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Spray Distribution


Limitations

Droplets counting by hand lens on water-sensitive paper is limited to a maximum of around 200 droplets per cm2, equivalent to 50 to 200 liters per ha of medium to coarse sprays. At higher volumes the water-sensitive paper can still be used for rough visual assessment of spray distribution and/or crop penetration.

Requirements for measurements with automatic image analyzers:

Accurate drop size measurements with the Optomax V Automatic Image Analyzer can only be made if the drop density is low enough for the majority of droplets not to overlap each other. The table below indicates the maximum drop density (n/cm2) or volume rate (l/ha) which should not be exceeded for a given drop size for Optomax V measurements:

n/cm sq

l/ha max

VMD

μm

600

12

100

200

24

200

80

33

300

50

48

400

30

55

500

The paper cannot be used under very humid conditions. Although it turns light blue at a relative humidity of 80% the stains produced by water droplets still show sufficient contrast to allow visual detection beyond this limit (mind finger prints).

It should not be used on humid or wet supports (e.g. early morning dew).

Exposed water-sensitive papers should not be retrieved while the deposit is still wet.

Pure water stains the water-sensitive paper in drop sizes as small as 50 μm even at temperatures of T=50°C and relative humidity of 20%. However,in field trials under tropical conditions the water-sensitive paper may not show all the spray droplets which have impacted on it. This is due to evaporation increasing the concentration of the droplets so much that they contain very little or no water.

As a general rule aqueous spray droplets smaller than 100 μm should be avoided under topical conditions.

Water-sensitive paper may not always be suitable for use at temperatures below 10°C.


 
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