Relationship between Droplet Distribution and Temperature, Relative Humidity in Greenhouse Low Volume Application

Abstract

Analysis of droplet sizes or their numbers is very important for the low volume application in a greenhouse.
In this paper, the relationships between numbers of droplet and five items were investigated. The five items were type of agricultural chemicals, discharge rate, application rate, dry bulb temperature and relative humidity.
The following conclusions were drawn from the experiments. Blow head was a Pneumatic Atomizing Nozzle with Spray Set-up No. 1, Fluid Nozzle 2050, Air Nozzle 64, made by Spraying System Co., (U. S. A)
(1) Mean numbers of droplet per 0.25mm₂ were 120-130 in droplet diameter of 0-5μm, 20-30 in 5-10μm, 2-10 in 10-100μm, respectively. The ranges of droplet number varied remarkably when spraying conditions differed.
(2) Multiple correlation coefficient values between droplet number and each item, at 1-7m distance from low volume sprayer, were 0.58-0.90. The values by droplet diameter ranges were 0.58-0.75 in 0-5μm, 0.66-0.75 in 5-10μm, 0.72-0.90 in 10-50μm, 0.74-0.86 in 50-100μm, respectively.
According as the droplet diameter was larger, multiple correlation coefficient became larger.
(3) In the case of 0-10μm in diameter, the items which have an effect on the numbers of droplet were discharge rate, dry bulb temperaturs and application rate in decreasing order. Meanwhile' beyond 50μm in diameter, those were dry bulb temperature, discharge rate, relative humidity. The differences between wettable powder and emulsifiable concentrate spraying had a least effect on numbers of droplet.
(4) The numbers of droplet sprayed at 21-24°C or higher were relatively more variable in the case of 0-10μm in diameter, and those sprayed at 18-21°C or lower were relatively more variable in the case of 10-100μm in diameter. Meanwhile, those obtained at 80% or higher in relative humidity were relatively more variable regardless of droplet diameter.
(5) Judging from the above results, it is considered that the optimum spraying conditions in greenhouse for low volume application is 15-24°C in temperature and 50-80% in relative humidity.