Application of Digital Image for Leaf Area Index Estimation of Soybean

Soybean (Glycine max) is an important crop as it contains high values of nutrition for human and animals. Soybean production is inadequate for domestic consumption. The amount of soybean production needs to be accurately estimated. The estimation can be done through the conversion of Landsat's Satellite image to LAI (leaf area index) related to crop yield. The leaf area of soybean was found to have direct relationship with growth and crop yield. However, this method has sonic disadvantages such as its dependence on the satellite's orbit (sixteen days), the presence of clouds, low resolution (30 m x 30 m) and high cost. Therefore, the reflection imagery was tested using digital camera of 8 million pixels with specific filters to take photo of visible light wavelengths and near-infrared light wavelengths. Eleven plants of soybean variety E50 at the ages of 25, 30, 40, 50, 60 and 75 days were sampled. Then, leaf area was determined with a leaf area meter. The LAI was measured with SUNSCAN probe. Dry weights of leaves, stems, and yield were weighted. Images were taken above the crop canopy at the heights of 1, 2, and 3 in, respectively. The images then converted into BW (black and white) for histogram analysis and, then converted into NDVI (normalized difference vegetation index) to compared with LAI. The result showed highly significant relationship between LAI and TDM (total dry weight) (y = 0.0062x + 1.54, r(2) = 0.80**) at vegetative stage. The LAI from leaf area meter was found to have highly significant relationship with LAI from SUNSCAN probe (y = 1.57x - 0.90, r(2) = 0.96**). The NDVI from the image histogram at near infrared and visible wavelengths were found to have highly significant differences. The height at which images were taken had no significant effect on the NDVI. The study also indicated that positions of the images had influential effects on LAI and the center position of the image showed highly significant relationship with LAI. It was also found that LAI and NDVI were significantly relate to each other at all heights which images were taken above the canopy (y = 7.64x - 1.40, r(2) = 0.67**)