Precision Agriculture, 4, 103–124, 2003
© 2003 Kluwer Academic Publishers. Manufactured in The Netherlands.
Quality Control Veriﬁcation and Mapping
for Chemical Application
D. K. GILES AND D. DOWNEY
University of California—Davis, Department of Biological and Agricultural Engineering, Davis, CA
Abstract. The quality of an agrochemical application is a combination of the efﬁcacy of deposit, productivity
of the operation, and avoidance of off-site movement. A GPS- and sensor-based system was developed to
document the quality of spray applications from a self-propelled sprayer. Conﬁrmation of the spray deposition
was accomplished with spray sampling surfaces (water sensitive paper) located at surveyed sampling points in
the test ﬁelds. An image analysis technique was developed to estimate quantitative and qualitative data, such
as relative droplet size spectra, and spray coverage from the cards. Relative performance of two ﬂow control
techniques, namely conventional pressure-based control and blended-pulse ﬂow control were documented.
Blended-pulse control produced a wider dynamic range and superior consistency of deposit when speed varied
over a 3:1 range, or a 6:1 variable rate range was desired. Real-time mitigation of spray drift was accomplished
through droplet size changes when sensed weather conditions and sprayer location suggested a potential hazard.
Keywords: GPS, GIS, mapping, spray deposition, spray drift, droplet size, variable rate
Agricultural production depends on effective, economical control of pests which may
directly consume or damage the crop, compete for nutrients, water, light, and other
resources, vector pathogens, or interfere with harvest operations. Efforts to develop non-
chemical control measures (e.g., Lumsden and Vaughn, 1993) and successful biological
controls are documented (e.g., U.S. Congress, 1995), however, agricultural chemicals
remain the primary tool for pest control.
Pesticides and many fertilizers are often applied as liquid solutions, emulsions, and
suspensions sprayed onto plant foliage, or onto the soil. Individual growers and custom
contractors commonly use ground vehicles for commercial spraying. Spraying consists
of three distinct processes, viz., production of droplets (Giles, 1997; Sidahmed, 1999),
transport of droplets to the target area and deposition of the droplets on the target sur-
face (Spillman, 1984). The characteristics of the spray system and the resulting droplet
diameters, velocities and dynamics signiﬁcantly affect the three primary demands on
chemical application. These demands are: 1) pest control efﬁcacy or plant response,
2) avoidance of environmental contamination, and 3) operational efﬁciency and produc-
tivity. Quite often, one or both of these demands must be compromised in order to meet
the competing demands. These demands are inﬂuenced by the control parameters of the
application—such as ground speed, spray pressure, application rate, and droplet size.
Efﬁcacy depends strongly on the characteristics of deposition. Contact fungicides,
insecticides, and herbicides rely on a physical interaction between the applied material
and the target pest. Uniform deposition of small, concentrated droplets can often provide