Plate Meter Overview and Formulas
The Jenquip and Handley Plate Meters are the ideal farm management tool to measure the quantity of dry matter in perennial ryegrass and white clover pastures
- Able to quantify pasture on farm (Average Pasture Cover)
- Correctly and consistently target a consistent pasture height
- A tool that almost anybody can use
When used in conjunction with regular farm walks the plate meter can be a vital cog in pasture management decisions. The data collected can also generate valuable information for future farm management decisions. The data collated can provide:
- Annual farm growth rates
- Individual paddock growth rates
- Seasonal average pasture targets
- More accurate information for feed budgets
- Information to build a feed wedge
Key points when using the pasture meter
- The plate meter measures height not kilograms of dry matter (kg DM)
- The equation that converts height to kg DM should be seen as a guide
- Maintenance is critical to ensure accuracy and reliability of reading
- Operators technique needs to be consistent
- Adverse environmental conditions will impact on accuracy
What does the Rising Pasture Meter measure?
The plate meter measures the compressed height of pasture. Each of the ‘clicks’ represents 0.5cm of compressed height i.e. a reading of 7 “clicks” represents a compressed pasture height of 3.5 cm.
Understanding the equation
The equation changes the compressed height (i.e. “clicks”) to a kg DM/ha. This equation is a ‘guide’ and not an absolute measure of quantity as the DM composition will change due to seasonal variations.
Range of the multiplier:
Using the NZ Standard Formula height x 140 + 500 there can be these variations
115 when grass is growing the fastest (e.g. low DM)
140 this is about the average (so best fit for the whole season)
185 used in very dry conditions of slow growth e.g. drought, frost (higher DM)
The key is to monitor residuals and adjust formulas to suit.
The UK uses two standard formulas
These are height x 140 + 500 and height x 125 + 640
Achieving consistent grazing height is the key to offering cows high quality pasture at every grazing. One of the main benefits of the plate meter is that it accurately assesses post grazing heights.
Maintenance of the Plate Meter
To ensure the plate meter gives consistent readings, routine maintenance needs to be carried out. Refer to the manufactures guidelines. The main problems associated with the plate meter are:
- Corrosion on the shaft
- Grass and mud build up on the plate and shaft
- Poor wheel alignment in the shafts grooves
- A bent shaft
- Flat batteries ( Electronic plate meter)
Check the operation of the rising Plate Meter prior to commencing the walk for:
- Charged battery (if using electronic meter)
- Freely moving shaft and correctly aligned cog
- A clean plate free of grass and mud
Once the farm walk has been completed ensure the plate meter is clean and dry and stored correctly.
Operator technique and procedures
Incorrect operator technique will cause inaccurate readings of the plate meter. The main operator problem is extra pressure applied to the plate meter when taking a measurement. The plate meter has been calibrated with the plate falling under its own weight. By creating extra force (slamming the plate down or using the plate meter as walking stick) the plate falls faster and the shaft can be pushed below the soil surface.
Rolling the plate meter when taking a measurement generally does not affect the measurement unless it is very pronounced.
When taking readings during the farm walk the following will need to be considered to ensure consistent measurement:
- Avoid gateways, troughs and fence lines
- Ensure the walk gives a fair representation of the paddock. To do this either walk diagonally across the paddock or walk a “w” within the paddock
- The readings should be random and not biased by the operator looking where to place the plate meter. A guide is to take a reading every 2-3 steps.
Video on using a plate meter
Adverse Weather Conditions
Weather conditions can impact on the accuracy of the plate meter. In extreme conditions postpone the walk until conditions improve. Factors to consider under different conditions:
- Do not plate the farm when the pasture is still frosted, wait until it has lifted
- If the soil is frosted apply pressure to the shaft to break the standing ice crystals so that the bottom of the shaft reaches the soil surface
- Strong wind conditions will compress long pasture resulting in lower readings
Heavy Rain and wet conditions
- In wet conditions water can accumulate on the plate. This accumulation of water increases the weight of the plate and results in lower readings. Regularly shake the plate to remove any surface water.
- After heavy rain pasture can also be ‘compressed’ resulting in a lower height reading
- Avoid areas of surface water as the plate meter will give inconsistent readings
- A snow fall on pasture will “compress” the pasture resulting in lower height readings
Avoid other pasture or weed species
The plate meter has been calibrated for perennial ryegrass/white clover swards. Different pasture species will give different readings, as the physical composition of the plants is significantly different.
Weed species such as thistles, buttercup and wire weed need to be avoided as they cause the plate meter to read “high” as they hold the plate above the ground. If paddocks have been topped in previous rounds beware of topped areas that contain weed stems. Often the weed stems are very hard and woody and create an ‘artificial’ residual for the plate meter.
The plate meter will not give an accurate assessment of pasture cover in badly pugged paddocks. Visual assessment should be used after calibrating the “eye” using the plate meter on paddocks that have not been pugged.