An Active Sensor Algorithm for Corn Nitrogen Recommendations Based on a Chlorophyll Meter Algorithm

摘要

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 (N-app) 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 N-app as a function of SISPAD. The resulting equation: N-app = 317 root 0.97-SIsensor represents the function for translating SIsensor to N-app. To validate the algorithm, SIsensor or values collected from small plots receiving varying N amounts were converted into N-app using the algorithm. Then N-app was converted into crop N balance (Nbajance) estimates, where N balance - applied N- ri N-app. Negative N-balance values indicate N deficiency while positive values indicate excess N. The N-balance 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 R-2 of 0.66. Relative yields plateaued at an N-balance near zero (-11 kg N ha(-1)), indicating the algorithm provided reasonable estimates of N-app for maximizing yields. The equation provides a basis for the use of active crop canopy sensors for in-season N management of irrigated corn