1) The document discusses how summer rainfall can benefit wheat production in Mediterranean environments of South Australia that typically receive most rainfall in winter. 2) Adding simulated summer rainfall of 50-100mm increased wheat shoot dry matter, PAR interception, and soil water content compared to control plots with only background rainfall. 3) Nitrogen is important for capturing the benefits of summer rainfall to maximize wheat yields.

1. Nitrogen is essential to capture the benefit of
summer rainfall for wheat in Mediterranean
environments of South Australia
Victor Sadras, Chris Lawson
Peter Hooper, Glenn McDonald
South Australian Research & Development Institute
Hart Field Site, The University of Adelaide
Funded by Grains R&D Corporation
Brisbane, September 2011

2. Climate gives rise to predictable types of ecosystems
Terry Chapin

3. Ryan et al. (2009) Advances in Agronomy 104:53-136

4. Background. Rainfall patterns as drivers of
cropping systems
What is the value of summer rainfall in regions
with winter-dominant rainfall?
What are the physiological mechanisms involved
in the conversion of summer rainfall to yield?
What is the role of nitrogen to capture the benefit
of summer rainfall?

5. Three features of rainfall shape
cropping systems
Amount
Seasonality
Size of events

7. Markham’s seasonality vector
Williamson (2007)

8. Rainfall seasonality drives initial soil water
maximum PAW = 146 mm
North-eastern environment South-eastern environment
summer rainfall winter rainfall
50 (a) Emerald 50 (b) Horsham
40 median = 124 mm 40 median = 27 mm
Frequency (%)
30 30
20 20
10 10
0 0
0 20 40 60 80 100 120 140 160 0 20 40 60 80 100 120 140 160
Plant available water at sowing (mm)
Sadras & Rodriguez (2009) Australian J Agr Res 58:657-669

9. power laws describe size-structure of rainfall
5
(a)
Horsham
Emerald
4 = -3.1
log number of events
3
2
= -1.9
1
0
0.0 0.5 1.0 1.5 2.0 2.5
log size of event
low
Sadras -1.6
& Rodriguez (2007) Australian J Agr Res 58:657

10. Size of rainfall events
Influence fate of water – evaporation, run-off, drainage
20
(a)
Runoff (mm)
15
10
5
0
150 200 250 300 350 400
Seasonal rainfall (mm)
12
(b)
Residuals (mm)
8
P < 0.0001
4
0
-4
2.8 3 3.2 3.4 3.6 3.8
Sadras (2003) Australian J Agr Res 54:341-351

11. Winter half year
Williamson (2007)

12. SE Australia vs. Syria
5
(a)
Horsham
4 = -3.1 Tel Hadya
log number of events
3
= -3.0
2
1
0
0.0 0.5 1.0 1.5 2.0
log size of event

13. Ryan et al. (2009) Advances in Agronomy 104:53-136

14. Climate of SE Australia shares important
features with those of the Mediterranean Basin
Australian wheat-based cropping systems match
the systems that evolved over centuries in the
Mediterranean basin
Australian wheat-based cropping systems are
not ill-adapted European transplants

15. Background. Rainfall patterns as drivers of
cropping systems
What is the value of summer rainfall in regions
with winter-dominant rainfall?
What are the physiological mechanisms involved
in the conversion of summer rainfall to yield?
What is the role of nitrogen to capture the benefit
of summer rainfall?

16. Yield benefit from summer rainfall?
Five trials @ Roseworthy, Hart, Spalding
Seasons: 2009 and 2010
controls (background rain) vs “summer rainfall” (+50 or 100 mm)
Sadras et al (2011) European Journal of Agronomy, in press

17. Benefit from 20% for controls ~2 t/ha
to 0 for controls ~6 t/ha
measured modelled
Yield of crops with additional
summer water supply (t/ha)
8
slope = 0.81 ± 0.097 slope = 0.75 ± 0.070
intercept = 1.4 ± 0.46 intercept = 1.7 ± 0.30
6
4
2
y=x y=x
0
0 2 4 6 80 2 4 6 8
Yield of controls (t/ha)

18. Background. Rainfall patterns as drivers of
cropping systems
What is the value of summer rainfall in regions
with winter-dominant rainfall?
What are the physiological mechanisms involved
in the conversion of summer rainfall to yield?
What is the role of nitrogen to capture the benefit
of summer rainfall?

19. 8000
control
***
Shoot dry matter (kg/ha)
+50 mm
+100 mm
**
6000
4000
***
2000
GS 32 GS 65 GS 95
0
0 50 100 150 200
Days after sowing

20. Cumulative PAR interception (%)
evapotranspiration (mm)
0
100
200
300
0
20
40
60
80
100
0
50
100
Days after sowing
150
200

21. 5 d after irrigation
0
***
Soil depth (cm)
***
-30 ***
*
*
-60 **
**
*
-90 control *
+50 mm *
+100 mm ***
-120 ***
0 10 20 30 40
Soil water content (mm)

22. sowing
0
Soil depth (cm)
-30
control
-60 *
+100mm
*
-90 **
**
**
-120 **
0 10 20 30 40
Soil water content (mm)

23. stem elongation
0
Soil depth (cm)
-30
-60
-90 control *
*
**
-120 **
0 10 20 30 40
Soil water content (mm)

24. flowering
0
Soil depth (cm) -30
-60
-90
*
-120 **
0 10 20 30 40
Soil water content (mm)

25. maturity
0
Soil depth (cm) -30
*
-60
-90
*
-120 *
0 10 20 30 40
Soil water content (mm)

26. Residual water at maturity in N-deficient crops
Roseworthy, 2010
0
maturity
Soil depth (cm)
-20
-40
low N
-60
high N
-80
-100
0 5 10 15
Soil water content (mm)

27. Grain number accounted for 88% of the variation in yield
8000
6000
Yield (kg/ha)
4000
2000 bare ground, Exps 1, 2
stubble, Exps 1, 2
high H, Exps 3-5 r = 0.94
low N, Exps 3-5 P <0.0001
0
0 5000 10000 15000 20000
2
Grain number (per m )

28. Grain number = Grain number (per m2) and anthesis)
f (CGR between stem elongation
20000
(c)
Grain number (per m )
(b)
2
P < 0.
Low N
15000
10000
5000 bare ground, Exps 1, 2
stubble, Exps 1, 2
high H, Exps 3-5
r = 0.65
low N, Exps 3-5 P <0.002
0
0 50 100 150 200 low
Crop growth rate (kg/ha/d) Nitrog

29. Variable 0 mm 0 mm +100mm +100mm P W PN P X
Low N High N Low N High N
Shoot biomass (t/ha) 12.3 11.8 12.2 15.6 ** ** **
Yield (t/ha) 5.8 5.6 5.7 7.2 ** ** **
Grain number (103 x m-2) 13.0 13.8 12.8 17.1 * ** *
Harvest Index 0.42 0.42 0.42 0.42 - - -
Grain size (mg) 42.7 39.3 42.5 40.2 - - -
RUE (g/MJ) 1.64 1.57 1.50 1.89 - * **
Biomass/ET (kg/ha. mm) 34.9 33.0 32.2 40.0 - - **
Yield/ ET (kg/ha. mm) 15.9 15.3 14.5 18.0 - * **

30. Variable 0 mm 0 mm +100mm +100mm P W PN P X
Low N High N Low N High N
Shoot biomass (t/ha) 12.3 11.8 12.2 15.6 ** ** **
Yield (t/ha) 5.8 5.6 5.7 7.2 ** ** **
Grain number (103 x m-2) 13.0 13.8 12.8 17.1 * ** *
Harvest Index 0.42 0.42 0.42 0.42 - - -
Grain size (mg) 42.7 39.3 42.5 40.2 - - -
RUE (g/MJ) 1.64 1.57 1.50 1.89 - * **
Biomass/ET (kg/ha. mm) 34.9 33.0 32.2 40.0 - - **
Yield/ ET (kg/ha. mm) 15.9 15.3 14.5 18.0 - * **

31. Variable 0 mm 0 mm +100mm +100mm P W PN P X
Low N High N Low N High N
Shoot biomass (t/ha) 12.3 11.8 12.2 15.6 ** ** **
Yield (t/ha) 5.8 5.6 5.7 7.2 ** ** **
Grain number (103 x m-2) 13.0 13.8 12.8 17.1 * ** *
Harvest Index 0.42 0.42 0.42 0.42 - - -
Grain size (mg) 42.7 39.3 42.5 40.2 - - -
RUE (g/MJ) 1.64 1.57 1.50 1.89 - * **
Biomass/ET (kg/ha. mm) 34.9 33.0 32.2 40.0 - - **
Yield/ ET (kg/ha. mm) 15.9 15.3 14.5 18.0 - * **

32. Variable 0 mm 0 mm +100mm +100mm P W PN P X
Low N High N Low N High N
Shoot biomass (t/ha) 12.3 11.8 12.2 15.6 ** ** **
Yield (t/ha) 5.8 5.6 5.7 7.2 ** ** **
Grain number (103 x m-2) 13.0 13.8 12.8 17.1 * ** *
Harvest Index 0.42 0.42 0.42 0.42 - - -
Grain size (mg) 42.7 39.3 42.5 40.2 - - -
RUE (g/MJ) 1.64 1.57 1.50 1.89 - * **
Biomass/ET (kg/ha. mm) 34.9 33.0 32.2 40.0 - - **
Yield/ ET (kg/ha. mm) 15.9 15.3 14.5 18.0 - * **

33. Variable 0 mm 0 mm +100mm +100mm P W PN P X
Low N High N Low N High N
Shoot biomass (t/ha) 12.3 11.8 12.2 15.6 ** ** **
Yield (t/ha) 5.8 5.6 5.7 7.2 ** ** **
Grain number (103 x m-2) 13.0 13.8 12.8 17.1 * ** *
Harvest Index 0.42 0.42 0.42 0.42 - - -
Grain size (mg) 42.7 39.3 42.5 40.2 - - -
RUE (g/MJ) 1.64 1.57 1.50 1.89 - * **
Biomass/ET (kg/ha. mm) 34.9 33.0 32.2 40.0 - - **
Yield/ ET (kg/ha. mm) 15.9 15.3 14.5 18.0 - * **

34. N-driven trade-off between WUE and NUE
Nitrogen utilisation efficiency
40
Water use efficiency
20
NUE
(kg grain/kgN)
30
(kg/ha mm)
15
10 20
5 10
WUE
0 0
0 100 200 300
Nitrogen rate (kg N/ha)
Sadras & Rodriguez (2010) Field Crops Research 118, 297–305.

35. Summary
1. Summer rainfall can contribute up to 20%
gains in yield of wheat in South Australia
2. Yield gains are related to early growth and
grain number
3. Grain number is a function of growth rate in
the window between stem elongation and
anthesis
4. Supply of both nitrogen and water in this
critical window is essential
5. Has the balance between growth before and
after anthesis been overemphasised?

37. The trade-off is universal –
applies to maize in USA corn-belt
Nitrogen utilisation efficiency
30 80
Water use efficiency
WUE
(kg grain per kg N)
(kg/ha/mm)
70
25
60
20 NUE
50
15 40
0 50 100 150
Nitrogen rate (kg N/ha)

38. The trade-off is universal –
applies to rice in Philippines
Nitrogen utilisation efficiency
65
Water use efficiency
6
WUE
(kg grain/kg N)
(kg/ha/mm)
60
4
55
2
NUE
0 50
0 150
Nitrogen rate (kg N/ha)