A Nonhazardous Buffer that can Replace Adams-Evans Buffer for Lime Requirement Determination.
Frank Sikora, University of Kentucky, Univ. of KY Soil Testing Lab, 103 Regulatory Service Bldg., Lexington, KY 40546 and Kathy Moore, Clemson University, Agricultural Service Laboratory, 171 Old Cherry Road, Clemson, SC 29634.
Para-nitrophenol in the Adams-Evans (AE) buffer used for determining lime requirement (LR) is considered a hazardous chemical due to its toxicity. The Moore-Sikora (MS) buffer was developed without hazardous chemicals that mimics AE soil-buffer pH and is currently used for routine soil testing at Clemson University. The MS buffer was designed by considering likely chemicals with pKas in the desired pH range, potential reaction of the components with soil, and longevity of the buffer during storage. Boric acid, 3-(N-Morpholino)propanesulfonic acid (MOPS), and 2-(N-morpholino)ethanesulfonic hydrate (MES) were considered for the new buffer. Once chemicals were identified, a technique of finding appropriate concentrations was employed by using an equation that could predict the acid titration of a buffer and refining pKa and concentration values until a match was found with experimental titrations of AE buffer. The MS buffer contains 211, 131, and 34.9 mM of boric acid, MOPS, and MES, respectively. The buffer also contains 200 mM KOH and 1 M KCl. The MS buffer was compared to AE buffer for determining soil-buffer pH values on 222 South Carolina soils and 41 NAPT soils. The MS soil-buffer pH values were highly correlated with AE buffer (r2 > 0.98). Soil-buffer pH was slightly less with MS buffer compared to AE buffer with a mean difference of 0.03 pH units. The lower soil-buffer pH with the MS buffer caused slightly higher LR compared to the AE buffer with a mean difference of 0.35 Mg ha-1. The slightly higher LR with the MS buffer compared to AE buffer is not expected to raise soil pH too high and may provide a benefit of ensuring enough lime is applied to reach the target soil pH.