University of Nebraska Lincoln R School of Natural Resources Water in Bioenergy Agroecosystems Workshop June 12-13, 2012 Ecosystem Scale Evapotranspiration.

University of Nebraska-Lincoln

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School of Natural ResourcesSchool of Natural Resources

University of Nebraska Lincoln

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Water in BioenergyAgroecosystems Workshop

June 12-13, 2012

Ecosystem Scale Evapotranspiration

Measurement in Temperate Rainfed Agriculture

Andrew E. SuykerUniversity of Nebraska-Lincoln


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Objectives

● Quantify evapotranspiration (ET) of rainfed maize ● Examine some key factors controlling ET

● Quantify water productivity ● Discuss ET measurement related issues


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Measurement Sites:Mead, NE

Rainfed Maize-SoybeanIrrigated Continuous Maize

Irrigated Maize-Soybean


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Rainfed Maize-Soybean Rotation

0

2

4

6

8

1/1/01 1/1/02 1/1/03 1/1/04 1/1/05 1/1/06 1/1/07 1/1/08 1/1/09 1/1/10 1/1/11 1/1/12

ET (m

m d

-1) M S M S M S M S M S M


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ET Summary: Rainfed Maize

Growing Season: May - September

YearAnnual

ETGS ET

NGS ET

NGS portion

GS Precip

Yield Residue

mm y-1 mm mm % mm Mg ha-1 Mg ha-1

2001 662 488 174 26 510 7.37 8.432003 615 467 148 24 350 6.52 6.572005 611 476 136 22 340 7.69 9.072007 623 472 151 24 606 8.64 7.632009 575 450 125 22 434 10.14 11.142011 607 481 126 21 502 8.22 9.12


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Variability of daily ET:

Growing Season

ETo: Reference ET (Allen et al., 1998)

0.0

0.4

0.8

1.2

1.6

0 2 4 6

ET

/ET o

LAI (m2m-2)

Adequate MoistureDry Periods

Rainfed Maize R2 = 0.66


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Non growing season ET

R² = 0.71

0.5

0.6

0.7

0.8

0.9

0.0 0.5 1.0 1.5 2.0

No

n-g

row

ing

sea

son

E/E

eq

Surface Mulch Biomass (Mg/ha)

2001-02

2002-03

2003-04

2004-05

2005-06Irrigated and Rainfed Maize and Soybean

Surface Residue (Mg/ha)


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ET from Rainfed Maize

(Growing Season)

Nebraska: 450-590 mm Illinois: 611 mm Kansas: 411-480 mm Iowa: 350-500 mm

Irrigated Maize (Mead): 500-580 mm


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ET from other Biofuel Crops

(Growing Season) Rainfed Miscanthus: 960 mm (Hickman et al., 2010)

Switchgrass: 760 mm (Hickman et al., 2010)

Sweet Sorghum: 160-515 mm (Stricevic et al., 2011)


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Water Productivity

0

5

10

15

20

0

2

4

6

8

1/1/07 1/1/08 12/31/08

Dry

Bio

mas

s (M

g ha

-1)

ET (m

m d

-1) Maize Soybean

WP = Dry above ground biomass ∑ET


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Normalized Water ProductivityNormalized WP by vapor pressure deficit (D)

WPD = aboveground biomass D: daytime average VPD

∑(ET/D) Tanner & Sinclair (1983):

For irrigated and rainfed maize, LAI>2 (Mead)

WPD = 6.9 ± 0.7 Pa

For irrigated and rainfed soybean, LAI>2, (Mead)

WPD = 2.8 ± 0.4 Pa

No significant difference among years

and management practices studied here

(Suyker and Verma, 2010)


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Normalized Water Productivity Tanner & Sinclair (1983):

Normalized WP by D

Estimated daytime D from daily max/min T

Estimated root biomass (total biomass)

Applying their Procedures:

WPD = 9.9 ± 1.0 Pa for maize

WPD = 4.3 ± 0.2 Pa for soybean

Tanner and Sinclair (1983) values:

WPD = 9.5 ± 1.1 Pa for maize: AZ,CA,CO,NE

WPD = 4.0 Pa for soybean: KS


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Normalized Water Productivity Normalize WP by ETo

WPETo = aboveground biomass

∑(ET/ETo)

For irrigated and rainfed maize, LAI>2 (Mead)

WPETo = 27.5 ± 2.3 g DM m-2

For irrigated sorghum (w and w/o fertilization)

WPETo = 25 and 33 g DM m-2

For irrigated and rainfed soybean, LAI>2, (Mead)

WPETo = 14.1 ± 3.1 g DM m-2

For C3 crops (chickpea, wheat, sunflower)

WPETo = 13 g DM m-2

Steduto and Albrizio (2005):


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ET Measurement Related Issues

● Energy Budget Closure Rn - Gs = H + LE

What are the causes for lack of closure?


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● Storage term (Gs) - energy stored in the soil - energy consumed in photosynthesis - energy stored in plants/mulch (Meyers and Hollinger, 2004)



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● Covariance Averaging Time (Mauder and Foken, 2006) - flux averaging time of 30 min not sufficient to capture low frequency flux contribution from turbulent organized structures and thermally induced mesoscale circulations



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● Angle of Attack (Nakai and Shimoyama, 2012) - flow distortion affects measurement of u, v, and w which causes fluxes to be underestimated.



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● Impact on Closure (Cava et al., 2008) Rn- Gs vs H + LE

Foken et al. 2011 Averaging time may not be as important for short vegetation


Raw FluxAOA

correctionStorage

TermAveraging

Time

Closure 0.82 0.88 1.02 1.01

R2 0.86 0.87 0.91 0.88


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Conclusions

● Rainfed maize growing season ET ranges 400-600 mm and up to 960 mm in other biofuel crops

● Leaf area explains a good share of daily ET variability

● Surface residue explains a good share of NGS ET variability


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Conclusions

● Normalized WP seems to be a conservative value and needs to be evaluated for crops at the ecosystem scale

University of Nebraska Lincoln R School of Natural Resources Water in Bioenergy Agroecosystems Workshop June 12-13, 2012 Ecosystem Scale Evapotranspiration.

Documents

lincoln slide

suyker university of

maize wp d

ground biomass et slide

et o wp eto

rainfed soybean

maize mead

ks slide