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ARS Home » Plains Area » Lincoln, Nebraska » Agroecosystem Management Research » Research » Publications at this Location » Publication #254002
Title: Comparison of Spectral Indices Derived from Active Crop Canopy Sensors for Assessing Nitrogen and Water Status

Author
item SHIRATSUCHI, LUCIANO - EMBRAPA
item FERGUSON, RICHARD - UNIVERSITY OF NEBRASKA
item SHANAHAN, JOHN
item ADAMCHUK, VIACHESLAV - UNIVERSITY OF NEBRASKA

Submitted to: International Conference on Precision Agriculture Abstracts & Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 5/7/2010
Publication Date: N/A
Citation: N/A

Interpretive Summary: In-season nitrogen management for corn using active canopy sensors relies on the use of algorithms that can trigger on-the-go N fertilization in the field based on crop canopy reflectance. Optical sensing equipment that employs this approach is commercially available and all use some vegetation index as the basis for input with an algorithm that dictates the N rate application in the field according to crop reflectance. For example, when the vegetation index ratio between a region in the field and a well-fertilized reference in the same field reach a certain level, nitrogen fertilizer is needed according to a function that describes the relationship between yield and sufficiency index readings. Regardless of the approach to be used, an understanding is needed of how these indices may be influenced by other crop factors including water stress. The objective of this study was to evaluate the performance of various spectral indices for measuring N status in corn, where spectral variability might be confounded by water-induced variations and previous crop influences on the reflectance spectra. The study was conducted in 2009 with experimental treatments of irrigation level (100 and 70% ET), previous crop (corn or soybean) and pre-plant nitrogen fertilizer rate (0, 75, 150 and 225 kg N/ha). Crop canopy reflectance was measured from V11 to V15 using two active sensors – a two band (880 and 590nm) and a three band (760, 720 and 670 nm) sensor. The DATT index was the least affected by water stress, with good ability to differentiate N rate with both crop rotations. The chlorophyll index (CI) and red normalized difference vegetation index (NDVIred) indices showed more variation due to water supply, and had only moderate ability to differentiate N rates. These preliminary results suggest that it is critical to select the appropriate sensor-determined vegetative index in order to separate crop water from N stresses. However, more research is needed to evaluate these indices under a wider range of water stress conditions.

Technical Abstract: Much of the previous evaluation of active crop canopy sensors for in-season assessment of crop N status has occurred in environments without water stress. The impact of concurrent water and nitrogen stress on the use of canopy sensors for in-season N management is unknown. The objective of this study was to evaluate the performance of various spectral indices for sensing N status of corn, where spectral variability might be confounded by water-induced variations in crop reflectance. The study was conducted in 2009 with experimental treatments of irrigation level (100 and 70% ET), previous crop (corn or soybean) and pre-plant nitrogen fertilizer rate (0, 75, 150 and 225 kg N/ha). Crop canopy reflectance was measured from V11 to V15 using two active sensors – a two band (880 and 590nm) and a three band (760, 720 and 670 nm). Among the indices studied, the MTCI index was the least affected by water stress, with good ability to differentiate N rate with both crop rotations. The CIamber and NDVIred indices showed more variation due to water supply, and had only moderate ability to differentiate N rates.