Field performance evaluation of Pulse-Width Modulation (PWM) and Pressure-Controlled (PC) systems for sensor-based nitrogen applications

Sensor-based N applications have shown promise for improving nitrogen use efficiency, but present significant challenges for application rate control due to highly variable and frequently changing target rates. If applications are to be made precisely, equipment systems used for sensor-based N applications must be designed to meet system demands. Pulse-width modulation (PWM) equipped systems have emerged as a technological advancement over traditional pressure-controlled (PC) systems for improving variable rate N application accuracy. Little research, however, has been done to assess the performance of PWM systems during sensor-based N applications in-field. This work analyzed as-applied data collected from in-field sensor-based N applications with pressure-controlled (PC) and PWM systems in Nebraska between 2015 and 2017 to quantify system requirements, appraise system performance, and determine performance impacting operational variables. It was found that systems should be capable of one-second rate changes of ±7.6 gal/ac, one-second flow rate changes of ±3 gpm, and turndown ratios of at least 6:1. PWM systems achieved application rates within 10% of the target rate 10% more often than PC systems, and showed less variability in application error. However, PWM systems still demonstrated significant application errors with an observed RMSE of 4.8 gal/ac. Speed change magnitude was found to be most associated with increases in percent application error. These findings substantiate that PWM systems effectively improve sensor-based N application accuracy versus traditional PC systems. However, collaborative efforts toward greater cohesion between sensor-based application expectations and application equipment capabilities are necessary for maximizing the effectiveness of sensor-based N applications.