31 October 1997

Grass DM spot-on with new devices

By Robert Davies

Two devices for more accurately measuring grass dry matter/ha are being developed at Aberystwyth.

Dr John Witty, a principal researcher at the Institute of Grassland and Environmental Research, believes that combining electronics and mechanical or barometric biomass assessments could provide much more accurate measurements than sward sticks and rising plate meters.

"These can give estimates ranging from 50% to 200% of the true figure," Dr Witty claims. "Getting it right every time would allow much more precise grazing management, reduce wastage, and cut concentrate costs. If a farmer could be certain that the next but one field to be grazed had enough grass he could move on and conserve the spare herbage."

He is hoping for funding to look at two measurement systems. The first uses a pole to which are attached five horizontal rods fitted with strain gauges. A base plate presses down the grass adjacent to the measurement area, and the rod lengths are staggered so that measurements at different depths do not interfere with each other.

As the pole is rotated in the crop the resistance at each point is measured and a micro-processor integrates the readings to give a profile of sward density at different depths. Calibration based on field trials would be used to convert readings into an immediately accessible estimate of fresh herbage yield.

Used in combination with an electronic moisture meter due to be launched next spring, the herbage dry matter/ha could also be assessed.

The alternative system is based on the resistance of a sward to air flow. Air is sucked through a tube, which is gradually lowered into the canopy. The resulting vacuum, monitored by a sensor within the tube, will depend on the volume of grass sucked in. Again a micro-processor would use the data to estimate yield.

"We believe that both systems are potentially viable and have applied for £30,000 of EU development funding. The application has been graded A so it stands a good chance of being accepted. If the systems can be shown to work well in trials I am sure that commercial manufacturers will be interested." &#42

IGERs John Whitty… developing new devices to provide more accurate measurements of grass.

Two new measurements systems which could allow much more precise grazing management than either the sward sticks or rising plate meters currently in use.