Measure it better, manage it better: new technology enables easier, accurate pasture mass measurements

The C-DAX Pasturemeter is a tow-behind attachment for a quad bike, which enables much quicker and more accurate pasture mass estimation.

One of the key drivers of pasture productivity is grazing management. How much and how often the pasture is grazed has a direct impact on both pasture production and quality.

Industry ‘best practice’ guidelines suggest that pre-graze covers of around 2800 kilograms of dry matter per hectare and post-graze residuals of around 1500kg DM/ha are optimal. Higher pre-graze covers result in lower pasture quality, as the grass contains more less digestible fibre, not enough protein and lower energy levels. Likewise, if the pasture is grazed too short, re-growth will be slower and plant deaths can mean less persistent pastures.

Funded by the Pastoral 21 feed programme, a team of researchers led by Dr Robyn Dynes has been working to improve pasture mass estimation techniques by developing what her colleague Dr Warren King calls “useful tools that could drive farm production by maximising use of pastures.”

In the past, the common tool to measure pasture was the Rising Plate Meter (RPM), which looks like a walking stick with a dinner plate attached to the bottom. The bottom of the stick is dropped into the pasture, and the plate is pushed upwards by the grass sward, giving an estimate of the pasture height. This height measurement is then used to calculate the pasture mass.

The RPM is a very subjective tool prone to operator error, and it takes many
measurements across a paddock to give a reasonable estimate, which makes it time-consuming and laborious to operate. As a result, very few New Zealand dairy farms actually use such technology to estimate pasture mass.

A new technology called the C-DAX Pasturemeter has recently been introduced to address the RPM’s shortcomings. The device is a towbehind attachment for a quad bike, which enables much quicker and more accurate pasture mass estimation.

It continuously measures average pasture height as the bike moves, thus enabling a wide area to be covered quickly. A calibration equation is then used to
convert height into pasture dry matter. The calibrations used to make this
conversion have, until recently, been based on restricted field data.

To address this issue, Dr Dynes’s team began a project to develop customised
calibrations to improve the accuracy of the C-DAX Pasturemeter.

The team selected a range of paddocks in regions across New Zealand, and each
month they measured the grass height and then cut, dried and weighed the grass to develop a set of calibrations converting grass height into pasture mass.

These measurements were repeated for a year, so that customised calibrations for each day by region could be calculated. The calculations were done for a number of dairy farms, as well as for beef and sheep farms in a reduced number of regions.

In a second phase of the project, the team then chose another set of farms that had quite different environmental parameters to the first pastures, and tested their
calibrations to determine how widely they could be applied. These experiments
showed that the calibrations were fairly robust even in quite different conditions
within each region.

The calibrations should give farmers greater confidence in their ability to measure pasture mass, and now that the calculations have been included in the C-DAX Pasturemeter package, it is even easier for farmers to use them.