Preliminary Success Using a Commercially Available Ultrasonic Sensor to Measure Forage Yield.

Efficient use of forage in grazing systems benefits from regularly quantifying available forage.  A rising plate meter is the most accepted technology for non-destructively estimating forage yield but this approach is hard to integrate into an on-the-go measuring system and with GPS technology.  Ultrasonic sensors emit a pulsed ultrasonic wave and determine the distance to an object based on the time it takes for the sound echo to return to the sensor.  Initial work in Australia, Germany and Sweden has demonstrated potential for this approach for measuring forage yield.  The ultrasonic sensor has the added benefit that it is compatible with GPS technology which will facilitate creation of forage yield maps.  A Senix TSPC-30S1 sensor emitting a pulse at 20 Hz (20 pulses per second) was mounted on an all-terrain vehicle (ATV) to estimate forage height.  The sensor pointed straight down (90-degree angle to the ground) and was between 1 and 1.5 m above the soil surface.  Results were compared with harvested dry weights and, in some cases, rising plate meter readings.  The technology was tested under a range of conditions in predominantly tall fescue (Lolium arundinaceum) pastures from May 2011 to February 2012.  The ultrasonic sensor readings typically resulted in better correlations with dry matter yield than did the rising plate meter.  There will be a need to account for dynamics of the ATV when determining the tare distance (distance between the sensor and bare ground).  Ultrasonic sensor technology has potential to be an effective tool to non-destructively estimate forage dry matter yield.