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Nitrogen is essential to capture the benefit of summer rainfall for wheat in Mediterranean environments of South Australia
Victor Sadras, Chris LawsonPeter Hooper, Glenn McDonald
South Australian Research & Development InstituteHart Field Site, The University of Adelaide
Funded by Grains R&D Corporation
Brisbane, September 2011
Climate gives rise to predictable types of ecosystems
Terry Chapin
Ryan et al. (2009) Advances in Agronomy 104:53-136
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?
Three features of rainfall shape cropping systems
Amount
Seasonality
Size of events
Williamson (2007)
Markham’s seasonality vector
0 20 40 60 80 100 120 140 1600
10
20
30
40
50
Plant available water at sowing (mm)
0 20 40 60 80 100 120 140 160
Fre
quen
cy (
%)
0
10
20
30
40
50(a) Emerald (b) Horsham
Rainfall seasonality drives initial soil water
median = 124 mm median = 27 mm
maximum PAW = 146 mm
Sadras & Rodriguez (2009) Australian J Agr Res 58:657-669
North-eastern environment summer rainfall
South-eastern environment winter rainfall
20 25 30 35 40
-3.6
-3.2
-2.8
-2.4
-2.0
-1.6
growing season off season
log size of event
0.0 0.5 1.0 1.5 2.0 2.5
log n
um
be
r o
f e
ve
nts
0
1
2
3
4
5
HorshamEmerald
P = 0.0004
(a)
(b)
fre
qu
en
cy o
f sm
all e
ve
nts
high
low
= -3.1
= -1.9
P = 0.08
Latitude (oS)
power laws describe size-structure of rainfall
Sadras & Rodriguez (2007) Australian J Agr Res 58:657
Size of rainfall eventsInfluence fate of water – evaporation, run-off, drainage
Sadras (2003) Australian J Agr Res 54:341-351
0
5
10
15
20
Ru
no
ff (
mm
)150 200 250 300 350 400
Seasonal rainfall (mm)
-4
0
4
8
12
2.8 3 3.2 3.4 3.6 3.8
Re
sid
ua
ls (
mm
)
(a)
(b)
P < 0.0001
Williamson (2007)
Winter half year
SE Australia vs. Syria
log size of event
0.0 0.5 1.0 1.5 2.0
log
nu
mb
er o
f eve
nts
0
1
2
3
4
5
HorshamTel Hadya
(a)
= -3.1
= -3.0
Ryan et al. (2009) Advances in Agronomy 104:53-136
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
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?
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
Benefit from 20% for controls ~2 t/ha to 0 for controls ~6 t/ha
Yield of controls (t/ha)
0 2 4 6 80
2
4
6
8
y = x
y = x
0 2 4 6 8
Yie
ld o
f cro
ps w
ith
ad
dit
ion
al
su
mm
er
wate
r su
pp
ly (
t/h
a)
y = x
slope = 0.75 ± 0.070 intercept = 1.7 ± 0.30
slope = 0.81 ± 0.097 intercept = 1.4 ± 0.46
measured modelled
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?
0 50 100 150 200
Sh
oo
t d
ry m
atte
r (k
g/h
a)
0
2000
4000
6000
8000control+50 mm+100 mm
GS 32 GS 65 GS 95
***
*****
Days after sowing
PA
R i
nte
rce
pti
on
(%
)
0
20
40
60
80
100
Days after sowing0 50 100 150 200
Cu
mu
lati
ve
evap
otr
an
sp
irati
on
(m
m)
0
100
200
300
5 d after irrigation
0 10 20 30 40
-120
-90
-60
-30
0******************
******
control+50 mm+100 mm
So
il d
epth
(cm
)
Soil water content (mm)
Soil water content (mm)
So
il d
epth
(cm
)
sowing
0 10 20 30 40
-120
-90
-60
-30
0
*
*********
control
+100mm
stem elongation
0 10 20 30 40
So
il d
ep
th
(c
m)
-120
-90
-60
-30
0
******
Soil water content (mm)
So
il d
ep
th
(c
m)
control
flowering
0 10 20 30 40
-120
-90
-60
-30
0
***S
oil
dep
th (
cm)
Soil water content (mm)
maturity
0 10 20 30 40
-120
-90
-60
-30
0
*
**
Soil water content (mm)
So
il d
epth
(cm
)
Residual water at maturity in N-deficient crops Roseworthy, 2010
0 5 10 15
-100
-80
-60
-40
-20
0S
oil
dep
th (
cm)
Soil water content (mm)
low N
high N
maturity
r = 0.94P <0.0001
Grain number (per m2)
0 5000 10000 15000 20000
Yie
ld (
kg/h
a)
0
2000
4000
6000
8000
bare ground, Exps 1, 2stubble, Exps 1, 2high H, Exps 3-5low N, Exps 3-5
r = 0.65P <0.002
Crop growth rate (kg ha-1 d-1)
0 50 100 150 200
Gra
in n
um
ber
(m-2)
0
5000
10000
15000
20000
bare ground, Exps 1, 2stubble, Exps 1, 2high H, Exps 3-5low N, Exps 3-5
P < 0.02
Nitrogen rate
low high
Gra
ins m
-2 per u
nit g
row
th ra
te
(ha d
kg
-1)
0
50
100
(b)(c)
Grain number accounted for 88% of the variation in yield
r = 0.94P <0.0001
Grain number (per m2)
0 5000 10000 15000 20000
Yie
ld (
kg
/ha
)
0
2000
4000
6000
8000
bare ground, Exps 1, 2stubble, Exps 1, 2high H, Exps 3-5low N, Exps 3-5
r = 0.65P <0.002
Crop growth rate (kg/ha/d)
0 50 100 150 200
Gra
in n
um
be
r (p
er
m2)
0
5000
10000
15000
20000
bare ground, Exps 1, 2stubble, Exps 1, 2high H, Exps 3-5low N, Exps 3-5
P < 0.02
Nitrogen rate
low high
Gra
ins m -2
pe
r un
it gro
wth
rate
(ha
d k
g -1)
0
50
100
(b)(c)
Grain number = f (CGR between stem elongation and anthesis)
Low N
Variable 0 mm 0 mm +100mm +100mm PW PN PX 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 - * **
Variable 0 mm 0 mm +100mm +100mm PW PN PX 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 - * **
Variable 0 mm 0 mm +100mm +100mm PW PN PX 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 - * **
Variable 0 mm 0 mm +100mm +100mm PW PN PX 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 - * **
Variable 0 mm 0 mm +100mm +100mm PW PN PX 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 - * **
N-driven trade-off between WUE and NUE
0 100 200 300
Wat
er u
se e
ffic
ien
cy(k
g/h
a m
m)
0
5
10
15
20
Nitro
gen
utilisatio
n efficien
cy(kg
grain
/kgN
)
0
10
20
30
40
Nitrogen rate (kg N/ha)
WUE
NUE
Sadras & Rodriguez (2010) Field Crops Research 118, 297–305.
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?
Summary
The trade-off is universal – applies to maize in USA corn-belt
0 50 100 15015
20
25
30
40
50
60
70
80WUE
NUE
Nitro
gen
utilisatio
n efficien
cy(kg
grain
per kg
N)W
ater
use
eff
icie
ncy
(kg
/ha/
mm
)
Nitrogen rate (kg N/ha)
The trade-off is universal – applies to rice in Philippines
0 150
Wat
er u
se e
ffic
ien
cy
(kg
/ha/
mm
)
0
2
4
6
50
55
60
65
WUE
NUE
Nitro
ge
n u
tilisation
efficiency
(kg g
rain
/kg N
)
Nitrogen rate (kg N/ha)