TREE CROPS AND CALIBRATION - theory
is theory and practice is practice and never the twain shall meet.
Off to the farm "R U NUTZ"
belonging to R J "Ozzie" Beaumont to see if I can come up
with some answers to the calibration problem in tree crops. Of late
I hear talk of "2000 litres per hectare". Where does that
come from?
The first thing I notice is there are
orchards with different varieties, varying tree-heights and widths.
Crown densities vary according to the variety. It is clear that
there is no standard spray-volume per hectare. I decide to look at
the sprayer used.
Ozzie uses a mistblower or as some
refer to it as an airblast sprayer. I take note of the nozzle-tips
used and find out that all products are applied at 20 bar pressure.
Anyway we decide to use a "practical"
example to see if we can come up with a volume per tree. Here's
the data used for the calculations.
Crop: Macadamia
Orchard : Tree density Inter-row
10 metres and intra-row 2.5 metres
Trees per 100 metre row: 41
Tree rows per hectare : 10 (Actually
11 rows but you're only spraying half of the two outer rows)
Trees per hectare : 410
Mistblower nozzles: 16 in total or 8
per side.
Flow rate at 20 bar : 3 litres per
minute per nozzle or 48 litres per minute for 16 nozzles.
Speed: This varies but we settle on a
slow 50 metres per minute or 100 metres per 2 minutes or 3 km per
hour.
Given this
speed the mistblower will spray 96 litres on 41 trees in 2 minutes.
Spraying both sides = 1 tree. So the litres per tree 96 ÷
41 = 2.342 l/tree. Wow! To
the third decimal place.
There are 410 trees per field hectare
so the volume per hectare is 2.342 x 410 =
960 l/ha.
IF WE LOOK AT A SPRAYRIG AND NOTE THE
NOZZLE-TIPS WE CAN CALCULATE THE TOTAL VOLUME OUTPUT AT A SPECIFIC
PRESSURE AND GIVEN THE SPEED WE CAN CALCULATE THE VOLUME PER HECTARE
FOR EACH ORCHARD TREE DENSITY.
Let's see if we use our old faithful
formula to calculate litres per hectare --- l/ha
l/ha = 600
x litres per minute ÷
speed km/hr x spacing in metres
l/ha = 600 x
48 ÷ 3 x 10 = 960 l/ha
Hey! That looks the same.
WATCH OUT; THIS IS FOR BOTH SIDES.
NOTE THE VOLUME IS FOR THE WHOLE SPRAYER OUTPUT.
GETTING BACK TO THAT 2'000 LITRES
PER HECTARE.
If
Ozzie wants to double the volume ("2'000 l/ha") the sprayer
has to travel at virtually 1.5 km/hr. Yawn!! When are
we getting there?
Given
the "2'000 litres per hectare", what must the total volume
output in litres per minute be?
l/min = l/ha x speed km/hr x swath or
row spacing in metres ÷ 600
l/min = 2'000 l/ha x 3km/hr x 10row spacing ÷
600 = 100 litres per minute for all nozzles. OR 6.25 l/min per nozzle.
As I drive away leaving a rather
bewildered Ozzie with a Teejet catalogue and some questions about
coverage and those 8 metre high trees, I reach for the speed dial on
my smart phone ................ HOUSTON; WE HAVE A
PROBLEM.
TEL INTL: +27137449928
TEL NATL: 013 744 9928
chemicon@telkomsa.net
