THE EFFECT OF IRRIGATION METHOD, WATER-SOLUBLE FERTILIZATION, PREPLANT NUTRIENT CHARGE, AND SURFACE EVAPORATION ON EARLY VEGETATIVE AND ROOT-GROWTH OF POINSETTIA

Rooted cuttings of 'Gutbier V-14 Glory' poinsettia (Euphorbia pulcherrima Willd, ex Klotzsch) were grown in 15-cm pots using two irrigation methods, two water-soluble fertilization schedules, and two preplant root-media fertilization rates. No difference in shoot growth occurred with either top watering with 33% leaching or subirrigation. The top 2.5 cm (top layer) contained nutrient concentrations up to 10 times higher than those measured in the remaining root medium (root zone) of the same pot with both irrigation methods. Constant applications of 28 mol N/m(3) water-soluble fertilizer (WSF) limited shoot and root growth as measured at 3 and 8 weeks compared to a weekly increase in the concentration df WSF from 0 to 28 mol N/m(3) in 7 mol N/m(3) increments over a 5-week period. The additional incorporation of 0.27 kg.m(3) mineral N to Metro Mix 510 before planting had no effect on fresh- or dry-weight accumulation. When the root-medium surface was covered by an evaporation barrier, 46% less water and 41% less N fertilizer were applied to plants bf similar size, and higher root-zone nutrient levels were maintained over the 8 weeks of the experiment. The evaporation barrier had the greatest effect on increasing root-zone nutrient concentrations and reducing the growth of subirrigated plants.