How drones can help you make management decisions
Sunday, October 4, 2015
Images of your fields captured by drones can, for instance, help you plan your nitrogen applications to greater effect
by DALE COWAN
I am certain by now that most people have heard of the use of drones in agriculture. This is our third year of using a drone (often referred to as an UAS or Unmanned Aerial System) on farmers' fields and we are already starting to make use of the captured images.
Most drone manufacturers offer a wide array of sensors (cameras) and most carry a standard colour – red, green, blue, often simply called RGB – and/or an infrared camera. All manufacturers provide software for flight planning and either include processing software or a cloud-based image analysis service to produce a map-based image report.
One of the main outputs is an NDVI (Normalized Difference Vegetative Index) using the red and near-infrared bands and sometimes a soil-adjusted index called a SAVI, which is used when bare soil is visible. This analysis is an indication of the amount of biomass (plant density) and relative "greenness" of a growing crop. What can be inferred from this kind of analysis is the variability in crop growth across a field landscape, and the greenness factor can indirectly indicate chlorophyll content.
The scale that is produced from the analysis is an index and therefore has no units. The range in values are from -1 to +1. For agricultural purposes the range from 0 to 1 is the most relevant, with zero indicating no biomass and one indicating the highest amount of biomass and green plant matter in relative terms.
The question is, what to do with the image analysis? How do we make use of the technology that claims to help us make better management decisions?
The question is best answered by asking, what you want to know. I will propose that we wish to manage nitrogen applications differently. We want to manage nitrogen systematically and split-apply a portion of our nitrogen on corn further on in the season to make sure we can meet the late-season requirements of 40 per cent of the nitrogen demand needed after VT (tassel stage) growth stage. What will an image show us relative to another strategy in the same field?
In the real example (right) of a SAVI-NDVI analysis, the east part had 180 pounds of actual N applied with 90 pounds pre-plant and 90 pounds side-dressed at V5 growth stage. The balance of the west side had 90 pounds of N pre-plant only. We had purposely planned to hold back the final 90 pounds until V8 growth stage and apply in crop with Agrotain treated urea with a high clearance spreader.
By flying the field with the drone ahead of time, we were able to see areas of differential growth and decided to fine tune the final N requirement on a variable rate basis using the NDVI values to create an application rate strategy. This field was flown in less than 20 minutes, the collected images processed and the application map prepared the following day and loaded into the applicators monitor system. Subsequent flights were performed to check on changes in crop growth.
In short, the drones provide a view from above that can be very revealing. When images are captured and analyzed when making a decision around a predetermined management strategy, they may often offer insight beyond the obvious. BF
Dale Cowan is a Certified Crop Adviser in Ontario and the Senior Agronomist and Sales Manager for Agris and Wanstead Co-operatives, located in southwestern Ontario.
