All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. Double-Buffer Methods Revisited with Focus on Ionic Strength and Soil/Solution Ratio Nutrient Management & Soil & Plant Analysis
Buff er solutions are commonly used in soil testing for a quick assessment of soil acidity and the lime required to neutralize the soil acidity. A soil-buff er pH is the pH of a soil and buff er mixture commonly determined aft er a soil-water pH (1:1 soil/water) (Soil and Plant Analysis Council, 2000) or a soil-salt pH (1:1 soil/0.01 mol L −1 CaCl 2 ) (Brown and Cisco, 1984). Th e lower the soilbuff er pH is from the original pH of the buff er solution, the greater the amount of soil acidity and the greater the lime requirement (LR).Early use of buff ers for quantifying soil acidity was reported by Schofi eld (1933), Mehlich (1939), andBrown (1943). Woodruff (1948a,b) later developed a buff er for Missouri soils. Th e Shoemaker-McLean-Pratt (SMP) (Shoemaker et al., 1961) and Adams-Evans (Adams and Evans, 1962) buff ers were developed around the same time in the early '60s to overcome the inadequacies of earlier buffers. Th e SMP buff er was calibrated for Ohio soils with high exchangeable Al and