An Active Sensor Nitrogen Application Algorithm for Corn Using a Chlorophyll Meter Based Sufficiency Index Concept.

Traditional N fertilizer management schemes for U.S. corn production systems have resulted in low N use efficiency, reduced water quality, and considerable public debate regarding N use in crop production. We have built a prototype high clearance N applicator configured with active sensors, controller, and nozzle/valve system designed to deliver spatially variable rates of N fertilizer in lieu of uniform at-planting applications to address these issues. This paper reports on the development of a sensor algorithm to be used for translating active sensor readings into N application rates, and efforts to validate the algorithm in small plot field studies. The active sensor used in our work is the Crop Circle ACS-210 manufactured by Holland Scientific of Lincoln, NE. The algorithm was developed by combining results from a long term field study showing chlorophyll meter readings can be used to assess corn N status and determine rate of N application along with results showing active sensor readings are highly correlated with chlorophyll meter assessments of canopy N status.   The resulting algorithm is proposed as a means for converting active sensor readings into corrective in-season N application rates that maintain grain yields. The algorithm was validated in a field study involving small plots receiving different amounts and timings of N.  Sensor readings were acquired on the dates N applications were made and the algorithm used to convert sensor estimated N deficiency.  Grain yields were also determined for these same plots.   The relationship of relative grain yields versus sensor estimated N requirements was described by a quadratic plateau regression model with a coefficient of determination of 0.64, indicating the sensor algorithm would provide a reasonably accurate assessment of in-season N requirements for maintaining grain yields.