Soil microorganisms increase Olsen phosphorus from poorly soluble organic phosphate: A soil incubation study

Abstract

The potential shortage of mineral phosphorus (P) sources and the shift towards a circular economy motivates the introduction of new forms of P fertilizers in agriculture. However, the solubility of P in new fertilizers as well as their availability to plants may be low. In this experiment, we incubated an agricultural soil poor in P (28 mg P2O5 kg−1) for 63 days in the presence of a range of organic and inorganic poorly soluble P forms commonly found in new fertilizers: hydroxyapatite (P-Ca), iron phosphate (P-Fe), phytic acid (P-Org) and a combination of P-Ca and P-Org (P-Mix). Cellulose and potassium nitrate (KNO3) were added to stimulate microbial activity at the beginning of the incubation. We included a positive control with triple superphosphate (TSP) and negative controls with no P application (with and without cellulose and KNO3). We assessed the fate of the different poorly soluble P forms in NaHCO3 extracts (Olsen P) over time as a proxy for plant-available P. Soil microbial biomass, fungal to bacterial ratio, soil respiration, enzymatic activities (β-glucosidase, arylamidase and acid and alkaline phosphatase), N mineralization and soil pH were also monitored. At the beginning of the incubation, TSP showed the highest Olsen P across all treatments and P-Fe showed higher levels of Olsen P than the other poorly soluble P forms (p