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How to use the Plate Meter
Walk the field or paddock to be measured and take a minimum of fifty random readings (plonks) as you walk across a representative part of the area, this will take into account the better and worse areas, so you get a true cover assessment.
It is advisable to take the same route across the field week after week so that you have comparable data. Do not "choose" where to plonk, it must be random so that you get the best and worst so that the measurement is representative of the field. If you just plonk the best parts of the field then you are only deceiving yourself into thinking there is more there than there actually is. The reason you need to take a minimum of fifty plonks is to even out the extremes of growth you may encounter.
Plate meters are designed for grass clover swards and are not for use on cereals or other crops. They are most accurate between 1200 and 3200kgDM/ha. (Read the manufacturer's recommendations on calibration.)
If the plate meter seems to be reading high then check:
- There is no grass wound around the bottom of the plate.
- That you are placing the plate meter vertically in the pasture and not rocking it like you would with a walking stick.
- Check the density of the pasture at the base. If the sward is really thick and dense at the base the reading may be correct as the density has a large affect on the plate meter reading.
Accuracy and technique is very important when "plonking" as inaccuracy can lead to pasture covers varying up to 600 kg DM/ha which can lead you to believe you have adequate covers or surplus when the reverse may be true. Place the plate on the top of the sward with no downward force and then push the shaft to the ground making sure the shaft remains vertical all the time; if you "rock it" as you would with a walking stick the measurement will be exaggerated compared to the actual cover. It is the plate moving up and down the central shaft that measures the readings. Using the correct technique there is no difference in readings between the electronic and mechanical plate meters.