Extraction of Aluminum from Aluminum-Organic Matter in Relation to

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48, 1984 mania. Soil Sci. Res. p. 251-277, Academic Publ. House, Bu- charest, Romania. 7. Hem, J.D. 1970. Study and interpretation of the chemical char-.
Published November, 1984

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SOIL SCI. SOC. AM. J., VOL. 48, 1984

mania. Soil Sci. Res. p. 251-277, Academic Publ. House, Bucharest, Romania. Hem, J.D. 1970. Study and interpretation of the chemical characteristics of natural waters. Geol. Survey Water Supply Paper 1473. USDI, Washington, DC. Maianu, A. 1964. Salinizarea secundara a solului (Secondary soil salinization). Academic Publ. House, Bucharest, Romania. Maianu, A. 1985. Salt accumulation in the rivers of North Dakota. J. Environ. Quality, (in press). Palmer, G. 1911. The geochemical interpretation of water analyses. U. S. Geol. Survey Prof. Paper 440-D. Piper, A.M. 1944. A graphic procedure in the geochemical interpretation of water analysis: Am. Geophys. Union Trans. 25:914-923. U.S. Geological Survey. 1949-1982. Water resources data for North Dakota. U. S. Geol. Survey, Water Data Reports. Prepared in cooperation with the State of North Dakota and with other agencies. U. S. Salinity Laboratory Staff. 1954. Diagnosis and improvement of saline and alkali soils. U. S. Dept. Agric. Handbook

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EXTRACTION OF ALUMINUM FROM ALUMINUM-ORGANIC MATTER IN RELATION TO TITRATABLE ACIDITY1 W. L. HARGROVE AND G. W. THOMAS* Abstract This study was conducted to further characterize aluminum (Al)organic matter complexes and their role in soil acidity. The objective was to determine the extractability of Al from organic matter and to relate it to titratable acidity. Two samples of muck were treated with A13+ in such a way as to achieve a range in Al saturation. The titratable acidity [determined conductimetrically with Ca(OH),] of selected samples was compared to the Al extracted with 1 M KC1, 0.5 M CuCl2, 2 M HC1,1 M NH4OOCCH3 (pH 4.8), 0.5 M CaCl2, and 0.33 M LaCl3. Results show that NH4OOCCH3 (pH 4.8) is a very poor extractant of Al associated with organic matter. For unbuffered salts, the effectiveness of the extractant generally decreased as the valence of the replacing cation decreased (i.e. La3+ > Ca2+ > K+). Copper is an exception to this rule as a result of its ionic structure and its tendency to form "inner sphere" complexes with organic matter, displacing a disproportionate fraction of the Al. Lanthanum extracts an amount of Al which seems well related to the titratable acidity and, thus, to the lime requirement. On the other hand, K + extracts far too little Al, while Cu2+ extracts all of the Al present. The use of LaCl3 to predict lime requirement on field soils (especially where organic matter is increasing such as for no-tillage, etc.) looks promising but needs widespread evaluation. Additional Index Words: copper chloride, lanthanum chloride, lime requirement, potassium chloride. Hargrove, W.L., and G.W. Thomas. 1984. Extraction of aluminum from aluminum-organic matter in relation to titratable acidity. Soil Sci. Soc. Am. J. 48:1458-1460.

ECENT WORK on reactions of aluminum (Al) with soil organic matter has underscored the imporR tance of organic matter in controlling Al equilibria, particularly in acid surface soils (Bloom, 1979; Bloom, 1981; Bloom and McBride, 1979; Bloom et al, 1979; Hargrove and Thomas, 1981b; Hargrove and Thomas

1982 a,b; Thomas, 1975). Results of these studies show that Al forms rather stable complexes with soil organic matter by reaction primarily with carboxyl groups and to a lesser extent with phenolic hydroxyl groups. The amount of complex formed is dependent on pH and on Al3"1" concentration in solution. The complexed Al is not readily exchangeable with neutral salts such as KC1 (Bloom et al, 1979; Hargrove and Thomas, 198la). Juo and Kamprath (1979) used copper chloride (CuCl2) as an extractant for estimating the potentially reactive Al pool in acid soils. They found that 0.5 M CuCl? extracted 1.6 to 12 times more Al than KC1 in a variety of surface soils and suggested that Al bound by organic matter was extracted by CuCl2. However, 0.5 M CuQ2 also extracted inorganic, polymerized, hydroxy-Al, and it could not be determined if 0.5 M CuCl2 quantitatively extracted Al from Al-organic matter. Subsequently, Hargrove and Thomas (198la) showed that Al could be extracted quantitatively from organic matter by 2 MHCL or 0.5 MCuCl2. However, interpretation of results obtained from extraction of mineral soils with respect to Al-organic matter is difficult since CuCl2 or HC1 may at least partially extract hydroxy-Al from interlayers and surfaces of clay minerals. Bloom et al, (1979) extracted three soils and one Al-peat sample with KC1 and LaCl3. For all four samples, LaCl3 extracted significantly more Al than did KC1, but the amount of Al extracted by LaCl3, expressed as a fraction of the total titratable acidity, was greater for the peat than for the mineral soils, suggesting that LaCl3 was more effective than KC1 in extracting Al from Al-organic matter. Gates and Kamprath (1983a) extracted several soils, including some Histosols, with KC1, LaCl3, and CuCl2 and found that the relative affinity of the displacing cations for organic matter, and therefore the effective displacement of Al from organic matter, was in the order Cu2+ > La3+ > K+. Furthermore, when soils were limed3 1based on the Al extracted by LaQ3, the residual Al " " extracted by KC1 after incubation was < 15% of the effective CEC. When soils were limed based on A13+ extracted by3+KC1, soils contained considerable exchangeable A1 after incubation. When soils were limed at rates predicted by the Al removed by CuQ2, practically no exchangeable A13+ remained after incubation, and the soil pH was about 6.0. Therefore, if neutralization of soil Al is the criterion for liming, LaCl3 extraction was a better predictor of lime requirement, while the lime rate predicted by CuCl2 was excessive. It can be inferred from these results that there is a considerable amount of Al associated with organic matter which is not extractable with KC1 but which does react with lime. This study was conducted to shed further light on this question. The objective was to determine the extractability of Al from Al-organic matter and relate it to titratable acidity. 1 Contribution from the Univ. of Georgia Agric. Exp. Stn. and the Univ. of Kentucky Agric. Exp. Stn. Supported by Hatch and State funds allocated to the Georgia Agric. Exp. Stn. and Kentucky Agric. Exp. Stn. Received 29 Mar. 1984. Approved 22 June 1984. * Assistant Professor, Agronomy Dep., Georgia Agric. Exp. Stn., Experiment, GA., 30212; and Professor, Agronomy Dep., Univ. of Kentucky, Lexington, KY 40546, respectively.

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NOTES Table 2—The total titratable acidity determined conductimetrically and the fraction of titratable acidity extracted by KC1, LaCl3, and CuCU.

Table 1—Aluminum extracted from organic matter by several solutions. Al Content by ashing, 1M cmol (Al) kg-' NH.OAcf

Fraction of Al extracted} 1M

HC1

1M KC1

0.5 M CaCl,

0.33 M LaCl,

0.5 M CuCl,

1.01 1.18 0.97 0.80 0.51

0.98 1.10 0.85 1.05 1.02

1.18 1.13 1.04

1.21 1.20 1.08 1.04 0.97

Sample source

Michigan source 12.3 12.4 17.9 38.4 51.9

0.04 0.05 0.05 0.06 0.14

0.98

0.37

0.46

1.06

0.40

0.65

0.83

0.51

0.77

1.03 1.03

0.22 0.14

0.39 0.29

Michigan

New York source 3.9 12.4 18.1 42.3 59.3

0.15 0.07 0.06 0.17 0.29

1.23 1.15 1.07 1.05 1.10

0.64 0.67 0.39 0.25 0.15

0.77

0.89 0.69 0.33 0.29

0.93 0.58

tpH = 4.8. t Al extracted)Al content by ashing.

Materials and Methods Two samples of well-humified muck were used in this study. The samples were prepared and treated with Al as described by Hargrove and Thomas (198la). Briefly, after pretreatment with 2M HC1 to remove exchangeable cations and saturate with H + , the samples were treated with solutions of various concentrations of A1C13, 1/3 neutralized A1C13, and 2/3 neutralized A1C13. These treatments resulted in Al contents ranging from about 4 to 60 cmol (Al)3+ kg"1. + The Al content of the H -saturated samples was < 1 cmol (Al) kg"1, indicating a very small amount of mineral matter in the muck. The total amount of Al in each sample was determined after ashing as described also by Hargrove and Thomas (198 la). Selected samples of Al-treated muck were extracted with 1 M KC1, 0.5 M CuCl2, 2 M HC1, 1 M NH4OOCCH3 (NH4OAc pH 4.8), 0.5 M CaCl2, and 0.33 M LaCl3 by adding 50 mL of each solution to 1.00 g of organic matter, shaking for 24 h, and filtering. The amount of Al in the filtrate was determined by atomic absorption spectroscopy. Conductimetric titrations were also conducted as described by Hargrove and Thomas (1982a). Briefly, these were carried out using 1.0 g organic matter in a 200-mL tall-form beaker fitted with a two-hole rubber stopper, one hole to admit the conductivity cell and the other for the buret tip. Enough distilled water was added to the sample to be titrated to cover the conductivity cell (about 130 mL) when placed in the titrating vessel. Base (0.022M Ca(OH)2) was added to the stirred sample in 1-mL increments at 2-min time intervals. Conductance readings were taken before each base addition.

Results and Discussion The Al content determined on an ashed sample and the Al extracted by NH4OAc, KC1, and HC1 are shown in Table 1. The Al removed by HC1 was identical within experimental error to the amount of Al determined by ashing and elemental analysis. Much less Al was removed by KC1 and NH4OAc. In fact, NH4OAc tended to remove less Al than did KC1. NH4OAc has been used to characterize reactive Al in whole soils (McLean et al, 1959); however it does not appear to identify reactive Al which is associated with organic matter. For unbuffered salts of different valence the effectiveness of the extractant decreased as the valence of the replacing cation decreased (Table 1). Thus, the or-

New York

Al content by ashing cmol(Al) kg'1 0 11.0 12.3 12.4 38.4 51.9 0 3.9 11.7 12,4 14.2 18.1 42.3 59.3

Fraction of Fraction of titratable titratable acidity extracted by Titratable acidity KC1 LaCl, CuCl2 acidity as AlJ't cmol(H+) kg-' 187 143 149 176 143 122

0 0.24 0.24

280 224 188 198

0 0.05 0.19

190 194 172 96

0.22

0.21 0.81 1.28

0.19 0.28 0.74 1.85

-

-

0.12 0.09 0.09 0.18 0.18 „ 0.03 0.09 0.12 0.15 0.12 0.18

0.24 0.24 0.24 0.63 0.66 ..

0.18

0.06 0.18 0.24 0.24 0.30

0.69 1.08

0.24 0.24 0.24

0.84 1.29 .. 0.06 0.18 0.24 0.27 0.30 0.78 1.80

t cmol ( + ) kg'1 as Al3*/cmol ( + ) kg"' as titratable acidity. This is assuming all of the Al is present as the Al3' ion.

der of their effectiveness was La3+ > Ca2+ > K + . Copper is an exception to this rule as a result of its ionic structure. The amount of Al removed by CuCl2 (Table 1) is identical to that measured by ashing. This result is consistent with the finding that Cu2+ forms "inner sphere" complexes with humic acid and with the 2+lyotropic series proposed by Bloom (1981) in which Cu is the most strongly held divalent cation. For LaCl3 the amount of Al extracted was the same

as that determined by ashing or by extraction with CuCl2 when the total amount was relatively low (less than about 40 cmol kg"1)- Results from previous work have shown that the greater the amounts of Al adsorbed, the greater the degree of hydroxylation (Hargrove and Thomas, 1982a). Therefore, it would seem that LaQ3 is very effective at removing the less hydroxylated and less polymerized Al species, which would also be the reactive Al in terms of ion exchange and soil acidity. The amount of Al removed by CaQ2 was intermediate between that removed by KC1 and LaCl3. The amount removed by KC1 is small and is generally < 10% of the total. The Al removed by LaCl3 is less than that removed by CuCl2 for large amounts. However, the Al removed by LaCl3 for large Al contents is still considerably more than that removed by KC1. It appears that KC1 extractions of soils with high organic matter contents do not include the reactive Al associated with organic matter. The titratable acidity (determined from conductimetric titrations with Ca(OH)2) and the fraction of total titratable acidity extracted by KC1, LaCl3, and CuQ2 are shown in Table 2. The amount of acidity titrated with Ca(OH)2 generally correlates well with the lime requirement measured by other methods (Thomas and Hargrove, 1984). The acidity titrated conductimetrically decreased with increasing Al contents, which would indicate that as the amount of complexed Al increased, the reactivity with lime decreased. However, when potentiometric titrations of peat were conducted over time, several weeks were

required to achieve stable pH values (Shepard et al, 1980), indicating that reaction of large amounts of

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hydroxy-Al associated with organic matter is quite slow. The fraction of the total titratable acidity exchanged by KC1 is quite small and does not exceed 0.18 (Table 2). The CuCl2, on the other hand, extracts all of the Al, and for large amounts of complexed Al, the amount extracted exceeds the titratable acidity determined conductimetrically. However, the LaCl3 extracts the same amount as CuCl2 when the total amount present is relatively small, but an amount less than or about equal to the titratable acidity when the total amount of Al is large. This result helps explain why the amount of Al extracted by LaCl3 in the studies of Gates and Kamprath (1983b) gave the best prediction of lime requirement on soils varying in organic matter content compared to KC1 (which was too low) and CuCl2 (which was excessive). The use of LaCl3 to predict lime requirement on field soils looks promising but needs more widespread evaluation. These results are important to acid soils in which organic matter is altered, whether by slow accretion (through changes in tillage practices), by decline through continuous cropping, by large additions (as sewage sludge or animal manures), or by removal of the surface soil (erosion). This study and others seem to justify greater emphasis on the role of organic matter in soil acidity.

PREPARATION OF LARGE CORE SAMPLES FROM STONY SOILS1 B. BUCHTER, J. LEUENBERGER, P. J. WIERENGA, AND F. RICHARD2

Abstract A method was developed to take large, undisturbed soil cores in stony soils. An undisturbed soil core was surrounded with concrete, frozen to — 22 °C and cut to shape with a diamond circular saw, leaving only core sample. The core sample was surrounded with paraffin to maintain its shape. Additional Index Words: hydraulic properties, leaching, hydrodynamic dispersion. Buchter, B., J. Leuenberger, P.J. Wierenga, and F. Richard. 1984. Preparation of large core samples from stony soils. Soil Sci. Soc. Am. J. 48:1460-1462.

OR MANY STUDIES it is desirable to take large core F samples which can be taken into the laboratory for detailed analyses. Such analyses may include determination of hydraulic properties, including the soil moisture release curve and hydraulic conductivity vs. water content relationship, and determination of the leaching characteristics of a soil. Techniques are available to take undisturbed core samples in soils with few or no stones. These include pressing a steel plate (Tackett et al., 1965), or plastic cylinder in the ground, or carving a soil core in-situ, and covering it with gypsum (Bouma and Dekker, 1981), epoxy resin and fiberglass (Benecke et al., 1976) or other materials. Unfortunately these techniques do not work or work poorly in soils with large stones (Coile, 1953; Reinhart, 1961). There have been a number of studies dealing with the hydraulic and leaching characteristics of stony soils (Mehuys et al., 1975; Russq, 1983), but these studies generally were performed with disturbed samples. For many studies it is desirable to use undisturbed cores. The purpose of this note is to describe a method for taking large undisturbed soil cores in stony soils. Procedure A soil core is prepared in the field by removing soil and rock from around a soil core leaving an undisturbed pedestal of soil having the required height. Soil is removed to within 5 or 10 cm of the desired outer diameter of the pedestal. Soil can be removed with shovels and picks or by hand where necessary. The pedestal itself should not be disturbed and left connected with the underlying soil. The pedestal generally has a very irregular outside diameter due to presence of stones and may have a larger base than top. A wooden frame is placed around the pedestal and the space between the frame and the pedestal filled with concrete. Concrete was also poured over the top of the sample. After the concrete had hardened for about 2 d, the frame with concrete and core sample is tipped over and concrete poured over the sample base. Because of the irregular shape of the pedestal, 1 Contribution from the Soil Physics Laboratory, Swiss Federal Inst. of Technology, ETH-Zentrum CH8092 Zurich, Switzerland. Received 27 Jan. 1984. Approved 13 June 1984. 2 Research Soil Physicist, Staff Research Associate, visiting Professor, and Professor of Soil Physics, respectively, Soil Physics, Swiss Federal Inst. of Technology, Zurich, Switzerland