Relationship between phosphate adsorption and forms of iron and aluminium oxides in Thai soils

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1 Symposium no. 28 Paper no Presentation: poster Relationship between phosphate adsorption and forms of iron and aluminium oxides in Thai soils WONGCHANDAENG Amara and KEERATI-KASIKORN Pirmpoon Department of Land Resources and Environment, Faculty of Agriculture, Khon Kaen University, Thailand Abstract The northeast region of Thailand possessed highly weathered soils. They contain a significant amount of iron and aluminium oxides which could be important factors responsible for high proportion of applied phosphate retaining. Very little information is available on which forms of iron and aluminium oxides are responsible for phosphate adsorption by the soils. This study was carried out to investigate the relationship between phosphate adsorption and forms of iron and aluminium oxides in selected soils of Northeast Thailand. Five soils of three depths containing variable amounts of crystalline, amorphous and organic bound iron and aluminium oxides were shaken for half an hour, twice a day for 7 days at 25 o C with 0.01 M CaCl 2 solution containing a series of known phosphate concentration. Soil solution ratio was 1:10. After filtration, the amount of phosphate remaining in the supernatant solution was measured. The amount of adsorbed phosphate was determined by the difference. Phosphate adsorption of all five surface soils and of only three subsurface ones could be described by the Langmuir equation. The calculated maximum adsorbed phosphate was significantly correlated with amorphous iron oxides (r = 0.849**) and organic bound iron oxides (r = 0.800**) and with crystalline aluminium oxides (r = 0.763**); whereas the crystalline iron oxide and both amorphous and organic aluminium oxides were not responsible for the adsorption. Keywords: phosphate adsorption, amorphous, crystalline, organic bound iron and aluminium oxides, Northeast Thailand Introduction The northeast region of Thailand possessed highly weathered soils. They contained an appreciable amount of iron and aluminium oxides which could be one of the important factors responsible for retaining high proportion of the applied phosphorus (Keerati-Kasikorn et al, 1996). The oxides could be divided into three forms according to chemical analyses, i.e. dithionite-citrate extractable representing crystalline and amorphous form, oxalate extractable representing amorphous while pyrophosphate extractable representing organic bound oxides (Mekeague et al., 1971). Soils in the northeast Thailand contained variable amount of different forms of iron and aluminium oxides (Unpublished data). There were studies on the phosphate forms in the northeast soils using a sequential method which divided phosphate forms into the following: water soluble, reductant soluble, aluminium, occluded aluminium, iron and occluded iron phosphate. Iron phosphate and reductant soluble phosphate were dominant in the

2 upland soil (Yimprasert, 1971) and lowland soil (Srisan et al., 1979) respectively. There was no information available on the relationship between phosphate adsorption and the form of oxides in the form of crystalline, amorphous and organic bound. Thus, the objective of this study was to determine the relationship between phosphate adsorption and the forms of iron and aluminium oxides in some of the northeast soils of Thailand. Materials and Methods Five different soil series were used. Their classification is shown in Table 1. some physical and chemical properties were in Table 2. Table 1 Classification of studied soil series of Northeastern Thailand. Soil series Symbol Family Great group Lob Buri Lb Typic Pellusterts; Veryfine, Grumusols montmorillonitic Ratchaburi Rb Aeric Tropaquepts; Fine, Hydromorphic Alluvial mixed, non-acid Yasothon Yt Oxic Paleustults; Fineloamy, Red Yellow Latosol Siliceous Korat Kt Oxic Paleustults; Fineloamy, Gray Podzolic siliceous Roi Et Re Aeric Paleaquults : Fineloamy, mixed Low humic grey Table 2 Some physical and chemical properties of five soil series of Northeastern Thailand. Soil Depth Avail.P CEC Particle size Texture O.M. (%) Total C (%) series (cm) (mg kg -1 ) (NH 4 OAC) %sand %silt %clay class Kt Yt SL SCL SCL SCL Rb C C C Re LS L L Lb L C CL The amount of iron and aluminium oxides in different forms of the soils were determined by methods described in Mekeague and Day (1966). They were extracted by dithionite-citrate-bicarbonate (DCB), oxalate, and pyrophosphate. Extractable DCB iron and aluminium oxides represented the crystalline and amorphous whereas the oxalate extractable represented only the amorphous. Therefore, the amount of crystalline oxides was obtained by the difference. Pyrophosphate extractable was the amount of organic complexed iron and aluminium oxides

3 The procedure for phosphate adsorption followed the method by Fox and Kamprath (1970) with seven day shaking time. Soil samples were shaken with 0.01 M CaCl 2 containing a series of phosphate concentration. Supernatant liquid was determined for phosphorus by the method described in Murphy and Riley (1962). Adsorbed phosphate was determined by difference. Result and Discussion Phosphate adsorption isotherms are shown in Figure 1. The adsorption of all surface and three subsurface soils could be described by Langmuir equation. The parameters are shown in Table 3. The adsorption maxima of all surface and subsurface are in the following order: Lb > Rb > Re > Yt > Kt. Table 3 Parameters calculated from the Langmuir equation. Soil series Depth (cm) Max. Ads. P (mg P kg -1 ) K + R 2 Lb ** ** ** Rb ** ** ** ** Yt ** ** ** ** Re ** ** NS Kt ** NS ** Tr = constant related to adsorption affinity

4 (a) Surface soil (a) Surface soil Lb 0-25 Yt 0-25 Rb 0-18 Adsorbed P (ugp g -1 ) Re 0-18 Kt [P] in equilibrium solution (ugp ml -1 ) (b) Subsurface 1 Adsorbed P (ugp g -1 ) Lb40-80 cm. Yt cm. Rb cm. Re cm. Kt cm [P] in equilibrium solution (ugp ml -1 ) Adsorbed P (ugp g -1 ) (c) Subsurface 2 (c) Subsurface 2 Lb cm Yt cm. Rb cm Re cm. Kt cm Rb cm. Yt cm [P] in equilibrium solution (ugp ml -1 ) Figure 1 Phosphate adsorption isotherms of five soil series of Northeastern Thailand

5 The amount iron and aluminium oxides in three different forms is shown in Tables 4 and 5. In general, the five soil series possessed iron oxides more than aluminium oxides. Mostly the crystalline form of iron oxides in all soils is in higher proportion than the amorphous and organic ones. The highest amount was found in Rb, Re and Yt soil series, following by the Lb and Kt. For aluminium oxides, the amount of different forms in all soils appears to be scattered and very low. Yimprasert (1971) use a sequential extraction method to study the form of phosphate in the upland and lowland soils of the Northeast region and reported that most of phosphate is in iron phosphate form, Aluminum phosphate was much less and water soluble one was very little. Using similar method for the paddy soil, Srisan (1979) reported that phosphate in the form of reductant soluble phosphate was the highest followed by iron phosphate whereas calcium phosphate and aluminium phosphate were in a trace amount. Water soluble and loosely bound phosphate were even lesser. Table 4 Amount of crystalline, amorphous and organic bound iron oxides in the five soil series of Northeastern Thailand. Dithionite-extractable Crytalline Amorphous Fe Pyrophosphate Fe Dept Series Fe Fe (cm) %Fe 2 O 3 %Fe 2 O 3 %Fe 2 O 3 %Fe 2 O 3 Lb Rb Yt Kt Re

6 Table 5 Amount of crystalline, amorphous and organic bound aluminium oxides in the five soil series of Northeastern Thailand. Series Depth (cm) Dithionite-extractable Crytalline Amorphous Al Pyrophosphate Al Al Al %Al 2 O 6 %Al 2 O 3 %Al 2 O 5 %Al 2 O 4 Lb Rb Yt Kt Re The relationship between phosphate adsorption capacity and iron and aluminium oxides in different forms is shown in Table 6. For iron oxides, the amorphous and organic complex forms were responsible for the adsorption but for aluminium oxides, the crystalline form was. Borggard et al. (1990) found the phosphate sorption maximum was significantly correlated with poorly crystalline Fe and Al oxides and well-crystallized Fe oxide. Freese et al. (1992) found that the total phosphate sorption measured was predominantly related to the amounts of amorphous iron and aluminium, but not to the crystalline iron. It appears that the relationship reported was inconsistant and could depend on other factors. As shown in Table 7, crystalline iron was related to clay percentage. Pyrophosphate extractable iron oxide crystalline as well as amorphous and pyrophosphate aluminium oxides related to organic matter and total carbon. It was interesting to see that available phosphorus which could partly be the retained phosphate in the soil was related to amorphous and organic bound iron which consistant with this study (Table 6). However, the relationship between available phosphorus and aluminium oxides was partly agreed

7 Table 6 Correlation between phosphate adsorption maxima and iron and aluminium oxides in different forms of five soil series of Northeastern Thailand. Max. Adsorbed P (mgp/kg) Correlation coefficient ( r ) Iron oxides + Aluminium oxides + Dithionite Crystalline Amorphous Organic bound Dithionite Crystalline Amorphous Organic bound NS NS 0.849** 0.800** 0.784** 0.763** NS NS + crystalline = dithioinite extractable minus oxalate extractable iron and aluminium oxides amorphous = oxalate extractable iron and aluminium oxides organic bound = pyrophosphate extractable iron and aluminium oxides Table 7 Correlation between maximum phosphate adsorption and some chemical properties. Correlation coefficient (r) Clay (%) Organic matter Avail.P CEC Total C (%) Adsorbed P max 0.568** 0.728** 0.717** 0.821** 0.735** Dithionite-exrractable Fe ** NS NS 0.344** NS Crystalline Fe ** NS NS 0.342** NS Amorphous Fe ** 0.682** 0.580** 0.712** NS Pyrophosphate Fe NS 0.756** 0.598** 0.462** 0.715** Dithionite-exrractable Al ** 0.375** 0.883** Crystalline Al NS ** 0.272** 0.326** 0.601** Amorphous Al NS 0.394** 0.426** NS 0.396** Pyrophosphate Al NS 0.678** 0.667** NS 0.671** + 53 samples of Northeast Thai soils. Conclusion Phosphate adsorption of all five surface soils and of only three subsurface ones could be described by the Langmuir equation. The calculated maximum adsorbed phosphate was significantly correlated with amorphous iron oxides and organic bound iron oxides and with crystalline aluminium oxides; whereas the crystalline iron oxide and both amorphous and organic aluminium oxides were not responsible for the adsorption. Acknowledgements The authors would like to thank Mr. Somsak Sukchan, Department of Land Development, Ministry of Agriculture and Cooperatives for collecting and classifying soil samples, Department of Land Resources and Environment and JICA Laboratory Annex, Faculty of Agriculture, Khon Kaen University for working facilities, and Khon Kaen University through the research project "Use of Sorption Isotherms to Determine Phosphorus Requirement of Northeastern Soils for Improving Phosphorus Fertilizer Application" for funding. References Borggaard, O.K., S.S. Jorgensen, J.P. Moberg and B. Raben-Lange Influence of organic matter on phosphate adsorption by aluminum and iron oxides in sandy soil. J. Soil Sci. 41: Fox, R.L. and E.J. Kamprath Phosphorus sorption isotherms for evaluating the phosphate requirement of soils. Soil Sci. Soc. Am. Proc. 34:

8 Freese, D., S.E.A. T.M. van der Zee and W.H. van Riemsdijk Comparison of different models for phosphate adsorption as a function on the iron and aluminium oxides of soils. J. Soil Sci. 43: Keerati-Kasikorn, P., S. Kaewrahun and V. Trelo-ges Effectiveness of vetiver and pasture crops on controlling runoff and loss of applied fertilizers on sandy soil of an undulating landform, pp In Proceedings of the First International Conference on Vetiver. A Miracle Grass. Chiangrai, Thailand. Mckeage, J.A. Brydon and N.M. Miles Differentiation of forms of extractable iron and aluminum in soil. Soil. Sci. Soc. Am. Proc. 35: Murphy, J. and J.P. Riley A modified single solution method for the detemination of phosphates in natural waters. Anal. Chem. Acta 27: Srisan, M., N. Chontanapab, O. Serayotsakon, P. Sangthong and K. Subsorn Chemistry and fertility of paddy soils. Report on Soil Chemistry and Fertility No.7. Dept. of Agric. Ministry of Agriculture and Cooperation. pp (in Thai). Yimprasert, S A study on the different forms of inorganic phosphorus of some selected northeast phosphorus of some selected northeast soils. Annual Report. Northeast Agricultural Centre, Khon Kaen, Ministry of Agriculture and Cooperative. pp (in Thai)

Effects of Shaking Times on Phosphorus Adsorption by Some Laotian Ferric and Haplic Acrisols

Effects of Shaking Times on Phosphorus dsorption by Some Laotian Ferric and Haplic crisols Souphalak tbandit*, Pirmpoon Keerati-Kasikorn*, Krirk Pannangpetch** and Jilavat Sanitchon** bstract Phosphorus