ELEMENTAL BIOAVAILABILITY IN NUTRIENT SOLUTIONS IN RELATION TO PRECIPITATION REACTIONS

In hydroponic plant nutritional research, nutrient solutions can be co nsidered as aqueous solutions of inorganic ions. In this aqueous solut ion, the ions are submitted to the laws of aquatic inorganic chemistry . This means that the ions are involved in the dynamic equilibria betw een complexation, dissociation, and precipitation reactions. These che mical reactions seriously impact elemental speciation and bioavailabil ity. As a result, plant roots experience a different nutritional compo sition. Ions withdrawn from the nutrient solution due to precipitation reactions, change the nutritional composition and are not available f or uptake by plant roots. Like complexes, precipitates can buffer a nu trient solution, exchanging nutrients as these decrease by plant uptak e. 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+), nitrat e (NO3-), ammonium (NH4+), or sulphate (SO42-), while calcium (Ca2+) a nd magnesium (Mg2+) form mainly at a higher pH precipitates with hydro gen phosphate (HPO42-). Preparing nutrient solutions with tap water, c alcium carbonate (CaCO3) is likely to precipitate. A good knowledge of the chemical reactions occurring in nutrient solutions is the first p rerequisite in hydroponic plant nutritional research.