A presentation delivered by Luke Mosely (Adelaide University) to the Soil Science Australia Workshop on salinity, sodicity and soil management under irrigated horticulture on the 19 Sept 2019 at Robinvale, Victoria.

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Before Drought After Drought

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From Quirk (1994). Advances in Agronomy 53.

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“Exchangeable” cations is an operational definition
based on soil extraction using an electrolyte solution of
given composition and pH but consensus is that it
includes diffuse ion swarm and outersphere complexes
(ie. not specifically absorbed inner sphere complexes)
Inner Sphere Complex
Diffuse ion
Outer
Sphere
Complex
Organic
Matter

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Mineral structure and surface complexes (incl.
organic matter) establish a charge, ions in diffuse ion
swarm (i.e. corresponding to bulk soil electrolyte
composition) are attracted to oppositely charged
surface which screens the charge at that surface
Na+
Na+
Ca2+
Na+
Ca2+
Na+
Na+
Ca2+
K+

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Higher ionic strength or higher charge cations (divalent
cf. monovalent) compresses electrical double layer,
particles can approach closely, van der Waals and other
attractive forces come into effect and allow aggregation
Na+
Na+
Ca2+
Na+
Ca2+
Na+
Na+
Ca2+ K+
Ca2+

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From Mosley et al. 2003
(Environmental Science & Technology
37, 3303-3308)

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From Mosley et al. 2003
(Environmental Science & Technology
37, 3303-3308)
From Ebeling et al. 2011
(Nanotechnology 22, 305706)
Sodicity

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1. Control (drainage only)
2. River Murray (RM) irrigation
3. Gypsum 15t/ha (plus 3 RM
irrigations)
4. Limestone 15 t/ha (plus 3 RM
irrigations)
5. Acid drainage single irrigation
(plus 3 RM irrigations)
6. Seawater single irrigation
(plus 3 RM irrigations)
Water Type EC pH SAR
dS/m
River Murray 0.252 7.31 1.7
Seawater 57.2 8.12 59.3
Acid drainage 39.8 3.42 34.8
100 mm irrigation water depth

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Drainage only resulted in increased soil salinisation, all
treatments receiving 3 irrigations had markedly
reduced salinity
Results – Soil Salinity

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Gypsum & limestone application (plus irrigation)
decreased exchangeable Na relative to control but
effects were not significantly different than for irrigation
only
Results – Exchangeable Sodium

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Gypsum & limestone application (plus irrigation)
increased exchangeable Ca relative to control but
effects were not significantly greater than for
irrigation only
Results – Exchangeable Calcium

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Free download on University of
Adelaide Press website:
https://www.adelaide.edu.au/pre
ss/titles/murray-soils/

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• Saline-sodic soils can be successfully
recovered in the LMRIA
• Irrigation water with low SAR and sufficient
dissolved Ca can recover soils without
adding gypsum (particularly useful in heavy
clays)
• Irrigation AND drainage important – keep
salt moving down out of root zone,
particularly important where shallow water
tables present such as in the LMRIA

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23. Cation Ionic Radius
(IR, nm)
Charge
(Z)
Ionic Potential (IP
= Z/IR, nm-1)
Na 0.102 1 9.8

24. Cation Ionic Radius
(IR, nm)
Charge
(Z)
Ionic Potential (IP
= Z/IR, nm-1)
Na 0.102 1 9.8
K 0.138 1 7.2
Ca 0.100 2 20
Mg 0.072 2 28
Fe 0.065 3 46
Al 0.054 3 56
From Sposito 2016, Chemistry of Soils 3rd Edition
Cations with IP <
30 nm-1 tend to
be found free in
soil solution
Cations with IP 30-
100 nm-1 tend to
hyrolyse and
precipitate as
insoluble metal
oxides
Cation affinity for soil surfaces: K+ > Na+ > Li+ > Ba2+ > Sr2+ > Ca2+ > Mg2+

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• Increasing evidence that Potassium can also influence soil
structural stability (although sodicity manifests more often
as Na normally more dominant in soil solution)
• Indices including K now developed, most notably the
Potassium Absorption Ratio (PAR) and Cation Ratio of
Structural Stability (CROSS, Rengasamy and Marchuk 2011):
𝐶𝑅𝑂𝑆𝑆 =
𝑁𝑎++0.56𝐾+
𝐶𝑎2++0.60𝑀𝑔2+
2
where cation concentrations are in mmol/L and 0.56 and
0.60 are coefficients relating the dispersive and flocculative
power of K and Mg, respectively, to Na and Ca, respectively.

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River Murray
water
Winery treated
wastewater
EC (μS/cm) 380 1286
pH 7.5 8
K+
(mmol/L) 0.09 3.22
Na+
(mmol/L) 1.75 7.00
Mg2+
(mmol/L) 0.32 0.29
Ca2+
(mmol/L) 0.27 0.75
Sodium Adsorption Ratio (SAR) 2.3 6.9
Potassium Adsorption Ratio (PAR) 0.1 3.2
Cation Ratio of Structural Stability
(CROSS)
3.7 13

28. Long-term results
showing build-up of
K+ in subsoils with
Mg2+ decrease and
slight decline of Na+,
and little change in
Ca2+
Note: BIL switched to NPEC since
2010 (see the horizontal line)

31. Site Turbidity (NTU)
BIL 2 (0 – 10 cm) 20
BIL 2 (10 – 20 cm) 21
BIL 2 (20 – 30 cm) 178
BIL 4 (0 – 10 cm) 19
BIL 4 (30 – 50 cm) 141

32. Sites Gypsum rate
(Calculated, t/ha)
BIL 2 (20 – 30 cm) 0.66 ± 0.05
BIL 4 (30 – 50 cm) 2.90 ± 0.19

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Adsorption of K, leaching of Na, Ca, Mg

35. Mike Carson and associates for providing the samples of
soils and the treated winery wastewater as well as
historical soil chemistry data provided by the North Para
Environmental Control (NPEC).
Tan Dang, Ivan Andelkovic, and Bogumila Tomczak for
assistance with laboratory analyses
Contact: luke.mosley@adelaide.edu.au