Evaluation of the optical OptRx® crop sensor for monitoring the spatial and temporal variability of pastures

Abstract

The estimation of pasture productivity is an important step for the farmer in terms of planning animal stocking, organizing animal lots and determining supplementary feeding needs throughout the year. The main objective of this work was to evaluate a active optical sensor ("OptRx®", which measures NDVI, Normalised Difference Vegetation Index) for monitoring aspects related to pasture variability and support to decision making for the farmer. The results showed the potential of NDVI for monitoring the evolution of spatial and temporal patterns of the vegetative state of biodiverse pasture. The higher NDVI were registered as pasture approached its greatest vegetative vigor, with a significan fall in the measured NDVI at the end of Spring, when the pasture began to dry due to the combination of higher temperatures and lower soil moisture content. This index was also effective for identifying different plant species (grasses/legumes) and variability in pasture yield. Furthermore, it was possible to develop calibration equations between the NDVI and pasture green and dry matter yield (kg/ha). Finally, an inverse relationship was obtained between NDVI and the pasture dry matter content (in %) in Alentejo dry-land farming systems.