Submitted to: International Conference on Precision Agriculture Abstracts & Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 5/20/2010
Publication Date: 7/18/2010
Citation: Sudduth, K.A., Kitchen, N.R., Drummond, S.T. 2010. Comparison of Three Canopy Reflectance Sensors for Variable-Rate Nitrogen Application in Corn. In: Proceedings of the 10th International Conference on Precision Agriculture, 18-21 July, 2010. Denver, Colorado. 2010 CDROM. Interpretive Summary: Concerns for the environment have made farmers and the public increasingly interested in technologies that help use fertilizers, including nitrogen (N), more efficiently. One way to increase N fertilizer efficiency is site-specific management, where varying amounts of N are applied based on differing crop needs in different areas of fields. Various approaches have been used to determine how much N is needed in these sub-field areas. One relatively new approach uses crop reflectance sensors mounted on the front of fertilizer applicators. These sensors assess the health of the crop through its reflectance characteristics and, coupled with a computer program, control how much N fertilizer is applied. Several commercial crop reflectance sensors are now available, each with a specific set of characteristics. The purpose of this research was to compare three commercial sensors used for N fertilizer application control in corn. We collected data with all three sensors multiple times over a corn crop and documented differences in their operating performance. For best results, users need to take these differences into account when using sensors to manage N in corn production. The importance of this research is that it makes scientists, farmers, and other users aware of differences between commercially available crop sensors, so that they can use them appropriately in N fertilizer application systems.
Technical Abstract: In recent years, canopy reflectance sensing has been investigated for in-season assessment of crop nitrogen (N) health and subsequent control of N fertilization. The several sensor systems that are now commercially available have design and operational differences. One difference is the sensed wavelengths, although these typically include wavelengths in both the visible and near-infrared ranges. Another difference is orientation – the sensors most commonly used in the US are designed to operate with a nadir (vertical) view of the crop, while some sensors developed in Europe and now becoming available in the US are designed to view the crop obliquely. Data comparing the different sensor designs is lacking. Thus, the objective of this research was to evaluate three different commercial canopy reflectance sensors used for N fertilization control in corn. Two units of each of three commercial sensors – GreenSeeker, Crop Circle, and CropSpec – were mounted to a high-clearance applicator for field data collection and operated according to manufacturer recommendations. Data were collected from five field experiments in 2009. Multiple blocks of randomized N rate response plots traversed each field. Each block consisted of 8 N treatments from 0 to 235 kg N ha-1. Crop canopy reflectance sensor measurements were obtained from the N response blocks at the time of side-dress N application. At one site, additional sensor measurements were obtained over a range of growth stages after N application. NDVI data from GreenSeeker and Crop Circle sensors were highly correlated at most field sites and overall, while data from those two sensors were less strongly related to CropSpec data. CropSpec NDVI was more strongly related to SPAD and leaf N content, while the other two sensors were more affected by crop height variations. For multiple data collection runs in a single day, less run-to-run variation was seen with the CropSpec. For best results, users need to take into account the differences among these commercial sensors, particularly between the two small-footprint nadir sensors (Crop Circle and GreenSeeker) and the large-footprint, oblique sensor (CropSpec).