Determination of critical nitrogen curve in cauliflower (Brassica oleracea var. Botrytis) with the NBI index of multiplex®

The concentration of nitrogen in plants is usually determined through chemical analysis, although there are alternatives such as the measurement of chlorophyll as an indirect estimate of the nitrogen content. Currently, the reflectance, transmittance and fluorescence methods in specific regions of the spectrum are used to diagnose the nutritional status of plants in nitrogen. The objective has been to evaluate the use of sensors based on the principles of fluorescence and transmittance in the same test plots. The tests were carried out at the Valdegon Farm, at the Agro-food Technological Research and Development Center of the Government of La Rioja, at Agoncillo (La Rioja), Spain, in the years 2012, 2013 and 2014. Periodic sampling of nitrogen in soil, plant biomass and sheet measurements with Multiplex (R) were carried out. For the NBI index of the Multiplex high correlations have been found with the nitrogen content of the plant, which has served, depending on the phenological state of the crop, to adjust some functions that relate the measurements made with the biomass of the crop in the case of the NBI index. In the critical curves obtained for the sensors, it is observed that from a biomass of approximately 1 Mg/ha (50% of covered ground) the measurement stabilizes and it is from this moment when deficit treatments start to be distinguished from the non-deficit ones. Therefore, these models could be used to determine a nitrogen-based nutritional deficit and be able to correct it by fertilization.