study on phosphorus supply management of poinsettia grown in peat-based substrate

poinsettia as an ornamental pot plant is widely grown in peat-based substrates with high phosphorus (p) fertilization. the aim of current study was to evaluate the p demand of poinsettia according to its depletion ability during the growth stages by using a mechanistic simulation model. for this purpose, rooted poinsettia cuttings were grown in the medium with 80: 20 (v: v %) peat+ mineral component (generally is called as clay) and treated with different p levels of 0, 10, 35, 100, and 170 mg p [l substrate]-1. the yield and quality performance of the plants were evaluated thoroughly. also, depletion of p around the root surface and the effect of buffering power on the depletion profile were assessed by means of mechanistic simulation model. the results showed that in peat-based substrates, p was transported to the root surface mainly by mass-flow. the simulation approach as well revealed that the well supplied plants cultivated in the peat-substrates needed a higher concentration gradient (30-50 µm) to drive the necessary flux and that the amount of plant available p (cs) was limiting at later growth stages. the optimum yield and quality of poinsettia was obtained at the p application rate of 35 mg l-1 substrate, with cs of 11-12 and 15-16 mg [l substrate]-1 at planting and 53 days after planting. it has been concluded that, to ensure a sufficiently high concentration gradient, p had to be supplemented by frequent fertigation at later growth stages but not at the early growing stage.