As part of the Cornell CALS PRO-DAIRY Technology Tuesdays series, Harrison Hobart discussed how drones can be used to track forage inventory. Hobart is a dairy farm specialist for Alltech.

Hobart received his drone license in April 2022. He currently flies a DJI Mavic 2 Pro drone which retails for about $3,000 and uses a 3-D mapping software called DroneDeploy. There are other software options available. DroneDeploy is cloud-based software accessed through an app on his smartphone. Using the app, he presets a flight pattern and then plugs the phone into the drone’s controller.

According to Hobart, DroneDeploy was originally designed to measure volume of materials in the aggregate industry through a process called photogrammetry. “In simple terms photogrammetry just means we’re taking several pictures of an object – in this case a feed pile – at many different angles. That, compounded with the GPS satellite data on each individual picture, allows us to stitch them together and create a 3-D model,” Hobart said.

To map a forage pile on a farm, Hobart opens the app and sets a perimeter around the area that he wants to model. Then he determines how high he wants to fly and how many photos he’s going to take. He typically flies to 150 to 200 feet altitude and takes between 100 and 300 photos, depending on the size of the feed pad.

Each flight takes about 10 to 15 minutes to complete, and except for taking off and landing, the drone basically flies itself. The photos are saved on an SD card. Hobart said some people have remarked that his quantity of photos is excessive, but he likes to err on the side of caution and take lots of photos.

Hobart cautioned about taking photos when there is rain, heavy snow or heavy fog. Drone imagery is based on line of sight – a line from the drone’s “eye” to a distant point – so certain weather conditions can distort the images. Hobart has had heavy snowflakes get in the way of the camera. With his drone model, wind doesn’t tend to be an issue; he recounted flying in gusts up to 35 mph. Drone operators should be aware of no-fly zones and make sure to get the appropriate clearance to fly in all locations.

Drone photos aren’t the only things that Hobart needs from a farm. He also needs to collect a core sample from the pile to obtain the density (dry matter in pounds per cubic foot) of the feed. Without this quantitative data, Hobart cannot accurately determine the tonnage of a pile. He weighs the core, and then checks the dry matter with a NIR4 Farm device from DairyOne to find the dry matter in pounds per cubic foot.

“I know some individuals that just use book values for density, but in my opinion, unless the farm has a really good handle on their packing density numbers, it’s just a shot in the dark,” Hobart said.

For example, the assigned density value for corn silage is 16 lbs./cubic foot. Hobart works with a farm that is very particular about their corn silage packing, and their average density is consistently 19 to 20 lbs./cubic foot. In this case, using the book value in the calculating step underreports the total tonnage of the pile by 19%.

“That’s why I think it really pays off in the grand scheme of this program to be checking those numbers. At least to have a good idea of the density of the piles you’re working with,” he said.

Once the photos are collected and the pile density established, Hobart heads to his office to upload the photos to the DroneDeploy software on his desktop computer. The program creates a 3-D model of the site on the farm, and Hobart is able to zoom in and set more specific points on the pile. Once those points are established, the program calculates the pile’s volume.

“Once the volume number is figured out, I’ll plug it into my reports, and then I’ll use those volume numbers along with the pile densities in order to calculate dry matter as fed tons,” Hobart said.

Close-ended bunks, overhangs, sloping dirt walls, overlapping piles and unclear pile edges can all impact the accuracy of Hobart’s calculations. Despite these nuances, he said he feels pretty comfortable getting a farm within two weeks of when a specific feed pile is going to be fed out. On a few operations, he has been able to predict when a pile of feed would run out within a few days.

This use of drones and 3-D mapping technology doesn’t stop at measuring the forage inventories. Hobart has also used the program to help map and plan feed pad extensions. The mapping software is able to show elevation changes and help determine the best route to go with the least amount of fill or the least amount of groundwork that has to be done to expand a feed pad. It also helps farmers to visualize how an expansion will look.

Hobart has also used the software to track dry matter loss and shrink on a feed pile. He’ll fly the drone over a fresh pile and then fly again once some feed has been removed. Each time he calculates the feed volume of the pile. By knowing these two volumes and the feed usage numbers, he can estimate the percentage lost from fermentation and/or shrink.

“The main question I always get asked is ‘How accurate are these numbers?’ and unfortunately, I can’t always give you a straight answer because it is always on a case-by-case basis. The answer is we can get very close. This mapping technology is very dialed in,” Hobart said.

by Sonja Heyck-Merlin