In The Paddock
Seasonal sheep flock management tips September 2002

Measurement of pasture cover

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Key points

• Monitoring pasture growth is a key to better livestock nutrition and greatly improved farm productivity
• There are effective tools available for measuring pasture cover and these are now being calibrated for sheep pastures
• By measuring how much pasture is present in a paddock, we can make accurate feed budgets, plan feed requirements and make better grazing management decisions
• Pasture cover estimates need to be adjusted for seasonal differences in the amount of dead matter in the sward
• WoolPro has set up PasturePlan, a nation-wide pasture measurement programme which will help farmers become familiar with pasture measurement

Pasture growth and feed availability have traditionally been estimated by eye. Stock have often been given what was available and then shifted when they looked ready to move. Feed surpluses and shortages have often taken us by surprise.

It no longer needs to be like this.

We now know how much pasture cover each class of stock needs to achieve optimum growth rates. And there are some effective tools available for measuring pasture cover, which are now being calibrated for use in sheep pasture.

By measuring how much pasture is present in a paddock, we can make accurate feed budgets, plan feed requirements and make better grazing management decisions. Shortages and surpluses will no longer arrive with the same element of surprise.

WoolPro believes monitoring pasture growth and quality are keys to better livestock nutrition and greatly improved farm productivity. For this reason the company has established PasturePlan, a nationwide pasture monitoring programme, on about 40 farms covering a range of climates and land classes.

Pasture cover varies greatly both between and within paddocks. For this reason a number of assessments need to be made to get a meaningful average figure for each paddock.

There are different proportions of high energy green leaf present in the sward at different times of the year. Dead material reaches quite high levels in summer and autumn, decays rapidly during winter and reaches low levels by early spring.

Allowance needs to be made for this when measuring the amount of pasture cover.

Cutting and weighing pasture is the traditional way to measure pasture growth. Cut pasture from a known area is weighed fresh and the dry matter percentage is estimated.

On PasturePlan farms the pasture cuts are dried and the dry matter percentage is calculated to obtain the DM cover per hectare.

While cutting and weighing pasture is laborious, it is the best way to calibrate pasture cover measuring devices and is used for this purpose in PasturePlan.

Measurement devices

A number of tools can be used to estimate pasture cover. But with each device a number of measurements need to be taken in each paddock and then averaged to get a valid estimate of feed cover.

In small paddocks with even pasture cover, 20 - 30 readings is adequate. In hill paddocks with uneven cover, more readings need to be taken.

Sward stick

Sward stick measurements are only indicative, but the stick is a useful way to get used to the concept of assessing pasture.

The sticks are given away for promotional purposes and are extremely portable, simple to use and are effective in all weather conditions. But they do not account for differences in pasture density.

Sward sticks are not calibrated for use on sheep pastures and recording measurements and making calculations in wet weather can be difficult.

Rising plate meters

Rising plate meters measure the compressed height of pasture. They are particularly accurate at pasture covers of 1300 - 3000 kgDM/ha and are widely used in the dairy industry.

Pasture readings are converted to average height or cover (kgDM/ha) using seasonal equations, graphs or conversion tables.

Manual versions (approximately $400), require the user to count and record information then calculate the final cover. Electronic versions ($600) do this electronically. Free software also allows for recording covers over time.

Rising plate meters can be used in all weather conditions. Care must be taken when using them on steep slopes. They are easily dismantled, but are not as portable as pasture probes.

Pasture probes

Pasture probes are electronic devices that measure the DM cover of pastures. They take both pasture height and pasture density into account.

However, pasture probes can overestimate cover when pastures are moist.

Pasture probes cost around $1,000. They are very portable (a gun bag or length of PVC pipe attached to an ATV makes an ideal carry case) and convenient to use, carrying out calculations and storing paddock data automatically. Data can be downloaded from a probe to a computer.

Probes and rising plate meters are being calibrated on sheep pastures as part of the PasturePlan programme.

Visual assessment

Visual assessment is obviously the quickest, least expensive and most convenient method of estimating pasture cover and can be carried out while travelling around the farm for other purposes. But the eye must first be trained and calibrated against pasture cuts, a probe or rising plate metre.

Tool calibration

Probes and rising plate meters can be calibrated by adjusting the readings on the probe or meter so they match an actual grass cut figure. This can be done easily at a PasturePlan farm on cutting day.

Measurement tools

Pasture probe: GrassMaster, Tru-Test Limited, Tel 09 978 8888, email grantj@trutest.co.nz, www.tru-test.com.

Electronic Rising Plate Meter: Farm Works, PO Box 433, Feilding. Tel 06 323 1371, fax 06 323 1371, email sales@farmworksnz.com, www.farmworksnz.com.

Rising plate-meter: Filips Folding Plate Pasture Meter, Jenquip, RD5, Feilding. Tel 06 323 6146 or 0800 353 537, email jenquip@clear.net.nz, www.jenquip.co.nz

Pasture dry matter ready reckoner

This ready reckoner is based on improved pastures on warmer North Island hill country with dry summers. Use the late spring column when estimating pasture DM in summer-moist areas.

More information

A Guide to Improved Lamb Growth, Chapter 6.

A Guide To Feed Planning, Chapters 1&2, Appendices 6&7.

In The Paddock, August 2002, Principles of Pasture Growth.

Your local farm consultant or veterinarian will also be able to help. Alternatively, contact your local WoolPro extension specialist: