Epsilon Archive for Student Projects

Abstract

Phosphorus (P) is an essential macronutrient for plants. For example, it is required for the transfer of energy, in the photosynthesis and as a component of the phospholipids in the cell membrane. Phosphorus can exist in several different forms, depending on the soil's pH-value. The plant can only absorb the primary (H₂PO₄⁻) and the secondary (HPO₄²⁻) forms, named orthophosphate (OP). Polyphosphate (PP) is a general term for several linked water soluble P molecules. The molecules are linked to each other by oxygen atoms, which determine the molecule's chemical properties and stability. PP are described as good sources of P fertilizers because of their water solubility and high concentration of P, which are said to increase the plant growth capacity by generating a better root system and growth. A more vigorous root system will generate a faster, stronger growth and earlier flower development. Condensed PP are also of interest as a micronutrient carrier.
The main question in this study is: can PP contribute to a better growth of plants than OP as a P-source? This paper provides a literature review and results from a greenhouse experiment with the aim to examine PP effect on growth and nutrient uptake. The Greenhouse experiment consisted of irrigation with a solution composed of 66 % PP and 34% as OP. The control was a solution containing 100 % OP applied as monokaliumphosphate KH₂PO₄. Model plants used were Pelargonium x hortorum 'Mårbacka' and Petunia x hybrida 'Origami Watermelon'. The trial continued for six weeks in controlled climate conditions desirable for optimum growth. Factors that were measured during growth and harvest were plant height, branching, leaf and flower development, and root development. Also, nutrient uptake was studied by leaf sample analysis. The results showed no significant difference between PP and control either on growth or on nutrient uptake.
The literature aimed to treat and compile the existing information that is published on PP impact of growth and the underlying mechanism behind. PP efficiency is relatively unexplored. There is literature that demonstrates both a better P utilization with PP compared with OP but also studies showing no increased effectiveness in compare to OP. The effectiveness of PP as P source depends on the soil's chemical reactions and environmental factors such as time, substrate, pH, and temperature and the plant's growth stage.