Preprints
https://doi.org/10.5194/egusphere-2024-1791
https://doi.org/10.5194/egusphere-2024-1791
18 Jul 2024
 | 18 Jul 2024
Status: this preprint is open for discussion.

Isotopic exchangeability reveals that soil phosphate is mobilised by carboxylate anions whereas acidification had the reverse effect

Siobhan Staunton and Chiara Pistocchi

Abstract. Mineral P is an increasingly scarce resource and therefore the mobilisation of legacy soil P must be optimised to maintain soil fertility. We have used isotopic exchangeability to probe the lability of native soil P in four contrasting soils following acidification and the addition of carboxylate anions (citrate and oxalate) in soil suspension. Acidification tended to cause immobilisation of soil P, but this was attributed to a salt effect. Addition of both citrate and oxalate led to marked increases in mobilisation of soil P. This would result from both competition between carboxylate and phosphate ions at adsorption sites and chelation of charge compensating cations. The carboxylate effects were similar at each level of acidification, indicating that effects were largely additive. This is not true for the most calcareous soil where calcium oxalate may have been precipitated at the highest oxalate addition. Promoting carboxylate anions in soil by soil amendment or the use of crops that exude large amounts of such organic anions is a promising approach to improve soil P availability.

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Siobhan Staunton and Chiara Pistocchi

Status: open (until 19 Dec 2024)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-1791', Anonymous Referee #1, 09 Aug 2024 reply
    • AC1: 'Reply on RC1', Siobhan Staunton, 30 Sep 2024 reply
  • RC2: 'Comment on egusphere-2024-1791', Anonymous Referee #2, 01 Dec 2024 reply
Siobhan Staunton and Chiara Pistocchi
Siobhan Staunton and Chiara Pistocchi

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Short summary
Mineral phosphate is a finite resource and so ways must be found to optimize the use of native soil P. We have used isotopic dilution to assess how acidification and the addition of citrate or oxalate modify the lability of soil P in four contrasting soils from the Mediterranean region. Acidification did not mobilise soil P, whereas both carboxylate anions promoted soil P lability. This suggests that soil amendments and the choice of crops that exude carboxylates could optimize P nutrition.