Role of soil minerals on organic phosphorus availability and phosphorus uptake by plants

Abstract

Organic phosphorus (OP) represents a significant fraction of the total P pool in soils. With the increasing use of organic resources to substitute mineral P fertilizers and the need to recover P from the soil, it is pivotal to gain insight into the interactions between various OP forms and soil minerals and their consequences on P availability. Here, we aim at elucidating the extent to which OP compounds adsorbed onto major soil minerals may be available to plants. Ryegrass (Lolium multiflorum) plants were grown in RHIZOtest devices in the presence of OP including myo-inositol hexakisphosphate (IHP), glycerophosphate (GLY), and glucose-6-phosphate (G6P) and inorganic P (IP) compounds that were previously adsorbed onto Fe and Al oxyhydroxides (goethite and gibbsite, respectively) and clay minerals (montmorillonite and kaolinite). Phosphorus availability and P uptake were then determined through rhizosphere and plant characterization. Irrespective of the type of mineral, ryegrass was able to take up about 3–18 % of adsorbed OP compounds. The magnitude of availability and uptake depended on the OP compounds and the type of soil minerals. The potential availability of OP adsorbed by different minerals was strongly mediated by mineral-OP interaction types and properties. The P uptake increased in the following order: kaolinite-OP ≪ gibbsite-OP ≤ goethite OP ≪ montmorillonite-OP. Phosphorus uptake from adsorbed OP compounds showed contrasting patterns compared to adsorbed IP and depended more on available P concentration in the rhizosphere rather than on the binding strength of OPs to the mineral surface.