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DIVISION S-6—SOIL & WATER MANAGEMENT & CONSERVATION

Ferrihydrite Influence on Infiltration, Runoff, and Soil Loss

^a USDA-ARS, National Sedimentation Lab., 598 McElroy Dr., Oxford, MS 38655
^b School of Natural Resources, Ohio State Univ., Columbus, OH 43210
^c USDA-ARS, Cropping Systems Research Lab., Lubbock, TX 79415

^* Corresponding author (frhoton{at}ars.usda.gov)

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY AND CONCLUSIONS REFERENCES

 
Soil aggregates low in organic matter and clay contents are generally susceptible to disintegration at low rainfall energies. This study was conducted to evaluate the effectiveness of ferrihydrite (Fe₅ HO₈·4H₂O) at stabilizing such aggregates, using five soils with a wide range of physical and chemical properties. The soils were amended with ferrihydrite at rates equivalent to 0, 0.34, 3.36, 16.80, and 33.60 Mg ha^-1, packed to a depth of 7.6 cm in plexiglass cylinders, and then exposed to simulated rainfall at an intensity of 64 mm h^-1 for 1.5 h. The erodibility data indicated that as ferrihydrite increased from 0 to 16.80 Mg ha^-1 on acid soils, infiltration increased an average of 21.5% while runoff and soil loss decreased 20 and 40%, respectively. Conversely, infiltration decreased 37% while runoff and soil loss increased 21 and 34%, respectively for alkaline soils. Further, sediment size distributions measured at these same ferrihydrite rates indicated that the >250-, and 250- to 53-µm fractions increased 24 and 22% for acid soils and decreased 15 and 14%, respectively in alkaline soils. The <53-µm fraction decreased 21% in the acid soils and increased 46% in the alkaline soils. These results suggest ferrihydrite develops a net positive charge in acid soil environments that leads to formation of bonds with negatively charged soil particles and an increase in water stable aggregation. Conversely, in alkaline soils, ferrihydrite becomes negatively charged which results in dispersion and aggregate instability. Thus, ferrihydrite appears to be an effective amendment for reducing runoff and soil loss from acid pH soils at amendment rates between 3.36 and 16.80 Mg ha^-1.

Abbreviations: AAO, acid ammonium oxalate • CDB, citrate-dithionite-bicarbonate • CEC, cation exchange capacity • Fe_o, AAO-extractable Fe • Fe_d, CDB-extractable Fe • OM, organic matter • WDC, water dispersible clay • ZPC, zero point of charge

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY AND CONCLUSIONS REFERENCES

 
SEVERAL MILLION hectares of soils in the USA are subject to excessive runoff and erosion losses because of low levels of aggregate stability attributable to an inadequate content of clay and organic C cementing agents (Langdale et al., 1985; Rhoton and Tyler, 1990; Rhoton et al., 1990). As water quality standards become increasingly more stringent, new approaches to soil loss and runoff reductions must be developed in the form of management practices that will improve the stability of surface soils to the extent that a reduction is realized in the sediment and contaminant loadings of water bodies. One potential solution to the problem is the use of Fe oxides to stabilize soil aggregates and increase infiltration.

The relationship between Fe oxides and soil aggregate stability (Duiker et al., 2003) indicate two opposing views that have evolved over the past two or three decades. In the opinion of some scientists (Shanmuganathan and Oades, 1982; Colombo and Torrent, 1991; Oades and Waters, 1991; Ferreira Fontes, 1992; Igwe et al., 1995; Rhoton et al., 1998) Fe oxides improve soil aggregation and should, therefore, increase resistance to soil erosion losses. Other researchers (Desphande et al., 1968; Greenland et al., 1968; Borggaard, 1983), however, indicate that Fe oxides have no effect on soil aggregation. There are a number of potential explanations for these conflicting opinions. Foremost is the difference in Fe oxide crystallinity between soil types. Specifically, the poorly crystalline Fe oxides are more reactive than well-crystallized forms due to greater surface area (Schahabi and Schwertmann, 1970). Other factors that determine the extent to which Fe oxides stabilize soil aggregates are soil pH, path of formation of the Fe oxides, the size of the Fe oxide crystals, the ionic composition of the soil solution, and the presence of certain organic molecules (Duiker et al., 2003). Unless these factors related to soil and Fe oxide characteristics are quantified, the role of Fe oxides in soil aggregate stability cannot be fully understood in terms of evaluating the performance of Fe oxides over a range of soil types.

The current research was conducted to evaluate the effectiveness of a naturally occurring ferrihydrite at stabilizing soil aggregates. This Fe oxide mineral species has the potential to have the greatest impact on stabilizing soil aggregates based on its chemical and physical properties. Ferrihydrite is a poorly crystalline, very fine grained, highly reactive, gel-like Fe oxide with a structure similar to hematite (Eggleton and Fitzpatrick, 1988) that forms under conditions favoring the rapid oxidation of Fe(II). It is a transient phase in the formation of other Fe oxides unless dissolution–crystallization reactions are poisoned by surface contaminants such as phosphate, organic acids, and Si (Childs, 1992). Ferrihydrite possesses a large specific surface area and a pH dependent surface charge. Due to its physical and chemical properties, ferrihydrite is commonly used as an industrial catalyst and filter material. The effectiveness of ferrihydrite as a soil-aggregating agent has been demonstrated under laboratory conditions by Schahabi and Schwertmann (1970) who determined that a synthetic ferrihydrite formed under laboratory conditions enhanced the water stability of soil aggregates to levels that exceeded those obtained with more crystalline Fe oxides (i.e., hematite, goethite, lepidocrocite). Recently, Duiker et al. (2003) reported similar findings for unamended soils containing naturally occurring, poorly crystalline versus crystalline Fe oxides from similar sources. Likewise, Rhoton et al. (1998) observed, on the basis of oxalate-dithionite extractable Fe contents, a relative abundance of ferrihydrite in soils occupying lower, wetter slope positions that were less erodible than upslope soils whose Fe oxide mineralogy was predominantly the crystalline goethite and hematite species.

Ferrihydrite is abundant in ground water seeps and ephemeral streams in the loess uplands of the lower Mississippi River Valley (Rhoton et al., 2002). The aquifers in this region contain high concentrations of dissolved Fe that is precipitated as ferrihydrite by aeration (oxidation) procedures at municipal water plants, and is filtered out before treatment of the water for human consumption. This byproduct, which poses a disposal problem to such municipalities, represents an abundant, inexpensive material for potential use as an aggregating agent to reduce runoff and soil loss. Our objective was to evaluate the effectiveness of this naturally occurring, poorly crystalline Fe oxide in terms of its ability to improve the water stability of aggregates derived from soils that have an inherently low aggregation index.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY AND CONCLUSIONS REFERENCES

 
Sample Collection and Analysis
Soil samples used in this study were obtained from representative A and B horizons in two widely separated geographic regions. Grenada silt loam (fine silty, mixed, active, thermic Oxyaquic Fraglossudalfs) and Routon silt loam (fine silty, mixed, thermic Typic Epiaqualfs) soils were collected from the southern Mississippi River Valley loess uplands near Senatobia, MS. Amarillo fine sandy loam (fine loamy, mixed, superactive, thermic Aridic Paleustalfs), Gomez loamy fine sand (coarse loamy, mixed, active, thermic Aridic Calciustepts), and Olton clay loam (fine, mixed, superactive, thermic Aridic Paleustolls) soils were collected from the Texas High Plains region near Lubbock, TX.

Soil samples were crushed, sieved to <2 mm, and used for basic characterization analyses. Samples for particle-size distribution were dispersed overnight in Na-hexametaphosphate, and then analyzed by the pipette method of Day (1965). Water dispersible clay (WDC) contents were estimated by the same pipette method except that distilled water was used instead of a chemical dispersant. Quantitative soil colors were measured with a Minolta CR-200 Chroma Meter (Minolta Corp., Ramsey, NJ). Soil pH was determined in a 1:1 soil/distilled water suspension (McLean, 1982). Soil organic C contents were determined with a LECO CN-2000 Carbon Analyzer (Leco Corp., St. Joseph, MI). Sodium citrate-dithionite-bicarbonate (CDB) and acid ammonium oxalate (AAO) extractable Fe contents in the soils were quantified by the procedures of Mehra and Jackson (1960) and Schwertmann (1964), respectively. Iron concentrations in the extracts were measured with a Perkin-Elmer 2380 atomic absorption spectrophotometer (Perkin-Elmer Corp., Norwalk, CT).

The Fe oxide used in the study was obtained as a ferrihydrite sludge from a Memphis, TN water treatment plant where it had been filtered from drinking water supplies before chemical treatment. Under laboratory conditions, the ferrihydrite sludge suspension was concentrated by repeated sedimentation and decantation to approximately 100 g L^-1. Subsamples were freeze- dried and characterized for color and AAO extractable Fe (Fe₀) following the same procedures used for soil samples. Total Fe, Al, and selected trace elements were measured by inductively coupled plasma optical emission spectroscopy (ICP-OES) following dissolution of the ferrihydrite component in aqua regia. The acid insoluble residues were collected, dried, and weighed. Additionally, the sludge was characterized for zero point of charge (ZPC) following the procedures of Van Raij and Peech (1972). Mineralogy was determined by powder x-ray diffraction (XRD) analysis with a Philips APD 3520 x-ray diffraction unit (Philips Electronic Instuments, Co., Mahwah, NJ) using CuK radiation (35kV, 20mA). Specific surface area was measured by the Brunauer-Emmett-Teller (BET) triple point method using a Micromeritics Flowsorb II 2300 surface area analyzer (Micromeritics Instrument Corp., Norcross, GA) with N₂ as the adsorbate.

Erodibility Measurements
Soil samples were air-dried, sieved to <8 mm, and split into fifteen 6.5-kg subsamples per soil. Each subsample was then amended with ferrihydrite (Fe sludge) at rates equivalent to 0, 0.34, 3.36, 16.80, and 33.60 Mg ha^-1, based on an acre furrow slice depth of 15.2 cm, and a weight of 2240 Mg ha^-1 (2 000 000 lbs acre^-1). The ferrihydrite was applied in a slurry form with a paint sprayer as the soil was rotated in a small capacity (56.4 L) cement-type mixture; the 0 treatment was exposed to exactly the same procedure as the ferrihydrite amended samples except that only water was sprayed on the sample. After ferrihydrite application, three subsamples (6.5 kg each) per amendment rate were combined in plastic trays (53.3 cm length by 38.1 cm width by 12.7 cm depth) that contained a 5-cm thick sand bed covered with a porous fabric. These samples were wetted to saturation from the bottom by adding distilled water through a network of perforated polyvinyl chloride (PVC) tubing (1.27 cm diameter) installed in the sand bed. The ferrihydrite-amended soils were then allowed to dry under greenhouse conditions to water contents <10% by weight. This wetting-drying cycle was then repeated once more over a 60-d period.

At the end of the wetting-drying cycles, individual 6.5 kg amended soil samples were packed to a depth of 7.6 cm in plexiglass cylinders (30.5 cm high by 26.7 cm i.d.) that were sealed at one end. The soil was placed on a 20.3-cm thick sand bed overlain by a porous fabric. The soil and sand bed was supported on a platform approximately 15 cm above the sealed bottoms of the cylinders. This arrangement permitted the soil samples to drain freely during the course of the rainfall simulator run. The soil surface was located approximately 2.5 cm below the top of the cylinder to lessen splash losses. Additionally, three holes (9.5 mm i.d.) were drilled through the cylinder wall, at the soil surface. Plastic tubing inserted in these holes and attached to a vacuum allowed for collection of all runoff without accumulation of water on the soil surface once the cylinders were tilted to the 10% slope used for each run.

Simulated rainfall was applied to three replications of each ferrihydrite amendment per soil, at an intensity of 64 mm h^-1 for 1.5 h with the multiple intensity rainfall simulator described by Meyer and Harmon (1979). All runoff and sediment generated during the simulated rainstorm were collected and weighed. Sediment samples were separated into >2, 2- to 1-, 1- to 0.5-, 0.5- to 0.25-, 0.25- to 0.125-, 0.125- to 0.053-, and <0.053-mm fractions, oven-dried at 105°C, and weighed. Estimates of infiltration were made by weighing the fully loaded cylinders in a dry condition, and again at the end of the rainfall simulator run. All statistical analyses utilized GLM Procedure of SAS version 8 (SAS Institute, 1999).

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY AND CONCLUSIONS REFERENCES

 
The unamended Texas soils (Amarillo, Gomez, Olton) had redder hues, coarser textures, lower OM and higher pH than those from Mississippi (Grenada, Routon). Despite their redder colors, the Texas soils had similar or lower Fe oxide contents than their Mississippi counterparts (Table 1). The differences in texture and OM are probably responsible for the substantially greater WDC contents of the Texas soils. High WDC generally also indicates a lower degree of aggregate stability.

View larger version (21K): [in this window] [in a new window]   Fig. 1. X-ray diffraction pattern of the Fe oxide sludge specimen used to amend soil samples showing (a) 2-line ferrihydrite (0.25 and 0.15 nm) and goethite (G), and (b) acid insoluble residue of quartz (Q) and kaolinite (K).

The fact that infiltration gradually increased on the acidic soils from Mississippi as the ferrihydrite amendment rates were increased suggests that soil pH and its effect on the electrical charge of the ferrihydrite is the dominant factor that determines infiltration. Specifically, at the pH of these soils (5.1 to 5.2) the ferrihydrite develops a net positive charge and thus forms a bond with the negatively charged clay and OM fractions. This results in improved aggregation and increased infiltration.

Runoff from the soils (Table 3) was inversely proportional to infiltration. The greatest runoff amounts were collected from the Routon B horizon, which had an average of 67.4 mm considering all amendment rates. As previously indicated, this soil had the least infiltration, an average of 16.2 mm. The Amarillo soil had the least runoff, at an average of 40.4 mm, and the highest infiltration, averaging 46.4 mm. The Routon B horizon and Amarillo represent the greatest disparity between infiltration and runoff. In most other instances, these two components were comparable in terms of how the applied rainfall was distributed. Relative to differences in runoff between ferrihydrite amendment rates, there were no significant (P < 0.05) changes until the rate reached or exceeded 16.80 Mg ha^-1. The Gomez, Grenada B, and Routon B materials showed no significant changes in runoff, regardless of amendment rate.

The soil loss data (Table 3) indicate that the Routon B and Olton soil materials produced the greatest amount of sediment, averaging 11.3 and 9.9 Mg ha^-1, respectively, over all amendment rates. The Grenada A and Routon A materials yielded the least amount of sediment, averaging 4.9 and 4.7 Mg ha^-1, respectively. These two soils also contained the highest concentrations of Fe_o and OM (Table 1). The remaining soils had sediment yields of 5.9 (Gomez), 5.5 (Grenada B), and 5.2 (Amarillo) Mg ha^-1. In terms of soil loss as a function of ferrihydrite amendment rates, the Texas soils generally became more erodible as rates were increased although few of the changes were significantly different from the 0 treatment until ferrihydrite amendments approached 16.80 and 33.60 Mg ha^-1. For the Gomez soil, no changes in soil loss were significantly different from the 0 amendment rate. The greatest increases in soil loss occurred in the Olton soil. These significant differences, which occurred after the addition of ferrihydrite at 0.34 Mg ha^-1 can probably be explained by the higher clay contents and the resulting greater exchange capacity (Table 1). At the highest pH levels, the soils with the greatest cation exchange capacity (CEC) will be the most affected by repeated additions of ferrihydrite, which presumably develops a net negative charge. In the case of Olton, the degree of dispersion and soil loss should increase accordingly. Conversely, the substantial decrease in soil loss for the Grenada A as a function of added ferrihydrite can also be attributed to a relatively high CEC. Unlike the Olton, however, the Grenada soil is strongly acid, which causes the ferrihydrite to develop a positive charge that contributes to greater soil aggregation and infiltration, and lower soil loss. The Routon A had a pH similar to Grenada A, but lower clay and OM contents that contributed to a substantially lower CEC, 5.7 versus 9.8 cmol kg^-1. Consequently, the ferrihydrite did not have as great an effect on aggregation.

Regression analysis of the infiltration and runoff data versus ferrihydrite amendment rate (Table 4) indicate a statistically significant relationship for all soils except Grenada B and Routon B. A possible explanation for the lack of a better relationship is that both materials had a very low OM content and CEC, which limited the effectiveness of ferrihydrite in terms of its ability to form aggregates. The only statistically significant interaction between ferrihydrite amendment rate and soil loss was recorded for the Amarillo and Olton soils. The low negative coefficient obtained for the high pH Gomez soil is probably because of interactions between the ferrihydrite and the high CaCO₃ content of the soil, which actually resulted in a slight decreasing trend in soil loss more similar to the acid soils. The exact mechanism involved in such a reaction is unclear at this time. The absence of a more significant relationship between soil loss and ferrihydrite content for the acid soils is not easily explained from the current data set. However, there are definite decreasing trends in soil loss (i.e., Grenada A, Routon B) with ferrihydrite rate.

	SUMMARY AND CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY AND CONCLUSIONS REFERENCES

 
Two groups of soils that are highly susceptible to erosion were treated with ferrihydrite, a poorly crystalline Fe oxide available as a byproduct of water treatment plants in regions that contain substantial concentrations of dissolved Fe in the ground water. Simulated rainfall was applied to these soils at an intensity of 64 mm h^-1 for 1.5 h after they had been amended with ferrihydrite at rates equivalent to 0.034, 3.36, 16.80, and 33.60 Mg ha^-1. Estimates of infiltration, runoff, and soil loss were made for all soils.

The data indicate that as the amendment rate increased, infiltration increased, and runoff and soil loss decreased for the two acid soils, Grenada and Routon. The changes in these parameters as a function of amendment rate were more pronounced in the A versus the B horizon of the Grenada soil, which had similar initial Fe_o contents but different OM contents. The Routon B horizon had much lower OM and Fe_o contents relative to the A horizon and responded more strongly to the ferrihydrite in terms of somewhat lower runoff and soil loss rates. For the higher pH Amarillo, Gomez, and Olton soils, infiltration decreased and runoff and soil loss increased with an increase in the ferrihydrite amendment rate.

The positive impact of ferrihydrite additions on the acid soils in terms of greater infiltration with less runoff and soil loss suggests an increase in aggregation. Conversely, the opposite is true for the high pH soils where infiltration decreased, and runoff and soil loss was increased by the addition of ferrihydrite. Apparently, in this case, the ferrihydrite promoted dispersion and aggregate instability. These differences in soil behavior can be attributed to the pH dependent charge characteristics of the ferrihydrite. The ZPC determined for the ferrihydrite used in this study was 6.8. At the strongly acidic pH values exhibited by the Grenada and Routon soils, the positively charged ferrihydrite bonded with negatively charged clay particles and OM to improve aggregation. At a soil pH above 6.8 the ferrihydrite developed a negative charge, which lead to increased soil dispersion with each additional increment. On the basis of the data collected from this group of soils, the use of ferrihydrite amendments to reduce runoff and soil loss is not recommended for soils with pH values exceeding 7.0, at this time. Conversely, ferrihydrite amendments show considerable promise in terms of improving aggregation for reductions in runoff and soil loss from acid soils. The data from these soils generally indicate that statistically significant increases in infiltration, and decreases in runoff and soil loss are realized between 3.36 and 16.80 Mg ha^-1 relative to the 0 treatment. Since our focus is on stabilizing the near surface zone of soils, we recommend that ferrihydrite be incorporated to a depth of only 2.5 cm. At an application rate of 16.80 Mg ha^-1 on an acre furrow slice basis, this translates into a ferrihydrite requirement of only 2.8 Mg ha^-1. Additional field research will be needed to develop methods of applying the ferrihydrite in slurry form using agricultural sprayer technology.

Received for publication June 11, 2002.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION SUMMARY AND CONCLUSIONS REFERENCES

 

• Borggaard, O.K. 1983. Iron oxides in relation to aggregation of soil particles. Acta Agric. Scand. 33:257–260.
• Childs, C.W. 1992. Ferrihydrite: A review of structure, properties and occurrence in relation to soils. Z. Pflanzenernähr. Bodenkd. 155:441–448.
• Colombo, C., and J. Torrent. 1991. Relationship between aggregation and iron oxides in Terra Rossa soils from southern Italy. Catena 18:51–59.
• Day, P.R. 1965. Particle fractionation and particle-size analysis. p. 545–568. In C.A. Black et al. (ed.) Methods of soil analysis. Part 1. Agron. Monogr. 9. ASA, Madison, WI.
• Desphande, T.L., P.J. Greenland, and J.P. Quirk. 1968. Changes in soil properties associated with the removal of iron and aluminum oxides. J. Soil Sci. 19:108–122.
• Duiker, S.W., F.E. Rhoton, J. Torrent, N.E. Smeck, and R. Lal. 2003. Iron (hydr)oxide crystallinity effects on soil aggregation. Soil Sci. Soc. Am. J. 66:606–611.
• Eggleton, R.A., and R.W. Fitzpatrick. 1988. New data and a revised structural model for ferrihydrite. Clays Clay Miner. 36:111–124.[Abstract]
• Ferreira Fontes, M.P. 1992. Iron oxide-clay mineral association in Brazilian Oxisols: A magnetic separation study. Clays Clay Miner. 40:175–179.[Abstract]
• Greenland, D.J., J.M. Oades, and T.W. Sherwin. 1968. Electron microscope observations of iron oxides in some red soils. J. Soil Sci. 19:121–126.
• Igwe, C.A., F.O.R. Akamigbo, and J.S.C. Mbagwu. 1995. Physical properties of soils of southeastern Nigeria and the role of some aggregating agents in their stability. Soil Sci. 160:431–441.
• Langdale, G.W., H.P. Denton, A.W. White, Jr., J.W. Gilliam, and W.W. Frye. 1985. Effects of erosion on crop productivity of southern soils. P. 251–270. In R.F. Follett and B.A. Stewart (ed.). Soil erosion and crop productivity, ASA, CSSA, and SSA, Madison. WI.
• McLean, E.O. 1982. Soil pH and lime requirement. p. 199–224. In A.L. Page et al. (ed.) Methods of soil analysis. Part 2. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI.
• Mehra, O.D., and M.L. Jackson. 1960. Iron oxide removal from soils and clays by a dithionite-citrate system buffered with sodium bicarbonate. Clays Clay Miner. 5:317–327.
• Meyer, L.D., and W.C. Harmon. 1979. Multiple intensity rainfall simulator for erosion research on row sideslopes. Trans. ASAE 22:100–104.
• Oades, J.M., and A.G. Waters. 1991. Aggregate hierarchy in soils. Aust. J. Soil Res. 29:815–828.
• Rhoton, F.E., and D.D. Tyler. 1990. Erosion-induced changes in the properties of a fragipan soil. Soil Sci. Soc. Am. J. 54:223–228.[Abstract/Free Full Text]
• Rhoton, F.E., D.L. Lindbo, and M.J.M. Römkens. 1998. Iron oxides–erodibility interactions for soils of the Memphis catena. Soil Sci. Soc. Am. J. 62:1693–1703.[Abstract/Free Full Text]
• Rhoton, F.E., J.M. Bigham, and D.L. Lindbo. 2002. Properties of iron oxides in streams draining the loess uplands of Mississippi. Appl. Geochem. 17:409–419.
• Rhoton, F.E., L.D. Meyer, and D.D. Tyler. 1990. Effects of past erosion on the interrill erodibility of a fragipan soil. J. Soil Water Conserv. 45:660–663.
• SAS Institute. 1999. The SAS system for windows. SAS Inst., Cary, NC.
• Schahabi, S., and U. Schwertmann. 1970. Der Einfluß von synthetischen Eisenoxiden auf die Aggregation zweier Lößödenhorizonte. (In German.) Z Pflanzenernähr. Bodenkd. 125:193–204.
• Schwertmann, U. 1964. Differenzierung der Eisenoxide des Bodens durch photochemische Extraktion mit saurer Ammoniumoxalat-lös-ung. (In German.) Z. Pflanzernernähr. Bodenkd. 105:194–202.
• Shanmuganathan, R.T., and J.M. Oades. 1982. Effect of dispersible clay on the physical properties of the B horizon of a red-brown earth. Aust. J. Soil Res. 20:315–324.
• Van Raij, B., and M. Peech. 1972. Electrochemical properties of some Oxisols and Alfisols of the tropics. Soil Sci. Soc. Am. Proc. 36:587–593.

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This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (6) Citing Articles via Google Scholar Google Scholar Articles by Rhoton, F. E. Articles by Upchurch, D. R. Search for Related Content PubMed Articles by Rhoton, F. E. Articles by Upchurch, D. R. GeoRef GeoRef Citation Agricola Articles by Rhoton, F. E. Articles by Upchurch, D. R. Related Collections Soil Mineralogy Soil Erosion Soil Chemistry