AN ELECTRONIC INSTRUMENT FOR PASTURE YIELD ESTIMATION

This is a preliminary report on an instrument being developed for the measurement of pasture yield in situ. In essence the instrument is an electrical capacitance measuring unit in which the introduction of herbage to a measuring head causes a change in the electrical capacitance of the system. This capacitance change is measured at a radio frequency and used as an indicator of the mass of herbage contained within the measuring head. The development and construction of the instrument is described and data are presented for 15 calibration series in which frequency change has been related to pasture yield. Within series the instrument accounts for approximately 90% of the variation in pasture sample yield measured either as wet, dry or organic matter. However, significant differences exist between series. These differences would give rise to bias if pasture yield were estimated from a prediction equation derived from the pooled data. Possible sources of the differences between series are discussed and avenues for further development indicated.