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A Buffer that Mimics the SMP Buffer for Determining Lime Requirement of Soil

Univ. of Kentucky, Division of Regulatory Services, Soil Testing Lab., 103 Regulatory Service Bldg., Lexington, KY 40546-0275

View larger version (24K): [in a new window]   Fig. 1. Calculation of soil buffer pH for SMP buffer (20 mL buffer + 10 mL water + 10 g soil) as a function of soil acidity neutralized shown as closed circles. The calculation was performed according to Eq. [9] with soil acidity as the dependent variable and is the sum of the individual calculations shown for triethanolamine, p-nitrophenol, chromate, and acetate.

View larger version (15K): [in a new window]   Fig. 2. Interlaboratory variation in SMP buffer pH on 87 samples from the NAPT program from 1999 through 2004. Interlaboratory variation is defined as the coefficient of variation (MAD/median x 100) and is plotted versus median SMP buffer pH.

View larger version (29K): [in a new window]   Fig. 3. Calculation of soil buffer pH for SMP buffer (100 mL buffer + 50 mL water + 50 g soil) and new buffer (50 mL buffer + 50 mL water + 50 g soil) according to Eq. [9] compared with experimental data from seven titrations of SMP buffer (100 mL buffer + 50 mL water) and new buffer (50 mL buffer + 50 mL water). The upper x axis shows the volume of 0.5 M HCl used in the experimental titrations with equivalent values of mmol soil acidity (g soil)–1 shown in the lower x axis calculated according to Eq. [10] assuming acidity in the titration originated from 50 g of soil.

View larger version (24K): [in a new window]   Fig. 4. Seven titrations of SMP buffer (100 mL buffer + 50 mL water) and seven titration of new buffer (50 mL buffer + 50 mL water) with 0.5 M HCl as the titrant shown on the upper x axis. The titrant acidity was calculated as mmole soil acidity (g soil)–1 in the lower x axis using Eq. [10] assuming 50 g of soil was contributing the acidity neutralized by the buffer. The regression analysis was performed considering the lower x axis. The 95% confidence intervals (CI) are presented for the intercept (b) and slope (m).

View larger version (24K): [in a new window]   Fig. 5. Comparison of soil buffer pH determined with the new buffer and SMP buffer on 255 Kentucky soils and 87 NAPT soils. Linear regression analysis is provided with 95% confidence intervals (CI) for intercept (b) and slope (m). Lines represent a 1:1 line where both variables are equal and an upper and lower boundary defined by NAPT interlaboratory variation (Eq. [12] and [13]).

View larger version (26K): [in a new window]   Fig. 6. Comparison of limestone recommendations determined with new buffer and SMP buffer on Kentucky and NAPT soils with soil-buffer pH less than 6.85. Linear regression analysis is provided with 95% confidence intervals (CI) for intercept (b) and slope (m). Lines represent a 1:1 line where both variables are equal and an upper and lower boundary defined by NAPT interlaboratory variation for SMP soil-buffer pH (Eq. [14] and [15]). Most symbols represent more than one data point.