PERFORMANCE OF A SLOW-RELEASE FERTILIZER BASED ON ORGANOBENTONITE-PHOSPHATE ON LETTUCE PLANTS

Abstract

In the search for greater efficiency of fertilizers, the viability of natural materials for slow release of nutrients has been investigated. This study had the purpose of evaluating the effect of an organobentonite-phosphate (OBP) fertilizer prepared by phosphate adsorption on an organbentonite (OB) on the growth of lettuce plants (Lactuca sativa L.). Eight treatments were evaluated in a floating root hydroponic system with different proportions of P provided by OBP (%) in Steiner solutions with or without reduced P (%): 1) 0/100, 2) 25/75, 3) 50/50, 4) 75/25, 5) 25/0, 6) 50/0, 7) 75/0 and 8) 100/0. The experimental design was completely randomized with six replications; the experimental unit was an individual plant. In addition, an experiment without plants was carried out in laboratory to evaluate the release of P from OBP. The release of P increased with a higher content of OBP; the P released at 35 days was higher in treatment 100/0 (7.27 mg L^-1) and lower in the 25/75 (3.27 mg L^-1) and 25/0 (2.18 mg L^-1) treatments. The consumption of P by the plants was higher in the treatments with more soluble fertilizer because the OBP released P slowly. Organobentonite can adsorb P and then release it gradually, indicating its potential use as a slow-release fertilizer.