Overview and Formulas

Plate Meter Overview and Formulas

Overview and formulas, Jenquip Plate Meters are the ideal pasture management tool to measure the quantity of dry matter in perennial ryegrass and white clover pastures and Jenquip Plate Meters have been well proven over many years by users throughout the world

The benefits of using the Rising Plate Meter are:

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 is a vital cog in pasture management decisions and consequently 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 measurement (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 and listed below are 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.

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:

Ground frost

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

Windy conditions

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

Snow

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.

Pugged paddocks

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.