Journal or Book Title
Proceedings of the Thirty-Fourth North Central Extension-Industry Soil Fertility Conference
Thirty-Fourth North Central Extension-Industry Soil Fertility Conference
November 17-18, 2004
Des Moines, IA
One method for refining nitrogen (N) application in corn is use of in-season crop sensing. To aid producers in making decisions regarding N rate adjustments, a calibrated relationship between sensor-derived information and expected N application need should be established. Nitrogen rate trials were conducted at multiple sites across Iowa in 2001-2003. Nitrogen was applied at or shortly after corn planting. Minolta SI'AD chlorophyll meter (CM) readings were collected at the R1 growth stage from the ear leaf. The results show a statistically significant quadratic-plateau relationship between relative chlorophyll meter (RCM) values and differential from economic optimum N rate (R' = 0.69, P < 0.001). The regression fit resulted in a 0.97 RCM value at zero differential from economic optimum N. A related study in 2003 at six N rate by crop rotation sites showed RCM values at the V15 and R1 growth stages were similar. This indicates adequate time is available to collect readings after significant corn N uptake and before making in-season N adjustments. This relationship between RCM value and differential from economic optimum N rate could be used by producers to determine additional N need.
Potash & Phosphate Institute
Sawyer, J. E.; Barker, D. W.; and Lundvall, J. P., "Using chlorophyll meter readings to determine N application rates for corn" (2004). Agronomy Conference Proceedings and Presentations. 35.