Multispectral imaging for leaf area index and dry mass evaluation of 'Tifton 85' bermudagrass under nitrogen fertilization/Imagens multiespectrais para avaliacao de indice de area foliar e massa seca do capim 'Tifton 85', sob adubacao nitrogenada

The purpose of this study was to verify the responses of 'Tifton 85'bermudagrass (Cynodon spp.) to nitrogen fertilization in terms of green leaf area and aerial dry mass, using indices calculated from spectral information contained in multispectral images, in comparison with indicators obtained by direct methods. The bermudagrass was managed under four N treatments (0; 100; 150 and 200 kg [ha.sup.-1]) using a completely randomized experimental design, with four repetitions. Twenty six days after a standardization cut, four canopy traits were determined: leaf area index (LAI), aerial dry mass (ADM), green coverage index (GCI), using a RGB camera and the Normalized Difference Vegetation Index (NDVI), using a multispectral camera. All the traits responded positively to nitrogen fertilization. However, while the GCI showed curvilinear relationships with LAI ([R.sup.2]=0.89) and ADM ([R.sup.2]=0.87), the NDVI showed linear relationships with both ([r.sup.2]LAI=0.62; [r.sup.2] ADM=0.64) without evidences of saturated responses. It was concluded that it is possible to evaluate nitrogen fertilizer on pastures of Cynodon spp., using image analysis. NDVI and ICV can be used as productivity indicators of 'Tifton 85' bermudagrass.