1. Introduction
Previous studies have pointed out that there are advantages to realizing site-specific and
variable-rate application of pesticides [1–3]. Broadcast application of chemicals without concentration
variance and spatial selection results in fields being sprayed without distinction. On the one hand,
over-application of chemicals not only increases the cost of crop production, but also increases the risk
of environmental contamination and the exposure hazards to operators. On the other hand, insufficient
application of chemical may cause a decrease of crop yield, or make the weeds chemical-resistant.
Conventional boom sprayers mix a measured quantity of pesticide with a defined amount of
carrier in a tank. Chemical application rates can only be varied by changing the liquid delivery pressure,
but the pressure changes also unexpectedly affect the droplet size spectra and spray distribution pattern
of the nozzles [4]. However, by using a direct injection system, chemical and carrier are kept separately
and mixed together when sprayed. The delivery pressure of carrier stream is maintained at the same
level, as are the pressure at the nozzles, the droplet size spectrum and the spray distribution pattern [5].
Through changing the chemical injection volume, the chemical application rate can be changed.