Jack Bremner's Role in Understanding Fixed Ammonium in Soils.

 

Jack Bremner was among the first soil scientists to point out that:  (1)  that fixed ammonium (FA) makes up a small but significant proportion of total N in surface soils and a larger proportion of total N in subsoils, and (2)  accurate measurement of FA in soils has a number of major challenges to overcome.  His first two papers concerning FA were published in 1959.  These papers proposed a new HF:HCl extraction method, showed that this method gave lower values than the drastic HF procedure of Rodriques and higher values than the double distillation method of Barshad, and showed that surface soils and subsoils averaged 5.6% and 21.5% of total N as FA, respectively.  Other papers published in 1959 and 1960 examined the ability of cation exchange resins and ball milling to remove FA from clay minerals and soils.  The widely used Silva-Bremner (KOBr: HF) procedure to determine FA in soils was first described in Methods of Soil Analysis (1965) and later published in the Proc. Soil Sci. Am. (1966).  Other articles evaluated Mogilevkina’s ignition method (1966) and compared and evaluated six other for determining FA (1967).  These studies established that the Silva-Bremner method gave the most consistent values for FA and lacked the defects apparent in other methods.  A landmark study (1967) showed that prolonged incubation led to a marked decrease in all forms of N except FA indicating that FA is unavailable to soil microorganisms.  Other papers and review articles showed that an HF modification was required to quantitatively recover FA using the Kjeldahl procedure (1967, 1992, 1996).  Jack Bremner played a major role in clarifying the nature of FA in soils.