EGU General Assembly 2020
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the Creative Commons Attribution 4.0 License.

The chemical interaction of biochar with iron and phosphate might explain the effects of biochar in alkaline and calcareous soils

Roberto Baigorri, Óscar Urrutia, Sara San Francisco, and José María García-Mina
Roberto Baigorri et al.
  • University of Navarra, Biological and Agricultural Chemistry, Pamplona, Spain

Due to the low consistency of the results obtained in field, the use of biochar as soil amendment is controversial. Thus, in general in acidic soils results are positive while in alkaline soils they are non-significant or even negative. The results regarding biochar action in acidic soils have been related to a lime-like effect due to its alkaline pH and the high doses normally used. However, the causes of biochar effects in alkaline soils remain unknown. We have used a well characterized biochar as a component of two complex N and PK granulated fertilizers at two different doses (1 and 5%). These fertilizers have been applied to wheat cultivated in pots containing an alkaline and calcareous soil and grown for 60 days. No effect was shown for the N-biochar fertilizer application. However, the PK-biochar fertilizer application caused a decrease in crop yield. Complementary, the absorption isotherms of Iron (Fe), Molybdenum (Mo), Manganese (Mn) and Phosphate (Pi) in biochar were also studied. The results showed that Fe was rapidly adsorbed in biochar, while Pi was only absorbed on the Fe-Biochar complex. Desorption experiments showed that P and Fe were no desorbed from the P-Fe-biochar complex by water or the Olsen reactant, while a partial desorption was observed when HCl 0.1 M was used. This blockage of Fe and P through Fe bridges in biochar could partially explain the negative effects in alkaline soils.

How to cite: Baigorri, R., Urrutia, Ó., San Francisco, S., and García-Mina, J. M.: The chemical interaction of biochar with iron and phosphate might explain the effects of biochar in alkaline and calcareous soils, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5384,, 2020


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displays version 1 – uploaded on 17 Apr 2020
  • CC1: Comment on EGU2020-5384, Tom Sizmur, 05 May 2020

    @Roberto, I found this fascinating. You highlight the Ca in the biochar itself quite a bit in the presentation. Are you suggesting that the Ca in the biochar is responsible for the liming effect? 

    • AC1: Reply to CC1, Roberto Baigorri, 05 May 2020

      Hello Tom,

      Thank you very much for you kindly comment. In our case the biochar appied yes, it was a Ca-biochar and in our oppinion is the responsible of a liming effect. In alkaline soil this limimg effect is irrelevant and biochar has not a positive effect.

      Best regards


  • CC2: Comment on EGU2020-5384, Tom Sizmur, 05 May 2020

    Many thanks Roberto,

    We also see positive effects in acidic soils and negative effects in alkaline soils. We clearly see that biochar has a liming effect, but not previously considered that the liming was due to Ca. We thought that it was just the adsorption of H+ ions on the surface of the biochar (i.e. attraction to aromatic groups).

    • AC2: Reply to CC2, Roberto Baigorri, 05 May 2020

      Yes, I agree with you that the liming effect is a pH-correction effect but our results showed a strong retention of Al and Fe in the adsortion kinetic experimets. This probably implied the carboxylic groups involvment. In any way we can not discard the adsorption of H+, that is the main cation involved in pH regulation in soils.

      Thanks for you comments Tom.

      Best regards