Active‐Optical Reflectance Sensing Corn Algorithms Evaluated over the United States Midwest Corn Belt

• DOI: 10.2134/agronj2018.03.0217
• Publication Date: 2018-11-01T19:56:05Z
• Authors: G. M. Bean; N. R. Kitchen; J. J. Camberato; R. B. Ferguson; F. G. Fernandez; D. W. Franzen; C. A. M. Laboski; E. D. Nafziger; J. E. Sawyer; P. C. Scharf; J. Schepers; J. S. Shanahan
• Keywords: 2. Zero hunger; Plant Sciences; Botany; Soil Science; Life Sciences; Plant Biology; Agriculture; 04 agricultural and veterinary sciences; Horticulture; Agronomy and Crop Sciences; Other Plant Sciences; 0401 agriculture, forestry, and fisheries; Agricultural Science

Core Ideas Active‐optical reflectance sensor algorithms perform poorly outside the area for which they were originally developed. The red edge waveband is more sensitive to N stress than the red waveband. Some active‐optical reflectance algorithms are dependent on the sensor for which they were developed. Uncertainty exists with corn (Zea mays L.) N management due to year‐to‐year variation in crop N need, soil N supply, and N loss from leaching, volatilization, and denitrification. Active‐optical reflectance sensing (AORS) has proven effective in some fields for generating N fertilizer recommendations that improve N use efficiency, but locally derived (e.g., within a US state) AORS algorithms have not been tested simultaneously across a broad region. The objective of this research was to evaluate locally developed AORS algorithms across the US Midwest Corn Belt region for making in‐season corn N recommendations. Forty‐nine N response trials were conducted across eight states and three growing seasons. Reflectance measurements were collected and sidedress N rates (45–270 kg N ha−1 on 45 kg ha−1 increments) applied at approximately V9 corn development stage. Nitrogen recommendation rates from AORS algorithms were compared with the end‐of‐season calculated economic optimal N rate (EONR). No algorithm was within 34 kg N ha−1 of EONR > 50% of the time. Average recommendations differed from EONR 81 to 147 kg N ha−1 with no N applied at planting and 74 to 118 kg N ha−1 with 45 kg of N ha−1 at planting, indicating algorithms performed worse with no N applied at planting. With some algorithms, utilizing red edge instead of the red reflectance improved N recommendations. Results demonstrate AORS algorithms developed under a particular set of conditions may not, at least without modification, perform very well in regions outside those within which they were developed.