MODELING OLIVE ECOPHYSIOLOGICAL RESPONSE TO SOIL WATER DEFICIT

C. Agnese, M. Minacapilli, G. Provenzano, G. RalloDipartimento

dei

Sistemi

AGro-Ambientali

XIV Convegno Nazionale di Agrometeorologia AIAM 2011 BOLOGNA, 7 - 8 - 9 giugno 2011

Objective

In this study we focus on crop water stress response, to insight

into the dynamic of crop water status and transpiration fluxes.

•

Investigate the relationships between soil - plant water status and measured transpiration

• Determine critical thresholds of soil water content/matric potential

•

Define the parameters of water stress functions, that can be expressed as transpiration reduction coefficients:

α: relative transpiration Ks: normalized plant water status (evaluated by means leaf water potentials)

Plant water stress models: α(h)

( ) 34

3 4

for <h h

h h hh h

α−

=−

( )

50

1

1ph

hh

α =⎛ ⎞

+ ⎜ ⎟⎝ ⎠

( )( )

( )*

*50

1

1

phh h

h h

α =⎡ ⎤−⎢ ⎥+⎢ ⎥−⎣ ⎦

( )( ) ( )

( )*

0*

0 max

1

11

phh h

h h

αα

α

=⎡ ⎤−−⎢ ⎥+⎢ ⎥−⎣ ⎦

Feddes (1976)

Modified

Feddes

van Genuchten (1987)

Dirksen

(1993)

Homaee (1999)Soil

pressure

head h

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

α [‐]

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

α [‐]

h 3h 4

( ) 34

3 4

for <a

h hh h h

h hα

⎛ ⎞−= ⎜ ⎟

−⎝ ⎠

111

rel shape

shape

D f

s f

eKe

−= −

−

(Steduto, 2009)

Plant water stress models: Ks (Drel )

lowupwpfc

fcrel qq

1D−−

−=

θθθθ

Relative Depletion (Drel

)

Wat

er S

tress

Coe

ffici

ent(

Ks)

Experimental layout

SIAS weather station

Soil water content

125 m

Sap Flow

Farm “Tenuta Rocchetta”

Lat. 37 °38’

36,8”

Long. 12° 50’

49,8”

Extension: 30 Ha

Crop: Table Olives

8 x 5 m (250 plant/Ha)

Fraction coverage: 0.35

Soil: Clay-Loam (USDA)

Irrigation: drip with four 8 l/h emitters/plant

Experiments: 2008 and 2009

Soil water retention curve

10

100

1000

10000

100000

0 0.1 0.2 0.3 0.4 0.5 0.6

θ [cm3 cm−3]

-h [c

m]

z=0

z=30

z=60

z=100

average

van Genuchten parameters θr θs α n  m Z

[cm] ρb 

[Mg m-3] [cm3 cm-3] [cm3 cm-3] [cm-1] [-] [-]

0 1.36 0.05 0.39 0.008 1.32 0.2430 1.31 0.05 0.56 0.0147 1.19 0.1660 1.38 0.06 0.39 0.0138 1.23 0.18

100 1.61 0.06 0.36 0.0223 1.18 0.15

Soil water content measurements

Diviner 2000 (Sentek )

FDR (Frequency Domain Reflectometry)

TDR (Time Domain Reflectometry)

Tektronics 1502C

Calibration of FDR sensorSite-specific equation calibration

Soil

wat

er c

onte

nt

[%]

θ  = 38.225 SF 3.4918

R2 = 0.92RMSE: 3.4 [% vol.]

0

5

10

15

20

25

30

35

40

45

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0Scaled Frequency [‐]

Curva calibrazione delcostruttore

Punti sperimentali

Manufacturer equation

Experimental data

Root spatial distribution

0.0 0.5 1.0 1.5 2.0 2.5

20

35

50

65

80

95

110

Prof

ondi

tà [c

m]

RLD [cm cm-3]

PROFILO 0°

d)

0.0 0.5 1.0 1.5 2.0 2.5RLD [cm cm-3]

PROFILO 45°e)

0.0 0.5 1.0 1.5 2.0 2.5RLD [cm cm-3]

PROFILO 90°f)

0.0 0.5 1.0 1.5 2.0 2.5

20

35

50

65

80

95

110

Prof

ondi

tà [c

m]

RLD [cm cm-3]

PROFILO 0°

d)

0.0 0.5 1.0 1.5 2.0 2.5RLD [cm cm-3]

PROFILO 45°e)

0.0 0.5 1.0 1.5 2.0 2.5RLD [cm cm-3]

PROFILO 90°f)

Root Length Density (RLD) distribution along three alignments

Dep

th (c

m)

Leaf Water Potential and Sap FlowTurner & Jarvis (1982)

Predawn LWP, ψpdMidday LWP, ψmdMidday SWP, ψmst

Scholander Chamber

Thermal Dissipation Probe

Potential Transpiration

,min

p

ap

a c

a

C VPDR

rT

r rr

ρ

λ γ

Δ +=

⎡ ⎤+⎛ ⎞Δ +⎢ ⎥⎜ ⎟

⎢ ⎥⎝ ⎠⎣ ⎦

(Jarvis and McNaughton, 1986)

rc,min =75 s m-1

( )( )

*

,mina c a

c aa

c ap

r e er r

r R T Tc

γρ

−= −

⎡ ⎤− −⎢ ⎥

⎢ ⎥⎣ ⎦

(Berni

et al., 2009)

For constantly irrigated plants rc

=rc,min

Δ[kPa

C-1]= slope of the saturation vapor pressure curveR [W m-2]= incoming radiation, ρ [Kg m-3]= air density, Cp [J Kg-1

K-1]= air specific heat, γ [KPa

K-1]= psychometric constant, VPD [KPa]= air vapor pressure deficit, λ [J Kg-1]= latent heat of vaporization, ra and rc,min [s m-1]: aerodynamic and the minimum canopy

resistance, respectively.

Results: Transpiration vs leaf water potentials

A decreasing trend of actual transpiration is evident at increasing absolute values of leaf or stem potentials

T a  = ‐0.067ψ pd  + 2.3218

R2 = 0.84

T a    = ‐0.0923ψ md   + 4.5138

R2 = 0.88

T a   = ‐0.0689ψ mst  + 3.5936

R2 = 0.81

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

3.0

0 5 10 15 20 25 30 35 40ψ pd ,ψ md and ψ mst [bar]

T a [mm d‐1] 

Midday stem water potentialMidday leaf water potentialPre‐dawn leaf water potential

Act

ual T

rans

pira

tion

[mm

d-1

]

Leaf/Stem water Potentials [bar]

0.0

0.5

1.0

1.5

2.0

2.5

5 10 15 20 25 30 35 40 45θ  [% vol.]

T a [mm d‐1]

1

10

100

1000

10000

100000

h [cm]

θ

[%]Ta

[m

m d

-1]

h [c

m]

0.0

0.5

1.0

1.5

2.0

2.5

5 10 15 20 25 30 35 40 45

θ  [% vol.]

T a [mm d‐1]

1

10

100

1000

10000

100000

h [cm]

Ta [

mm

d-1

]

θ

[%]h

[cm

]

Plant-Soil water relationships and definition of critical thresholds

FDR 10-120 cm FDR + TDR 45-65 cm

The values of actual transpiration are practically constant for soil water contents higher than a threshold value θ* and drastically decrease, till a minimum value, for lower soil water contents.

θ* θ*

h* h*

0

3

5

8

10

13

15

18

20

23

25

5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45

θ [% vol.]

ψpd [bar]

ψpd

[bar

]

θ

[%]10

15

20

25

30

35

40

5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45

θ [% vol.]

ψmd [bar]

10

15

20

25

30

35

40

5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45θ  [% vol.]

ψmst [bar]

Plant-Soil water relationships and definition of critical thresholds

θ*

Despite the difficulty to identify an unambiguous value of the critical SWC, θ∗≈16% (h ≈

40 m) previously obtained, can be considered acceptable. The observed uncertainty could be due to xilematic potentials adjustment occurring when the plant is kept under soil water deficit for long time periods.

θmin

Modeling olive response to soil water deficit

Non linear models give a comparable results. Non-linear water stress models better reproduced the initial phase of the transpiration reduction process.Convex shape in the initial phase evidences that reductions of Ta become critical only for extreme water stress conditions.

Unfortunately, the absence of Ta/Tp measurements lower than 0.6, does not permit to clearly choose the best shape describing the olive response to the highest water stress.

Rel

ativ

e Tr

ansp

irato

n, T

a/Tp

[-]

h [m]

h [m]

0.00.10.20.30.40.50.60.70.80.91.01.1

0 20 40 60 80 100 120 140 160 180 200 220 240h  [m]

T a/Tp [‐]

( ) 4

3 4

ih hh

h hα

−=

−

0 20 40 60 80 100 120 140 160 180 200 220 240h  [m]

( ) 4

3 4

a

ih hh

h hα

⎛ ⎞−= ⎜ ⎟

−⎝ ⎠

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

0 20 40 60 80 100 120 140 160 180 200 220 240h  [m]

T a/Tp [‐]

( )

5 0

1

1p

i

hh

h

α =⎡ ⎤⎛ ⎞⎢ ⎥+ ⎜ ⎟⎢ ⎥⎝ ⎠⎣ ⎦

0 20 40 60 80 100 120 140 160 180 200 220 240h  [m]

( )( )( )

*

*50

1

1

p

i

hh h

h h

α =⎡ ⎤−⎢ ⎥+⎢ ⎥−⎣ ⎦

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

0 20 40 60 80 100 120 140 160 180 200 220 240h  [m]

T a/Tp [‐]

( )( ) ( )

( )*

0*

0 max

1

11

p

i

hh h

h h

αα

α

=⎡ ⎤−−⎢ ⎥+⎢ ⎥−⎣ ⎦

111

rel shape

shape

D f

s f

eKe

−= −

−(Steduto, 2009)

Modeling olive response to soil water deficit

0.00.10.20.30.40.50.60.70.80.91.0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0D rel [-]

Ks

(pre

daw

n L

WP)

f s : 2.89r : 0.90

RMSE: 0.14

a)

00.10.20.30.40.50.60.70.80.9

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1D rel [-]

Ks

(mid

day

SWP)

f s : 1.41r : 0.86

RMSE: 0.15

b)

Even in this case the stress function shape is convex (fshape

>0)

Conclusions

•Critical threshold, θ*, resulted approximately 16% and the corresponding

soil matric potential equal to 40m.

•The highest stress was detected for θ=11% and h=200 m.

•With exception for Feddes linear, all the other investigated models showed

a good agreement with experimental data.

•Non-linear models better reproduced the initial phase of the transpiration

reduction process, showing a convex shape typical of xerophyte, for which

the reductions of actual transpiration is critical only for extreme water

stress conditions.

•Future work should allow to investigate on values of Ta/Tp <0.6.

Thank you!