ARS | Publication request: Nadir and oblique canopy reflectance sensing for N application in corn

Submitted to: ASABE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: August 2, 2011
Publication Date: August 7, 2011
Citation: Sudduth, K.A., Kitchen, N.R., Drummond, S.T. 2011. Nadir and oblique canopy reflectance sensing for N application in corn. ASABE Annual International Meeting, August 7-10, 2011, Louisville, Kentucky. Paper No. 1111261.

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: Canopy reflectance sensing can be used to assess in-season crop nitrogen (N) health for subsequent control of N fertilization. The several sensor systems that are now commercially available have design and operational differences, including sensed wavelengths, size of the sensed area, and nadir vs. oblique sensing orientation. Data comparing the different sensor designs is lacking. Thus, the objective of this research was to evaluate three different commercial canopy reflectance sensors 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. Data were collected multiple times on plots with eight different N rates 0 to 235 kg N ha-1. Relative NDVI data from GreenSeeker and Crop Circle sensors were most highly correlated, while data from those two sensors were less strongly related to CropSpec data. CropSpec NDVI was more strongly related to SPAD readings as an indication of leaf N, while the other two sensors were more affected by crop height variations. For multiple data collection runs in a single day, somewhat 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).