GROWTH-RESPONSE, NUTRIENT LEACHING, AND MASS-BALANCE FOR POTTED POINSETTIA .1. NITROGEN

Single-pinched poinsettias (Euphorbia pulcherrina 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 conc entrations 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 g rowth measurements and N leaching. Shoot dry masses and leaf and bract areas of plants fertigated with 60% NO3-N mere 11% to 26% greater tha n 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 f ertigation was 1.7 g at the 0 LF and 3.3 g at the 0.4 LF. Leachate N c oncentration ranged from 170 to 850 mg.L-1. Nitrogen recovery was 74% to 91%, and the percentage of fertigation N recovered in leachate rang ed 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 s hoots, and 68% to 75% mas found in the leachate. Even with a 0.2 LF, > 50% of the N recovered mas found in the leachate. Premium marketable q uality 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 th e environment, good marketable quality poinsettias could be grown at a LF of less than or equal to 0.2 with 210 mg.L-1 N fertigation if qual ity irrigation mater is available and if a small reduction in growth i s acceptable.