The Target Seedling:Plant Water Relations

John G. MexalPlant & Environmental Sciences

New Mexico State UniversityLas Cruces, NM

Outline

• Define the importance of water relations in seedlings,

• Describe how it’s measured, • Explain how to interpret the data, • Give an overview regarding new

knowledge/culturing regimes/target expectations over the past 20 years

• Use water to achieve and maintain Target

Importance of Water– Seedling after Colombo et al. 2001

Seedling Attributes

Morphological

Diameter

Height

Dry Weight

Root System

Balance

Bud Morphology

Physiological

Photosynthesis

Moisture Stress

Electrical Impedance

Root Growth

Cold Hardiness

Dormancy

Chemical

Nutrients Carbohydrates

DNA Others

Importance of Water-- Manager

• Too little → Fail to achieve Target

• Too much → Increased utility costsIncreased fertilizer costsIncreased pest pressureIncreased runoff hazard

How is water status measured?

•Water Potential (ψ)= Chemical free energy of water; basically the ability of water to do work.

– Pure, free water: ψ = 0 [zero ability to do work]

•Pascal (Pa) = SI derived unit of pressure, stress, Young's modulus and tensile strength. Measures force per unit area.

– -0.03 Mpa = -30 kPa = -30,000 Pa = -0.3 bars ≈ -⅓ atm = “FC”– -1.5 Mpa = -1,500 kPa = -1,500,000 Pa = -15 bars ≈ -15 atm = “PWP”

Rules of Thumb:•Water flows from high concentration (high ψ) to low concentration (low ψ)•The steeper the gradient, the faster the water movemento High humidity to low humidityo Low salt concentration (soil) to high salt concentration (plant cell)

Putting Water Relations in ContextRelative Humidity Comparison

R.H.(%)

ψ(MPa)

Maximum Pore Size (μ)

20.00 -222.0 --

50.00 -50.0 0.03

92.7 -10.0 0.3

99.27 -1.00 3

99.93 -0.10 0.3

99.99 -0.01 30

99.999 -0.001 300

100.00 0 n.a.

How do nurseries schedule irrigation?

0102030405060708090

100

0102030405060708090100

Technique• Visual/Tactile• Container Weight• Measurement– PMS– Medium

• Water Budget• Nothing/Wilting

Measuring the water status of seedlingsA few ‘caveats’

• What are you measuring?– Balance of water remaining in a

container?– Balance of water remaining in a

block of containers?– A seedling after a night of

recovery?

Container weight vs xylem water potentialKhadhuri, unpubl.

30 50 70 90 110-1.5

-1.2

-0.900000000000001

-0.600000000000001

-0.3

0

f(x) = − 0.000164159 x² + 0.0314563 x − 1.77469R² = 0.348007595784752

f(x) = − 0.0000326799 x² + 0.00726442 x − 0.700277R² = 0.12505593138112

mild

• Weak correlation between medium moisture content and seedling water potential

• Essentially no correlation if moisture content > 50%

Moisture Content (% w/w)

Xylem Water Potential (MPa)

Utility of soil mositure sensors Picea glauca Lamhamedi et al. 2005

• Variability changes through growing season

• Weak correlation to seedling growth

• Crop Tracking Recos:– 11-19 sensors/2 sprinklers– OR– Measure 4 seedlings

Preferred irrigation scheduling tool!!

Measuring the water status of seedlingsA few ‘caveats’

• What are you measuring?– Balance of water remaining in a

container?– Balance of water remaining in a

block of containers?– A seedling after a night of

recovery?– These are ‘response variables’

• Shouldn’t you measure the independent variables?– Radiation– VPD– T

Measuring the water status of seedlings Pan Evaporation

ETo = 0.75 Ep

ETo (mm/d)

Wikipedia Calif. Agric.

Advantages:• Integrates drivers of ET• Radiation• VPD• Temperature

• Estimates real-time soil moisture loss (overestimates)

• Use with data recorder

Measuring the water status of seedlings Atmometer -- Etgage™

ETga

ge (m

m/d

)0.

0

2

.5

5

.0

7.5

10

.0

0.0 2.5 5.0 7.5 10.0

Penman-Monteith (mm/d)

Advantages:• Integrates drivers of ET• Radiation• VPD• Temperature

• Predicts soil moisture loss• Can be used to convert ETo

estimates to ETg • Use with data recorder

Current or historic climate

• Good examples: California:

http://wwwcimis.water.ca.gov/cimis/images/etomap.jpg

Northwest Region: http://www.usbr.gov/pn/agrimet/monthlyet.html

Canada: http://climate.weatheroffice.gc.ca/climateData/dailydata_e.html

• State Climatologists:– Archive historic weather data– Develop climate-based tools – Use both historic and real time

data

Irrigation Scheduling-CanadaScagel, pers. comm.

PET = evaporation + transpiration from a crop under non-stressed conditions

ETo = evaporation + transpiration from a ‘reference crop’ (grass) under non-stressed conditions; also referred to as ETr– Crop coefficient (kC) = ETC / ETO

Definitions: PET vs ETo

Penman-Monteith Equation (FAO):ETo = 0.408Δ(Rn – G) + γ(900/[T + 273]) μ2(es –

ea) Δ + γ (1 – 0.34μ2)

where ETo = reference evapotranspiration [mm day-1],Rn = net radiation at the crop surface [MJ m-2 day-1],G = soil heat flux density [MJ m-2 day-1],T = air temperature at 2 m height [°C], μ2 = wind speed at 2 m height [m s-1],es = saturation vapor pressure [kPa],ea = actual vapor pressure [kPa],es - ea = saturation vapor pressure deficit [kPa],Δ = slope vapor pressure curve [kPa °C-1],γ = psychrometric constant [kPa °C-1].

Available historic and real time ETo datahttp://www.usbr.gov/pn/agrimet/monthlyet.html

0.00

2.00

4.00

6.00

8.00

10.00 Forest GroveBrookings

0.00

2.00

4.00

6.00

8.00

10.00

EchoLakeview

ETo (mm/d)

ETo (mm/d)

Reference ET (cm/yr)

Coastal InteriorBrookings 91 Lakeview 134

Forest Grove 104 Echo 146

San Diego 118 Calexico 182

Real time data or Long-term average for scheduling?http://www.usbr.gov/pn/agrimet/agrimetmap/agrimap.html

• Long-term average of nearby station = good first approximation• Does not replace management responsibilities– see June 2009

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec0.00

5.00

10.00

15.00

Aberdeen-long term average

2009

ETo (mm/d)

Daily pecan ET compared to ETo in the Mesilla Valley, NM (Sammis et al. & Bawazir et al.)

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec0123456789

10

Eto 20012002 20032004 20052001b 2002b2003b 2006b

ET or ETo (mm/d)

Daily pecan ET compared to ETo in the Mesilla Valley, NM (Sammis et al. & Bawazir et al.)

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec0123456789

10

Eto 20012002 20032004 20052001b 2002b2003b 2006b

Phase 1E only

ET or ETo (mm/d)

Daily pecan ET compared to ETo in the Mesilla Valley, NM (Sammis et al. & Bawazir et al.)

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec0123456789

10

Eto 20012002 20032004 20052001b 2002b2003b 2006b

ET/ ETo (mm/d)

Phase 2Leaf expansion

Daily pecan ET compared to ETo in the Mesilla Valley, NM (Sammis et al. & Bawazir et al.)

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec0123456789

10

Eto 20012002 20032004 20052001b 2002b2003b 2006b

Phase 3ET = ETo

ET or ETo (mm/d)

Daily pecan ET compared to ETo in the Mesilla Valley, NM (Sammis et al. & Bawazir et al.)

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec0123456789

10

Eto 20012002 20032004 20052001b 2002b2003b 2006b

Phase 4Senescence

ET or ETo (mm/d)

Wonderful! But I don’t grow pecans. What does this mean for me?

• Phase 1 =• Phase 3 = • Phase 4 =• Phase 2 =

JanFeb

Mar

AprM

ayJun Jul

AugSep

OctNov

Dec0

1

2

3

4

5

6

7

8

9

10

Eto200120022003200420052001b2002b2003b2006b

ET or ETo (mm/d)

Wonderful! But I don’t grow pecans. What does this mean for me?

• Phase 1 = emergence (E only)

• Phase 3 = ET = Eto– Pecans = Fescue =

Pistachio = Mesquite = Creosote = Pine = Bermuda grass = Kentucky blue grass

• Phase 4 = applies only to deciduous crops

• What about Phase 2?

D 1-7

D 9-14

D 14-21

D 7-8

Zone of Absorption

Wonderful! But I don’t grow pecans. What does this mean for me?

• Phase 1 = emergence (E only)

• Phase 3 = ET = Eto– Pecans = Fescue =

Pistachio = Mesquite = Creosote = Pine = Bermuda grass = Kentucky blue grass

• Phase 4 = applies only to deciduous crops

• What about Phase 2?

JanFeb

Mar

AprM

ayJun Jul

AugSep

OctNov

Dec0

1

2

3

4

5

6

7

8

9

10

Eto

ET or ETo (mm/d)

Wonderful! But I don’t grow pecans. What does this mean for me?

• Phase 1 = emergence (E only)

• Phase 3 = ET = Eto– Pecans = Fescue =

Pistachio = Mesquite = Creosote = Pine = Bermuda grass = Kentucky blue grass

• Phase 4 = applies only to deciduous crops

• What about Phase 2?

JanFeb

Mar

AprM

ayJun Jul

AugSep

OctNov

Dec0

1

2

3

4

5

6

7

8

9

10

Eto

ET or ETo (mm/d)

What about Phase 2?

• Linear relationship between budbreak and ‘full’ canopy closure

• ‘Full’ effective coverage occurs at 65% to 70% of canopy coverage.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8Effective Crop Canopy

100%

?

What about Phase 2?

• Linear relationship between budbreak and ‘full’ canopy closure

• ‘Full’ effective coverage occurs at 65% to 70% of canopy coverage.

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8Effective Crop Canopy

100%

30%

Recommendations

• Use all the tools at your disposal

• Rely on the drivers of ET• Radiation• Vapor Pressure Deficit• Temperature• Eto vs ETg

• Historical data covers >90% of environmental situations

• Maintain comfort zone with physical tools

• Pressure chambers• Scales• Moisture sensors

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec0.00

5.00

10.00

15.00

2009

ETo (mm/d)

Physiological effects of moisture stress conditioning

Parameter Effect References

Photosynthesis/Biomass accumulation

↓ Cleary ‘71; Cregg ‘94; Nzokou & Cregg ‘10; McMillan & Wagner ‘95

Transpiration ↓ Seiler & Johnson ‘85, ’88; Villar-Salvador et al. ’99

Carbohydrates ↑ Villar-Salvador et al. ’99

Osmotic adjustment ↑↔

Seiler & Johnson ‘85, ‘88Seiler & Cazell ‘90; Villar-Salvador et al. ’99

R:S ↔ McMillan & Wagner ‘95

Root Growth Potential ↓ Vallas Cuesta et al. ‘99; Villar-Salvador et al. ’99

Cold-hardiness/Dormancy ↑

↑↔

Almeida et al. ‘94; Timmis & Tanaka ‘76; Zaerr et al. ’81Blake et al. 1979

Survival ↓↔

Vallas Cuesta et al. ’99van den Driessche ‘91

How fast can we fall off the cliff?Landis, et al. 1989

Target Values Weight Loss (kg) Etg Guidelines

Ψ (MPa) Content (%) (mm)

0.00 482 0.00 -- Saturated, too wet

~390 ~1.60 ~8.7 ‘Field Capacity’ (drainage)

-0.01 235 4.04 ~13.3 Upper limit for rapid growth

-0.05 130 5.77 9.6 Lower limit for rapid growth

-0.10 98 6.26 2.7 Hardening phase

>10.0 0 7.89 9.0 Ovendry medium

Eto (mm/d)

0.00

2.00

4.00

6.00

8.00

10.00

EchoLakeview

Low soil moisture determines seedling water potential (after Dinger and Rose 2009)

Soil Moisture (m3/m3)

Xylem Water Potential (MPa)Management Implications• High soil moisture is weakly

correlated with seedling water status

• Low soil moisture is highly correlated

• Slope = steep– 0.05 m3/m3 = 1.25 MPa– Difficult to regulate???

0.15 0.2 0.25 0.3 0.35 0.4-3

-2.5

-2

-1.5

-1

-0.5

0Control ψpd2Control ψmd3Treated ψpdTreated ψmd

Low soil moisture determines seedling water potential (after Dinger and Rose 2009)

Soil Moisture (m3/m3)

Xylem Water Potential (MPa)Management Implications• High soil moisture is weakly

correlated with seedling water status

• Low soil moisture is highly correlated

• Slope = steep– 0.05 m3/m3 = 1.25 MPa– Difficult to regulate???

0.15 0.2 0.25 0.3 0.35 0.4-3

-2.5

-2

-1.5

-1

-0.5

0f(x) = 15.6271186441 x − 5.30593220339R² = 0.830922917521944f(x) = 19.4915254237 x − 5.22627118644R² = 0.913417043084276

Control ψpd2Control ψmd3Treated ψpdTreated ψmd

Scheduling irrigation to harden ‘Target’

• Avoid incomplete wetting• Monitor uniformity• 1-3 days can mean

difference between hardening and death

• Root pruning alters soil moisture volume

Dumroese