Application Performance of Unmanned Aerial Systems (UAS) for Seeding Cover Crop

Abstract

The use of unmanned aerial systems (UAS) for applying dry solid products, especially cover crop seed, has increased rapidly in the United States in recent years. Limited information currently exists on the application performance of dry spreading systems on UAS; therefore, studies were conducted to evaluate the spreading performance, in terms of applied rate and distribution uniformity, of cereal rye – one of the widely used cover crops – applied with a commercially available UAS (DJI Agras T25). The first study evaluated the calibration and metering accuracy of the UAS, while also investigating the material distribution within the single-pass and simulated overlap patterns across varying application rates (22.4, 33.6, 44.8, 56.0 & 64.3 kg ha-1) and flight speeds (6, 7, 8, 9 & 10 m s-1). Results showed that the actual flow rate (kg min-1) differed from the flow rates suggested by the manufacturer’s internal calibration, resulting in significant under-application of cereal rye (9.5% – 17.7%) during the field tests. The single-pass spread patterns showed leftward skewness, indicating greater material distribution (51% to 64%) towards the left and lower material deposition (29% to 40%) towards the right of the spread swath. The simulated overlap spread pattern analysis indicated no effect of application rate or flight speed on the distribution uniformity of cereal rye; however, application method affected spreading uniformity, with the one-direction application method (CV = 19 – 28 %) exhibiting improved material deposition within the swath compared to the progressive method (CV = 22 – 39 %). The second study investigated the effects of application height (3.0, 3.8, and 4.6 m) and spinner-disc speed (700, 1000, and 1300 rpm) on the distribution uniformity of cereal rye within the swath applied with the UAS. Additionally, the effects of hopper metering gate design (medium and large gates with varied-size openings) and spinner-disc design (straight and curved vanes) on material distribution were evaluated across varying application rates. Results showed that both application height and spinner-disc speed affected cereal rye distribution within the swath, with single-pass spread patterns showing lower material deposition at an application height of 4.6 m and a spinner-disc speed of 700 rpm compared to other heights and speeds. Similarly, the maximum single-pass swath increased with application height (from 11.0 to 13.4 m) and spinner-disc speed (from 10.2 to 14.5 m). The distribution uniformity for overlap patterns was similar across application heights (CV = 30 – 33 %), whereas the spinner-disc speeds of 1000 and 1300 rpm (CV values of 31 and 26, respectively) demonstrated improved spreading uniformity compared to the 700 rpm (CV = 38%). The medium metering gate showed a wider single-pass swath than the large gate, but the mean applied rate and distribution uniformity (CV = 37%) were similar across the two gate designs. Similarly, the spinner-disc with curved vanes exhibited greater material deposition, a wider single-pass swath, and greater leftward skewness than the straight-vane disc; however, the spreading distribution for the overlap spread pattern was comparable (CV = 29 – 34 %) across both disc designs. Overall, the results from these studies show promising potential for UAS as an effective technology for applying cover crop seed; however, proper calibration and the selection of optimal operational parameters are highly recommended to ensure accurate and uniform application.