Effect of a biofertiliser on the growth of poinsettia

The experiment was aimed to evaluate the effect of a biofertiliser containing the purple nonsulfur anoxygenic phototrophic bacterium Rhodobacter capsulatus (Ores, PSBIO System, Italy) on the growth of two poinsettia cultivars, ‘Peterstar’ and ‘Maren’, in comparison with the usual nitrogen fertigation. The plants were grown in a PMMA covered greenhouse, in 18 cm diameter pots filled with a peat based commercial substrate. Five treatments were compared: 1) the untreated control; 2) 120 mg N as NH4NO3 per pot applied fortnightly from the pinching until the middle of November (in total 1320 mg N/pot); 3)-4)-5) biofertiliser Ores applied four times, the doses being 20 ml per pot of solution containing 0.75, 1.5 and 3 ml of the commercial product per litre of water, respectively. Before potting, the rootballs of the plants were immersed in the biofertiliser, then the biofertiliser was injected three more times at monthly intervals into different zones of the substrate. The experimental design was a split-plot, the cultivars being in plots and the treatments in sub-plots; there were three blocks and 8 replicates, with 240 plants total. Two weeks after potting, all the plants were pinched to eight nodes, and then fertilised every twenty days with a solution containing (mM) 1.5 P, 8 K, 3.5 Ca, 1.7 Mg, 9.5 Na, 8.0 Cl, 2.7 S, 0.04 Fe and micronutrients. Plant growth was controlled by the “cool morning” technique. Cv. Maren was a little affected by treatments; nevertheless, Ores at the highest dose reduced plant diameter and size of bract crowns. On the contrary, ‘Peterstar’ was favoured by Ores at 0.75 ml L-1 and, subordinately, 1.5 ml L-1, that enhanced many growth parameters compared with the control, and in some case also in comparison with the usual nitrogen fertigation.