Preprints
https://doi.org/10.5194/soil-2020-81
https://doi.org/10.5194/soil-2020-81

  13 Jan 2021

13 Jan 2021

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

Zinc lability and solubility in soils of Ethiopia – an isotopic dilution study

Abdul W. Mossa1, Dawd Gashu2, Martin R. Broadley1, Sarah J. Dunham3, Steve P. McGrath3, Elizabeth H. Bailey1, and Scott D. Young1 Abdul W. Mossa et al.
  • 1School of Biosciences, University of Nottingham, Sutton Bonington Campus, Nottinghamshire LE12 5RD, UK
  • 2Centre for Food Science and Nutrition, Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia
  • 3Sustainable Agriculture Sciences Department, Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ, UK

Abstract. Zinc (Zn) deficiency is a widespread nutritional problem in human populations, especially in sub-Saharan Africa (SSA). The Zn concentration of crops consumed depends in part on the Zn status of soil. Improved understanding of factors controlling the phyto-availability of Zn in soils can contribute to potential agronomic interventions to tackle Zn deficiency, although there are major knowledge gaps for many soil types in SSA.

Soil samples (n = 475) were collected from a large part of the Amhara Region of Ethiopia where there is widespread Zn deficiency. Zinc status was quantified by measuring several fractions: pseudo-total (Aqua-Regia digestion; ZnTot), available (DTPA-extractable; ZnDTPA), soluble (dissolved in 0.01 M Ca(NO3); ZnSoln) and isotopically exchangeable Zn using the enriched stable Zn isotope 70Zn (ZnE). Soil geochemical properties were assessed for their influence on Zn lability and solubility.

ZnTot ranged from 14.1 to 291 mg kg−1 (median = 100 mg kg−1) whereas ZnDTPA in the majority of soil samples was less than 0.5 mg kg−1 indicating widespread phytoavailable Zn deficiency in these soils. The labile fraction of Zn in soil (ZnE as %ZnTot) was low, with median and mean values of 4.7 % and 8.0 % respectively. Labile Zn partitioning between the solid and the solution phases of soil was highly pH-dependent where 94 % of the variation in the partitioning coefficient of 70Zn was explained by soil pH. Similarly, 86 % of the variation in ZnSoln was explained by soil pH.

Zinc distribution between adsorbed ZnE and ZnSoln was pH controlled. Notably, Zn isotopic exchangeability increased with soil pH. This contrasts with literature on contaminated and urban soils and may arise from covarying factors such as contrasting soil clay mineralogy across the pH range of the soils used in the current study. These results could be used to improve agronomic interventions to tackle Zn deficiency in SSA.

Abdul W. Mossa et al.

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Abdul W. Mossa et al.

Abdul W. Mossa et al.

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Short summary
Zinc deficiency is a widespread nutritional problem in human populations, especially in sub-Saharan Africa (SSA). Crop Zn depends in part on soil Zn. Zinc status of soils from the Amahara region, Ethiopia was quantified by measuring pseudo-total, available, soluble and isotopically exchangeable Zn and soil geochemical properties were assessed. Widespread phytoavailable Zn deficiency was observed. The results could be used to improve agronomic interventions to tackle Zn deficiency in SSA.