Root-medium Nutrient Concentration and Growth of Poinsettia at Three Fertilizer Concentrations and Four Leaching Fractions

Abstract

`V-14 Glory' poinsettias (Euphorbia pulcherrima Willd. ex Klotzsch) were fertilized at every irrigation with solutions containing 7, 14, or 28 mol N/m 3 at four leaching fractions (LFs) of 0, 0.1 to 0.2, 0.3 to 0.4, or 0.5 to 0.6 or with subirrigation. The N applied ranged from 44 to 464 mmol/pot applied over 12 to 25 irrigations. Medium NO 3 -N and K concentrations and electrical conductivity were highest at the highest fertilizer concentration and lowest LF throughout cropping. Phosphorous concentration in the medium declined until week 12, when phosphoric acid was added for pH adjustment. Subsequently, medium P concentration was highest in treatments with the highest LF. Final shoot height, plant dry mass, and leaf area decreased as fertilizer concentration increased. Highest fresh mass, bract area, and shoot: root ratio were obtained with 14 or 28 mol N/m 3 and a 0.55 LF or with 7 mol N/m 3 and a 0.15 LF. Leaf N concentration was lower with subirrigation than with surface application. Leaf P and Mg were lower at higher LFs or with subirrigation, but leaf K was not influenced by the treatments.