Relationship between spectral response and manganese concentrations for assessment of the nutrient status in rose crop

The present research was conducted on a Freedom rose (Rosa sp.) variety grown in greenhouses in the municipality of Tocancipá, Cundinamarca department (Colombia), to assess the relationship between reflectance and manganese content in leaves. A randomized complete block design was implemented, including five treatments with different manganese doses (0%, 25%, 50%, 75%, and 100% of the commercial dose, which is 2 mg L-1), each with five replicates. Samplings at five phenological stages were carried out, with 10 plants analyzed per treatment for each sampling, totaling 50 plants per sampling. Spectral responses were taken from the adaxial surface of the leaves using a FieldSpec® 4 spectroradiometer, covering a wavelength from 350 to 2500 nm. As the concentration of manganese in the leaves decreased, the reflectance values increased, showing an inverse relationship between these two parameters. The increase in reflectance values was particularly pronounced in the spectral regions between 560 nm and 840 nm. Among the vegetation indices evaluated, GNDVI, DATT4, DATT2, and D1 stood out; DATT4 and GNDVI showed the most promising results. DATT4 exhibited correlations greater than 0.6 during the “palmiche” (induction of the floral primordium) and “rice” (flower bud less than 4 mm in diameter) phenological stages, while GNDVI presented correlations of 0.64 in the “chickpea” (peduncle with an average length of 4 cm) phenological stage and 0.52 in the “scratch color” (the color of the petals could be observed) phenological stages.