ok so this has been bugging me for a while and i keep going back and forth on it. currently flying a Mavic 3 Multispectral for NDVI mapping on corn and the results are decent but ive been talking to a few agronomists who swear that a good RGB setup with the right processing pipeline can catch nitrogen stress almost as early as multispectral if you know what to look for in the color channels.

part of me thinks thats probably true for mid-to-late season stuff when stress is visible but early season when youre trying to catch things before they tank yield, i dont see how RGB gets you there. NDRE especially seems like the thing that earns its keep in those early windows before anything looks visually off to the naked eye.

running the data through Pix4Dfields right now. maybe the software side matters more than i'm giving it credit for and im just not extracting what i could from the RGB flights. anyone actually done a side by side on the same field same timing and compared the outputs

yeah we did a pretty rough comparison last summer, nothing super scientific but same field same days with a P4 Multispectral and a Phantom 4 Pro just for grins. early in the season the RGB caught almost nothing useful, the NDVI maps from the multispectral were already showing variability zones that didn't show up in the RGB processed imagery until like two weeks later. by then you've missed the variable rate application window so what's the point really. i think the agronomists are right in a general sense but the timing aspect is what they're glossing over.

I'm newer to the ag side of this but work in photogrammetry and from what i understand the NDRE band is really where the early detection lives, NDVI kind of saturates in dense canopy and NDRE holds up better. so if you're already flying the M3M you probably have that covered depending on which band combo you're using in Pix4D. might be worth checking what indices you're actually exporting becuase the default settings arent always the most useful ones for early stress.