WORKSHOP ON EFFECTIVE AND SAFE USE OF

HERBICIDES

Udensi U. E.

EQUIPMENT CALIBRATION

(KNAPSACK)

• WHAT DOES CALIBRATION DO?

Sprayer calibration: (1) readies your sprayer for operation and

(2) diagnoses nozzle tip wear and this will give you optimum performance of your tips and equipment 

EQUIPMENT CALIBRATION- KNAPSACK

Calibration of sprayers is an important activity in any weed control or spraying program. It ensures that herbicide active ingredient is applied correctly at the product labelled rate. Application in excess of the recommended rate can lead to the following:

• Crop damage • Environmental pollution and

• Use becomes uneconomical.

WHEN DO WE NEED TO CALIBRATE A SPRAYER ?

Calibration can take place as follows:

• When spraying for the first time with a new sprayer

• At the beginning of each season

• After changes of nozzle tips, spraying pressure or speed

• When the sprayer has done close to 100 ha of spraying

Factors that may affect calibration

Canopy height/density of target species

Canopy density and height of vegetation may affect calibration. Low vegetation and/or scattered clumps will require less solution per hectare than taller and dense vegetation with greater leaf surface.

Nozzle and pressure

The first step in sprayer calibration is to determine the correct nozzle type and size (flow rate) . Therefore it is important to select the correct nozzle material. Nozzle size depends on the desired application rate, ground speed and nozzle spacing. For most herbicide application using knapsack sprayers the suggested pressure ranges from 100 to 200 kPa (15 - 30 psi)

Ground conditions of area

For knapsack sprayers the ground conditions (slash, slope, undulating, etc.) will affect the workers walking speed, which directly affects the delivery rate per hectare. If conditions vary substantially within the site or from site to site, the equipment should be recalibrated.

Calibrating a knapsack sprayer Three measurements are important when calibrating a new and old knapsack -

1. The walking speed of the operator expressed in meter per second or kilometres per hour (Km/h)

2. The output per minute of the sprayer expressed in Litres

3. The width of each pass of the sprayer, commonly known as the Swath Width expressed in metres.

Sprayer Calibration

• Importance

• Procedure

• Area volume method

• Time-volume method

 Steps in Knapsack Sprayer Calibration

Carry out a pre-operation service and prepare the sprayer for the job.

• Install the appropriate spray tip (nozzle)

• Partially fill the sprayer with clean water and dye.

• Pump up the spray unit to a selected pressure

• Ensure there is no leakage from equipment.

• Test spray sample cards to check spray droplet pattern. If necessary adjust or change nozzles and pressure to achieve desired spray droplet pattern.

Measure the effective swath width of the nozzle

Steps in Knapsack Sprayer Calibration-Contd.

Mark out a 50m2 calibration plot in the area to be sprayed with a peg in each corner.

Fill the sprayer to a known level or mark.

Spray the calibration plot at the pressure and speed you will use when you do the job.

When you have finished spraying the calibration plot, Note the amount of water taken to refill the tank to the original level or mark.

Calculate the litres used and determine spray output in litres per hectare

Thank you