Design, Development and Field Evaluation of a Map-Based Variable Rate Granular Application Control System

Site-specific application of agricultural chemicals including granular fertilizers is an effective way of resource saving and environmental protection. The objective of this research was to develop and evaluate the performance of a map-based variable rate row crop granular fertilizer placement system. The applicator system consists of an AVR microcontroller for controlling the driving step motor of a fertilizer metering screw and a ground driven wheel integrated with a rotary encoder for the applicator displacement and speed measurement. Initially, the applicator was calibrated in laboratory to derive a relationship between the step motor speed and input frequency and the rate of fertilizer application as a function of metering screw rotational speed. Laboratory evaluations included Calibration of metering screw rotational speed with stepper motor input frequency and material discharge rate and measurement of the lag time when changing the application rate from low to high and vis-versa. In the field tests, a factorial experiment with a split-split design was used to investigate the effects of fertilizer type (urea and triple super phosphate), applicator forward speed (3, 6 and 9 km/s) and application rate (75, 125 and 175 kg/ha) on precision of application rate (the percent of deviation between actual and target rates). The results showed forward speed and application rate both had significant effect on precision of application rate, while fertilizer type had no significant effect. The precision of application rate decreased when forward speed and/or application rate was increased.