Elemental bioavailability in nutrient solutions in relation to precipitation reactions

Abstract

In hydroponic plant nutritional research, nutrient solutions can be considered as aqueous solutions of inorganic ions. In this aqueous solution, the ions are submitted to the laws of aquatic inorganic chemistry. This means that the ions are involved in the dynamic equilibria between complexation, dissociation, and precipitation reactions. These chemical reactions seriously impact elemental speciation and bioavailability. As a result, plant roots experience a different nutritional composition. Ions withdrawn from the‐nutrient solution due to precipitation reactions, change the nutritional composition and are not available for uptake by plant roots. Like complexes, precipitates can buffer a nutrient solution, exchanging nutrients as these decrease by plant uptake. This research looks into the precipitation reactions that occur in hydroponic nutrient solutions. In the concentration range of nutrient solutions, no precipitates are formed involving potassium (K⁺), nitrate (NO₃ ^‐), ammonium (NH₄ ⁺), or sulphate (SO₄ ^2‐), while calcium (Ca²⁺) and magnesium (Mg²⁺) form mainly at a higher pH precipitates with hydrogen phosphate (HPO₄ ^2‐). Preparing nutrient solutions with tap water, calcium carbonate (CaCO₃) is likely to precipitate. A good knowledge of the chemical reactions occurring in nutrient solutions is the first prerequisite in hydroponic plant nutritional research.