Elemental bioavailability in nutrient solutions in relation to complexation reactions

Abstract

Nutrient solutions for plant production are aqueous solutions of inorganic ions, prepared by dissolving salts. The nutrients in these solutions are not completely present as free ions. Dissociation, complexation and precipitation reactions seriously impact elemental speciation and bioavailability. As a result plant roots experience a different nutritional composition. This research describes for the six essential macronutrients the complexation reactions occurring in nutrient solutions, using an inorganic chemical approach. A good knowledge of the chemical reactions occurring in nutrient solutions is the first prerequisite in hydroponic plant nutritional research. The formation of the complexes is represented in figures as a function of the free anion concentration. In nutrient solutions a considerable amount of Ca²⁺, Mg²⁺ and SO₄ ^2‐ is present as the soluble complexes CaSO₄ and MgSO₄, reducing their free ion concentration and changing their uptake. The different dissociation forms of carbonate and phosphate, present in nutrient solutions, also form soluble complexes.