How Rising Platemeters Work

Rising platemeters use a simple plate and shaft mechanism to measure the height of the pasture at a given point. This makes taking consistant measurement easy, therefore ideal when multiple people are using the platemeter to record data.

When the unit is set down on the pasture the 'plate' sits on the top of the pasture while the shaft protrudes down to the soil. The amount the shaft moves gives the compressed height of the pasture in that area. Electronic Rising Platemeters will automatically store the data after each measurement is taken. The figure must be hand recorded if using the Manual Rising Platemeter.

By collecting and number of readings over a given area (30-50 plonks per paddock is recommended) an average compressed pasture height can be obtained. This average is automatically calculated when using the Electronic Rising Platemeters, but must be manually calculated if using a Manual Rising Platemeter.

Tips:

Follow the same route each time
Try to have the same person do the walk each time. Different people have different styles which will be reflected in the results from the platemeter.
Do weekly walks during the spring. A Platemeter will usually pick a trend before you can by eye.
Don't "roll" the platemeter. IE. Hold it completely vertical when you plonk down and back up.
Learn to draw up a feedwedge (or more easily, use P-Plus Coverwalks to draw your wedge for you).

Rising Platemeter Calculations

Once you have collected all your data it is time to process it so the data becomes useful.

If you are using a Electronic Rising Platemeter the 'Average Pasture Height' will already be calculated for you. If you have collected your data using a Manual Rising Plate Meter, you will need to work out the 'Average Pasture Height' for the area sampled. ........

Using the ‘Average Pasture Height’ the ‘Kilograms of Dry Matter per Hectare’ can be calculated.......

Using the "Standard NZ Dairy Pasture Winter Equation" (see below)

To work out the total ‘Kilograms of Dry Matter’ for that area the KgDM/ha must be multiplied by the size of the area sampled.........

Equations under use in New Zealand are as follows:

IMPORTANT NOTE:
These equations are influenced by seasonal differences. Up to date equations can be found on various websites.
We suggest starting with DairyNZ.

Months Rising Plate Meter Equations	Dairy Pastures
Winter (April-Sept)	Plate meter Reading x 140 + 500
October	Plate meter Reading x 115 + 850
November	Plate meter Reading x 120 + 1000
December	Plate meter Reading x 140 + 1200
January	Plate meter Reading x 165 + 1250
February	Plate meter Reading x 185 + 1200
March	Plate meter Reading x 170 + 1100

Worked Example:

Required Data:

Current Display Value: 720cm
Initial Display Value: 420cm
Number of Samples: 30 plonks
Sample Area: 10ha
Sample was taken in May

First calculate the Average Pasture Height:

Now that the Average Pasture Height has been calculated, the KgDM/ha can be found:

And finally the Total Dry Matter for the sampled area: