Most guys spread by feel. Fill it, drive, empty it, repeat. The trouble is you have no idea whether you’re putting on twice what the crop needs or half. Manure spreader calibration takes an afternoon and pays every season.
Why calibrate
- Apply the rate your nutrient plan calls for.
- Avoid burning crops or wasting nutrients.
- Stay within regulations.
- Use manure to replace bought fertiliser.
Step 1: Know your load weight
Weigh a full spreader on a weighbridge, or with portable scales. Or weigh the tractor and empty spreader, then full. The difference is your load.
Step 2: Measure spread width
Spread a load on a flat area. Lay out trays or tarps across the path at regular spacing. Weigh what lands on each. The effective width is where the rate drops to about half of the centre rate on each side. Your extension service can give exact methods.
Step 3: Measure the area covered
Measure the length of the strip covered by one load. Multiply by effective width. That’s the area for one load.
Step 4: Work out the rate
Load weight divided by area equals application rate. Compare with your target.
Step 5: Adjust and set overlap
To change rate:
- Change ground speed.
- Change floor chain or apron speed.
- Change door opening if your spreader has one.
Drive passes at your effective width so edges overlap properly. Too far apart leaves stripes. Too close doubles up.
Recheck
Recheck when manure type, moisture or the spreader changes. Wet manure and dry manure spread very differently.
Simple tarp method
Lay a tarp of known size, spread over it, weigh what’s on it. Divide by tarp area. Quick check of rate.
Why calibrate
If you don’t know your rate, you can’t know your nutrients. Too much wastes manure and risks runoff. Too little short changes the crop. Calibration tells you how much you’re really putting down.
Step one: weigh a load
Weigh the spreader full and empty on a scale, or estimate from a known volume and density. The difference is the load weight.
Step two: measure the area
Spread one load and measure the length of the strip and the effective width. Multiply for the area.
Step three: work out the rate
Divide the load weight by the area. That’s your rate per acre or hectare.
Step four: check the pattern
Lay trays or tarps across the spread width. Weigh what lands in each. You’ll see where it’s heavy and light, and how much overlap you need.
Step five: adjust
Change floor speed, gate opening or ground speed to hit your target rate. Set your driving width for even overlap.
Repeat
Recalibrate when manure type or moisture changes, and at least once a season.
Keep records
Write down settings and rates for each manure type. Next time you spread, you start from known settings.
Quick questions
Can I calibrate without a scale? Estimate with known volumes, but a weighbridge or portable scale is better.
How many trays do I need? Enough to cover the full width, evenly spaced.
Does speed change rate? Yes. Faster ground speed lowers the rate if floor speed stays the same.
From the show floor
Most farmers I meet have never calibrated. The ones who have often cut fertiliser bills. It takes an afternoon.
Common mistakes
- Calibrating once and never again.
- Measuring width as the full throw instead of the effective width.
- Ignoring moisture changes.
Where to start this week
Pick one manure source and one field. Weigh a load, spread it, measure the strip. Do the rate maths on the back of an envelope. Write the floor speed, gate and ground speed next to the result. That one card in the cab is the start of a calibration record you’ll use for years.
Quick questions
How long does calibration take? Usually an afternoon for one manure type.
Do I need special trays? Shallow bins or tarps of the same size work fine.
What if my rate is way off? Change floor speed first, then ground speed.
Should my contractor calibrate? Ask them. A good contractor will know their rates.
Machines that make it easier
Spreaders with consistent floor speed and a good beater pattern make calibration stick. See LEO rear discharge and side discharge spreaders.
Bottom line? If you don’t measure it, you’re guessing with your fertiliser bill.
