Extraction with 0.01 m CaCl2 underestimates the concentration of phosphorus in the soil solution

The aim of this paper was to compare the concentration of P in soil extracts prepared with water and a ‘soil solution proxy’ (‘SSP’, that is, a salt solution similar in ionic composition and strength to the actual soil solution) with that in 0.01 m CaCl₂ extracts, which is usually taken as a measure of soil P intensity. Seventy widely ranging agricultural soils from the Mediterranean part of Spain were used. Soil/solution ratio was 1:10 and extraction time 3 days. For 0.01 m CaCl₂, a short extraction time of 30 min was also used as the reference method. CaCl₂‐P(3 days) and CaCl₂‐P(30 min) were not significantly different for the 40 noncalcareous soils group, but CaCl₂‐P(3 days) was significantly larger than CaCl₂‐P(30 min) for the 30 calcareous soils group. The Water‐P/CaCl₂‐P(30 min) ratio was not significantly related to any soil property, its mean being 6.3 for the noncalcareous and 5.8 for the calcareous soils group. The mean SSP‐P/CaCl₂‐P(30 min) ratio was 2.6 for the noncalcareous and 3.1 for the calcareous soils group, and decreased slightly with increasing ionic strength of the soil solution in the noncalcareous soils group. These results are consistent with the promoting influence of the Ca ion and ionic strength on P adsorption by permanent‐charge soils. The fact that extraction with 0.01 m CaCl₂ generally results in underestimation of the actual concentration of P in the soil solution should be considered when CaCl₂‐P is used as a soil P test.     

The effect of pH upon the copper and cupric ion concentrations in soil solutions

Soil samples whose pH had been adjusted to between 4.5 and 7.5 either for long periods in the field or short periods in the laboratory were incubated after wetting with water or 0.01 m CaCl₂. Copper concentrations in the soil solutions decreased only slightly as the solution pH increased, but free cupric ion concentrations decreased considerably. The copper concentrations were smaller and the proportion of copper present in solution as cupric ion at a given pH was larger when CaCl₂ rather than water was used. Complexed organic species made up most of the copper in all solutions. The duration of pH adjustment did not affect these results. Copper adsorption isotherms were determined on the soils using low equilibrium solution concentrations. As a given copper concentration the quantity of copper adsorbed increased and the proportion of copper in solution present as cupric ion decreased with pH increase; again the duration of pH adjustment did not affect the results.     

Certification of an air‐dry soil for pH and extractable nutrients using one hundredth molar calcium chloride

Abstract

The preparation of an air‐dry river‐clay soil as reference soil material for pH and extractable nutrients with a 0.01 M calcium chloride (CaCl₂) solution and the homogeneity testing are described. Recommended values for pH and the concentrations of ammonium‐nitrogen (NH₄‐N), total soluble nitrogen (N), phosphorus (P), sodium (Na), potassium (K), and magnesium (Mg) using the unbuffered 0.01M CaCl₂ are given. With respect to nitrate‐nitrogen (NO₃‐N), the sample proved not to be sufficienctly homogeneous. The certified soil sample has also been used as a sample in the International Soil‐Analytical Exchange (ISE), a continuous proficiency testing scheme. The values found by the ISE laboratories compared well with the certified values.     

Predicting Liming Needs of Soybean Using Soil pH,Aluminum, and Manganese Soil Tests

Abstract

Whether a tropical soil should be limed or not for a particular crop is strongly dependent on the levels of soil aluminum (Al) which can be determined with soil tests. Soil pH is used to predict whether lime is needed in less‐weathered soils, although some evidence indicates a soil Al test would be more accurate. The objectives of this study were to determine and to compare the accuracies of four soil tests to separate soils requiring lime from those that do not, and to determine the cause of acid‐soil injury to soybean [Glycine max (L.) Merr.]. Soybean was grown in the greenhouse on four surface soils representing the major land resource areas of Louisiana and were amended with eight rates of lime, yields determined, and soils analyzed for soil pH, extractable Al, CaCl₂‐extractable Al, CaCl₂‐extractable manganese (Mn), and Al saturation. Acid‐soil injury in soybean grown on the Litro clay and Stough fsl was probably caused by soil‐Al effects while low soil calcium (Ca) and high soil Mn was likely responsible for lower yields from the Mahan fsl. Leaf Ca from the limed Mahan‐soil treatment was 5‐fold greater and leaf‐Mn 7‐fold less than control levels. Regression analyses’ R² values were similar for all soil tests except for CaCl₂‐extractable Mn, which was lower. Soil tests were compared across soil type by selecting treatments that had the same 85% relative yield. Using this data subset, there was no difference in the soil pH among the four soils, while there were significant differences among soils for all other soil test measurements indicating the superiority of soil pH for identifying acid‐soil injury. Critical test values were 5.1 soil pH, 30 mg kg^‐1 extractable Al, 7% Al saturation, 0.7 mg‐kg^‐1 CaCl₂‐extractable Al, and 9 mg‐kg^‐1 CaCl₂‐extractable Mn.     

The pH of bodenburg silt loam soil as related to forest cover and time under cultivation

Abstract

Soil pH's were evaluated at three time intervals following land clearing at two locations in the Matanuska Valley. Seasonal fluctuations of pH values over a seven‐year period as determined in water (pH_w,) and 0.01 M CaCl₂ (pH_s) were additionally evaluated at these locations. A statistical rise in soil pH occurred at both locations with clearing and subsequent cultivation. Soil reaction differences related to season and year were not consistent and were not related to a definite pattern. No relationship between monthly or seasonal precipitation and the soil reaction was found. The correlation coefficient between pH_w and pH_s was highly significant. Work of other investigators is discussed in the interpretation of the data collected.     

Modelling trace metal extractability and solubility in French forest soils by using soil properties

Soil/solution partitioning of trace metals (TM: Cd, Co, Cr, Cu, Ni, Sb, Pb and Zn) has been investigated in six French forest sites that have been subjected to TM atmospheric inputs. Soil profiles have been sampled and analysed for major soil properties, and CaCl₂‐extractable and total metal content. Metal concentrations (expressed on a molar basis) in soil (total), in CaCl₂ extracts and soil solution collected monthly from fresh soil by centrifugation, were in the order: Cr > Zn > Ni > Cu > Pb > Co > Sb > Cd , Zn > Cu > Pb = Ni > Co > Cd > Cr and Zn > Ni > Cu > Pb > Co > Cr > Cd > Sb , respectively. Metal extractability and solubility were predicted by using soil properties. Soil pH was the most significant property in predicting metal partitioning, but TM behaviour differed between acid and non‐acid soils. TM extractability was predicted significantly by soil pH for pH < 6, and by soil pH and Fe content for all soil conditions. Total metal concentration in soil solution was predicted well by soil pH and organic carbon content for Cd, Co, Cr, Ni and Zn, by Fe content for Cu, Cr, Ni, Pb and Sb and total soil metal content for Cu, Cr, Ni, Pb and Sb, with a better prediction for acidic conditions (pH < 6). At more alkaline pH conditions, solute concentrations of Cu, Cr, Sb and Pb were larger than predicted by the pH relationship, as a consequence of association with Fe colloids and complexing with dissolved organic carbon. Metal speciation in soil solutions determined by WHAM‐VI indicated that free metal ion (FMI) concentration was significantly related to soil pH for all pH conditions. The FMI concentrations of Cu and Zn were well predicted by pH alone, Pb by pH and Fe content and Cd, Co and Ni by soil pH and organic carbon content. Differences between soluble total metal and FMI concentrations were particularly large for pH < 6. This should be taken into account for risk and critical load assessment in the case of terrestrial ecosystems.     

Calibration of the single‐ and double‐buffer SMP lime requirement methods by root elongation bioassay

Abstract

Chemical and biological lime requirement (LR) reference values of 154 soils were obtained by six months of incubation of each soil with five levels of calcium carbonate (CaCO₃). Levels of CaCO₃ addition differed among soils according to their characteristics. Chemical LR values were based on the individual neutralization curves to achieve a desired pH (pH_d) value of 5.5, 6.0, and 6.5 in water or 5.0, 5.5, and 6.0 in 0.01M calcium chloride (CaCl₂). Biological LR values were estimated to achieve 90% relative root elongation on each soil after a growth period of 48 h using wheat cv Abe. Chemical values of LR suggest that SMP method is valid for a wide range of mineral soils from different geographic regions. However, the proportion of soil acidity reacting with the buffer is not constant. Results indicate that values obtained with the routine methods need to be calibrated with equations different from the originals. The use of curvilinear models to adjust one single pH of the soil‐buffer system improved substantially its accuracy, allowing the single‐buffer (SB) results to be comparable to the more time consuming and labourious double‐buffer (DB) technique. No advantage was noticed with the use of curvilinear equations for DB technique. The adoption of pH_d in 0.01M CaCl₂ leads to an increase of precision of the predicted LR. Regression equations are provided for calculating LR rates to different pH_d values. Accuracy is high (r²=0.887) even for pH values (5.0 in 0.01M CaCl₂) lower than normally considered in methods based on buffer solutions. An overestimation of biological LR values was observed with both SMP methods. Notwithstanding, a calibration can be also made with the root bioassay, adjusting the chemical values to lime rates based on biological constraints related with aluminum (Al) toxicity. Regression equations are provided. Once more, the use of quadratic model for SB method allows an accuracy (r²=0.836) comparable with the DB technique (r²=0.850).     

Predicting soil solution chemical attributes from more easily measured soil and soil solution parameters

Abstract

An understanding of how soil solution ionic strength (I_s) and major cation activities influence crop growth is often limited by the extensive measurements required to characterize ionic composition and subsequent speciation exercises. Easily measured solution and soil attributes need to be identified that can predict these important solution parameters. Soil and soil solution chemical properties of four Ultisols in the Coastal Plain and Piedmont of North Carolina were used to develop models to predict ionic strength and solution cation attributes. GEOCHEM‐PC‐predicted I_s was linearly related to electrical conductivity (EC) across soils (r²=0.92), confirming that I_s for soil solutions with complex composition can be estimated from their electrical conductivity. Models of the form lnM_s=a+blnEC+clnM_E, or modifications thereof, were developed for predicting solution aluminum (Al), calcium (Ca), magnesium (Mg), and postassium (K) levels (M_s) from a knowledge of EC and either soil exchangeable cation #OPM_E) or cation saturation (MSAT_E) attributes. For each cation, total and free solution concentration and activity in absolute and saturation terms were investigated. The best models explained, at most, 68% of the variability associated with total solution Al concentration (Al_s‐T) or 74% when Al_s ‐T was expressed as a percent of major solution cations. Greater than 85% of the variability associated with solution Ca and Mg could also be accounted for, but only 67% of the variability associated with solution K could be explained. Including soil pH and interaction terms (M_ExEC, M_ExpH, and ECxpH) in models improved the relationship for total Al concentration (R²=0.87) and solution Ca parameters (R² ≥0.93), but not for solution Mg and K indices. None of the models could account for >30% of the variability associated with free concentration and activity of Al³⁺, suggesting that the prediction of these parameters for a particular Al species could not be made from a knowledge of soil pH, solution EC, and M_E or MSAT_E data.     

Assessment of Suitable Extractants for Predicting Plant-available Potassium in Indian Coastal Soils

The suitability of seven chemical extractants was evaluated on 24 Indian coastal soils for prediction of plant-available potassium (K) to rice (Oryza sativa L. var. NC 492) grown in modified Neubauer technique. Average amounts of soil K extracted were in descending order: 0.5 M NaHCO₃ > neutral 1 N NH₄OAc > 0.02 M CaCl₂ > Bray and Kurtz No.1 > 1 N HNO₃ > 0.1 N HNO₃ > distilled water. The highest simple correlation with plant K uptake was obtained with 0.1 N HNO₃-K (r = 0.848) and lowest with CaCl₂-K (r = 0.805). Predictive models were developed using plant K uptake as the dependent variable and extractable soil K, sand, silt, soil pH, and electrical conductivity as the independent variables. Based on the final R² and ease of measurement, distilled water, 1 N NH₄OAc, and 0.1 N HNO₃ models were the best predictors of plant-available K in coastal soils when used along with sand or soil pH.     

Performance of Soil Electrical Conductivity and Different Methods for Mapping Soil Data from a Small Dataset

The performance of different methods for making soil maps from a small dataset was assessed. Soil samples obtained at five different depths were taken from 39 locations within an arable field in Sweden and analysed for clay content, soil organic matter content, pH (H₂O), K-HCl, P-AL, K-AL and Mg-AL. Detailed and densely sampled soil electrical conductivity (EC) data with a distinct border between two different regions was used for dividing the field into two zones. Averages from these zones gave better prediction for most variables than interpolation without respect to the border. With the border taken into account, cokriging with EC as a covariable improved the prediction, whereas the improvement with ordinary kriging and inverse distance weighting (IDW) was insignificant. Direct interpretation of EC by a simple linear regression model gave reasonable predictions for clay content. In general, even the simplest interpolation method improved the prediction compared to field average.     

Time‐dependent zinc desorption in soils

Abstract

Time dependent zinc (Zn) desorption in eight benchmark soils of India was studied in relation to various pH values and ionic strengths. Soil samples were equilibrated in solutions containing 10 μg Zn g^‐1 soil at pH 5.5,6.5, and 7.5 for 48 h at 25±2°C, and adsorbed Zn extracted with calcium chloride (CaCl₂) for various periods of time. Desorption of Zn decreased with increasing pH, and the desorption rate decreased abruptly at pH 7.5. In contrast, an increase in the equilibration period and ionic strength of the background electrolyte increased Zn desorption. Four rival kinetic models were fitted and evaluated for their suitability for describing the Zn desorption process. Reaction rate constant (ß) calculated from the Elovich model for the different soils ranged from 9.99 to 25 (mg Zn kg^‐1)^‐1. The different kinetic models tested indicated that Zn desorption in soils was a diffusion controlled process. The desorption was rapid in the first 4 h, followed by slower phase in the rest of the time at all the pH values indicating a biphasic desorption, characteristic of a diffusion controlled process. The ß value for the Elovich equation showed a strong association with soil clay content and cation exchange capacity (CEC). Further, the best prediction of Zn desorption reaction rate constant could be made using multiple‐regression equation with soil clay content and CEC as variables.     

Critical Olsen P and CaCl2‐P levels as related to soil properties: results from micropot experiments

The usefulness of soil phosphorus (P) tests used in routine soil analyses is limited by the fact that a single measurement cannot encompass all P‐related factors potentially affecting plant performance. In this work, we performed micropot (15 mL) experiments to test the hypothesis that the predictive value of two common soil P tests (Olsen P and CaCl₂‐P) can be improved by considering properties commonly measured in laboratory analyses. Forty‐nine sets of soils ranging widely in properties were used for this purpose, each set consisting of samples with similar properties but differing in P status. Ryegrass and turnip were grown in a chamber for 30 days in two separate experiments and their yields at harvest recorded. The critical Olsen P and CaCl₂‐P levels, which were taken to be those corresponding to 95% asymptotic yield as calculated from data fitted to a Mitscherlich equation, were greater for turnip than for ryegrass, probably as a result of the difference in yield (49 and 160 mg dry matter/micropot on average for ryegrass and turnip, respectively) and hence in P requirements between the two species. Critical Olsen P spanned narrower ranges than critical CaCl₂‐P in both crops and is therefore seemingly the more robust of the two tests. Both critical P values exhibited moderate correlations with soil properties. Thus, critical Olsen P was (a) lower in soils with a medium pH – which is consistent with the fact that the bicarbonate solution method tends to overestimate plant‐available P in strongly acid and calcareous soils; (b) positively correlated with pH and carbonate content in calcareous soils; and (c) uncorrelated with soil properties in noncalcareous soils. On the other hand, critical CaCl₂‐P in some soil groups was negatively correlated with some properties increasing the P buffering capacity of soil (e.g. Fe oxide content). Taken together, our results suggest that routinely measured soil properties help to predict critical Olsen P better than critical CaCl₂‐P.     

Salinity induced effects on the nutrient status of soil,corn leaves and kernels

Abstract

The effect of salinity in inducing soil macro and micronutrient deficiencies that can decrease crop growth was evaluated in a corn (Zea mays L.) field located in east central Wyoming. In this study water soluble Na was found to be a better predictor of salinity than pH and other cations. Soil saturated paste extracts had electrical conductivities that were negatively correlated with soil total K, Cu, Fe, and Mn. Total N, NO₃‐N, PO₄‐P, Zn, pH, and water soluble Na, Ca, and Mg of the soil were positively correlated with EC. Significant positive relationships existed between soil EC and N, P, Mo, and Zn, and negative relationships with K, Cu, Fe, and Mn of corn leaves and kernels. Concentrations of nutrients in the kernels were positively correlated with corresponding nutrient concentrations in the leaves and with AB‐DTPA extractable soil nutrients. The analysis of variance of EC data indicated that soil samples possessing high salinity were higher in pH and contained significantly higher soluble Na, Ca and Mg, total N, N0₃‐N, PO₄‐P, and Zn and significantly lower Mn compared to samples having low salinity. The kernel weight per cob and plant height were significantly reduced as salinity increased.     

Soil solution concentration of Cd and Zn canbe predicted with a CaCl2 soil extract

Risk assessment of heavy metals in soil requires an estimate of the concentrations in the soil solution. In spite of the numerous studies on the distribution of Cd and Zn in soil, few measurements of the distribution coefficient in situ, K_d, have been reported. We determined the K_d of soils contaminated with Cd and Zn by measuring metal concentrations in the soil and in the soil solution and attempted to predict them from other soil variables by regression. Soil pH explained most of the variation in logK_d (R² = 0.55 for Cd and 0.70 for Zn). Introducing organic carbon content or cation exchange capacity (CEC) as second explanatory variable improved the prediction (R² = 0.67 for Cd and 0.72 for Zn), but these regression models, however, left more than a factor of 10 of uncertainty in the predicted K_d. This large degree of uncertainty may partly be due to the variable degree of metal fixation in contaminated soils. The labile metal content was measured by isotopic dilution (E value). The E value ranged from 18 to 92% of the total metal content for Cd and from 5 to 68% for Zn. The prediction of K_d improved when metals in solution were assumed to be in equilibrium with the labile metal pool instead of the total metal pool. It seems necessary therefore to discriminate between ‘labile’ and ‘fixed’ pools to predict K_d for Cd and Zn in field contaminated soils accurately. Dilute salt extracts (e.g. 0.01 m CaCl₂) can mimic soil solution and are unlikely to extract metals from the fixed pool. Concentrations of Cd and Zn in the soil solution were predicted from the concentrations of Cd and Zn in a 0.01 m CaCl₂ extract. These predictions were better correlated with the observations for field contaminated soils than the predictions based on the regression equations relating logK_d to soil properties (pH, CEC and organic C).     

Relationship between ph measured in water and calcium chloride for soils of Southwestern Australia

Abstract

Soil pH in southwestern Australia (WA) is usually measured either in water (pH_w) or 0.01M CaCl₂ (pH_Ca). There are no published relationships to convert one pH to the other. This has been done in this paper for 236 WA soils: pH_Ca=0.918 pH_w‐0.3556, r²=0.9401. It is, therefore, concluded that, for the majority of soils within WA, it is likely that the linear model proposed for all soils would give the best relationship.     

Extraction of soil phosphorus with calcium chloride solution for prediction of plant availability

Abstract

Soil and vegetative samples of ley and cereals were collected four times during the growing season from field and pot trials with different phosphorus (P) fertilisation levels. The soil samples, dried and of field moisture condition, respectively, were extracted by 0.01M calcium chloride (CaCl₂) at two different soil:extractant ratios (1:2 and 1:10), and analysed by inductively coupled plasma emission spectrometry (ICP) for content of P. The plant samples were digested in concentrated nitric acid (HNO₃) and the P content determined by ICP. Calcium chloride‐extractable P content was lowest in the middle of the growing season, while plant P was highest in the beginning of the season. Phosphorus extracted by CaCl₂ solution was higher at a soil:extractant ratio of 1:10 than at 1:2, and also when drying the soil before extraction. A soil:extractant ratio of 1:2 minimizes the risk of coming too near the limit of determination. However, if organic soils are also to be included, a ratio of 1:10 has to be used in order not to have all the solution absorbed by some types of soils. The solution of ammonium lactate/acetic acid (AL) extracted nearly two powers of ten more P than CaCl₂ solution. There was a good relationship between the methods. If calcareous or very acid soils had been included, a less good relation would have been expected. Plant P content varied more in straw than in grain between different treatments. Measuring CaCl₂‐extractable P with ICP might be able to predict plant uptake of P by plants. This would be a great advantage when using 0.01M CaCl₂ as a universal extradant.     

Remediation of a Magnesium‐Contaminated Soil by Chemical Amendments and Leaching

The deposition of magnesium (Mg)‐rich dust from magnesite mining activities has resulted in serious land degradation. However, the main factors limiting plant growth in Mg‐contaminated soils are unclear. Moreover, little information is available on the remediation of Mg‐contaminated soils. In this study, remediation of soils contaminated with Mg‐rich dust was investigated in a pot experiment using maize as the indicator plant. There were five treatments: (i) control; (ii) leaching; (iii) application of CaCl₂; (iv) leaching + CaCl₂ application; and (v) application of Ca(H₂PO₄)₂ · H₂O. Soil properties and growth of maize (Zea mays L.) seedlings were measured. Leaching alone significantly decreased soluble Mg concentration. Leaching + CaCl₂ application greatly increased exchangeable Ca concentration and decreased soil pH by 0·3 units. Application of CaCl₂ alone increased soluble Mg concentration sharply, which directly inhibited the germination of maize seeds. Application of Ca(H₂PO₄)₂ · H₂O significantly increased the concentrations of exchangeable Ca and available phosphorus and decreased soil pH by 1·7 units. The biomass of maize seedlings increased in the order of control = leaching < leaching + CaCl₂ < < Ca(H₂PO₄)₂ · H₂O. These results suggested that the plant growth in Mg‐contaminated soils was limited primarily by Ca deficiency and secondarily by high soil pH when exchangeable Ca was sufficient. High soil pH suppressed plant growth probably mainly by inhibiting phosphate uptake from the soil. Applying acid Ca salt with low solubility is an attractive option for the remediation of Mg‐contaminated soils. Copyright © 2015 John Wiley & Sons, Ltd.     

Soil pH,extractable aluminum and tree growth on acid minesoils

Abstract

Paper birch and hybrid poplar were grown in acid minesoils amended with different rates and types of lime. Growth of the trees was correlated with soil pH, Ca, Mg, K, P and three measures of extractable Al ‐ 1 N KCl, 0.01 M CaCl₂ and H₂O extractable Al. Correlations between soil pH and extractable Al and between the three measures of extractable Al were also determined. Soil pH accounted for the largest share of the total variation in root and shoot growth of both species over all soils. Correlations between tree growth and extractable Al for all soils combined were low and generally non‐significant. Significant correlations were obtained between soil pH and extractable Al and between the three measures of extractable Al, however, the relationships varied among soils.     

Maize growth and mineral acquisition on acid soil amended with flue gas desulfurization by‐products and magnesium

Abstract

The large amounts of coal combustion by‐products (CCBs) generated by coal burning power plants must be utilized or discarded, and beneficial use of these materials are desired. One beneficial use of CCBs could be application to agricultural land. Information about the use of one kind of CCB (flue gas desulfurization by‐product, FGD‐BP) on soil is limited. Maize (Zea mays L.) was grown (greenhouse) on an acid soil [Umbric Dystrochrept, pH_Ca (1:1, soil: 10 mM CaCl₂) 4.2] amended with two high CaSO₄ FGD‐BPs (5 and 15 g#lbkg^‐1 soil) and CaCQ₃ (2.5 and 5.0 g#lbkg^‐1 soil) at varied calcium/magnesium (Ca/Mg) equivalency ratios (0/0, 1/0, 1/0.01, 1/0.05, 1/0.1, and 1/0.5) to determine treatment effects on growth traits [shoot and root dry matter (DM) and total and specific root length (RL)], mineral concentrations in leaves, and soil pH and electrical conductivity [(EC) 1:1, soil:water]. Magnesium deficiency symptoms were induced on leaves of plants grown with and without low Mg, and the Mg to Ca ratio in each amendment needed to be about 1 to 20 to alleviate Mg deficiency. Shoot and root DM and total RL of plants grown with FGD‐BPs became higher as Mg increased. Specific RL (total RL/root DM, root fineness) was not affected by FGD‐BP and only slightly by Ca/Mg ratio. Shoot concentrations of Mg increased; Ca, phosphorus (P), and manganese (Mn) decreased; and potassium (K), sulfur (S), iron (Fe), zinc (Zn), and copper (Cu) remained relatively constant as amendment and Mg increased. On unamended soil, aluminum (A1) and Mn concentrations in shoots were above normal. Enhancement of growth was closely related to increased soil pH compared to added Mg for CaCO₃ amended soil and to increased Mg compared to increased soil pH for FGD‐BP amended soil. Except at the highest level of Mg where soil pH increased, added FGD‐BPs and Mg had only limited effect on increasing soil pH. Soil EC increased from added FGD‐BPs but not from added Mg, and EC was not sufficiently high to be detrimental to plants. Maize grown on this acid soil amended with FGD‐BPs received benefits when caution was used to alleviate mineral deficiencies/toxicities inherent in the soil.