Measuring Wheat Senescence with a Digital Camera

Abstract

Documenting crop senescence rates is often difficult because of the need for frequent sampling during periods of rapid change and the subjective nature of human visual observations. The purpose of this study was to determine the feasibility of using images produced by a digital camera to measure the senescence rate of wheat and to compare the results with changes in greenness determined by two established methods. Measurements were made as part of an experiment to determine the effects of elevated C02 and limited soil nitrogen on spring wheat (Triticum aestivum L.) at the University of Arizona's Maricopa Agricultural Center, near Phoenix, AZ. “Greenness” measurements were made during senescence of the crop with a color digital camera, a hand‐held radiometer, and a SPAD chlorophyll meter. The green to red (GIR) for each pixel in an image was calculated and the average GIR computed for cropped images from a digital camera representing 1 m2 for each treatment and sample date. The normalized difference vegetation index (NDVI) was calculated from the red and near‐infrared canopy reflectances measured with a hand held radiometer. A SPAD reading was obtained from randomly selected flag leaves. All three methods of measuring plant greenness showed similar temporal trends. The relationships between GIR with NDVI and SPAD were linear over most of the range of G/R. However, NDVI was more sensitive at low values than G/R. GIR was more sensitive above GIR values of 1.2 than SPAD because the upper limits of SPAD measurements were constrained by the amount of chlorophyll in the leaf, while GIR responded to both chlorophyll concentration in the leaves as well as the number of leaves present. Color digital imaging appears useful for quantifying the senescence of crop canopies. The cost of color digital cameras is expected to decrease and the quality and convenience of use to improve.

Use of a Networked Digital Camera to Estimate Net CO2Uptake of a Desiccation‐Tolerant Moss

“…Adamsen et al (1999) were some of the earliest users of digital cameras, and they examined senescence in a wheat canopy over 1-m 2 areas by using a ratio of green to red pixel values. Lukina et al (1999) used digital images to estimate the vegetation coverage and biomass of wheat, and Purcel (2000) compared captured images with under-canopy measurements of light for estimating total ground cover of soybean.…”

“…The color index of green : red ratio (Adamsen et al 1999) chosen for this study provided the best signal of color change in the field compared to several other methods investigated. Total reflectivity was not considered a good index because dead samples also increased in reflectivity upon hydration.…”

Estimating Paddy Rice Leaf Area Index with Fixed Point Continuous Observation of Near Infrared Reflectance Using a Calibrated Digital Camera

“…Recently, the feasibility of using single-lens refl ex digital cameras for mapping was reported (Kunii and Murai, 2008). In fact, several authors have shown favorable results using color video or still digital cameras, or multiband cameras equipped with a near infrared band-pass fi lter for assessing crop coverage or leaf greenness (e.g., Kawashima and Nakatani, 1998;Adamsen et al, 1999;Purcell, 2000;Zhou and Robson, 2001;Matsuda et al, 2003;Jia et al, 2004;Ku et al, 2004;Casadesus et al, 2007;Omine, 2007;Takemine et al, 2007;Crimmins and Crimmins, 2008;Okada and Ikeba, 2008;Takada et al, 2009;Sakamoto et al, 2010).…”

Iron formulation affects in vitro storage of hops: An image analysis

“…Color analysis is used to study plant cells or biological products in such widely varied plant systems as wheat senescence (Adamsen et al, 1999) and fruit grading to determine picking time for apples (Schrevens and Raeymaeckers, 1992).…”