RESPONSE OF ECKESPOINT LILO POINSETTIA TO NITRITE, SUBSTRATE PH AND ETRIDIAZOLE IN A SUBIRRIGATION SYSTEM

Poinsettias (Euphorbia pulcherrima Willd. 'Eckespoint Lilo') were grown in pH-adjusted (4.5, 5.5 or 6.5) sphagnum peat substrates and subirrigated using a complete nutrient solution with three concentrations of nitrite (0, 1.75 and 3.5 mol m(-1)). The substrate also was either treated with a nitrification inhibitor (etridiazole) or remained untreated. There was a linear decrease in leaf and bract areas,rop dry weight, plant height and root growth with increasing nitrite concentration. This response occurred at a rate of 10% mol(-1) NO2- m(-3) at a substrate pH of 4.5 or 5.5 and 6% mol(-1) NO2- m(-3) at a substrate pH of 6.5. Leaf and bract areas and top dry weight were greater at pH 4.5 than at pH 6.5. Etridiazole did not affect the response of plant growth to nitrite and (or) substrate pH.