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The University of Georgia Soil, Plant, and Water Laboratory (SPW) uses a single-addition titration for estimating soil lime requirement. The lime requirement depends in part on a soil's pH buffering capacity (described as lime buffer capacity [LBC] in mgCaCO3 kg-1 per pH unit), which is estimated from the rise in soil pH after Ca(OH)2 is added and allowed to react for 30 mm. The 30-mm reaction time has not been sufficient to reach equilibrium between the soil and Ca(OH)2, resulting in an underestimation of the LBC. As a corrective measure, the SPW adjusts the agricultural lime recommendations to account for the lack of equilibrium. This study investigated the rate of pH change after Ca(OH)2 is added to acid soils. Specifically, the objectives of this study were to: (i) determine the time in which the Ca(OH)2-treated samples reached pH equilibrium; and (ii) determine if a relationship exists between the LBC estimated from a 30-mm equilibration and the LBC estimated from the time in which the sample had reached an equilibrium pH. The 25 soils used in this study were equilibrated for up to 96 h. Results indicated that the soils had reached an equilibrium pH by 84 h after the addition of Ca(OH)2. The ratio (mean of 84- and 96-h LBC/30-min LBC) could be predicted with the equation 1.4742 + 0.0023(30-mm LBC) (r2 = 0.82). This relationship allows the current titration procedure with 30-mm equilibration time to be used to predict the equilibrium LBC, which in turn can be used to calculate more accurate lime recommendations. [ABSTRACT FROM AUTHOR]

Incubation of soil with CaCO3 is generally considered a reliable method to determine the lime requirement (LR) of acid soils. Because of their considered reliability, these incubations are often used to calibrate buffer methods; however, one study reported that the use of room temperature incubation with CaCO3 overestimated the actual LR determined by field testing. The objective of this study was to compare the pH change following CaCO3 incubations for 60 d with those following 3-d incubations with Ca(OH)2 and to determine the possible role of soil N reactions causing any differences in pH change. Seventeen soils were incubated with either CaCO3 for 60 d at approximately 85% field capacity or for 3 d with an equivalent amount of Ca(OH)2 solution plus water to maintain a 1:1 soil/solution ratio. Both were incubated at room temperature (23 ± 2°C), followed by measurement of pH (1:1 in water). Ammonium-N and NO3--N were analyzed at Days 0 and 60 of the incubation. Soil pH was lower following the 60-d CaCO3 incubation than after the 3-d incubation with Ca(OH)2. The analysis of N transformations indicated that positive values of H+ (more H+ was produced than consumed) were generated from nitrification after 60 d of incubation in 14 out of 17 soils. Furthermore, incubations with soils that have been air dried produced a flush of nitrification that increased the ionic strength and decreased pH even further. These effects from long-term incubation would erroneously increase the LR. Incubation with Ca(OH)2 for 2 to 4 d avoids these errors. [ABSTRACT FROM AUTHOR]

Buffers for determining a soil's lime requirement (LR) sometimes contain hazardous chemicals. Our objective was to implement a single-addition titration with calcium hydroxide [Ca(OH)2] to determine the LR of soils. The soil pH buffering capacity is calculated from the rise in pH from a single addition of base. The LR is calculated from the soil pH buffering capacity, the target pH, and initial soil pH. The LR of 531 randomly selected client samples determined by single-addition titration were slightly higher than by the Adams-Evans (AE) buffer procedure when LRs were less than 1800 lb per acre. The new procedure recommended about 11% less lime than AE at LRs greater than 1800 lb per acre. Independent evaluations of samples that gave the most widely different LR revealed that the single-addition titration was more accurate and more precise than the AE buffer. [ABSTRACT FROM AUTHOR]

Direct titration of acid surface soils is often used to measure soil acidity. However, titration has not been used for routine determination of the lime requirement (LR) in soil testing laboratories, because it is too time-consuming, requiring multiple additions of base and long equilibration times between additions. Since soil pH as a function of added base can be described well by a linear equation, titration may be adopted by soil testing laboratories using a minimum number of base additions. Our objective was to evaluate the accuracy of a simplified titration procedure, based on an initial pH reading and a second reading following the addition of one dose of Ca(OH)2, followed by extrapolation to the target pH. Seventeen soils were titrated with Ca(OH)2 in both water and 0.01 M CaCl2 with a 30-min interval between additions. The slopes from the first two data points of the titration in water were frequently in error for estimation of the slopes regressed by all data points to pH 6.5. However, the first two data points in the 0.01 M CaCl2 titration were found to be more reliable for estimating the slopes. Both the initial pH in water and in 0.01 M CaCl2 were used to calculate the LR with the two-point slope in 0.01 M CaCl2. The LR predicted using the initial pH in 0.01 M CaCl@ gave better estimates of the LR than the initial water pH when compared with the standard 3-d Ca(OH)2 incubation. A linear regression of LR by the single addition method in 0.01 M CaCl2 (Y) on LR determined with the 3-d Ca(OH)2 incubation (X) gave the linear equation Y = 0.88 X, r² = 0.93. It is concluded that the LR predictions with the single addition method in 0.01 M CaCl2 are sufficiently accurate to justify further evaluation under routine laboratory conditions. [ABSTRACT FROM AUTHOR]