Soil Lime Requirement by Direct Titration with a Single Addition of Calcium Hydroxide

Abstract

et al., 1990; Owusu-Bennoah et al., 1995) used for comparison with other procedures to determine the LR. Direct titration of acid surface soils is often used to measure soil Studies by Magdoff and Bartlett (1985) indicated that acidity. However, titration has not been used for routine determinathe titration curves of acid surface soils are approxition of the lime requirement (LR) in soil testing laboratories, because it is too time-consuming, requiring multiple additions of base and mately linear. Weaver et al. (2004) found that the titralong equilibration times between additions. Since soil pH as a function tion data of pH vs. added base were described well by of added base can be described well by a linear equation, titration a linear equation in the pH range of 4.5 to 6.5 for a may be adopted by soil testing laboratories using a minimum number group of soils from the coastal plain of Georgia. Liu et of base additions. Our objective was to evaluate the accuracy of a al. (2004) continued titration studies with a wider range simplified titration procedure, based on an initial pH reading and a of 17 soils from throughout Georgia. They found that second reading following the addition of one dose of Ca(OH) 2 , folat least 30 min were needed between additions of 0.022 M lowed by extrapolation to the target pH. Seventeen soils were titrated Ca(OH) 2 with no background electrolyte to reach a with Ca(OH) 2 in both water and 0.01 M CaCl 2 with a 30-min interval stable pH. Titrations to a target pH of 6.5 were linear between additions. The slopes from the first two data points of the titration in water were frequently in error for estimation of the slopes with 15 of the 17 soils giving r 2 values Ͼ 0.992. regressed by all data points to pH 6.5. However, the first two data To adapt a titration procedure for routine determinapoints in the 0.01 M CaCl 2 titration were found to be more reliable tion of the LR, a minimal number of pH measurements for estimating the slopes. Both the initial pH in water and in 0.01 M would be required to reduce measurement time. In titra-CaCl 2 were used to calculate the LR with the two-point slope in 0.01 tions conducted by Liu et al. (2004), the first three data M CaCl 2. The LR predicted using the initial pH in 0.01 M CaCl 2 gave points after addition of Ca(OH) 2 gave slopes and interbetter estimates of the LR than the initial water pH when compared cepts by linear regression that were similar to those for with the standard 3-d Ca(OH) 2 incubation. A linear regression of LR the whole titration to a target pH of 6.5. The soil pH by the single addition method in 0.01 M CaCl 2 (Y) on LR determined without Ca(OH) 2 additions was not used in the linear with the 3-d Ca(OH) 2 incubation (X) gave the linear equation Y ϭ regression because the pH value was depressed below 0.88 X, r 2 ϭ 0.93. It is concluded that the LR predictions with the the y intercept in over 50% of the soils. The LR was single addition method in 0.01 M CaCl 2 are sufficiently accurate to justify further evaluation under routine l...

Evaluation of Common Lime Requirement Methods

“…‡ Theoretical soil pH after application and reaction of lime. the University of Georgia to determine the LR from the two-point Ca(OH) 2 method proposed by Liu et al (2005). This allowed comparison between full titration curves (with no corrections) and a two-point titration.…”

“…A new method proposed by Liu et al (2004Liu et al ( , 2005 is also free of hazardous chemicals and uses a titration with 0.022 M Ca(OH) 2 to measure the pH buffering capacity of a soil with a single addition of Ca(OH) 2 . They found that an average of 80% of the LR from their standard 3-d Ca(OH) 2 incubation was measured by using a Ca(OH) 2 titration.…”

Comparison of Methods to Determine Crop Lime Requirement Under Field Conditions

“…Such a linear response was observed in several studies (Liu et al, 2005;Hoskins and Erich, 2008;Wolf et al, 2008). A target pH of 6.5 is recommended for corn and soybean in Iowa (Sawyer et al, 2002).…”

“…Therefore, work has been done to develop alternative methods for determining lime needs without using hazardous chemicals. Some researchers have tried direct titrations using single additions of Ca(OH)2 (Liu et al, 2005;Kissel et al, 2007;Thompson et al, 2010). The modified Mehlich buffer was developed by Hoskins and Erich (2008) primarily to overcome the drawbacks of the SMP buffer procedure (i.e., tmstable buffer pH readings, rapid electrode degradation, poor precision of results, and the production of hazardous waste in the laboratory).…”

Evaluation of Four Buffer Solutions for Determining the Lime Requirement for Ohio Soils

“…Most of the buffers used to estimate LR contain hazardous components, including hexavalent chromium and barium, and there is a general trend toward developing buffers without these hazardous constituents (Hoskins 2005;Sikora 2006) or alternative methods of LR determination (Liu et al 2005). The Sikora and modified Mehlich buffers were designed to mimic the SMP and Mehlich buffers, respectively, but without the hazardous constituents.…”