Thank you guys I will check out the linked sites; I haven't purchased the drone yet. I do not want to spend, too much (1-2k in €) so maybe I will use a service instead. I am pretty familiar with GIS, and I use it on a regular basis for the orchard (I am experimenting with almond as we have a warmer microclimate here in the valley).
here's a paper looking at which indexes work with corn, wheat and irrigation water, it's very likely each crop will have an index that is more accurate;
"The following spectral indices were examined: Difference Vegetation Index (DVI), Normalized Difference Vegetation Index
(NDVI), Enhanced Vegetation Index (EVI), Difference Water Index (DWI), Normalized Difference Water Index (NDWI), Difference
Drought Index (DDI) and Normalized Difference Drought Index (NDDI). "
