Soil Research Soil Research Society
Soil, land care and environmental research

Positive charge discovered across Western Australian wheatbelt soils challenges key soil and nitrogen management assumptions

M. T. F. Wong A B and K. Wittwer A

A CSIRO, Private Bag 5, Wembley, WA 6913, Australia.

B Corresponding author. Email:

Australian Journal of Soil Research 47(1) 127-135
Submitted: 28 April 2008  Accepted: 4 December 2008   Published: 18 February 2009


Nitrogen management in Western Australia (WA) and in cropping areas elsewhere in Australia assumes that soil contains negligible or no positive charge and is therefore unable to retain nitrate against leaching. The amount of water needed to displace nitrate is thus assumed to be the drainable volume of water held by the soil (1 pore volume), and in sandy soils about 100 mm drainage is assumed to be required to displace nitrate by 1 m. The clay mineralogy of the highly weathered soils of the WA wheatbelt is dominated by kaolinite and iron and aluminium oxides. This mineralogy suggests likely occurrence of positive charge and anion exchange capacity (AEC), since these minerals can carry positive charge under normal acidic field situations. We measured AEC of soils sampled widely across the WA wheatbelt by independent leaching and batch equilibration methods of charge measurement. This showed widespread occurrence of positive charge and AEC in these soils. AEC ranged from 0 to 2.47 mmolc/kg and is linearly correlated with the potassium chloride or monocalcium phosphate extractable sulfate content of the soil. This correlation provides a rapid screening method to identify soils with positive charge. Application of ion-chromatographic theory showed that AEC has a large effect in delaying nitrate leaching by up to 12.5 pore volumes. The most highly charged soil (2.47 mmolc/kg) thus needed 12.5 times more water to displace nitrate than currently assumed. This potentially large delay in nitrate leaching affects the optimum amount and time of fertiliser application, rates of soil acidification attributed to nitrate leaching and the benefit of ameliorating subsoils to allow roots access to subsoil water and leached nitrate. It also calls into question the use of anions such as bromide to trace water flow and estimate recharge in these soils.

Additional keywords: anion exchange capacity, AEC, leaching delay, nitrate adsorption, pore volume, variable charge, charge : sulphate ratio.


Asseng S Fillery IRP Anderson GC Dolling PJ Dunin FX Keating BA 1998 Use of the APSIM wheat model to predict yield, drainage, and NO3 - leaching for a deep sand. Australian Journal of Agricultural Research 49 363 377 doi:10.1071/A97095

Blair GJ Chinoim N Lefroy RDB Anderson GC Crocker GJ 1991 A sulfur test for pastures and crops. Australian Journal of Soil Research 29 619 626 doi:10.1071/SR9910619

Bolland MDA Posner AM Quirk JP 1976 Surface charge on kaolinites in aqueous suspension. Australian Journal of Soil Research 14 197 216 doi:10.1071/SR9760197

Bolland MDA Windsor DP 2007 Converting reactive iron, reactive aluminium, and phosphorus retention index (PRI) to the phosphorus buffering index (PBI) for sandy soils of south-western Australia. Australian Journal of Soil Research 45 262 265 doi:10.1071/SR07026

Bowden JW Posner AM Quirk JP 1977 Ionic adsorption on variable charge mineral surfaces. Theoretical-charge development and titration curves. Australian Journal of Soil Research 15 121 136

Clay DE Zheng Z Liu Z Clay SA Trooien TP 2004 Bromide and nitrate movement through undisturbed soil columns. Journal of Environmental Quality 33 338 342

Donn MJ Menzies NW 2005 a Simulated rainwater effects on anion exchange capacity and nitrate retention in Ferrosols. Australian Journal of Soil Research 43 33 42

Donn MJ Menzies NW 2005 b The effect of ionic strength variation and anion competition on the development of nitrate accumulations in variable charge subsoils. Australian Journal of Soil Research 43 43 50 doi:10.1071/SR04036

Donn MJ Menzies NW Risiah V 2004 Chemical characterisation of deep profile Ferrosols under sugarcane in wet tropical northern Queensland. Australian Journal of Soil Research 42 69 77 doi:10.1071/SR03052

Gerritse RG Adeney JA 1992 Tracers in recharge – effects of partitioning in soils. Journal of Hydrology 131 255 268 doi:10.1016/0022-1694(92)90221-G

Gilkes RJ Hughes JC 1994 Sodium fluoride pH of South-western Australian soils as an indicator of P-sorption. Australian Journal of Soil Research 32 755 766 doi:10.1071/SR9940755

Gillman GP 2007 An analytical tool for understanding the properties and behaviour of variable charge soils. Australian Journal of Soil Research 45 83 90 doi:10.1071/SR06117

Gillman GP Sumpter EA 1986 Surface charge characteristics and lime requirements of soils derived from basaltic, granitic and metamorphic rocks in high-rainfall tropical Queensland. Australian Journal of Soil Research 24 173 192 doi:10.1071/SR9860173

McArthur WM (2004) ‘Reference soils of south-western Australia.’ (Eds DAW Johnston, LJ Snell) (Australian Society of Soil Science Incorporated (Western Australian Branch): Perth, W. Aust.)

McKenzie NJ , Jacquier D , Isbell R , Brown K (2004) ‘Australian soils and landscapes. An illustrated compendium.’ (CSIRO Publishing: Collingwood, Vic.)

Moody PW , Cong PT (2007) SCAMP: A decision support system for sustainable soil management of upland soils. In ‘Field and Laboratory Handbook and Interpretative Guidelines’. ACIAR Technical Report. (Australian Centre for International Agricultural Research: Canberra)

Mott CJB (1988) Surface chemistry of soil particles. In ‘Russell’s soil conditions and plant growth’. 11th edn (Ed. A Wild) pp. 239–281. (Longman: Essex, UK)

Qafoku NP van Ranst E Noble A Baert G 2004 Variable charge soils: their mineralogy, chemistry and management. Advances in Agronomy 84 159 215 doi:10.1016/S0065-2113(04)84004-5

Rasiah V Armour JD Menzies NM Heiner DH Donn MJ 2004 Impact of pre-existing sulphate on retention of imported chloride and nitrate in variable charge soil profiles. Geoderma 123 205 218 doi:10.1016/j.geoderma.2004.02.001

Rasiah V Armour JD Menzies NM Heiner DH Donn MJ Mahendrarajah S 2003 Nitrate retention under sugarcane in wet tropical Queensland deep soil profiles. Australian Journal of Soil Research 41 1145 1161 doi:10.1071/SR02076

Rayment GE , Higginson FR (1992) ‘Australian laboratory handbook of soil and water chemical methods – Australian soil and land survey handbook.’ (Inkata Press: Melbourne, Vic.)

Robertson MJ Isbister B Maling I Oliver Y Wong MTF Adams M Bowden JW Tozer P 2007 Opportunities and constraints for managing within-field spatial variability in Western Australian grain production. Field Crops Research 104 60 67 doi:10.1016/j.fcr.2006.12.013

Tabatabai MA (1982) Sulfur. In ‘Methods of soil analysis. Part 2. Chemical and microbiological properties’. 2nd edn (Eds AL Page, RH Miller, DR Keeney) pp. 501–538. (American Society of Agronomy, Inc., Soil Science Society of America Inc.: Madison, WI)

Verberg K , Braschkat J , Hochman Z , Moore AD , Helyar KR , Probert ME , Hargreaves JNG , Simpson RJ (2003) Modelling acidification processes in agricultural systems. In ‘Handbook of soil acidity’. (Ed. Z Rengel) pp. 135–187. (Marcel Dekker, Inc.: New York)

Wild A (1981) Mass flow and diffusion. In ‘The Chemistry of soil processes’. (Eds DJ Greenland, MHB Hayes) pp. 37–80. (Wiley: Chichester, UK)

Wong MTF Asseng S 2007 Yield and environmental benefits of ameliorating subsoil constraints under variable rainfall in a Mediterranean environment. Plant and Soil 297 29 42 doi:10.1007/s11104-007-9316-3

Wong MTF Asseng S Robertson MJ Oliver Y 2008 Mapping subsoil acidity and shallow soil across a field with information from yield maps, geophysical sensing and the grower. Precision Agriculture 9 3 15 doi:10.1007/s11119-008-9052-6

Wong MTF Asseng S Zhang H 2006 A flexible approach to managing variability in grain yield and nitrate leaching at within-field to farm scales. Precision Agriculture 7 405 417 doi:10.1007/s11119-006-9023-8

Wong MTF , Hairiah K , Alegre J (2004) Managing soil acidity and aluminium toxicity in tree-based agroecosystems. In ‘Below-ground interactions in tropical agroecosystems. Concepts and models with multiple plant components’. (Eds M Van Noordwijk, G Cadisch, CK Ong) pp. 143–156. (CABI Publishing: Oxfordshire, UK)

Wong MTF Hughes R Rowell DL 1990 a Retarded leaching of nitrate in acid soils from the tropics: measurement of the effective anion exchange capacity. Journal of Soil Science 41 655 663 doi:10.1111/j.1365-2389.1990.tb00234.x

Wong MTF Hughes R Rowell DL 1990 b The retention of nitrate in acid soils from the tropics. Soil Use and Management 6 72 74 doi:10.1111/j.1475-2743.1990.tb00805.x

Wong MTF van der Kruijs ACBM Juo ASR 1992 Leaching loss of calcium, magnesium, potassium and nitrate derived from soil, lime and fertilizers as influenced by urea applied to undisturbed lysimeters in south-east Nigeria. Fertilizer Research 31 281 289 doi:10.1007/BF01051280

Wong MTF Wild A Juo ASR 1987 Retarded leaching of nitrate measured in monolith lysimeters in south-east Nigeria. Journal of Soil Science 38 511 518 doi:10.1111/j.1365-2389.1987.tb02286.x

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