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 ۸۰: ۲۰ (V: V %) peat+ mineral component (generally is called as clay) and treated with different P levels of ۰, ۱۰, ۳۵, ۱۰۰, and ۱۷۰ mg P [L substrate]-۱. 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 (۳۰-۵۰ 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 ۳۵ mg L-۱ substrate, with Cs of ۱۱-۱۲ and ۱۵-۱۶ mg [L substrate]-۱ at planting and ۵۳ 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.