The role of low molecular weight organic acids in the release of phosphorus from sewage sludge-based biochar

Abstract

Low molecular weight organic acids (LMWOAs) are common and abundant compounds in the environment, responsible for the release of the nutrients from rhizosphere into the soil solution and, therefore, facilitating the availability of these nutrients for plants. Sewage sludge biochar (SSB) is considered to be a potential source of phosphorus (P) in soil. In this context, the efficacy of twelve LMWOAs in releasing SSB-bearing P was tested in a laboratory extraction experiment. Moreover, the potential effects of (i) biochar pyrolysis temperature (varying from 220°C to 620°C) and (ii) other elements in SS, to estimate the P bonds attacked predominantly by the LMWOAs, were also assessed. The results revealed citric acid was the most effective extraction agent enhancing the mobility of the SSB-derived P. P release was strongly affected by biochar pyrolysis temperature (the highest P release was from the 320°C biochar, significant at p < 0.05). Moreover, the results showed that P was released preferably from Fe-P bearing compounds in SS. Citric acid was recorded as less effective at releasing other nutrients, such as Ca, Mg, K, indicating the exceptional performance of citric acid in P release from biochar without substantial effect on the other nutrients.

KEYWORDS:

• biochar
• organic acids
• phosphorus
• leachability

Acknowledgements

The authors thank NAZV QK1710379 project and European Regional Development Fund – Project No. CZ.02.1.01/0.0/0.0/16_019/0000845 for financial support. Correction and improvement of language was provided by Proof-Reading-Service.com Ltd., Devonshire Business Centre, Works Road, Letchworth Garden City SG6 1GJ, United Kingdom.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data that support the findings of this study are openly available in Mendeley Data: https://doi.org/10.17632/5vf53yy24p.1.

Additional information

Funding

This work was supported by European Regional Development Fund [grant number CZ.02.1.01/0.0/0.0/16_019/0000845]; National agency for agricultural research [grant number QK1710379].