Canopy-based normalized difference vegetation index sensors for monitoring cotton nitrogen status.

摘要

Crop reflectance using ground-based sensors has the potential to provide information on crop N status in real-time. However, the unique physiological and structural characteristics of cotton (Gossypium hirsutum, L.) complicate normalized difference vegetation index (NDVI)-based inferences on cotton N status. Therefore, the objectives of this study were to (i) determine the sensitivity of selected sensors and resulting NDVI measurements to different levels of fertilizer N; (ii) determine relationships between sensors and biophysical measurements; and (iii) compare absolute NDVI readings reported by each sensor. Field trials were conducted during crop years conducted from 2008 through 2010 at Mississippi State, MS. Fertilizer N rates of 0, 45, 90, and 135 kg N ha-1 were applied and replicated four times to establish N-induced growth differences. Sensors used included the Yara N Sensor (Yara International ASA, Oslo, Norway), GreenSeeker (GS) Model 505 Optical Sensor Unit (NTech Industries, Inc., Ukiah, CA) and Crop Circle (CC) Model ACS-210 (Holland Scientific, Inc., Lincoln, NE). Sensor readings failed to consistently predict cotton leaf N status before early flowering; however, plant height relationships with NDVIs were strong. Comparison of sensor response curves to fertilizer N resulted in no significant differences in slope values, although consistent, significant differences in y intercepts were noted beginning at early flowering and continuing through peak flowering. Greater accuracy in the detection of cotton leaf N status may require the utilization of an index which is less responsive to changes in plant height or canopy architecture. Furthermore, the magnitude of canopy reflectance-based NDVI values differed across sensors.