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 fertilisers: 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 mineralisation 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 < 0.05). During the incubation, the levels of Olsen P decreased over time for TSP (positive control). Contrastingly, Olsen P increased significantly over time for all the poorly soluble P forms and the negative controls, indicating an increase in plant available P. Particularly, levels of Olsen P for the P‐Org treatment roughly doubled (shifting from 16.5 mg kg‐1 to 32.9 mg kg‐1) over the whole incubation period. The rate of increase in Olsen P was positively correlated with microbial biomass C: P ratio (p < 0.01) for all poorly soluble treatments. The higher levels of Olsen P for the P‐Org treatment were also explained by a positive correlation with fungal biomass. Our results show that poorly soluble forms of P may be made available to plants under the influence of the microbial community, with a stronger effect for organic P forms.

Combination of Lolium perenne L. and Festuca arundinacea Schreb. improve yields under low phosphorus availability

“…Measuring soil microbial activities and biomass throughout the growing season might have yielded different results as the activities of soil microorganisms could be time-dependent (Gao et al 2021). Other P related enzymes, such as phytase, could have also dominated the P release from poorly soluble P forms (Rizwanuddin et al 2023) and their effects might have been different depending on the most abundant poorly soluble P species in the soil (Velasco-Sánchez et al 2024). Activities could also have been markedly different at deeper soil layers, where the root biomass was dominated by Fa (Fairbanks et al 2020).…”

Struvite and biodiversity to improve phosphorus use in agricultural fields

“…Measuring soil microbial activities and biomass throughout the growing season might have yielded different results as the activities of soil microorganisms could be time-dependent (Gao et al, 2021). Other P-related enzymes, such as phytase, could have also dominated the P release from poorly soluble P forms (Rizwanuddin et al, 2023) and their effects might have been different depending on the most abundant poorly soluble P species in the soil (Velasco-Sánchez et al, 2024). Activities could also have been markedly different at deeper soil layers, where the root biomass was dominated by Fa (Fairbanks et al, 2020).…”