Great Plains NTA2007 Material Rate - Manual (Page 40)

38 Great Plains Manufacturing, Inc. Contents Appendix VRG Air Drills
167-085B Contents Appendix 2012-01-03
Appendix
Density Adjustment
If your material (seed or fertilizer) has a density that is
materially different from the reference material listed at
the top of each chart, you can compensate for it.
Density variance is only one of many factors that can
cause an actual rate to vary from a chart rate.
Compensating your initial target rate helps reduce the
error, but rely on calibration for the most accurate field
results.
1. Weigh a known volume of your material, and
compute the density in the same units used in the
table (kilograms per litre, pounds per bushel or
pounds per cubic foot). Be sure to subtract out the
container weight.
The example chart is based on 0.96 kg/litre (60#/ft
3
)
reference material that is 134% heavier. If the chart
values for 50.0 kg/litre (49.9 lbs/ac), a variable rate
gearbox setting of 32, and a Calibration Constant of
82478, are used, too little material will be applied.
2. Divide the reference material density by the
measured actual material density, to obtain a
correction factor.
3. Multiply the target field rate by the factor to yield an
adjusted chart rate.
4. Look up the adjusted rate in the chart, and use the
settings for it.
Note: If the adjusted chart rate would correspond to an
apparent variable rate gearbox setting below 20,
use another chart (Low Range chart or lower Flute
Stars chart).
Example: target dry fertilizer rate is
Metric
U.S. customary
56 kg/Ha 50 pounds per acre
Example: sample weight is:
Metric
U.S. customary
4 litres weighs 2.9 kg.
Your material density is:
0.72 kg/litre
One gallon of your material
weighs 6 pounds.
A gallon is 0.134 cubic feet.
Your material density is: 6
÷
0.134 which is:
44.8 pounds per cubic foot.
Example: factor calculation
Metric
U.S. customary
chart mtl: 0.96 kg/litre
factor: 0.96
÷ 0.72
which is: 1.34
chart mtl: 60 lbs/cu-ft
factor: 60
÷ 44.8
which is: 1.34
Factor
ReferenceMaterialDensity
MeasuredMaterialDensity
-----------------------------------------------------------------------------
=
Example: density adjustment
Metric
U.S. customary
if the target field rate is 56
kg per hectare, the
adjusted chart rate is:
56 x 1.34
which is an adjusted target
rate of: 75 kg/ha if the target field rate is 50
pounds per acre, the
adjusted chart rate is:
50 x 1.34
which is an adjusted target
rate of: 67 pounds per acre
AdjustedRate FieldRate Factor
×
=
Example: adjusted rate look-up
Metric
U.S. customary
Look up 75.
Closest chart value is 76.3
Use those settings:
(Gearbox 37, Cal.Const.
83099) and calibrate Look up 67.
Closest chart value is 68.1
Use those settings:
(Gearbox 37, Cal.Const.
83099) and calibrate