Pervasive use of P2O5, K2O, CaO, MgO, and basic cations, none of which exist in soil

The use of abbreviations in a title of a paper is usually discouraged, even N (nitrogen) and P (phosphorus). However, in this case the abbreviations in the title make perfect sense, even if they refer to nonsensical molecules, as we explained in a recent Editorial for Plant and Soil (Lambers and Barrow 2020). Upon reading our article, the Editor in Chief of Biology and Fertility of Soils invited us to slightly modify our text and make it available to readers of that journal. Inevitably, this text, therefore, involves some degree of self-plagiarism.

When Carl Sprengel (Sprengel 1828; as cited in Jungk 2009) and Justus von Liebig (1855) did their ground-breaking work on plant nutrition, little was known about the chemical nature of the nutrients they showed were needed by plants. Justus von Liebig largely based his presentation of the chemicals on the doctrine of Berzelius (1814). As Geoffrey Leeper deplored in a Note on Chemical Terms in his well-known textbook,

Unfortunately, archaic usages have lingered in soil science long past their time. Thus, the double-oxide theory of salts – the doctrine of Berzelius in 1820, that magnesium sulphate is MgO.SO3- persists in two fields. Firstly, many writers still record elements as their oxides; calcium appears not as the simple element, but as CaO (which does not exist in soil) and phosphate appears as P2O5, which is quaintly referred to as ‘phosphoric acid’. The phosphate radicle (PO4), which does exist, should surely be preferred, or alternatively the element (P), which many Americans have already adopted. These can be converted into one another on the basis 1.00 part of P is equivalent to 2.29 P2O5 and to 3.06 P04. (Leeper 1948)

More than 70 years after Leeper published his textbook that became the bible in the discipline, P2O5, K2O, and CaO still do not exist in soil, but the terms continue to be used in the literature. It is understandable why some fertilizer companies, but not those in Australia or New Zealand, like to print P2O5 on their package, as they give the impression they sell far more than is in the bag. It is a mystery, however, why soil science analytical laboratories persist showing their data as was common in the nineteenth century. When one of us (HL) recently shared Geoffrey Leeper’s Note on Chemical Terms with some of his colleagues, a professor in one of the disciplines of agricultural sciences in Germany responded: “Even in exams all this is still existing although I repeatedly argue against it in my lectures. I am going to forward the pdf to my students.” That is not surprising, since even top journals in agronomy persist with these nonsensical terms (Lopes and Guimarães Guilherme 2016; Song et al. 2019). Also, in horticultural journals, authors still get away with P2O5 (Ortas 2019). One would hope that authors who publish in Biology and Fertility of Soils would stick to Leeper’s advice, but, alas, this turns out not to be the case (Samaddar et al. 2019; Van Dommelen et al. 2009; Tawaraya et al. 2012).

One of us (HL) decided to do a search in his own EndNote library, to be astounded by the number of papers and journals he stumbled across when looking for P2O5 in his PDF files, even when looking only at publications after 2000. He got the impression that there is likely no journal in which the nonsensical chemical formulas do not appear, and that the use of terms is pervasive in a wide range of countries and disciplines. Aliyu et al. (2019) in PLoS ONE consider it appropriate to feed cassava P2O5 and K2O, Li et al. (2020) and Wang and Ning (2019) in Frontiers in Plant Science believe P2O5 is suitable to grow rice and maize, respectively, and New Phytologist publishes papers showing trees use P2O5 (Weber et al. 2018; Edwards et al. 2015). Respectable soil science journals and ditto soil scientists, who one assumes would be familiar with their bible (Leeper 1948), have not yet taken his advice on board either (Vos et al. 2019). Ectomycorrhizal fungi supposedly cope with P2O5, K2O, and CaO as well as MgO (Schmalenberger et al. 2015). And if you thought that scientists focussing on transcriptome analysis or molecular biology were ahead of the game, you will be disappointed (Li et al. 2019; Giri et al. 2018). Also, highly prestigious journals happily continue with nonsensical chemical formulas (Li et al. 2007). Leeper (1948) felt than many Americans had already adopted the use of P, but even American soil scientists (Weyers et al. 2016; Ranatunga et al. 2009) and ecologists (McKee et al. 2002; Griffin et al. 2001) continue to use the obsolete terms. HL gave up on his embarrassing search in his EndNote library, feeling sorry for Geoffrey Leeper who did his very best to stop the use of terms that belong to the nineteenth century.

In a reply to one of us (NJB), some agronomists justified their use of P2O5 by pointing out that it was part of their country’s fertilizer regulations and was used by American fertilizer manufacturers. NJB replied: “You are preparing a manuscript that you hope will be read by international scientists. In a science communication you should use the language of science. It is not relevant that your country’s bureaucracy and North American fertiliser manufacturers use outmoded terminology. You should use P not P2O5.”

If some fertilizer companies want to continue their outdated practice of selling phosphorus, calcium, magnesium, and potassium attached to oxygen that is not really in the fertilizer bag (http://ifadata.fertilizer.org/ucSearch.aspx), then that is their business, even though we do not endorse it and would like to see them change their wicked ways. However, in academic writing, the use of P2O5, CaO, K2O, and MgO must really stop. We have moved on since Jöns Jakob Berzelius (1814) and Justus von Liebig (1855). It is high time we acted upon Geoffrey Leeper’s advice (Leeper 1948), and used chemical formulas that belong in the twenty-first century, rather than the 1800s.

Equally, egregious is the use of terms such as “base exchange” and “basic cations.” Although less common these days, these terms still appear in the scientific literature (Nakano et al. 2001; Cai et al. 2015; Zeng et al. 2017). They also appear in manuals of soil analysis (NCR-13 2011) and are very common in the extension literature. Leeper (1948) was at his acerbic best when dealing with them. “The other relic of the double-oxide theory is the term ‘base exchange,’ which is still often used instead of cation exchange. This deplorable term ‘base exchange’ has caused untold confusion. The cations which take part in exchange reactions include calcium, magnesium, ammonium, and hydrogen. Of these, hydrogen is the essence of acidity, and it is the height of absurdity to call it a ‘base.’ Ammonium is a weak acid, by virtue of its tendency to liberate hydrogen ion (NH4+ ⇌ NH3+ H+), so its salt ammonium chloride is acid to methyl red. The ions of the metals calcium and magnesium, though one could hardly call them acids, are most certainly not bases. A base is something which reacts with or removes acid, that is, hydrogen ion; it would be interesting to learn from the champions of the term ‘base exchange’ what interactions Ca++ and H+ have with one another. This fallacy comes from the days when it was the bases CaO and MgO that were exchanged, as compared with the ions Ca++ and Mg++ of to-day.”

The terms “base exchange” and “basic cations” are rationalized by Bache (2008) as follows. “Base saturation… is a partial misnomer because a base is a chemical compound that can react with an acid to form a salt; calcium hydroxide, Ca(OH)2, is an appropriate example. In the present context, however, it is now understood to mean the cation of the base, that is, Ca2+, as distinct from the cations H3O+and [Al(H2O)6]3+, which are acids.” We do not think it appropriate to use terms that are misnomers; it would be better if in this context we also used terms that belong in the twenty-first century: cation exchange, exchangeable cations, and cation saturation.

References

  1. Aliyu IA, Yusuf AA, Uyovbisere EO, Masso C, Sanders IR (2019) Effect of co-application of phosphorus fertilizer and in vitro-produced mycorrhizal fungal inoculants on yield and leaf nutrient concentration of cassava. PLoS One 14:6. https://doi.org/10.1371/journal.pone.0218969

    CAS  Article  Google Scholar 

  2. Bache B (2008) Base saturation. In: Chesworth W (ed) Encyclopedia of soil science. Encyclopedia of Earth Sciences Series. Springer, Dordrecht, pp 52–54

    Google Scholar 

  3. Berzelius JJ (1814) An attempt to establish a pure scientific system of mineralogy: by the application of the electro-chemical theory and the chemical proportions. R. Baldwin, Edinburgh

    Google Scholar 

  4. Cai Z, Wang B, Xu M, Zhang H, He X, Zhang L, Gao S (2015) Intensified soil acidification from chemical N fertilization and prevention by manure in an 18-year field experiment in the red soil of southern China. J Soils Sediments 15:260–270. https://doi.org/10.1007/s11368-014-0989-y

    CAS  Article  Google Scholar 

  5. Edwards PJ, Fleischer-Dogley F, Kaiser-Bunbury CN (2015) The nutrient economy of Lodoicea maldivica, a monodominant palm producing the world’s largest seed. New Phytol 206:990–999. https://doi.org/10.1111/nph.13272

    CAS  Article  PubMed  Google Scholar 

  6. Giri J, Bhosale R, Huang G, Pandey BK, Parker H, Zappala S, Yang J, Dievart A, Bureau C, Ljung K, Price A, Rose T, Larrieu A, Mairhofer S, Sturrock CJ, White P, Dupuy L, Hawkesford M, Perin C, Liang W, Peret B, Hodgman CT, Lynch J, Wissuwa M, Zhang D, Pridmore T, Mooney SJ, Guiderdoni E, Swarup R, Bennett MJ (2018) Rice auxin influx carrier OsAUX1 facilitates root hair elongation in response to low external phosphate. Nat Commun 9:1408. https://doi.org/10.1038/s41467-018-03850-4

    CAS  Article  PubMed  PubMed Central  Google Scholar 

  7. Griffin KL, Anderson OR, Gastrich MD, Lewis JD, Lin G, Schuster W, Seemann JR, Tissue DT, Turnbull MH, Whitehead D (2001) Plant growth in elevated CO2 alters mitochondrial number and chloroplast fine structure. Proc Natl Acad Sci U S A 98:2473–2478. https://doi.org/10.1073/pnas.041620898

    CAS  Article  PubMed  PubMed Central  Google Scholar 

  8. Jungk A (2009) Carl Sprengel—the founder of agricultural chemistry: a re-appraisal commemorating the 150th anniversary of his death. J Plant Nutr Soil Sci 172:633–636. https://doi.org/10.1002/jpln.200900065

    CAS  Article  Google Scholar 

  9. Lambers H, Barrow NJ (2020) P2O5, K2O, CaO, MgO, and basic cations: pervasive use of references to molecules that do not exist in soil. Plant Soil. https://doi.org/10.1007/s11104-020-04593-2

  10. Leeper GW (1948) Introduction to soil science. Melbourne University Press, Parkville

    Google Scholar 

  11. Li L, Li S-M, Sun J-H, Zhou L-L, Bao X-G, Zhang H-G, Zhang F-S (2007) Diversity enhances agricultural productivity via rhizosphere phosphorus facilitation on phosphorus-deficient soils. Proc Natl Acad Sci U S A 104:11192–11196

    CAS  Article  Google Scholar 

  12. Li Q, Ding G, Yang N, White PJ, Ye X, Cai H, Lu J, Shi L, Xu F (2019) Comparative genome and transcriptome analysis unravels key factors of nitrogen use efficiency in Brassica napus L. Plant Cell Environ 43:712–731. https://doi.org/10.1111/pce.13689

    CAS  Article  PubMed  Google Scholar 

  13. Li Z, Guo F, Cornelis J-T, Song Z, Wang X, Delvaux B (2020) Combined silicon-phosphorus fertilization affects the biomass and phytolith stock of rice plants. Front Plant Sci 11:67. https://doi.org/10.3389/fpls.2020.00067

    Article  PubMed  PubMed Central  Google Scholar 

  14. Lopes AS, Guimarães Guilherme LR (2016) A career perspective on soil management in the cerrado region of Brazil. Adv Agron 137:1–72. https://doi.org/10.1016/bs.agron.2015.12.004

    Article  Google Scholar 

  15. McKee KL, Feller IC, Popp M, Wanek W (2002) Mangrove isotopic (δ15N and δ13C) fractionation across a nitrogen vs. phosphorus limitation gradient. Ecology 83:1065–1075. https://doi.org/10.1890/0012-9658(2002)083[1065:Minacf]2.0.Co;2

    Article  Google Scholar 

  16. Nakano T, Yokoo Y, Yamanaka M (2001) Strontium isotope constraint on the provenance of basic cations in soil water and stream water in the Kawakami volcanic watershed, central Japan. Hydrol Process 15:1859–1875. https://doi.org/10.1002/hyp.244

    Article  Google Scholar 

  17. NCR-13 (2011) Chapter 7 Potassium and other basic cations. In: Brown JR (ed) Recommended chemical soil test procedures for the North Central Region, No 221 (Revised). Missouri Agricultural Experiment Station SB 1001, Columbia, MO, pp 31–33

  18. Ortas I (2019) Comparison of indigenous and selected mycorrhiza in terms of growth increases and mycorrhizal dependency of sour orange under phosphorus and zinc deficient soils. Eur J Hortic Sci 84:218–225. https://doi.org/10.17660/eJHS.2019/84.4.4

    Article  Google Scholar 

  19. Ranatunga TD, Taylor RW, Bhat KN, Reddy SS, Senwo ZN, Jackson B (2009) Inorganic phosphorus forms in Soufriere Hills volcanic ash and volcanic ash-derived soil. Soil Sci 174:430–438. https://doi.org/10.1097/SS.0b013e3181b6deab

    CAS  Article  Google Scholar 

  20. Samaddar S, Truu J, Chatterjee P, Truu M, Kim K, Kim S, Seshadri S, Sa T (2019) Long-term silicate fertilization increases the abundance of actinobacterial population in paddy soils. Biol Fertil Soils 55:109–120. https://doi.org/10.1007/s00374-018-01335-6

    CAS  Article  Google Scholar 

  21. Schmalenberger A, Duran AL, Bray AW, Bridge J, Bonneville S, Benning LG, Romero-Gonzalez ME, Leake JR, Banwart SA (2015) Oxalate secretion by ectomycorrhizal Paxillus involutus is mineral-specific and controls calcium weathering from minerals. Sci Rep 5. https://doi.org/10.1038/srep12187

  22. Song Z, Feng X, Lal R, Fan M, Ren J, Qi H et al (2019) Optimized agronomic management as a double-win option for higher maize productivity and less global warming intensity: a case study of northeastern China. Adv Agron 157:251–292. https://doi.org/10.1016/bs.agron.2019.04.002

    Article  Google Scholar 

  23. Sprengel C (1828) Von den Substanzen der Ackerkrume und des Untergrundes (about the substances in the plow layer and the subsoil). Journal für Technische and Ökonomische Chemie 2:397–421

    Google Scholar 

  24. Tawaraya K, Hirose R, Wagatsuma T (2012) Inoculation of arbuscular mycorrhizal fungi can substantially reduce phosphate fertilizer application to Allium fistulosum L. and achieve marketable yield under field condition. Biol Fertil Soils 48:839–843. https://doi.org/10.1007/s00374-012-0669-2

    Article  Google Scholar 

  25. Van Dommelen A, Croonenborghs A, Spaepen S, Vanderleyden J (2009) Wheat growth promotion through inoculation with an ammonium-excreting mutant of Azospirillum brasilense. Biol Fertil Soils 45:549–553. https://doi.org/10.1007/s00374-009-0357-z

    CAS  Article  Google Scholar 

  26. von Liebig J (1855) Principles of agricultural chemistry with special reference to the late researches made in England. Walton & Maberly, London

    Google Scholar 

  27. Vos HMJ, Koopmans GF, Beezemer L, de Goede RGM, Hiemstra T, Van Groenigen WJ (2019) Large variations in readily-available phosphorus in casts of eight earthworm species are linked to cast properties. Soil Biol Biochem:107583. https://doi.org/10.1016/j.soilbio.2019.107583

  28. Wang C, Ning P (2019) Post-silking phosphorus recycling and carbon partitioning in maize under low to high phosphorus inputs and their effects on grain yield. Front Plant Sci 10:784. https://doi.org/10.3389/fpls.2019.00784

    Article  PubMed  PubMed Central  Google Scholar 

  29. Weber R, Schwendener A, Schmid S, Lambert S, Wiley E, Landhäusser SM, Hartmann H, Hoch G (2018) Living on next to nothing: tree seedlings can survive weeks with very low carbohydrate concentrations. New Phytol 218:107–118. https://doi.org/10.1111/nph.14987

    CAS  Article  PubMed  Google Scholar 

  30. Weyers E, Strawn DG, Peak D, Moore AD, Baker LL, Cade-Menun B (2016) Phosphorus speciation in calcareous soils following annual dairy manure amendments. Soil Sci Soc Am J 80:1531–1542. https://doi.org/10.2136/sssaj2016.09.0280

    CAS  Article  Google Scholar 

  31. Zeng M, De Vries W, Bonten LTC, Zhu Q, Hao T, Liu X et al (2017) Model-based analysis of the long-term effects of fertilization management on cropland soil acidification. Environ Sci Technol 51:3843–3851. https://doi.org/10.1021/acs.est.6b05491

    CAS  Article  PubMed  Google Scholar 

Download references

Author information

Affiliations

Authors

Corresponding author

Correspondence to Hans Lambers.

Additional information

Publisher’s note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Lambers, H., Barrow, N.J. Pervasive use of P2O5, K2O, CaO, MgO, and basic cations, none of which exist in soil. Biol Fertil Soils 56, 743–745 (2020). https://doi.org/10.1007/s00374-020-01486-5

Download citation