2021 Volume 90 Issue 2 Pages 211-221
To monitor the effect of additional fertilizer application, we measured leaf area expansion in farmer’s paddy fields using multispectral images (MS images) collected using unmanned aerial vehicles (UAV). Leaf area index (LAI) growth rate (LGR), which is defined as the slope of linear regression for time-series LAI, was used for evaluation. The image analysis, which considered fluctuations of solar radiation conditions, was applied to obtain LAI from images, and compared with LAI measured by LAI-2200. Three levels of ammonium sulfate (0, 10, 15 g m-2) were set as additional fertilizer treatments in 4 transplanted fields (2 Hitomebore, 2 Manamusume and 1 Datemasayume) and 4 direct seeded fields(Hitomebore)of a juridical agricultural union in Sendai (total 72 test plots, the area of which was 3 x 3 m). The additional fertilizer increased the number of panicles. However, there were no significant effects on the yield components. Both LAI-2200-based and MS-image-based LGRs at the center of the plot revealed significant effects only for the transplanted Hitomebore. However, significant effects were detected in both transplanted and direct seeded test plots in LGRs between the center and outside area (2 m from center) based on MS images. These results imply that the MS image by UAV can be used to monitor the effects of the fertilizer applied. The method will be useful to determine the optimal amount of fertilizer for each field by optimizing LAI growth.
