Purpose: Calibration is the process of adjusting application equipment to ensure that the right rate is being delivered per unit of area. Frequent calibrations reduce application errors and guarantee that the prescribed amount of pesticide is applied. An unregulated applicator can:
> deliver a sub-dose of pesticide, which will not contribute properly for the control of the pest but will waste already limited financial resources of the farmer.
> deliver an overdose of pesticide, which will not only waste financial resources but also contribute to groundwater and soil contamination.
How often should we calibrate our equipment? Ideally, calibration should be performed as frequently as before every operation, but sometimes this is impractical. Do calibrate your application equipment whenever conditions change, such as:
> changed between fields with different soil properties.
> changed pesticide formulation.
> changed application rates.
What do you need to perform a calibration? Common tools needed for calibration are:
> measuring tape at least 50 feet long.
> marking stakes or flags.
> paper bags or any other type of container to collect application material.
>balance or scale to weigh granules. It is important to use a scale with good resolution (ounces or grams),.
> calculator, pencil and paper for annotations.
A few bits of advice:
> check and clean the applicator before calibration.
> always refer to the equipment’s operation manual and to the pesticide label for additional information.
> record settings used in previous calibrations; they can be used as initial settings in new calibrations.
> calibrate each applicator due to differences in output caused by normal manufacturer's tolerance or uneven wear.
> clean the applicator frequently, especially before storage. It will prolong its usable life.
A word of caution:
Agricultural chemicals can be dangerous if misused. Improper selection or use can seriously injure or kill persons, animals or plants. Pesticide misuse also can cause serious damage to the environment and water supply. Always use care when dealing with pesticides and follow label instructions carefully.
Recommendations:
The amount of granular material applied to a given area is dependent on several factors. Please consider each and every one of them when performing a calibration.
Ground Speed -- Granule flow through an orifice is not always proportional to ground speed. Make calibration checks at the same speed that you plant and hold speed as constant as possible during planting.
Orifice Area – The area of the metering orifice must be adjusted to regulate the flow rate. The orifice area is determined by the orifice setting.
Product – Granular pesticide products can vary considerably in size, shape and density. Recalibrate whenever you change brands or even from one year to another.
Weather conditions – Temperature and humidity changes do have an effect in granules and the associated flow rate. Recalibrate when conditions change.
Width of application – Calibration should determine the proper amount of pesticide per unit of area.
If you are applying a pesticide in a band, be aware that the area treated is the area contained in the band and not the total area.
For crop rows, pesticide application rate is given as “in-the-row,” usually a weight (in ounces) per 1,000 linear feet of row. For example: 1½ to 3 oz per 1,000 linear feet.
Calibration Procedures:
Follow these basic steps for the calibration of granular applicators:
> Try to calibrate the equipment in the same soil conditions as the application area. Try using the largest practical distance possible to account for variations. A minimum course length distance of 200 feet is recommended.
> Determine the ground speed that is going to be used during planting. Maintain constant speed during calibration and during planting.
> Fill hoppers at least half full and operate the applicator until the granules are feeding from all units.
> Use containers to collect granules from each unit during calibration. Weigh granules using a scale.
> Calculate the application rate according to the following formula:
AR ( lbs/ac)= (weight (oz) x 32,670)÷(course length (ft) x band or row width (in))
> In-the-row applications can be directly determined by measuring total weight in 1,000 feet and comparing to the recommended rate.
> Compare the amount collected or calculated with the recommended rate. If needed, reset applicator and recalibrate the unit until desired rate is achieved.
> Calibrate each unit and compute an average rate for the equipment. Individual units with an application rate that is equal to ± 10% variation of the average should be recalibrated.
REFERENCES:
ASAE EP371, Preparing granular applicator calibration procedures.
ASTM E550-87, Standard guide for preparing granular pesticide ground applicator procedures.