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Missouri Ag News Headlines |
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Calibration Necessary Step Even with Variable-Rate Technology
By: Kent Shannon, University of Missouri Extension - 03/23/2018
One item often overlooked when using variable-rate technology (VRT) is the calibration of application equipment. Currently, no standard procedures exist for calibrating VRT. While calibration of spreaders, planters, and sprayers is needed for uniform
application, it is even more critical to calibrate VRT controlled equipment. In a few cases, traditional calibration procedures will work but do not ensure proper operation over the expected range of varying application rates. The goal of calibration is to minimize
application errors so target rates can be achieved with a certain level of confidence. The following suggestions cover how one should approach the calibration of equipment utilizing VRT.
VRT usually relies on either ground speed radar (GSR) or a global positioning system (GPS) receiver as input for actual ground speed. If a GSR is used, yearly calibration of this sensor is important so the variable-rate controller will properly adjust application
rates with ground speed variations. An improperly calibrated GSR will lead to application errors. Follow either equipment or GSR manufacturers' recommendation for the proper calibration procedure.
Prior to calibration of equipment with VRT, one must determine the range of planned application rates for the product(s) to be used during a variable rate application. This range will be used to ensure that the software and hardware setup will properly operate
over the expected range of rates once an acceptable setup is determined during calibration. For example, one might decide to vary corn seeding rates from 24,000 to 36,000 seeds/acre. Knowing this information, select the median rate (30,000) to start
calibrating the planter equipped with VRT.
Make sure all hardware and software are in proper operating condition. Replace any worn hardware, especially those controlling metering and distribution of material.
If rates of inputs are going to be varied over a wide range, especially for lime application, check the distribution pattern at the median rate followed by a check at the minimum and maximum application rates. This procedure will ensure proper distribution over
the range of desired application rates. If a distribution issue exists, the rate variation should be limited to a smaller range.
Specific equipment checks include:
- Granular/Dry Applicators:
- For spinner spreaders, this includes the divider, spinner-discs, and especially the spinner fins.
- For pneumatic applicators, check the metering mechanism, fan, tubes, and deflectors. Worn tubes can have an impact on material transportation to the deflectors while worn deflectors can impact distribution.
- Sprayers - select a nozzle that is capable of handling the expected application rates, spray pattern, ground speed, and pressure.
- Planters - check all drives and individual metering element(s) on each row unit.
Specific items to consider include following manufacturers' recommendations, calibrating annually and watching for pattern shifts especially for spinner spreaders. In addition:
- Dry Product Density: If the intentions are to use variable-rate blended products, then make sure the products have similar density and particle size. It is not advisable to blend products if these differences exist since pattern uniformity will be greatly affected
over the range of application rates. This issue is more important for spinner spreaders than pneumatic applicators.
- Perform individual distribution tests for different granular products especially if they have different density and particle sizes. For example, potash will require a different calibration than lime.
Sprayers:
- Take any pressure readings at the boom.
- Ensure nozzles are within 5% of the manufacturers operating specifications.
If the spray mixture is significantly altered by the addition of adjuvants, it is recommended to compare the output mixed rate to water and ensure that the values are within 5%. If 5% is exceeded, calibration must be conducted utilizing the spray mixture.
Planters:
- Ensure proper seed drop and that the planter settings/configuration can cover the range of expected seeding rates.
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