Evapotranspiration ET from Dedicated Energy Crops Ashlynn Stillwell

Evapotranspiration (ET) from Dedicated Energy Crops Ashlynn Stillwell CE 394 K. 2: Surface Water Hydrology Spring 2010 5/4/10

Outline • • • Increasing biofuels production Methods of calculating ET Results for Mead Irrigated site CO 2 from crops Future work Questions Ashlynn Stillwell Hydrology 5/4/10 #2

Increasing Biofuels Production • Energy Independence and Security Act (2007) mandates 36 Bgal/yr by 2022 • General consensus that new land will be cultivated • Additional crops might lead to additional ET [earthfirst. com] [EISA, Schnoor et al. , USDA] Ashlynn Stillwell Hydrology 5/4/10 #3

Ameri. Flux Sites for Analysis • ARMS SGP Main – Corn/soybeans rotation – Lamont, OK • Fermi Agricultural – Corn/soybeans rotation – Winfield Township, IL • Mead Irrigated – Continuous corn – Mead, NE • Rosemount G 19 Alternative [Ameri. Flux] – Corn/soybeans rotation – Rosemount, MN Ashlynn Stillwell Hydrology 5/4/10 #4

Methods of Calculating ET • Reference ET 0 (Penman-Monteith equation) – ET 0 for well-watered grass – Kc crop factors adjust to ET • FAO CROPWAT 8. 0 software • Energy balance method • Scaling of latent heat flux (using eddy covariance instruments) Ashlynn Stillwell Hydrology 5/4/10 #5

Penman-Monteith equation Reference evapotranspiration ET 0 Crop factors Kc Net radiation Soil heat flux Air temperature Wind speed Vapor pressure deficit • Slope of vapor pressure curve • Psychrometric constant • Pressure • • • Ashlynn Stillwell Hydrology 5/4/10 #6

ET Variation throughout Day Crop Evapotranspiration (P-M) for Day 204 Mead Irrigated | 2005 corn crop | near Mead, NE 30 ET (mm/d) for hourly time steps 25 20 15 10 5 0 0: 00 -5 4: 00 8: 00 12: 00 16: 00 20: 00 Time of Day Ashlynn Stillwell Hydrology 5/4/10 #7

FAO CROPWAT 8. 0 software • Input data – Climate – Precipitation – Crop (some built-in) – Soil (some built-in) • Output: Crop Water Requirements Ashlynn Stillwell Hydrology 5/4/10 #8

Energy Balance / Scaling of Latent Heat • Energy balance method [Tanner] • Scaling of latent heat flux (when measured directly with eddy covariance instruments) [Hyun] Ashlynn Stillwell Hydrology 5/4/10 #9

Comparison of ET Methods Mead Irrigated - Evapotranspiration Corn Crop 2005 12 700 500 ET (mm/d) 8 400 6 300 4 200 2 Cumulative ET (mm) 600 10 100 0 50 100 ET 0 150 200 Day of Year P-M Tanner LE 250 300 Cumulative ET (LE) 350 Ashlynn Stillwell Hydrology 5/4/10 #10

Cumulative ET for Methods ET Calculation Method Reference ET 0 Cumulative ET (mm) Percent Error 1, 089 66% Penman-Monteith 707 8% FAO CROPWAT software 770 17% Energy Balance (Tanner) 824 26% Scaling Latent Heat Flux 656 baseline Indirect calculations overestimate ET compared to direct measurements Ashlynn Stillwell Hydrology 5/4/10 #11

CO 2 from Crop Cultivation Mead Irrigated - CO 2 Concentration Corn Crop 2005 900 800 CO 2 (mmol/mol) 700 600 500 400 300 200 100 0 0 Crop growing season 50 100 150 200 Day of Year 250 300 350 No statistical difference between pre- and post-growth CO 2 Ashlynn Stillwell Hydrology 5/4/10 #12

Conclusions • Direct measurement of latent heat flux provides lowest magnitude of ET • Penman-Monteith equation with Kc provides good approximation • Crops sequester CO 2, but other operations emit CO 2 • (Not shown here; in paper) – Highest ET at ARMS SGP Main site (Oklahoma) – Comparable ET from corn vs. soybeans

Future Work • Write report • Beyond CE 394 K. 2 – Satellite- and GIS-based methods of calculating ET – Change from native vegetation to energy fuel crop Ashlynn Stillwell Hydrology 5/4/10 #14

Questions? Data Acknowledgments Office of Biological and Environmental Research of the U. S. Department of Energy as part of the Atmospheric Radiation Measurement Program Ameri. Flux Network, Oak Ridge National Laboratory Ashlynn Stillwell Hydrology 5/4/10 #15