EFFECT OF A NITROGEN FERTILIZER, BASED ON MODIFIED BENTONITE AND SURFACTANT HDTMA IN THE GROWTH OF HYDROPONIC LETTUCE (Lactuca sativa L.).

In order to improve the efficiency of fertilizers, we investigate the feasibility of the use of abundant and inexpensive materials that contribute to the slow release of a fertilizer. The aim of this study was to evaluate the effect of a fertilizer, prepared by nitrate (NO3 -) adsorption, a modified bentonite (OBN) and surfactant hexadecyltrimethylammonium (HDTMA), on the growth of lettuce plants (Lactuca sativa L.) and the concentration of NO3 - under a hydroponic system. The hypothesis was that the application of a fertilizer based on OBN and HDTMA, releases NO3 - in the nutrient solution and has a positive effect on the growth of lettuce. The experimental design was totally random. First experiment: eight treatments with six repetitions (48 experimental units): OBN/fertilizer in a Steiner solution 0/100, 25/75, 50/50, 75/25, 25/0, 50/0, 75/0 and 100/0. Second experiment: 15 treatments with six repetitions (90 experimental units): 15 doses of HDTMA with 0 up to 35 mg L-1 . OBN reduced the dry biomass between 50 and 70 %. The number of leaves decreased from 25 to 50 %, the length and width of leaves fell between 40 and 55 %. The foliar area fell between 68 and 78 %. Water absorption decreased 60 %, the concentration of NO3 - decreased between 35 and 60 % and electric conductivity descended between 15 and 25 % of the concentration applied. The surfactant HDTMA darkened the root and affected the absorption of water and nutrients. Organobentonite can be used as an adsorbent of mineral elements and as a fertilizer, since it released amounts of the NO3 - in the nutrient solution. The type of surfactant can be changed to reduce phytotoxicity and eliminate the negative effects on growth.