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Water in Bioenergy Agroecosystems Workshop June 12-13, 2012

Water in Bioenergy Agroecosystems Workshop June 12-13, 2012. Ecosystem Scale Evapotranspiration Measurement in Temperate Rainfed Agriculture Andrew E. Suyker University of Nebraska-Lincoln.

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Water in Bioenergy Agroecosystems Workshop June 12-13, 2012

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  1. Water in BioenergyAgroecosystemsWorkshopJune 12-13, 2012 Ecosystem Scale Evapotranspiration Measurement in Temperate RainfedAgriculture Andrew E. Suyker University of Nebraska-Lincoln

  2. ●Quantify evapotranspiration (ET) of rainfed maize ● Examine some key factors controlling ET ● Quantify water productivity ● Discuss ET measurement related issues Objectives

  3. Rainfed Maize-Soybean Measurement Sites: Mead, NE Irrigated Continuous Maize Irrigated Maize-Soybean

  4. M S M S M S M S M S M Rainfed Maize-Soybean Rotation

  5. ET Summary: Rainfed Maize Growing Season: May - September

  6. Variability of daily ET: Growing Season R2 = 0.66 ETo: Reference ET (Allen et al., 1998)

  7. Non growing season ET Irrigated and Rainfed Maize and Soybean Surface Residue (Mg/ha)

  8. 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

  9. ET from other Biofuel Crops (Growing Season) RainfedMiscanthus: 960 mm (Hickman et al., 2010) Switchgrass: 760 mm (Hickman et al., 2010) Sweet Sorghum: 160-515 mm (Stricevic et al., 2011)

  10. Water Productivity WP = Dry above ground biomass ∑ET Maize Soybean

  11. Normalized Water Productivity Normalized 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)

  12. 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

  13. 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):

  14. ET Measurement Related Issues ●Energy Budget Closure Rn- Gs = H + LE What are the causes for lack of closure?

  15. ET Measurement Related Issues ● Storage term (Gs) - energy stored in the soil - energy consumed in photosynthesis - energy stored in plants/mulch (Meyers and Hollinger, 2004)

  16. ET Measurement Related Issues ● 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

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

  18. ET Measurement Related Issues ● Impact on Closure (Cava et al., 2008) Rn- Gsvs H + LE Foken et al. 2011 Averaging time may not be as important for short vegetation

  19. 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

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

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