In 2010, the Farm Journal Test Plots crew mapped 1,500 acres of corn with three ground-based Normalized Difference Vegetation Index (NDVI) sensors. Of that, 600 acres were also mapped with aerial and satellite images.
One of the goals of the Farm Journal Test Plots is to stay up-to-date with emerging technologies that can help you farm more efficiently and take yields higher. In the past five years, one of the biggest technologies to come on the scene has been NDVI (Normalized Difference Vegetation Index) mapping.
NDVI maps are a tool for in-season scouting and year-to-year field management. The data collected can help you refine management zones and production practices.
Acres mapped. In 2010, the Farm Journal Test Plots crew went to the field with all of the commercially available technologies to create NDVI maps. There are multiple ways to collect data for the maps: equipment-mounted sensors, images taken from airplanes and satellite imagery.
For the ground-based sensors, the crew used OptRx available from Ag Leader Technology, CropSpec from Topcon and GreenSeeker from Trimble. The aerial images were gathered by GeoVantage, and the satellite imagery was provided by Satshot.
The crew gathered NDVI images with all of the sources across 600 acres of corn. Using the ground-based sensors, an additional 900 acres of corn was NDVI mapped.
|With one set of sensors externally mounted on the tractor cab and two more across the sidedress toolbar, the test plots crew used three displays to map the real-time data.
Installation of the sensors required a simple setup: a head unit, module and monitor to operate in the cab. The OptRx and GreenSeeker sensors were installed on a sidedress toolbar, a CropSpec sensor was mounted on both sides of the tractor cab and the fields were mapped when sidedressing nitrogen. Although the sensors can apply algorithms to determine nitrogen rates, the crew used the sensors solely for mapping.
"The advantage of the ground-based sensors is that the farmer controls when the map is created," says Isaac Ferrie, who works on the test plots. "These sensors provide instant data and require little or no calibration."
Ferrie notes that there is a learning curve when operating the sensors and that farmers are responsible for processing their own maps. The resolution of the map varies by system; all of the sensors we used were set to create a map based on the 40' swath of the sidedress toolbar.
"With the GreenSeeker and OptRx sensors, we were able to gather maps that were very comparable in results," says Brad Beutke, who also works on the test plots. "With the CropSpec mounted on the cab, it takes a much wider angle reading of the crop, and we had some interference with dust. After refining those maps, taking into account the direction of the wind, we were able to achieve maps that mimicked those of the other sensors."
The ground-based sensors generate a NDVI map with each sprayer or sidedress pass. The aerial imagery maps provided by GeoVantage are captured by using an airplane outfitted with cameras.
"To schedule the flights, the company needs a significant amount of acres in the area
to send a plane," Ferrie says. "But this method of mapping doesn’t require the farmer to buy, install and calibrate equipment. The maps are uploaded to a password-protected website for download."
The satellite images from Satshot are collected every time a satellite orbit crosses your fields. This allows maps to be gathered multiple times throughout the season, but the data can only be collected during daylight hours and some shots can be disturbed by cloud cover.
"Satshot can access historical data from your fields as well," Beutke says. "Not only can you get multiple maps for the current season but multiple years, when available."
Dig into details. The test plots crew has learned that the real value of NDVI maps is their detail compared with yield monitor maps. NDVI maps give a snapshot of the crop when management changes can be made. When both maps are collected, the NDVI map can be an in-season progress report and the yield map the report card.
- Early Spring 2011