New buffer pH method for rapid estimation of exchangeable acidity and lime requirement of soils

Abstract A new buffer pH method (BpH) for the rapid estimation of unbuffered salt‐exchangeable acidity (ACe) and lime requirement (LR) has been developed. The buffer reagent, consisting of sodium glycerophosphate, acetic acid, trletlianolamine, ammonium chloride and barium chloride, was useful within the pH range 3.8 to 6.6. Delta values from BpH were converted into buffer pH acidity values (AC) and calibrated against ACe of 91 mineral soils and 100 acid Histosols. The correlation coefficients between AC and ACe were 0.966 and 0.956 for the mineral soils and Histosols, respectively. The corresponding regression equations in terms of meq/100 cm were ACe ‐ ‐0.54 + 0.96 AC and ACe = ‐7.4 + 1.6 AC for mineral soils and Histosols, respectively. To predict lime requirement of mineral soils a curvilinear equation was required. The equation, LR in meq CaCO3/100 cm3 = 0.1 (AC)2 + AC, was tested successfully against rates of lime carried out under laboratory conditions and against crop response in the greenhouse. Field studies on acid Histosols with maize and soybeans showed optimum yield when the rate of lime added was approximately equivalent to ACe. Key words: Mineral soilsHistosolsBuffer pH acidity Notes Contribution No. 76–1, Agronomic Division, North Carolina Department of Agriculture.