Preprints
https://doi.org/10.5194/bg-2021-53
https://doi.org/10.5194/bg-2021-53

  01 Mar 2021

01 Mar 2021

Review status: this preprint is currently under review for the journal BG.

Effect of organic carbon addition on paddy soil organic carbon decomposition under different irrigation regimes

Heleen Deroo1,2, Masuda Akter3, Samuel Bodé2, Orly Mendoza1, Haichao Li1, Pascal Boeckx2, and Steven Sleutel1 Heleen Deroo et al.
  • 1Department of Environment, Ghent University, Ghent, Belgium
  • 2Isotope Bioscience laboratory, Department of Green Chemistry and Technology, Ghent University, Ghent, Belgium
  • 3Soil Science Division, Bangladesh Rice Research Institute, Gazipur, Bangladesh

Abstract. Anaerobic decomposition of organic carbon (OC) in submerged rice paddies is coupled to the reduction of alternative soil electron acceptors, primarily Fe3+. During reductive dissolution of Fe3+ from pedogenic oxides, previously adsorbed native soil organic carbon (SOC) could be co-released into solution. Incorporation of crop residues could hence indirectly, i.e. through the stimulation of microbially mediated Fe3+ reduction, promote the loss of native SOC via enhanced dissolution and subsequent mineralisation to CO2 and CH4. Our aim was to estimate the relevance of such a positive feedback during the degradation of added OC, and to investigate the impact of irrigation management on this mechanism and on priming effects on native SOC decomposition in general. In a six-week pot experiment with rice plants, two Bangladeshi soils with contrasting SOC-to-reducible-Fe (SOC : Feox) ratios were kept under a regime of alternate wetting and drying (AWD) or continuous flooding (CF), and were either amended with maize shoots or not. The δ13C signatures of dissolved organic C and emitted CH4 and CO2 were used to infer the decomposition of added maize shoots (δ13C = −13.0 ‰) versus native SOC (δ13C = −25.4 ‰ and −22.7 ‰). Addition of maize residues stimulated the reduction of Fe as well as the dissolution of native SOC, and the latter to a larger extent under CF, especially for the soil with the highest SOC : Feox ratio. Estimated Fe-bound SOC contents denote that stimulated SOC co-release during Fe reduction could explain this positive priming effect on SOC dissolution after the addition of maize. However, priming effects on SOC mineralisation to CO2 and CH4 were lower than for SOC dissolution, and were even negative under AWD for one soil. Enhanced reductive dissolution of Fe-bound SOC upon exogenous OC addition therefore does not necessarily lead to stimulated SOC mineralisation. In addition, AWD irrigation was found to decrease abovementioned priming effects.

Heleen Deroo et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-53', Guanghui Yu, 17 Mar 2021
  • RC2: 'Comment on bg-2021-53', Anonymous Referee #2, 21 Mar 2021

Heleen Deroo et al.

Heleen Deroo et al.

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Short summary
We wanted to assess if and how incorporation of exogenous organic carbon (OC) such as straw could affect decomposition of native soil organic carbon (SOC) under different irrigation regimes. Addition of exogenous OC promoted dissolution of native SOC, partly because of increased Fe reduction, leading to more net release of Fe-bound SOC. Yet, there was no proportionate priming of SOC-derived DOC mineralisation. Water-saving irrigation can retard both priming of SOC dissolution and mineralisation.
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