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Open AccessArticle

Evaluating Two Crop Circle Active Canopy Sensors for In-Season Diagnosis of Winter Wheat Nitrogen Status

1
College of Resources and Environmental Sciences, China Agricultural University, Beijing 100193, China
2
National Engineering and Technology Center for Information Agriculture (NETCIA), Key Laboratory for Crop System Analysis and Decision Making, Ministry of Agriculture, Jiangsu Key Laboratory for Information Agriculture, Jiangsu Collaborative Innovation Center for the Technology and Application of Internet of Things, Nanjing Agricultural University, Nanjing 210095, China
3
Precision Agriculture Center, Department of Soil, Water and Climate, University of Minnesota, St. Paul, MN 55108, USA
4
Department of Geography, Minnesota State University, Mankato, MN 56001, USA
*
Author to whom correspondence should be addressed.
Agronomy 2018, 8(10), 201; https://doi.org/10.3390/agronomy8100201
Received: 21 August 2018 / Revised: 17 September 2018 / Accepted: 20 September 2018 / Published: 21 September 2018
(This article belongs to the Special Issue Sensing and Automated Systems for Improved Crop Management)
Active crop canopy sensors can be used for non-destructive real-time diagnosis of crop nitrogen (N) status and guiding in-season N management. However, limited studies have compared the performances of two commercially available sensors with three different wavebands: Crop Circle ACS-470 (CC-470) and Crop Circle ACS-430 (CC-430). The objective of this study was to evaluate the performances of CC-470 and CC-430 sensors for estimating winter wheat (Triticum aestivum L.) N status at different measurement heights (40 cm, 70 cm and 100 cm) and growth stages. Results indicated that the canopy reflectance values of CC-470 were more affected by height compared to the CC-430 sensor. The normalized difference red edge (NDRE) and red edge chlorophyll index (CIRE) of CC-430 were stable at the three different measuring heights. The relationships between these indices and the N status indicators were stronger at the Feekes 9–10 stages than the Feekes 6–7 stages for both sensors; however, the CC-430 sensor-based vegetation indices had higher coefficient of determination (R2) values for both stages. It is concluded that the CC-430 sensor is more reliable than CC-470 for winter wheat N status estimation due to its capability of making height-independent measurements. These results demonstrated the importance of considering the influences of height when using active canopy sensors in field measurements. View Full-Text
Keywords: active canopy sensor; measurement height; in-season nitrogen management; nitrogen nutrition index; plant nitrogen concentration; precision nitrogen management active canopy sensor; measurement height; in-season nitrogen management; nitrogen nutrition index; plant nitrogen concentration; precision nitrogen management
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Cao, Q.; Miao, Y.; Shen, J.; Yuan, F.; Cheng, S.; Cui, Z. Evaluating Two Crop Circle Active Canopy Sensors for In-Season Diagnosis of Winter Wheat Nitrogen Status. Agronomy 2018, 8, 201.

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