Tuesday, November 14, 2006 - 10:00 AM

Translating Ramped Calibration Strip Data into Fertilizer N Recommendations.

James Schepers1, Bill Raun2, John J. Meisinger3, John Solie2, and John Shanahan4. (1) 113 Keim Hall, Univ of Nebraska, Lincoln, NE 68583-0915, (2) Oklahoma State Univ, Ag Hall, Stillwater, OK 74078, (3) Bldg 163F Room 6, BARC-East , 10300 Baltimore Ave, Beltsville, MD 20705-2350, (4) USDA-ARS, Lincoln, NE 68583-0934, United States of America

Using crop vigor and color to make in-season fertilizer N recommendations is challenging in that many factors affect the observations or measurements. Even more forethought needs to go into making a responsible fertilizer recommendation in order to ensure producer profitability and yet avoid losses to the environment associated with excess N. The concept of using a ramped calibration strip to assess crop response to soil N availability and weather is an integration of ideas and allows users to tune their decision to the current growth stage, cultivar, local weather, and cultural practices. Ideally, crop comparisons between the bulk field and N rate areas should directly indicate the amount of fertilizer N that would be needed to remove the stress, but this relationship changes with original N status of the soil and the crop development stage when the comparison is made. Crop canopy sensor and SPAD meter data collected from N rate studies during the growing season will be summarized in order to evaluate strategies for addressing how to incorporate the level of N stress and growth stage into in-season fertilizer N recommendations for corn. The idea is set forth to use a sliding factor based on growth stage or GDD to compensate for the relative proportion of total N in the crop at the time of sensing (i.e., a factor of 1.5 at V8 that diminishes to1.0 at VT and to 0.0 at R2 for corn).