Calibration determines boom spray output in litres per hectare. A properly calibrated boom spray is vital for effective weed and pest control. Poorly calibrated sprayers are costly: Apply too little, Spray failure. Apply too much,Pasture damage. Calibration doesn’t take long and is easy if you follow these 7 steps: 1. Part fill the tank with water (no chemical). 2. Start the tractor and set the engine revs to PTO speed. 3. Turn on the unit and ensure that all nozzles are spraying correctly (a full even spray in both directions with no drips or squirts). 4. Check that the pressure is in the correct range of 200–300kPa (approx. 30– 40p.s.i.). 5. Using a plastic measuring cylinder with 20mL graduations, measure the output of each nozzle for one minute. Write down each result measured to the nearest 10mL.
6. Calculate the average nozzle output per minute. (Replace nozzles with an output varying by more than 20mL from the average.) 7. Use this average and the table above to obtain boom spray output in litres per hectare. For boom sprays with nozzle spacings other than 500mm apart, use a calculator and the following formula to obtain L/ha output:
boom spray output ( L /iha) Ei 600 H av. nozzle output ( mLLimin) nozzle spacing ( mm) H speed ( km /ih) When spraying, tractor speed must be constant for accurate application. Do not spray using a tractor without a tachometer. Install one or use another tractor.
Measuring the Speed
If the speedometer doesn’t work, or if non-standard tyres or wheels are fitted, you need to measure the speed: 1. Start the tractor and adjust the revs to PTO speed. 2. Select a suitable gear to give a comfortable speed of travel over the country to be sprayed. The spray boom shouldn’t bounce up and down at this speed. 3. Begin travelling about 20m before a starting mark and start timing using a watch as you pass the start. 4. After 30 seconds, drop out a marker to mark the finishing point. 5. Measure the distance covered in metres. 6. Use a calculator to work out the speed: speed (km/h) = (distance covered in 30 sec) × 0.12 Record the speed and gears used on the dash with a spirit pen. It is worthwhile getting the speed for the gears above and below that selected initially.
Remember:
Calibrate your spray unit before each major spray operation and after fitting any new equipment.
Setting up and Calibrating the Seeder
Accurate seed placement is possible only if care and time are taken in setting up the seed drill. There are 8 steps to follow, although some don’t apply to conventional sowing.
Seeder Levelling
To ensure that all tines are sowing at the same depth, adjust the machine on a level surface. If Caldow boots are fitted, ensure that the front tip is 6–8mm lower than the ‘heel’.
Coulter Alignment
Pull the machine into the ground to check alignment. Poor alignment results in 2 cuts in the undisturbed sod and can leave open furrows. If alignment is out, raise the machine, slightly loosen the nuts on the coulter assembly and reposition using a straight-edge and a heavy hammer. Recheck in the ground. The next 4 adjustments must be made in the paddock after you have run the machine at the speed at which you propose to sow.
Tine Tension
Correct tension allows the tine to vibrate, creating loose soil (tilth) while maintaining the correct point angle. Tine tension should be in the range 260–400N (60–90 lbs). Use lower tensions on sandy friable soils. Too much tension results in excessive point wear.
Depth
Sowing depth is not as critical as the amount of loose soil over the seed. Check the depth to the bottom of the furrow after travelling at least 200m. The rule of thumb for depth is: ‘to the first knuckle of your index finger’. For early autumn or spring sowings, when warm, dry conditions after sowing are likely, this depth is necessary. In cold, wet winter conditions, sow more shallowly.
Tilth and Speed
The amount of loose soil covering the seed is critical, regardless of the depth of the furrows. Aim for only 5–10mm of loose soil over the seed.
Warning:
More seed fails to emerge by being buried under too much soil than by any other cause. There is too much tilth if less than 5% of the seed and fertiliser is visible in the furrow. Speed must be increased (up to 12km/h) to throw more loose soil out of the furrow. There is too little tilth if a high percentage of seed and fertiliser is visible in the bottom of the furrow. A single loop of heavy chain attached at either side of the seeder can be used to sweep soil from the edges into the furrow. Whatever device you use must follow the contour of the ground and not bulldoze loose soil on top of the seed. In conventional seedbeds, deep seed burial is also likely, especially where the seedbed is loose and fluffy. • Rolling to firm the seedbed before sowing is recommended for loose seedbeds. • If using harrows, try to direct the seed tubes back so the seed lands in the last row of the harrows. • When direct-drilling, a good rule of thumb is that 5% of the seed and fertiliser should be visible in the furrow.
Soil Types and Moisture
Often both soil type and moisture will vary within a paddock and as sowing proceeds. Try to sow different soil types in separate blocks and check the soil cover over the seed with changes in soil type. Pasture sowing is shallow, so large changes in moisture can occur throughout the day, necessitating constant checking of the cover.
Calibration
The simplest method of calibrating sowing rate when seed and fertiliser are mixed is to put a bag of fertiliser (50kg) in the box, sow one fifth of a hectare, check the amount used and make adjustments if necessary. When seed and fertiliser are sown from separate boxes, calibrate the seeder in the workshop using a jack and rotating the drive wheel. Always calibrate the seed first and isolate the drive to the fertiliser box, even if it is apparently empty.
- Determine the number of wheel revolutions to travel 100m using the formula: revolutions = 16 ÷ wheel radius (m)
- Turn the drive wheel a few turns to ensure that the seed or fertiliser is flowing down all tubes.
- Place a tarpaulin under the seeder (or buckets under the hoses), then rotate the wheel the number of revolutions you calculated in step 1.
- Check to see that all tubes have delivered similar amounts, then collect and weigh the total amount of material.
- Compare the result with the amount required, which is easily calculated using this simple formula:
amount required (kg) = sowing rate (kg/ha) × machine width (m) ÷ 100
