economic optimum recommendations (130%, 100%, 70%, 50%, and 0% of the full rate).  The same treatments are positioned on the same plots from year to year (i.e. the 70% N treatment for continuous corn is in precisely the same field location from year to year).  Preliminary results, comparing the 100% N rate to the 70% N rate across all locations in 2008 are shown in Table 1.

Table 1. Percentage yield reduction between 100% N rate and 70% N rate by location and crop rotation.

Year of data	Location	Continuous Corn		Corn / Soy Rotation
3rd	Johnston, Iowa	43%	**	No change	NS
2nd	Champaign, Illinois	29%	**	7%	NS
2nd	Mankato, Minnesota	17%	**	1%	NS
2nd	Windfall, Indiana	51%	**	20%	NS
1st	York, Nebraska	5%	NS	5%	NS

** significant at 0.05