Growth response, nutrient leaching, and mass balance for potted poinsettia .2. phosphorus

Poinsettias (Euphorbia pulcherrima Willd. ex Klotzsch 'V-14 Glory') grown as single-pinched plants and received constant fertigation of Hoagland solution with N at 210 mg.L-1 of 100% NO3-N or 60% NO3-N : 40% NH4-N; P at 7.8 and 23 mg.L-1; and leaching fractions (LPs) of 0, 0.2, or 0.4, The P at 23 mg.L-1 used in this study was about half the P concentration typically provided from a 20N-4.4P-16.6K fertilizer at 200 mg.L-1 N fertigation, The total P applied via fertigation ranged from 51 mg at the 0 LF to 360 mg at the 0.4 LF, The leachate P concentration ranged from 0.2 to 46 mg.L-1, With P at 7.8 mg L-1, the percentage of total P recovered in the leachate was 6% to 7%, At 23 mg.L-1 P fertigation, however, the total P recovered in the leachate with 60% NO3-N treatment was 2-times greater than with 100% NO3-N treatment, This result is attributed to a lower substrate pH, which resulted from NH4-N uptake and nitrification processes with 60% NO3-N fertigation, The P concentration in the recently matured leaves with 7.8 mg L-1 P fertigation was in the normal range of 0.3% to 0.6%, Fertigation P can be reduced by up to 80% and still be sufficient for producing quality poinsettias. Reducing the fertigation P concentration is beneficial because it reduces P leaching, reduces fertilizer costs, and reduces luxury consumption.