CASE STUDY: USING DRONE-ACQUIRED IMAGERY TO MANAGE A HIGH BIOMASS CROP
In 2016, a paddock of Commander barley near Moree, NSW was assessed as having high-yield potential. Nevertheless, at growth stage 30, areas of crop within the paddock were seen starting to lodge.
Applying a growth regulator to the crop was a good option to reduce the lodging, but applying the full rate to the entire crop was considered unwarranted and expensive at $30/hectare.
Agronomist Brad Donald, of B&W Rural Moree, estimated that applying a growth regulant to prevent lodging in the high crop biomass areas could potentially increase yields by 0.5 tonnes/ha and, with barley worth $200/t, this would generate an additional $100/ha.
Persistent cloud cover at the time prevented the use of satellite normalised difference vegetation index (NDVI) imagery. Instead, Donald generated an approximation NDVI map of the paddock using 700 images collected using a modified Canon S100 camera with a near Infrared (NIR)/blue/green lens that filters out the NIR wavelengths, mounted on an AgEagle fixed-wing drone.
The images were stitched together using offline Agisoft Photoscan software then georeferenced to fit the coordinates of the 128ha paddock.
Georeferencing is the process of assigning real-world coordinates to each pixel of the digital image. These coordinates are often obtained by collecting coordinates with a GPS device for few easily identifiable features in the image. Using these sample coordinates, or ground control points (GCPs), the image is warped to fit the area being surveyed.
SMS Advanced Mapping software was then used to estimate the NDVI of each pixel in the composite image, highlighting the high biomass zones (Figure 1), which were the areas of the crop at risk of lodging and amounted to 72ha. Field inspection confirmed that the areas of highest biomass in the paddock were also identified on the map as areas with NDVI ≥ 0.43.
From the drone image, Donald produced the variable rate (VR) prescription spray map (Figure 2), which was loaded into the spray unit controller and used to apply the growth regulant.
By varying the water rate of the spray unit, the high biomass zones (green) were sprayed at the full rate of Moddus Evo (400 mL/ha) with a water volume of 80 L/ha, and the remainder of the paddock (red) received half the rate by lowering the water volume to 40 L/ha.
The result was a reduction in cost of the product and increased yield due to a reduction of lodging. Additional un-costed, but significant, benefits in this case from the application of growth regulant included ease of harvest and improved stubble management for the next season.
The advantages of using a drone in this instance were:
• Rapid capture of images, which were unavailable from other sources due to cloud cover
• Timely processing of images and critical decision-making • Making observations at a time when the paddock was untrafficable due to wet conditions.
Left: This paddock of Commander barley near Moree was sprayed with two different rates of growth regulant Moddus Evo to avoid yield losses to lodging. A strip down the centre of the paddock was left unsprayed and clearly stands out in this photo, showing a much greater level of crop lodging than the rest of the paddock.
Above, Figure 1: NDVI-approximation map generated from 700 images taken with a drone-mounted camera using an NIR/B/G lens that filters out the NIR wavelengths to show variability in crop biomass.
Above, Figure 2: Spray application map showing high (80 L/ha, green) and low (40 L/ha, red) application rate zones.