OptRx
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PN 2006020–ENG Rev. H
N Algorithm
— The OptRx Crop Sensor Module uses an N algorithm to calculate an N rate through a Sufficiency Index
reading.
NDRE vs. NDVI
—Both are vegetation indices that compare scanned crop vigor and biomass (and algorithms) against the
reference strip to assess plant health.
–NDVI is used in early growth stage crops as it picks up variances in small plant vigor better than NDRE
–NDRE does a better job at picking up variances in biomass at later growth stages
•
NDRE is more effective in later growth stages or in larger plants such as corn because the algorithm provides
more response at higher vegetation index (VI) rates.
•
NDVI is more effective in earlier growth stages or in smaller plants where the algorithm is used to gain a more
accurate reading at lower VI values. However, in later stages, NDVI’s scanning tends to saturate at higher VI
values which results in less response to changing VI values and recommended rates.
Rate Increment
(shown in Crop Sensor Setup) — An optional increment that the display can use to round the N rate
applied, if the operator desires. For example, if the operator enters the number 5 and the display is applying a rate of 27,
the number will be rounded to 25.
Reference Strip
— The healthiest portion of your field where you are satisfied that N is sufficient. This allows a baseline
of optimum crop performance that the system can compare against other cropland.
Reflectance
— The light reading of the plant measured by individual light spectral wavelength. The comparison of
different reflectance values can be used to determine the health of the plant.
VI
— Vegetation Index. The recorded value from remote sensing that displays a comparison of crop vigor and biomass of
the scanned plant. This value, which is taken from a reference scan of a Reference Strip, uses a ratio that indicates the health
of the plant. NDVI and NDRE are examples of different vegetation indexes.
VI Minimum
(shown at Settings screen) — The threshold below which the Crop Sensor applies the minimum rate. This
setting is used to apply a minimum amount of N on ground with damaged or diseased crops.
VI Reference
(shown at Settings screen) — The value of a healthy crop biomass used in reference for calculating the
proper N application rate. The VI Reference value is determined by the creation of a Reference Strip.
VI Zero
(shown at Settings screen) — The threshold below which the Crop Sensor applies a zero rate. This setting is used
to prevent applying N over bare ground or permanently damaged crops.
Troubleshooting OptRx Error Messages
The OptRx Crop Sensors have error messages to inform the user of complications in communication and performance. The
following error messages are the most common ones. Follow the recommended troubleshooting steps to correct these
errors.
Error Message:
“Sensor Lost Communication”
Possible Cause:
The cabling between the OptRx sensor and the ACS Master Module is disconnected.
Solution:
Check all connections and cables for disconnections, cuts, breaks, or crimps in the line.
Error Message:
“Bad Data”
÷
NOTE!: The “Bad Data” error messages are disabled when user does not intend to log data or while the reference
strip is being created.
Possible Cause:
The sensors are either too far from the crop or too close to the crop.
NDVI Normalized Difference Vegetation Index =
Near Infared Reflective - Red Reflective
Near Infared Refl Red Reflective
NDRE Normalized Difference Red Edge=
Near Infared Reflective - Red Edge Reflective
Near Infared Refl Red Edge Reflective
