A study was conducted in a large pistachio farm in Madera County, California, to assess the spatial variability in water status and irrigation needs by using high-resolution thermal imagery acquired by an unmanned aerial system. We determined the Crop Water Stress Index (CWSI) of two fields, 130 ha each, based on canopy temperature measurements of individual tree crowns, thus assessing the spatial variations in tree water status within each field. The CWSI of each potential management unit (sectors encompassing about 175 trees) was then calculated and related to the days since last irrigation (DSLI) in F1 and F2. The relationship between CWSI and DSLI was established to calculate the average CWSI corresponding to the whole area that was irrigated on the same day. This value was afterward compared with the actual CWSI value of each management unit as a proxy of the spatial variability in CWSI. This information was used to calculate the deviation of each irrigation unit from the fixed irrigation schedule for the whole fields. Our results show that it is feasible to use high-resolution thermal imagery for integrating the crop response in irrigation performance assessment and for providing recommendations at the farm scale.

Chris Wylie and Richard Paslay, from Agri-World Cooperative, are also acknowledged. This work was funded by the Spanish Ministry of Science and Innovation (CONSOLIDER CSD2006-0067 and AGL2009-13105).

Peer reviewed