Scouting is an important part of managing your crops but, when you have a lot of ground to cover, it can be expensive and difficult to stay on top of these important regular field checks.
Rather than delaying scouting trips and risk missing small issues before they get too big to control, Normalized Difference Vegetation Index (NDVI) imagery provides a way for you to remotely monitor crop health. NDVI imagery is often captured by satellites and is a great additional tool at your disposal at all times for quickly and remotely spotting variability in your orchard.
In this blog, we’ll cover the basics of NDVI and walk through practical ways growers and advisors can use it to save time and improve decision-making.
NDVI is a quantifiable way of remotely measuring how “green” or “healthy” an area is based on how it’s reflecting light. It’s calculated by measuring the difference between near-infrared (reflected by leaf cells) and red light (absorbed by chlorophyll), which shows you the difference between dense, healthy, chlorophyll-rich vegetation, and sick or stressed tree vegetation.
On an NDVI map:
Greener areas generally indicate healthier plants
Red or lighter areas often signal stress
You can see an example of an NDVI map below, which is a screenshot from our Semios Hub app.
Semios’ NDVI offering uses satellite imagery captured by Sentinel-2 satellites, which is taken roughly every five days. However, cloud cover prohibits satellites from creating accurate NDVI imagery, and whenever that is the case, you will find the most recent clear image in our Hub software instead. In Semios Hub, you can when an image was taken by the satellite by hovering over it:
NDVI is most useful when it supports decisions you’re already making. Here are a few common use cases:
NDVI is a useful tool when planning your scouting trips. You can quickly pinpoint where to check first by looking for areas that show a lower NDVI index than the rest of your orchard.
Problems like water stress, nutrient deficiency, pest infestations, or an issue with the soil can all cause a drop in NDVI. For example, if a pest is too small to show up properly in camera traps or it’s a pest that mainly damages leaves, a decline in NDVI can act as an early warning sign. Similarly, if you have a leaking irrigation valve somewhere that is causing part of a block to be over-watered, you’ll be able to detect stressed trees in your NDVI imagery long before you’ll be able to see the physical signs of phytophthora or crown rot in your orchard.
Another way NDVI can be used is to track changes over different periods of time.
On the Semios Hub app, users can track both short-term and long-term change:
Short-term change compares your two most recent images, helping you spot quickly developing problems.
Long-term change compares your most recent image with an image taken 30 to 45 days before, helping you track more gradual problems that are developing over time.
These changes show up as different colors on the map:
Red is a decrease in chlorophyll denseness.
Yellow means there has been little to no change.
Blue is an increase in chlorophyll denseness.
Based on the time of the year in the example above, the drop in greenness is likely due to the cold weather setting in and leaves falling off the trees between image dates.
To access NDVI on Semios Hub:
While NDVI can show you where an issue is happening, you need to know the cause to fix the problem. By combining NDVI with on-farm data collected from Semios sensors, growers can evaluate potential causes behind the drop in NDVI.
If a block expresses consistently low NDVI values and you’re worried your crops may be under water stress, the Available Water Content Graph and Infiltration Map in Semios Hub can help you confirm it. You can compare the drop in NDVI and whether it aligns with either a decrease or increase in soil moisture level shown in the Available Water Content Graph. On the other hand, the Infiltration Map shows how far down water is traveling through the soil profile. You can use it to check whether the irrigation you’re putting on is hitting the right depth to reach the roots.
If you’re expecting a nutritional deficiency problem, and NDVI values stay low even after a fertilizer application, the Salt Map in Semios Hub can be used to confirm the issue. The Salt Map helps you monitor relative salt concentration at different soil depths. You can assess whether fertilizer is moving too deep into the profile away from the root zone. It can also be used to check whether you have a salt buildup problem.
Weather is another factor that can explain sudden changes in NDVI. A heat wave, storm, or extended dry period can quickly affect vegetation health. By combining Semios weather data with NDVI, you can get an idea of whether the change in NDVI can be explained by the recent weather events.
When labor is becoming a challenge and growers are being asked to do more with fewer resources, NDVI supports you with:
A high-level view of your crops’ status without extra boots on the ground
Early visibility into potential issues, helping direct your scouting efforts
A way to monitor change throughout the season
If you’d like to add NDVI to your crop management toolkit, connect with our team to get a demo and see how it works: Talk to our team >