Compared to current N management practices, sensors are better able to account for within field spatial variability and year-to-year changes in rainfall and the soil’s capacity to mineralize and supply N. This method has the potential to better match fertilizer N supply with crop N need. Use of sensors minimizes the potential for over- and underapplications of nitrogen. Research results suggest this approach not only allows the grower to maximize yields and profitability, but also leads to the highest crop NUE and reduced potential for environmental pollution (Hong et al., 2007; Shanahan et al., 2008). This Crop Insights will discuss the active canopy reflectance sensor systems ("crop sensors") commercially available and their potential for improving N management in corn production.
The width of the variable-rate application should be considered when deciding how many sensors should be installed on a given applicator. A minimum of 2 or 3 sensors on different rows should be used for representing the entire applicator swath width, with more sensors needed as applicator width increases (Roberts et al., 2009).
The CropSpec uses a two-sensor configuration that installs one sensor positioned at an oblique 45° angle on each side of the top of the applicator cab (Figure 7). The sensor footprint is larger (6 to 10 feet) and integrates more crop area (2 to 3 rows wide) than that of the other two commercial sensors. Hence, only one CropSpec sensor configuration is required per fertilizer applicator.
Because leaf structure and color along with canopy architecture are sometimes defining characteristics of hybrids, reflectance patterns can vary between hybrids even under adequately fertilized conditions. For these reasons, great care should be taken when comparing sensor data between fields that have different cropping histories, growth stages, and/or hybrids. Normalizing data to an adequately fertilized area within a field that has only received a little extra N should make it possible to make a reliable comparison between fields, hybrids, etc.
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