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An Active Sensor Algorithm for Corn Nitrogen Recommendations Based on a Chlorophyll Meter Algorithm
- Solari, Fernando, Shanahan, John F., Ferguson, Richard B., Adamchuk, Viacheslav I.
- Agronomy journal 2010 v.102 no.4 pp. 1090
- Zea mays, corn, nitrogen, plant nutrition, nutritional status, canopy, sensors, reflectance, algorithms, chlorophyll, nitrogen fertilizers, fertilizer rates, mathematical models, equations, nitrogen balance, accuracy, model validation, grain yield, irrigated farming
- In previous research we found active canopy sensor reflectance assessments of corn (Zea mays L.) N status have potential for directing in-season N applications, but emphasized an algorithm was needed to translate sensor readings into appropriate N application (Napp) rates. The objectives of this work were to: (i) develop an active canopy sensor algorithm based on a SPAD chlorophyll meter algorithm and (ii) validate the active canopy sensor algorithm using data collected from a companion study. We derived the sensor algorithm using a linear relationship between sensor sufficiency index (SIsensor) and SISPAD values established in the previous research and a published SPAD algorithm employing a quadratic equation to calculate Napp as a function of SISPAD. The resulting equation: Napp=317 represents the function for translating SIsensor to Napp. To validate the algorithm, SIsensor values collected from small plots receiving varying N amounts were converted into Napp using the algorithm. Then Napp was converted into crop N balance (Nbalance) estimates, where Nbalance = applied N-Napp. Negative Nbalance values indicate N deficiency while positive values indicate excess N. The Nbalance values were compared with relative yields and a quadratic-plateau model fit to the data set for both growth stages (V11 and V15), producing an R2 of 0.66. Relative yields plateaued at an Nbalance near zero (–11 kg N ha–1), indicating the algorithm provided reasonable estimates of Napp for maximizing yields. The equation provides a basis for the use of active crop canopy sensors for in-season N management of irrigated corn