AIMS - Real time measurement of pasture quantity

Summary

The key objective of this project was to establish a calibration curve, using Normalised Difference Vegetation Index (NDVI) values recorded from the Green Seeker active optical sensor, to estimate green pasture biomass for mixed species pastures on the Northern Tablelands of NSW.  This would provide an advantage over existing subjective measures and be used to develop feed budgets that inform grazing management decisions to control pasture and livestock performance. 
The relationship between estimates of NDVI and pasture biomass was developed from the following design.  On each of three properties, one mixed species pasture paddock, managed with a single intensive grazing management method, had 12 pasture measures taken on three occasions each year over a two year period. These measures included NDVI and pasture height before pasture was harvested, sorted and dried to allow calculation of green and total pasture biomass. On one of these properties, the effect of grazing method (TechnoGraze® system and rotational grazing) on the relationship between NDVI and pasture mass was evaluated. In the third year of the project, the suitability of calibrations was tested across site and year.

On their own, NDVI values were not a useful means for estimating green pasture biomass with problems arising from wide variation in NDVI values for a particular level of green pasture biomass and high sensitivity of NDVI values to green pasture biomass above 1500 kg DM/ha. Pasture height provided a good measure of total pasture biomass. The combined product of NDVI x pasture height greatly improved the accuracy of predicting green pasture biomass with a predictive accuracy of 80% and a residual error of 342 kg DM/ha.
The results from this project highlight considerable potential for regional equations, based on NDVI and pasture height, to provide accurate estimates of green pasture biomass.   However, a process to automate the collection of pasture height will be a critical next step in the commercial application.  Such developments will also provide a useful means for estimating total pasture biomass.

Ultimately, estimates of green and total pasture biomass need to be included in feed budgeting approaches to enable producers to derive value through better management of pastures and livestock.  This could occur in a number of ways but developing connectivity of this technology with existing applications appears a sensible approach for industry to progress.