Mehlich Buffer Research Articles

Investigating the accuracy and comparability of various lime prediction methods for Irish grassland mineral soils

AbstractSoil pH is a foundational element of agronomy, profoundly influencing biological, chemical and physical soil processes. Adjusting soil pH is a paramount factor for enhancing soil health and productivity with far‐reaching environmental benefits. Over time soil naturally tends towards acidity, a process expedited by intensive agriculture practices. To determine the extent of necessary pH corrections, precise soil pH testing is imperative. Various methods including buffer systems, titrations, lime incubations and algorithms considering soil texture are used to assess a soil's lime requirement and each method carries distinct advantages and disadvantages. The Shoemaker–McLean–Pratt (SMP) buffer method is extensively used in Ireland and internationally; however, safety concerns owing to the use of hazardous chemicals required within the method have been highlighted. This study investigates various soil lime requirement tests and compares their performance against a lime incubation study. A proposed alternative to the SMP buffer test for Irish grassland soils is also investigated. Analysis of results obtained indicates that the SMP buffer method demonstrated the highest r2 value of .497 when correlated with lime incubation results, while the calcium hydroxide titration method closely aligns with the SMP buffer method with an r2 value of .816, followed by the modified Mehlich buffer method with an r2 value of .763.

A comparison of soil liming requirement methodologies in temperate, Northern European pedo‐climates

AbstractBackgroundLiming agricultural land is essential to optimise crop yield and soil nutrients. Despite the importance of pH management in agricultural soils, liming applications have been decreasing in the United Kingdom for decades. There is no comparison of contemporary and historical liming requirement (LR) methods for Northern European, temperate climate mineral soils high in organic matter (OM).AimsThe aims of this research were to thoroughly comparatively analyse current methodologies and to ascertain which soil characteristics contribute to LR reactions.MethodsAnalysis compared methods for determining liming values common in the United Kingdom (Scottish Agricultural College [SAC] look‐up chart, RothLime model), Europe and the United States (Shoemaker–McLean–Pratt, Sikora, Modified Mehlich buffers), and the 30‐min calcium hydroxide titration developed by the University of Georgia.ResultsRothLime and SAC highly underestimated the LR value in acidic soils. The buffers highly over or underestimated LRs. The UGA titration method is a cheap, easy and accurate method which could be utilised for high OM soils but requires further calculation development. The characteristics most associated with soil–lime reactions in this experiment were measures of exchangeability (cation exchange capacity and loss on ignition, and by proxy, lime buffering capacity).ConclusionsThere is an opportunity to create buffer calculators and titration equations adapted to high OM soils. These are suggested for further development, through a larger diversity of UK soil types grouped by buffering capacity ranges. Including soil exchangeability factors in lime management calculations may contribute to more accurate values and therefore better resource management. Increasing LR accuracy for site‐specific soil pH management, used in precision agriculture technologies, is a necessary tool for the conservation of natural resources like limestone, managing resource use efficiency, and for optimising yields.

Remote-Sensing-Based Sampling Design and Prescription Mapping for Soil Acidity

Soil acidification is a major problem in the inland Pacific Northwest. A potential solution is the application of lime to neutralize acidity and raise pH. As lime is an expensive input, precision variable rate application is necessary. However, high-resolution mapping of pH and buffer pH for lime prescription requires costly sampling and analysis. To reduce the amount of sampling needed, remote sensing, which correlates with soil pH and buffer pH, can be used to determine optimal sampling locations and allow optimal interpolation. We used soil and crop data from the Washington State University R.J. Cook Agronomy Farm to develop an optimal sampling plan for a farmer’s property, followed that sampling design, and used the measured pH and buffer pH to fit a Bayesian hierarchical model using remote sensing variables specific to that farmer’s land. Following this, a new model was developed for the research farm with similar covariates. Ultimately, on the farmer’s field, we observed a root mean square error (RMSE) of 0.2487 for soil pH at a depth of 0–10 cm and 0.1221 for modified Mehlich buffer at 0–10 cm of depth. For the research farm, where buffer pH was not measured, we saw an RMSE of 0.3272 for soil pH at 0–10 cm of depth and 0.3381 for soil pH at 10–20 cm of depth. The ability make predictions of soil acidity with uncertainty using this technique allows for prescription lime application while optimizing soil sampling and testing. Further, this paper serves as a case study of on-farm research.

English

Soil acidity is one of the major constraints of crop production in the Ethiopian highlands where precipitation is high enough to leach basic cations leaving the soil acidic. Liming is the major practice used to ameliorate the problem of soil acidity. Currently farmers use Ag lime in their fields to reduce soil acidity. However, the suitability of the existing methods of lime requirement (LR) has not yet being determined. Shoemaker-McLean-Pratt (SMP) single buffer, Adams-Evans buffer, Modified Mehlich buffer, titration with single addition of Ca (OH)2, and exchangeable aluminum methods were evaluated using the CaCO3 moist incubation method. The result revealed that the LR estimated by the buffer methods and titration highly correlated with the incubation LR since the correlation coefficient(r) was ≥ 0.98. The modified Mehlich buffer was better in predicting the LR on average, for target pH values of 5.5, 6.0, 6.5, 6.8 and 7.0 as r = 0.99 and as the standard error of estimate (Sy.x) 0.57, the minimum among the buffer methods. The modified Mehlich buffer should be calibrated further with the reference CaCO3 incubation using a set of soils and a calibration equation to calculate the lime requirement. Key words: Acidity, lime requirement, calibration, buffer methods, incubation.

Comparison of Methods to Determine Crop Lime Requirement Under Field Conditions

Little field research has evaluated the effectiveness of pH buffer methods free of hazardous chemicals, such as Sikora and Mehlich methods, for estimating lime requirement (LR). This study assessed how Shoemaker–McLean–Pratt (SMP), Sikora, and Mehlich buffers, titratable acidity (TA), and soil properties relate to the LR under on-farm conditions. Experiments were established in 2.54- to 6.42-ha areas of 14 Iowa fields. Replicated treatments were a control and 6.7 Mg ha−1 of effective CaCO3 equivalent. Soil samples (19–48 per site, 15-cm depth) were collected before liming and after a crop harvest (6–12 mo after liming). Soil pH ranged from 4.60 to 8.05 across all samples. Mean SMP, Sikora, and Mehlich buffer pH values differed (P < 0.05) and were 6.43, 6.36, and 5.77, respectively. The mean difference between SMP and Sikora buffers was explained by small differences in six of eight loess-derived soils and increasing difference with increasing soil organic matter (OM) and clay. The Mehlich buffer showed the best relationship with LR (r2 = 0.28), which was followed by Sikora (r2 = 0.18) and SMP (r2 = 0.12). Sikora and Mehlich buffers performed better than SMP or TA and include no hazardous chemicals. Consideration of OM increased the proportion of LR variation accounted for by the Mehlich or Sikora buffers to r2 = 0.32 and 0.24, respectively. The improvement, although small, can be easily implemented for routine estimation of LR because OM is measured together with pH and buffer pH in samples submitted to laboratories.

Evaluation of Modified Mehlich and Sikora Buffer Methods as an Alternative to Modified Woodruff Buffer in Determining Lime Requirement for Missouri Soils

The modified Woodruff buffer (MWB) test is used to determine lime requirement (LR) for Missouri soils. Though this method is proven to work for Missouri soils, it uses p-nitrophenol, which is a hazardous substance. Soil-testing laboratories are under increasing pressure to reduce hazardous wastes, which must be collected and disposed of following U.S. Environmental Protection Agency protocols. The goal of this study was to evaluate the modified Mehlich buffer (MMB) and the Sikora buffer (SB) as alternatives to the MWB in determining the LR for Missouri soils. Thirty soils were collected from major agricultural areas in Missouri, treated with calcium carbonate (CaCO3), and incubated for 90 days. Soil pHs [0.01 M calcium chloride (CaCl2) 1:1] was regressed against CaCO3 rate, and the actual LR was estimated for each soil to raise the soil pHs to target levels of 5.8, 6.3, and 6.8. The MWB, MMB, and SB pHs were regressed against the actual LR for all 30 soils to evaluate the effectiveness of each test for estimating the LR. The MMB and SBs were found to be as good as or better than MWB in predicting LR in Missouri soils. Both buffers (MMB and SB) were found to be equally effective in generating accurate estimates of the LR to raise soils to pHS 5.8, 6.3, and 6.8 (for pH values 5.8: R2 = 0.76, 0.82, 0.81; for pH values 6.3: R2 = 0.80, 0.88, 0.86; and pH values 6.8: R2 = 0.77, 0.89, 0.87 for MWB, MMB, and SB, respectively). A test to evaluate the stability of the buffers over time indicated that MMB had the shortest bench life (about 21 days) when compared to the MWB and SB, thus making it less feasible for use by soil test laboratories. Based on performance and stability, SB is a better alternative than MWB for Missouri soils.

A comparison of lime requirements by five methods on grassland mineral soils in Ireland

Liming is necessary for good nutrient availability and crop growth. Lime use in Ireland is now the lowest in half a century. A recent study shows that grassland mineral soils in Ireland has a mean pH of 5.4 and mean lime requirement (LR) of 9.3 t/ha ground limestone. There have been a number of studies in the USA to re-evaluate LR, but little activity in the European Union (EU) in recent years. The primary aim of our research was to compare five methods for estimating LR, which included the Shoemaker–McLean–Pratt (SMP) buffer method currently used in Ireland (IRL), the Sikora buffer method used at the University of Kentucky (UKY), Ca(OH)2 titration used at University of Georgia (UGA), the modified Mehlich buffer method used at Penn State University (PSU) and the UK RothLime model, using 57 representative grassland mineral soils from Ireland with a pH range from 4.8 to 6.6. The secondary aim was to explore an alternative to the SMP buffer that does not involve the use of toxic chemicals. The results show good agreement between the pH measured by the Irish and three US laboratories and reasonably good agreement in LR estimated by five methods. The main conclusions are: (1) a significant proportion of grassland on mineral soils in Ireland would benefit from liming to increase soil pH, (2) on average, LRs as recommended in Ireland are higher than those advised elsewhere, (3) the target pH in Ireland is high compared with that in other countries and should be reduced from pH 6.5 to 6.2, (4) the SMP buffer method should be replaced by a suitable alternative and, in principle, any of the four methods studied would be suitable, (5) to find the most suitable alternative for accurate LR advice it would be necessary to compare the different methods to the actual LR from incubation of representative soils with calcium hydroxide.

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

Lime is used as a soil amendment to achieve the optimum pH suitable for good crop growth. Buffer pH (BpH) measurements have been calibrated to relate the linear drop in pH of the soil–buffer system to the amount of lime needed to neutralize soil to a certain pH level. The amount of lime required to neutralize soil acidity, called the lime requirement (LR), is obtained from soil–limestone (CaCO3) incubations. In this study, 13 soils from Ohio were incubated with CaCO3 for a period of 1 month to determine the LR to achieve different target pHs. This LR was then regressed with the different BpHs of four buffer solutions [(1) Shoemaker, McLean, and Pratt (SMP), (2) Sikora, (3) Mehlich, and (4) modified Mehlich] to obtain calibration equations. The Sikora and modified Mehlich buffers are variations of the SMP and Mehlich buffers, respectively, but they are designed to promote buffering without use of any hazardous constituents [i.e., chromium(VI) in SMP buffer and barium in the Mehlich buffer]. This study was done to verify the applicability of the buffers that do not contain any hazardous constituents and to calibrate these buffers for predicting lime requirement needs for Ohio soils. Comparing the calibrated equations of the SMP and Sikora buffers with CaCO3‐incubation LR recommendations revealed that the SMP and Sikora buffer solutions were not significantly different, and a single calibrated equation can be used for these two buffers to determine LR predictions in Ohio. The Mehlich and modified Mehlich calibration equations differed significantly from the SMP calibration equations and were not as highly correlated with CaCO3‐incubation LR recommendations using a linear model (r2 < 0.54). Thus, it is possible to use the Mehlich and modified Mehlich for determining lime recommendations, but they require a correction factor such as inclusion of the initial soil pH to improve the precision of the LR prediction. We also found the various buffers tested in this study were better able to predict LR rates for greater LR soils than low LR soils. In conclusion, successful laboratory tests to predict LR for Ohio soils are possible using alternative buffers that do not contain hazardous constituents.

Predictors of Lime Needs for pH and Aluminum Management of New York Agricultural Soils

Periodic lime addition is recommended for naturally acidic agricultural soils, as soil pH affects nutrient availability and the toxicity of elements such as Al. Currently, lime requirements (LRs) for New York soils are derived from the actual and target pH, and exchange acidity (EA) determined by BaCl2–triethanolamine (TEA) titration, a time‐consuming and toxic‐waste‐generating procedure. Our objectives were to: (i) calibrate and evaluate four buffer pH methods and EA as predictors of LRs; and (ii) determine the impact of CaCO3 addition on Morgan‐extractable Al (MEA). Forty‐three soils, ranging in EA from 4.1 to 18.6 cmolc kg−1, were collected from New York agricultural areas. Eighteen soils were incubated at 21°C for 12 wk with CaCO3 added at six rates. The EA‐based method was highly correlated with incubation LR (r2 &gt; 0.96, RMSE &lt; 0.62) across the 18 soils. A comparison of LRs derived by EA and buffer pH applied to all 43 soils showed the highest correlation and lowest RMSE for the modified Mehlich (MM) and Mehlich buffers (r2 = 0.91, RMSE = 0.88–0.89). The MM buffer has the advantage of not generating toxic waste. These buffers were followed by the Shoemaker–McLean–Pratt (r2 = 0.90, RMSE = 0.96) and Sikora (r2 = 0.87, RMSE = 1.09) buffers. Final MEA levels could be accurately predicted when initial MEA, CaCO3 application rate, and soil organic matter (OM) content were known. The MM buffer is an acceptable replacement of the EA‐based method for predicting LRs, and initial MEA and OM level are necessary to determine the amount of CaCO3 needed for a specific target MEA.

Modification of the Mehlich Lime Buffer Test

Routine use of the Shoemaker, McLean, and Pratt (SMP) lime buffer method resulted in chronic problems with electrode reference junction degradation, stability of readings relative to contact time, and generation of hazardous waste. During method recalibration, the Mehlich buffer was chosen for parallel evaluation with SMP, with the goal of improving method performance and eliminating of hazardous waste. The Mehlich buffer was modified by substituting calcium (Ca) for barium (Ba). The modified Mehlich (MM) buffer was found to be identical to the original with respect to buffering power and linearity over an extended pH range of 3.0–6.6. Seven agronomic soils were incubated with eight rates of calcium carbonate for 90 days. Regression analysis was performed to predict lime requirement (LR) to several target pH levels, based on pH measured in each buffer alone or in both water and buffer. Slightly better predictability was obtained using multiple regressions, with R2>0.95 in all cases. Significant but minor differences occurred between the newly calibrated buffers in extended comparisons. The MM buffer was superior to the SMP during routine usage, with fewer adverse effects on electrodes and the elimination of hazardous waste.

Comparison of Shoemaker–McLean–Pratt and Modified Mehlich Buffer Tests for Lime Requirement on Pennsylvania Soils

The Shoemaker–McLean–Pratt (SMP) buffer test is commonly used in Pennsylvania and throughout the United States to determine the lime requirement (LR) of acid soils. The buffer contains potassium chromate, a carcinogen, and all waste must be collected for disposal in a hazardous waste facility. An alternative to the SMP buffer is the Mehlich buffer. Although the Mehlich buffer contains barium chloride (BaCl2), also a hazardous and regulated compound, calcium chloride (CaCl2) has been shown to be an effective substitute. The goal of this study was to compare the SMP buffer and the modified Mehlich buffer (CaCl2 substituted for BaCl2) for estimating LR on PA soils and to determine if the modified Mehlich buffer could provide an effective alternative to the SMP test. Twenty‐two agriculturally important Pennsylvania soils with pH values ranging from 4.5 to 6.4 were collected, and the actual LR of each soil was determined by incubating soils for 3 months with calcium carbonate. The modified Mehlich buffer was a more accurate predictor of the lime required to raise soils to either pH 6.5 (r2=0.92) or 7.0 (r2=0.87) in comparison to the SMP buffer (r2=0.87 and 0.82, respectively). Comparison of calibration equations for Mehlich buffer versus lime requirement derived in this study were similar to those developed on soils from other states and geographic regions.

Evaluation of Common Lime Requirement Methods

Accurately estimating lime requirements (LR) of acidic soils has been a concern since liming practices began. The objectives of this study were to: (i) determine if the Shoemaker-McLean-Pratt (SMP) buffer is accurately predicting the LR of Kansas soils, (ii) calibrate the SMP and Mehlich buffers to accurately estimate the LR of Kansas soils to specific target pH values, and (iii) compare the effectiveness of 60-d incubations vs. field-observed lime response in determining LR. Kansas soils were used to evaluate the current LR according to the SMP buffer and calibrate SMP and Mehlich methods. Slope values (SMP LR vs. 60-d LR) 0 indicated that the SMP either overestimated the LR at low values or underestimated the LR at relatively high LR values compared with 60-d incubations with CaCO 3 . Calibration of the Mehlich buffer to a target pH of 6.8 provided a better fit than the SMP buffer but the opposite was true at target pHs of 5.5 and 6.0. Titration with 0.022 M Ca(OH) 2 resulted in a LR (target pH 6.8) 55% less than that measured by the 60-d incubation. Evaluation of the SMP buffer, Mehlich buffer, and Ca(OH) 2 titration method on 12 soils indicated that the LR estimated by the Mehlich buffer was not significantly different than the LR from the 60-d incubation. Comparison of the LR from 60-d incubations with field-observed lime response showed that the actual LR in the field was greater than that predicted by the 60-d incubation, which warrants further investigation.

A lime requirement test for maritime Canada, and response time and effect of liming source on soil ph

Abstract An experiment was conducted to determine which of the two lime requirement tests (LRT) used in Maritime Canada (Adams‐Evans, SMP) are most appropriate, and to evaluate the effect of two sources of limestone (calcitic and dolomitic) on soil pH during a four month incubation period. Four soils, varying in texture from loamy sand to silty loam, and three rates of each lime were used in the study. The LRT showed that for three of the four soils, the two tests recommended similar amounts of lime; the middle rate of lime was the amount suggested by the LRT. Based on the final month analysis, it was noted that both the Adams‐Evans and SMP methods over‐estimated the lime requirement; consequently, the Mehlich buffer was tried on the four soils and compared to the other methods. The result showed that the soil pH stabilized after about two months of incubation. There was a very different pH response to the two lime sources, calcitic lime increased soil pH about 0.5 units above that for dolomitic lime; however, the difference was somewhat soil and rate‐dependent Lastly, the data indicated that the recommended rate of dolomitic lime suggested by the Mehlich LRT was the most appropriate.

Lime requirement determination of tropical peat soil using buffer‐pH methods

Abstract A study was conducted to calibrate and evaluate five buffers for the lime requirement (LR) determination of tropical peat soil. The buffers tested were the Shoemaker‐McLean‐Pratt (SMP); Mehlich; 0.1M ammonium acetate (NH4OAc); 0.1M barium acetate [(Ba(OAc)2]; and 0.1M calcium acetate [Ca(OAc)2]. Calibration was done by comparing the precision of linear regression equations adjusted to the relationships between the LR rates required to achieve pH 5.0 measured in a 1: 4 (soiltwater) ratio as determined by incubation and soil‐buffer pH values. Incubation LR using calcium carbonate (CaCO3) to achieve pH 5.0 by peat soil was utilized to calibrate each buffer. Evaluation was carried out by assessing the LR from the calibrated buffers which estimate the LR nearest to the target pH of 5.0. The calibration study showed that the SMP and Mehlich buffers were less precise than the Ba(OAc)2, NH4OAc, and Ca(OAc)2 buffers. The evaluation study indicated that the Ba(OAc)2 buffer is the most accurate, followed by...

Buffer Ph methods for estimation of lime requirement of tropical acid soils

Abstract Lime requirements (LR) of 26 agricultural acid soils were estimated using the following buffer methods: Shoemaker‐McLean‐Pratt (SMP) single buffer (SMP‐SB), SMP double buffer (SMP‐DB), Mehlich buffer method for crops with high LR (MEHLICH I), and Mehlich buffer methods for crops with low LR (MEHLICH II). The LR were determined to three pH targets (6.5, 6.0 and 5.5). The LR values were then evaluated through regression analysis using LR values obtained by the Ca(OH)2 titration (for the 6.5 pH target) and moist CaCO3‐incubation (for the 6.0 and 5.5 pH targets) as reference methods. All the buffer methods were well correlated with the reference methods but the SMP‐DB gave the best results for both high and low LR soils, and was particularly impressive at the lowest pH target.

A Comparison of Several Methods of Determining Lime Requirements of Soils

AbstractBuffer‐indicated lime requirements of four groups of soils using several buffer methods were related to CaCO2 incubation‐measured lime requirements through regression analysis. Salt accumulated during the incubation period had marked effect on the amount of lime required to bring the soils to pH 6.5. Results from all buffer methods were highly correlated with incubation‐measured values. Slopes and intercepts of regression lines revealed the marked tendency for the Woodruff buffer to indicate too much at low lime requirement levels and too little at high levels. The Mehlich buffer at pH 8.1 indicated approximately the correct amount for soils of high lime requirement but too much for those at low levels. Peech alterations of the Mehlich and the regular Mehlich method gave the same results. The Shoemaker, McLean, and Pratt method was found to be relatively rapid, accurate, and especially well adapted for soils requiring &gt;4,000 lb of lime per acre, having &lt;pH 5.8, containing &lt;10% organic matter, and having apprecitable quantities of soluble Al.