The experiment was conducted on April 4, 2015 at
Qianlishan Agricultural Co. Ltd in Wan’an County,
Jiangxi province. The spray experiment was designed
as six treatments with five replications. The droplet
distribution effect of citrus tree with natural round type
and open center shape was tested under the condition of
same operating speed (1.0 m/s) and three working heights
(e.g. the distance between the UAV and the top of the
canopy were 0.5 m, 1.0 m and 1.5 m, respectively). In
order to avoid the test error caused by droplet drift, a row
of plants was left as a protected area between two
different treatments.
The top, middle (2/3 plant height), and lower (1/3
plant height) parts of citrus trees crown were flagged by
hanging nine white pulp paper cards from inside to
outside parts of the plants (Figure 2). Each sampling
paper card size was 76 mm×50 mm which was nearly the
same size as a grapefruit leaf. The spray solution was
300 times Ponceau 2R (99.5% purity). Paper cards were
collected one by one in zip lock bags after spraying and
dried.