Ask the Experts — Using Drones to Create More Accurate Prescriptions

We wrapped up our recent Ag Drone Insights 2 webinar with a short Q&A session, during which attendees from around the globe submitted their questions live. These were answered by the event’s three expert presenters: Michael Dunn of Anez Consulting, Gustavo Miolano of Geosistemas SRL and Nathan Stein, senseFly’s ag solutions manager. This post details their responses in full, covering: viticulture, soy bean evaluation, when in the season to fly, optimal flight heights and more.

Our presenters answered the following questions:

ag_drone_insights_speakers Gustavo Miolano (Geosistemas SRL), Michael Dunn (Anez Consulting), and Nathan Stein (senseFly)

Can drones be used for soy beans to evaluate N, K and P levels on the field?

Michael Dunn, Anez Consulting: We work quite a bit with soy beans and there are certain deficiencies that are more obvious in beans than others. One of them is potassium deficiency, which results in chlorosis of the upper portions of the plant, and combined with soil sampling of the plant and tissue sampling, you should do a fairly good job with delineating potassium deficiency out of aerial imagery.

What experience do you have in using the red edge band to compute NDVI or any other index to assess different crop problems like fertilisation or disease control?

Nathan Stein, senseFly: In my own fields here, I can attest that using the red edge band in a formula called the NDRE—similar to the NDVI, but instead of the red, you’re using the red edge—it does a pretty good job of detecting nitrogen stress and had really great correlation last year. In fact, I discovered a missed pass of anhydrous that I put on the field. It detected it fairly early in the stage of the crop and I never really applied anything to it later on in the year, but found out it was about a hundred bushel difference, obviously because nitrogen is important. It was a very good tool though and very effective.

In my own fields, I can attest that using the red edge band in a formula called the NDRE … does a pretty good job of detecting nitrogen stress and had really great correlation

Gustavo Miolano, Geosistemas SRL: I want to add one experience I’ve had with red edge. We have been doing some assessments in wheat fields. Red edge is correlated, at least here , with winter wheat for protein content. So, not much for yield, but for protein. You can know which part of the field is going to have a high level of protein, so when you are harvesting you can go and look at the good wheat, and leave the rest to sell in a separate channel. I don’t know if in the rest of the world if this is similar but here you can get more money if the protein level is high in the wheat, so it is an interesting use for us here in the wheat zone, really interesting.

index_map An NDVI Map depicting corn health in a field.

At which stage of plant growth should data collection start and how often should flights be performed?

Michael Dunn, Anez Consulting: It’s obviously pretty crop specific—when to start, when to stop. Generally for corn, in my experience, we like to be close to canopy or starting our imagery acquisition, and then all the way up until just before tassel. There are a couple of issues with later season flights, especially after tassel, requiring higher image overlaps to get good processing, but also after pollen shed the reflectance of the crop can change for reasons that don’t necessarily reflect yield potential or crop health.

In terms of the operations and how often to fly—what is the optimal flight height above ground level and what are the optimal image overlap settings that you find work best in the field?

Michael Dunn, Anez Consulting: Depends on what you are trying to accomplish, I suppose. For doing stand count, lower is better. If you are just looking for NDVI, I would say as high as you can legally go.

For doing stand count, lower is better. If you are just looking for NDVI … as high as you can legally go

Nathan Stein, senseFly: For most cases, I think using exactly what Michael said. You fly very low for maybe an RGB image or stand count or, depending on what kind of crop it is, if it’s a vegetable crop or something, if it’s wheat or corn, you’re going to fly around whatever legally you can do.

Is NDVI only used for nitrogen assessment or is it also useful for gauging potassium and phosphorous deficits?

Michael Dunn, Anez Consulting: NDVI is really just a measure of crop health and that can be affected by many factors. Typically in corn and other grass family crops. Nitrogen is most likely going to be driving poor health issues, but it very well could be potassium. We have some very sandy soil that is actually magnesium deficient and we can see poor NDVI values from that as well. Or we could be looking at flood stress or drought where we have poor NDVI values as well as wheat issues, especially with weeds with a naturally lower NDVI value are above the crop you are sensing.

Watch senseFly’s full Ag Drone Insights 2 webinar on demand: