Growth Response, Nutrient Leaching, and Mass Balance for Potted Poinsettia. I. Nitrogen

Abstract

Single-pinched poinsettias (Euphorbia pulcherrima Willd. ex Klotzsch `V-14 Glory') received 210 mg·L-1 constant N fertigation from Hoagland solution with N sources of 100% NO3-N or 60% NO3-N : 40% NH4-N, P concentrations of 7.8 or 23 mg·L-1, and leaching fractions (LFs) of 0, 0.2, or 0.4. The P fertigation rates did not significantly affect plant growth measurements and N leaching. Shoot dry masses and leaf and bract areas of plants fertigated with 60% NO3-N were 11% to 26% greater than those fertigated with 100% NO3-N. Shoot dry mass at the 0 LF was 27% smaller than those at the 0.4 LF. The total amount of N applied via fertigation was 1.7 g at the 0 LF and 3.3 g at the 0.4 LF. Leachate N concentration ranged from 170 to 850 mg·L-1. Nitrogen recovery was 74% to 91%, and the percentage of fertigation N recovered in leachate ranged from 51% at the 0.2 LF to 74% at the 0.4 LF. With a 0.4 LF and 210 mg·L-1 N fertigation, 15% to 22% of the recovered N was found in the shoots, and 68% to 75% was found in the leachate. Even with a 0.2 LF, >50% of the N recovered was found in the leachate. Premium marketable quality poinsettia were produced with N at 210 mg·L-1 from 60% NO3-N : 40% NH4-N fertigation solution at the 0.4 LF. To reduce N leaching to the environment, good marketable quality poinsettias could be grown at a LF of ≤0.2 with 210 mg·L-1 N fertigation if quality irrigation water is available and if a small reduction in growth is acceptable.