Preliminary evaluation of eggshells as a source of phosphate on hydroponically grown tomato (Solanum lycopersicum L.) seedlings

Phosphorus (Pi) is one of the most limiting factors in plant nutrition as it is the least mobile and available nutrient to plants in most soil conditions. The management of Pi fertilization in agriculture raises ecological, economic, and social issues, since phosphate rock minerals are the only significant global resources of Pi and they will be rapidly depleted. Eggshell waste is a big problem for food companies producing different types of egg products, since the eggshell waste is very often simply discarded and disposed at landfills, with high costs related to their disposal. The aim of this work was the characterization of eggshells as a Pi source for plants, using tomato (Solanum lycopersicum L cv Marmande) as a model species. Plants were grown hydroponically being exposed to adequate and limited Pi availability, with or without eggshell powder. Plant growth performance was characterized by analyzing changes in fresh weight, protein, chlorophyll concentration, carotenoid content, and measuring the plant’s capability to accumulate phosphate. The addition of eggshell powder to the nutrient solution significantly improved plant growth and increased protein and chlorophyll concentration, not only with respect to P-deficient control, but also with P-sufficient ones. Furthermore, eggshell powder significantly increased Pi accumulation in P-deficient plants, suggesting that eggshell waste could be a suitable material as Pi source for tomato plants, thus contributing to the environmentally friendly disposal of this waste.