A presentation delivered by Sam North (NSW DPI) to the Soil Science Australia Workshop on salinity, sodicity and soil management under irrigated horticulture on the 19 Sept 2019 at Robinvale, Victoria.

1. 30+ years of research into the
management of salinity and
sodicity in irrigated Riverine
Plains soils
Sam North
NSW DPI, Deniliquin

2. Why manage salinity and sodicity
Salinity – affects plant growth
Sodicity – affects soil aggregate stability
Root zone salinity needs to be < threshold levels for max plant growth
• Osmotic effect
• Specific ion toxicity
• Nutritional disorders
Sodicity affects soil – infiltration, hydraulic conductivity
• If Na reaches levels that cause dispersion, then the ability to leach is lost.
• Salts then accumulate in the root zone to production limiting levels
Quirk & Schofield – Threshold Electrolyte Concentration
Salinity can only be managed when sodicity is managed

3. 1. Leach salts – strategic leaching crop
Thompson et al (1997) Final report for Project DAN8
Thompson, Hume, Slavich (1997)
• rice – wheat – 2 yrs pasture
• Red sodosol – 10 cm clay loam over heavy clay
• Treatments
• Control = channel water 0.15 dS/m
• Low salinity = 3 dS/m on wheat; 2 dS/m on sub-clover
• High salinity = 4.5 dS/m on wheat; 3 dS/m on sub-clover

4. Leach salts – effectiveness of fresh water
1 rice
crop
2 rice
crops
3 rice
crops
4 rice
crops
2 rice
crops
3 rice
crops
4 rice
crops
.1 rice
crop
Thompson et al (1997) Final report for Project DAN8

5. Leach salts – irrigation strategies
Soil = red chromosol (RBE)
Crop = lucerne
3 years – GW irrigated
Alternating highly saline-sodic
GW (6 dS/m; SAR 16) with CW did
not affect infiltration
Season average applied water
salinity may be used to estimate
effects on soils and plants
LF = 0.01 as shallow WT (1 m)
Followed by 2 years fresh water
60, 120 & 180 mm ET-R
Leaching better with 180 cf 120
SAR same pattern but less
affected
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 1 2 3 4 5 6 7 8
ECe (dS/m)
Depth(m)
GW
CW
60 mm
120 mm
180 mm
Slavich & Peterson (2002) AJEA 42, 281-290
North & Thompson - unpublished

6. Leach salts – winter rainfall
Bethune & Batey (2002) AJEA.42; 273-279
Bethune & Batey (2002)
• Tatura
• perennial pasture
• Red chromosol – 15 cm loam over heavy clay
• 10 years of saline irrigation
• Oct 1987 to Mar 1997, three treatments
• Control – 0.1 dS/m
• Low salinity = 2.5 dS/m & 12.5 SAR
• High salinity = 4.5 dS/m & 17.1 SAR
• Apr 1997 to Apr 1998 – fresh water at 0.1 dS/m

7. Bethune & Batey (2002)
• Red chromosol – Lemnos loam = 15 cm loam over heavy clay
• Changing from saline (2.5 & 4.5 dS/m) to fresh (0.1 dS/m) water reduced
infiltration
2.5 dS/m to 0.1 dS/m
4.5 dS/m to 0.1 dS/m
Saline irrigation Fresh water
irrigation
Bethune & Batey (2002) AJEA.42; 273-279
2. Changing to lower EC water - pasture
Cultivating the pasture reduced infiltration to near zero

8. Changing to lower EC water - lucerne
Soil = red chromosol (RBE)
Crop = lucerne
No gypsum prior to fresh water
Water-table had dropped
The soil remained stable due to:
1. Soil type – loam topsoil
2. No cultivation – intact stand
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 1 2 3 4 5 6 7 8
ECe (dS/m)
Depth(m)
GW
CW
60 mm
120 mm
180 mm
Slavich & Peterson (2002) AJEA 42, 281-290
North & Thompson - unpublished

9. 3. Effectiveness of gypsum
Bridge (1968) - use of gypsum to maintain ECiw > TEC
• Problem = pasture establishment on sodic soils
• Riv clay - ESP = 23; TEC = 1 dS/m; ECiw = 0.1 dS/m
• Solution = water-run gypsum to raise ECiw to 1 dS/m
• 75 mm irrigation = 0.6 t/ha gypsum cf 2-3 t/ha spread
Mehanni & Bleasdale (1983)
• High water-table under chromosol (A hor: 32% clay; ESP 8.3; ECw 7.8 dS/m)
• Gypsum ONLY effective when water-tables controlled
• Decreased ESP (8.3 down to 3.7%)
• Increased hydraulic conductivity (1.12 to 24.4 cm/day), infiltration (by
40%;), Cl leaching (by 33%) and yields (by 30-45%)
• Ripping (alone or with gypsum) was of no benefit
Mehanni & Rengasamy (1990)
• no effect of gypsum if ECiw > TEC (3.8 dS/m)

10. Effectiveness of gypsum
Slavich & Thompson (1993)
• 3 grey vertosols (1 highly saline); 2 sodosols
• Rice leached Cl beyond 90 cm
• Gypsum significantly increased Cl leaching
• Gypsum enhanced reduction in sodicity of surface soil under rice crops
Key messages
• Gypsum needs to be in surface soil to enhance leaching
• Leaching fractions of at least 0.1 required for salt balance for average
ECiw of 0.75 to 1.1 dS/m
• Better leaching with deep WT cf shallow
Highly saline, grey vertosol Red sodosol
Greater leaching with light soils, high ECiw & high gypsum rates

11. 4. Effectiveness of rainfall
Annualrechargebelow1.0mdepth(mm)
Hillston
Walpeup
Lucerne rotation
Medic rotation
Non-fallow rotation
Fallow rotation
Recharge below the root-zone is episodic
10% of annual recharge events account for 25-85% of long-term total recharge
Zhang et al (1999) Ag. Wat. Mgt. 42; 237-249

12. Effectiveness of rainfall – soil monitoring
NSW Murray valley soil monitoring
• 28 CW sites - 2002 & 2004
• 10 GW sites - 1996 & 2006
• 12 Deniboota sites – 1947 & 2017
Key observations
1. CW presents no risk re sodification
2. GW use poses a considerable risk
3. Rainfall over past 70 years has leached Cl but not Na
- impact on soil stability ??
North et al (2018) Sth NSW Research results. NSW DPI

13. McNeal et al (1968) – USSL Riverside
• Soil stability with saline/sodic water depends on clay mineralogy
• Kaoline & sesquioxides stable and 2:1 clays not
• Relationship also varies according to stress on soil aggregates
Shaw (1995)
• Unified soil property and sodicity model of salt leaching
• Soil sensitivity to Na: sand < kaolinite < montmorillonite < mixed
• Murray – soils are co-dominant kaolin/illite except SMC (+ smectite)
Shaw, Thorburn (2000)
• ANZECC guidelines (2000) – prediction of leaching fraction
Bennet & Raine (2012)
• No universal relationship between TEC & SAR & soil properties
Flocculated
Dispersed
5. Effect of soil type - Queensland

14. Summing up
• Soil stability is dependent on: clay content, clay mineralogy, organic
matter, cultivation, EC & SAR
• Control water-tables first
• Salinity can be managed by leaching with fresher water
• Na and dispersion can be managed with gypsum
• Winter rainfall can leach salts (climate change ?)
• Apply gypsum to dispersive soils before low EC water is applied
(e.g. in autumn) – water run gypsum??
• Reclamation is possible - gypsum; summer leach crop; surface irrig
DO NOT
• Cultivate dispersive soils
• Bare fallow
DO
• Apply a leaching fraction (> 0.1)
• Adopt conservation farming

15. Two goals
1. Keep RZ salinity below production limiting thresholds
2. Ensure soils remain flocculated so salts can be leached