Indice SPAD en el crecimiento y desarrollo de plantas de lisianthus en función de diferentes dosis de nitrógeno en ambiente protegido

Abstract

The cultivation of lisianthus in Brazil is little studied in relation to the ideal growing conditions, especially with regarding the nutritional status of plants. The diagnosis of nutritional status in relation to plant nitrogen can be done through analysis of its contents in the leaf. The aim was to evaluate the growth and development of plants of lisianthus in pots under different nitrogen levels in a protected environment, and then establish a critical value of the chlorophyll content or SPAD on the leaves of the need for monitoring of nitrogen. The design was completely randomized with six treatments and a split plot, consisting of six levels of nitrogen as ammonium nitrate (50, 100, 150, 200, 250 and 300 mg/pot). The SPAD was obtained by the leaves of lisianthus by a chlorophyll meter SPAD-502 to identify the exact moment that there is a need for nitrogen. The increasing quadratic polynomial model represented the physiological development of plant lisianthus in relation to increasing the dosis of nitrogen with trend of positive correlation. The quadratic polynomial model represented the descending SPAD that decreased throughout the growth and development of the culture of lisianthus, and also in relation to the increasing availability of photosynthetically active radiation (PAR). The greater availability of PAR radiation only increases the SPAD index with increasing dosis of nitrogen. The period of greatest need for nitrogen was established at the SPAD, which covers the period between 63 and 105 DDPi, ranging from 52.14 to 52.78 SPADs for the cultivation of lisianthus, associated with a higher dosis of nitrogen used (300mg) and range from 233 to 261 W m–2 of PAR radiation, responsible for the greatest number of flower buds of lisianthus.