What is subsoil manuring? • A mechanical/engineering intervention • Large volumes (10-20 t/ha) of Nitrogen rich manures placed within the clay matrix of soil in a single deep ripping operation.

1. Subsoil Manuring
Crop and Soil responses to an innovative practice
in the low‐medium rainfall regions of Victoria
Renick Peries, Melissa Cann & Darryl Pearl (DEDJTR) &
Jaikirat S Gill & Peter Sale (LTU)

2. What is subsoil manuring?
• A mechanical/engineering intervention
• Large volumes (10-20 t/ha) of Nitrogen rich manures
placed within the clay matrix of soil in a single deep
ripping operation.

3. The problem with dense clay subsoils (HRZ)
Low macro‐porosity ……roots cannot breathe
High bulk density ……roots struggle to penetrate
Low infiltration ……cannot capture rainfall in subsoil
Frequently sodic ….. high sodium…ESP% > 15%

4. OUR APPROACH TO SOLUTIONS?
(VICTORIAN HRZ VS LOW TO INTERMEDIATE RAINFALL REGIONS)
• Low water productivity despite high rainfall
• Dense clay subsoils with low macro-porosity
?

5. Increasing the capacity to store PAW:
Catch more, store more grow more

6. Soil pit showing manure placed at depth
Photo: courtesy of SFS

7. subsoil manuring- benefits & setbacks
• Improves connectivity between
topsoil & subsoil
•Improves aeration & conductivity
•Improves bucket size
•Improves soil biology ?
•Improves yield & WUE
•Currently Expensive

8. Subsoil manuring: how does it transform clay?
manure
microbes
polysaccharides
+
clay particles
clay aggregates
Roots
clay particles
clay aggregates

9. SSM plot 30‐40 cmControl plot 30‐40 cm
……… 4 years after treatment
The amended clay layer is transformed
Increased macro‐porosity ……roots can now breathe, less waterlogging
Lower bulk density ……roots readily penetrate into subsoil
Rapid infiltration ……readily capture rainfall in subsoil

10. Crop and soil responses
in the low-intermediate rainfall zone

12. Rainfall @ the Mallee trial sites
2014 Site Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec RF(T) RF(GS)
Ouyen 3 64 6 63 21 10 17 4 62 3 25 15 292 179(84)
Hopetoun 8 9 14 64 22 21 23 8 14 2 26 7 211 154(92)
Charlton 5 8 36 56 23 35 24 7 13 11 41 16 275 169(57)
2015 Site Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec RF(T) RF(GS)
Ouyen 30 6 0.4 38 22 31 18 14 12 10 33 3.6 219 146(69)
Hopetoun 40 15 0.4 21 26 32 19 15 27 26 38 64 324 165(98)
Charlton 37 14 8 19 25 31 28 26 17 6 24 8.2 243 152(51)
Site Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec L‐T/(GS) mean
Ouyen 20.9 24.3 20.0 21.7 31.5 29.2 30.6 32.2 32.6 34.4 27.8 25.6 331.1 (212)
Hopetoun 33.9 14.2 17.6 21.5 25.0 24.1 26.3 24.8 23.2 22.7 29.9 29.3 293.3 (168)
Charlton 24.3 27.2 28.3 32.2 42.7 48.1 43.2 45.2 42.6 41.8 28.4 26.8 430.8 (296)

13. YEAR Rainfall period Rainfall
(mm)
Decile
ranking
Comments
Summer (Dec.‐Feb.) 91 7.3
Autumn (Mar.‐May) 90 7.5
2014 Winter (June‐August) 30.7 0.4 The 4th driest winter on record from 1913
Spring (Sept.‐Nov.) 90 5.6
Growing Season (Apr‐Oct.).) 179 3.9
Total Annual (Jan.‐Dec.) 293 3.9
Summer (Dec.‐Feb.) 51 3.9
Autumn (Mar.‐May) 61 4.8
2015 Winter (June‐August) 63 2.3
Spring (Sept.‐Nov.) 56 2.5
Growing Season (Apr‐Oct.) 146 1.8
Total Annual (Jan.‐Dec.) 218 1.3
Mean annual rainfall (1880‐2015) 330
Amounts and decile rankings for seasonal rainfall at Ouyen in 2014 and 2015,
from Ouyen Post Office recording station

14. YEAR Rainfall period Rainfall
(mm)
Decile
ranking
Comments
Summer (Dec.‐Feb.) 17 0.6 The second driest on record since 1998.
Autumn (Mar.‐May) 100 8.0
2014 Winter (June‐August) 52 1.7 .
Spring (Sept.‐Nov.) 42 0.6 The second driest on record since 1998.
Growing Season (Apr‐Oct.).) 154 2.3
Total Annual (Jan.‐Dec.) 211 1.3 The 3rd driest since on record since 1998.
Summer (Dec.‐Feb.) 62 6.4
Autumn (Mar.‐May) 150 10 The wettest on record since 1998.
2015 Winter (June‐August) 76 2.4 .
Spring (Sept.‐Nov.) 49 2.6
Growing Season (Apr‐Oct.) 155 2.7
Total Annual (Jan.‐Dec.) 246 3.3
Mean annual rainfall (1904‐2015) 502
Amounts and decile rankings for seasonal rainfall at Hopetoun in 2014 and 2015
measured at the nearby weather station at Wirrbibial Downs.

15. YEAR Rainfall period Rainfall
(mm)
Decile
ranking
Comments
Summer (Dec.‐Feb.) 22 1.2
Autumn (Mar.‐May) 113 6.3
2014 Winter (June‐August) 66 0.8 The 5th driest on record since 1952.
Spring (Sept.‐Nov.) 74 2.7 .
Growing Season (Apr‐Oct.).) 223 1.7
Total Annual (Jan.‐Dec.) 279 1.3 .
Summer (Dec.‐Feb.) 64 4.8
Autumn (Mar.‐May) 52 2.1
2015 Winter (June‐August) 85 1.6 The 4th driest on record since 1956.
Spring (Sept.‐Nov.) 47 0.8 The 4th driest on record since 1952.
Growing Season (Apr‐Oct.) 176 0.9 The 5th driest on record since 1952.
Total Annual (Jan.‐Dec.) 243 0.9 The 5th driest on record since 1954.
Mean annual rainfall (1954‐2015) 425
Amounts and decile rankings for seasonal rainfall at Charlton in 2014 and 2015
measured at the nearby weather station in Donald St., Charlton

16. Effect of subsoil manuring on the macro-porosity, saturated
hydraulic conductivity, and bulk density in the 10-30 and 30-50 cm
deep subsurface layers
Site Treatment
Macro‐porosity
(%)
Sat. Hydraulic
Conductivity (cm/hr)
Bulk Density
(g/cm3)
Depth (cm) Depth (cm) Depth (cm)
10‐30 30‐50 10‐30 30‐50 10‐30 30‐50
Ouyen
Control 18.9 13.1 1.67 0.84 1.39 1.46
Manured 17.5 15.6 1.67 1.05 1.38 1.41
Significance NS NS NS * NS *
P‐value 0.14 0.18 0.49 0.02 0.10 0.02
Hopetoun
Control 10.1 ‐ 0.33 ‐ 1.39 ‐
Manured 13.1 ‐ 0.65 0.15 1.33 1.38
Significance * ‐ *** ‐ * ‐
Charlton
P‐value
Control
Manured
Significance
P‐value
0.013
9.4
12.5
*
0.03
‐
‐
‐
‐
‐
0.001
0.47
0.76
NS
0.10
‐
‐
0.11
‐
‐
0.02
1.39
1.35
*
0.04
‐
‐
1.41
‐
‐

19. Grain/fodder yield obtained from the different
Mallee sites where SSM was attempted in 2014
Site 2014 2015
Treatment Crop Gr. Yield
(t/ha)
Crop Yield (Gr/Fodder)
(t/ha)
Ouyen SSM Barley 1.6 Wheat 0.86
Control Barley 0.3 Wheat 0.68
Hopetoun SSM Wheat 1.3 Vetch 0.32
Control Wheat 1.72 Vetch 0.34
Charlton SSM Wheat 0.41 Barley 1.17
Control Wheat 0.9 Barley 1.17

20. NO – SSM will NOT work
in dry country
YES – SSM will work in
dry country
• Not enough rain to open up
/ fill “subsoil bucket”
• Chemical constraints limit SSM
• Remote manure sources.
• SSM more cost‐effective, farmer‐
friendly; not reliant on manures
• Very effective water capture, top‐
soil and subsoil
• Chemical constraints not limit SSM

21. Conclusions:
• These trials were conducted in ‘tough’ environments in ‘tough’ times. Below average rainfall at
most sites impacted on crop growth and root proliferation.
• Inadequate rainfall to fill the bucket and to drive crop growth and root proliferation that will
trigger soil change, appeared to result in limited success with SSM in the low tomedium rainfall
zones.
• Despite the above, changes were still observed at some sites in the physical parameters
monitored.
• Timing of rainfall appeared to be important to trigger soil-root-microbial interactions: something
that could not be expected in sub-optimal rainfall years.
• Marginal differences in seasonal crop water use was observed that also resulted in small
differences in grain yield.
• Some sites showing exceptional results are worthy of being followed up for a few more years to
better understand the process of subsoil change in the low to medium rainfall zone.
• Chemical constraints may have contributed to inconsistent soil physical change contrary to the
expectation from SSM.

22. CURRENT STATUS OF THE PRACTICE OF SSM
• One paddock scale SSM machine in Victoria (1000+ ha)
• 4-5 Small scale SSM plot machines in Victoria, Southern NSW
SA, WA and Tasmania
• .

23. Thank You