Design, development and field evaluation of a map-based variable rate granular fertilizer application control system

Abstract

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 to 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 the 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 among the step motor speed, the input frequency, and the rate of fertilizer application as a function of metering
screw rotational speed. Laboratory evaluation included measurement of the lag time while changing the application rate from
low to high and vice 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 that
the forward speed and the 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 application rate were increased.
Keywords: precision agriculture, travel speed, fertilizer type, application rate