Jack Bremner’s Role in Understanding Fixed Ammonium in Soils

1. Jack Bremner’s Role in Understanding Fixed Ammonium in Soils Darrell W. Nelson University of Nebraska

2. Nature of Fixed Ammonium (FA) • Some soils contain ammonium in a form not extracted by neutral salt solutions. This ammonium is said to be “fixed” • FA was present in parent rock material or fixed during pedogenic soil forming processes • FA is present largely between the layers of 2:1 type clay minerals such as vermiculite and illite

3. Nature of Fixed Ammonium (FA) • SSSA defines FA as ammonium that cannot be replaced by a neutral potassium salt solution such as 1 or 2 M KCl • FA is more precisely entitled “non-exchangeable ammonium”

4. Brief History of FA Research • Rodrigues (1954) extracted ammonium from tropical soils with a strongly acidic mixture of HF and sulfuric acid and estimated ammonium by distilling the extract with NaOH. He stated that 14-78% of total N in soils studied was FA and the proportion increased with soil depth and that FA has a major impact on the C:N in soils. • Rodrigues, G., 1954. J. Soil Sci. 5:264-274

5. Brief History of FA Research • Bremner and Harada (1959) and Bremner (1959) confirmed the presence of FA in soils using a HF:HCl extracting mixture. Their research showed that 3-8% (avg. 5.6%) of total N in surface soils was FA and that 9-44% (avg. 21.5%) of N in subsoils was FA. Their research also showed that the Rodriques method gave high results as a result of deamination of OM. • Bremner, J.M. and T. Harada. 1959. J. Agric. Sci. 52:137-146 • Bremner, J.M. 1959. J Agric. Sci. 52:147-160

6. Brief History of FA Research • Jack Bremner conducted additional studies on the nature of FA by examining the effects of ball milling (Bremner et al., 1959), extraction with cation exchange resins (Scott et al., 1960) and intensive cropping (Keeney and Bremner, 1964) on release of ammonium from soils. • Bremner, J.M., F.J. Stevenson, and P.M. McDonnell. 1959. Nature 183:1414-1415 • Scott, A.D., A.P. Edwards and J.M. Bremner. 1960. Nature 185:792 • Keeney, D.R. and J.M. Bremner. 1964. Proc. Soil Sci. Soc. Am. 28:653-656

7. Methods for Determining FA • Difference in ammonium released by distillation with NaOH and KOH (Barshad, 1951) • Extraction with acidic mixtures containing HF. Rodriques (1954) used HF:sulfuric acid. Bremner (1959) and Bremner and Harada (1959) used HF:HCl mixtures to release FA from clay minerals. • Barshad, I. 1951. Soil Sci. 72:361-371

8. Methods for Determining FA • Extraction with acidic HF solutions after removal of organic N and exchangeable ammonium with hot KOH (Dhariwal and Stevenson, 1958 and Stevenson et al. 1958); hydrogen peroxide:KCl (Schachtschabel, 1961); and KOBr:KOH (Bremner, 1965; and Silva and Bremner, 1966). • Dhariwal, A.P.S. and F.J. Stevenson. 1958. Soil Sci. 86:343-349. • Stevenson, F.J., A.P.S. Dhariwal, and M.B. Choudri. 1958. Soil Sci. 85:42-46.

9. Methods for Determining FA • Schachtschablel, P. 1961. Z. Pflanzenernaehr. Dung. Bodenkd. 93:125-136. • Bremner, J.M. 1965. Inorganic forms of nitrogen. P.1179-1237. In C.A. Black, et al. (ed). Methods of soil analysis. Part 2. Agron. Mongr. 9. ASA, Madison, WI • Silva, J.A. and J.M. Bremner. 1966. Soil Sci. Soc. Am. Proc. 30:587-594.

10. Methods for Determining FA • Determine total N by Kjeldahl analysis after removal of OM by heating soils at 400 degrees C for 24 to 72 hours (Mogilevkina, 1964) • Mogilevkina, I.A. 1964. Soviet Soil Sci. 2:185-196.

11. Comparison of Methods for FA Determination • Bremner (1959) compared the HF:HCl extraction methods to other methods. He found that his method gave quantitative release of FA from soils and that his values were markedly lower than those of Rodriques (1954) and higher than those of Barshad (1951).

12. Comparison of Methods for FA Determination • Nelson and Bremner (1966) evaluated Mogilevkina’s (1964) method and showed that heating at 400 degrees C led to loss of FA and the Kjeldahl procedure used failed to quantitatively recover N in the residue from heating. Mogilevkina’s method was found to give much lower FA values in Iowa soils than other methods studied. • Nelson, D.W. and J.M. Bremner. 1966. Soil Sci. Soc. Am. Proc. 30:577-582.

13. Comparison of Methods for FA Determination • Bremner et al. (1967) evaluated all proposed methods for FA and found defects in all methods except the KOBR:HF method of Silva and Bremner (1966). The main defect being that pretreatments used to eliminate interference by organic N compounds are inefficient or lead to gain or loss of FA and that procedures used to release FA are not quantitative or lead to formation of ammonium from organic compounds. • Bremner, J.M., D.W. Nelson and J.A. Silva. Soil Sci. Soc. Am. Proc. 31:466-472.

14. Comparison of Methods for FA Determination (continued) • Bremner et al. (1967) concluded that the method of Rodriques gave high values and Moglivekina’s method gave low values. Schachtschabel’s method leads to high values because the peroxide:KCl pretreatment is inefficient and leads to fixation by clay minerals of ammonium formed by decomposition of OM during pretreatment. The HF methods of Dhariwal and Stevenson and Bremner (1959) have extractant mixtures that do not give quantitative release of FA from soils

15. Conclusions • Jack Bremner conducted the definitive research on FA in soils. • The Silva and Bremner (1966) method is the standard procedure for determining FA in soils. • Other studies have allowed an improved understanding of FA in soils including the availability of FA for mineralization by soil microbes.

16. Conclusions • In addition to his work on FA, Jack Bremner has made seminal contributions to many aspect of soil nitrogen research as evidenced by his election to the National Academy of Science. • Among his most important contributions was the mentoring/education of numerous graduate students in the conduct of high quality research. I greatly profited from my mentoring by Jack Bremner and will be forever in his debt.