Variable Rate System For Side‐Dressing Liquid N Fertilizer

Variable rate applicators vary in complexity, ranging from rigs that control flow rate, change chemicals, and vary application pattern to those that only modulate flow rate. This chapter describes a rate-only variable applicator that uses the DICKEYjohn control system for site-specific side-dressing of liquid nitrogen (N) fertilizer in maize and evaluates its accuracy and response time. Liquid N fertilizer was carried in a 133 L stainless steel tank, mounted on the applicator. Liquid applicators that vary flow rate in response to nozzle pressure and ground speed are perhaps the easiest to adapt for rate-only variable application. Initial flow rates of 0, 5.7, and 9.5 L min-1 were varied to attain target flow rates ranging from 7.6-20.8 L min-1. Accuracy and response time of the DICKEYjohn control system should be independent of the flow rate and the direction of change in the flow rate.