Application of digital image for leaf area index estimation of feild corn

Abstract

A production of field corn in Thailand is important to an animal feed industry. It was considerd as an index for an increase in livestock production. The estimation of field corn production could be done by various means. One way is to convert Landsatûs Satellite imagery to LAI in relationship with crop yield. This method shows a correlation between the leave of field corn and a plant growth and yield . However, this type of imaging has some disadvantages : its dependence on the satelliteûs orbit (sixteen days), the presence of clouds, its low resolution (30 m x 30m), and high cost. The reflection imagery was done with a digital camera that took picture in the visible and near- infrared wavelengths. Leaf area index could be done anytime during a growing season without causing destructive effects. The field corn variety Suwan 4452 was used in this study. Plant samples were collected five times, eleven repetitions each, from a vegetative phase to a reproductive phase (35, 45, 55, 65, and 85 days after planting). Leaf area was determined with a leaf area meter. Dry weight of leaves, stems, and yield was determined. Imaging was done with a digital camera with a filter of 780 nm wavelength. The camera imaging resolution was 8.0 mega pixels. The images were captured at the heights of one, two, and three meters, respectively, above the crop canopy. These image were converted to BW for a histogram analysis. Then, the BW images were converted to NDVI for a comparison with LAI. The LAI was measured with Sunscan probe. The result showed a highly significant relationship between LAI and TDM (total dry weight) (y = 208.33x - 212.7, R2 = 0.73**) from the vegetative stage to the panicleinitiation stage. The LAI collected from a leaf area meter was consistent with the LAI from Sunscan probe (y = 1.5193x + 0.3527, R2 = 0.91**). The values obtained from image histogram means at 780 nm were significantly different from that of the visible. And the heights at which the images were taken had no effect on the histogram means. However, the study showed that positions of the images had an effect on the LAI. The center position of the image was correlated with the LAI. This relationship was obtained from the histogram means at near-infrared wavelength and the LAI (y = 6.31x + 0.39, R2 = 0.75**).