NEBRASKA WATER AND ENERGY FLUX MEASUREMENT, MODELING, AND RESEARCH NETWORK

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: HATCH
• Reporting Frequency: Annual
• Accession No.: 0223500
• Project Start Date: Aug 1, 2010
• Project End Date: Jul 31, 2015
• Program Code: [(N/A)]- (N/A)

Project Director
Irmak, S.

Recipient Organization
UNIVERSITY OF NEBRASKA
(N/A)
LINCOLN,NE 68583

Performing Department
Biological Systems Engineering

Non Technical Summary
Surface energy and water vapor fluxes play a critical role in understanding the response of agro-ecosystems to changes in environmental and atmospheric parameters. These fluxes play a crucial role in exploring the dynamics of water and energy use efficiencies of these systems. Quantification of the fluxes is also necessary for assessing the impact of land use and management changes on water balances. Accomplishing these goals requires measurement of water vapor and energy exchanges between various vegetation surfaces and microclimates for long-enough periods to empathize the behavior and dynamics involved with the flux transfer. Other networks of flux towers have been collecting data on exchange processes between biosphere and atmosphere for multiple years across the globe to better understand the functioning of terrestrial ecosystems and their role in regional and/or continental and global carbon, water, and energy cycles. However, there is an imperative need for these kinds of networks to increase in intensity due to the great diversity among ecosystems and agro-ecosystems in species composition, physiological properties, physical structure, microclimatic and climatic conditions, and great diversity in management practices. Since water use is impacted greatly by local atmospheric, soil, and management conditions, the existing flux networks cannot provide information and data on water use of various cropping systems on a given local or regional level. Measurement of water use of diverse vegetation surfaces will enable water regulatory agencies and water users to make timely and better decisions on water resources planning, management, and allocation. The Nebraska Water and Energy Flux Measurement, Modeling, and Research Network (NEBFLUX) is a comprehensive network that is designed to measure surface energy and water vapor fluxes, microclimatic variables, plant physiological parameters, soil water content, surface characteristics, and their interactions for various vegetation surfaces. The NEBFLUX is a network of micrometeorological tower sites that uses mainly Bowen ratio energy balance systems (BREBS) to measure surface water vapor and energy fluxes between terrestrial agro-ecosystems and microclimate. At present, ten BREBSs and one eddy covariance system are operating on a long-term and continuous basis for vegetation surfaces ranging from tilled and untilled irrigated and rainfed croplands, irrigated and rainfed grasslands, to Phragmites (Phragmites australis)-dominated cottonwood (Populus deltiodes var. occidentalis) and willow stand (Willow salix) plant communities. The NEBFLUX project will provide good quality flux and other extensive supportive data on plant physiology [leaf area index, stomatal resistance, within-canopy radiation parameters, productivity (yield and/or biomass), and plant height], soil characteristics, soil water content, and surface characteristics to the micrometeorology, water resources engineering, and science community on broad spectrum of agro-ecosystems.

Animal Health Component

(N/A)

Research Effort Categories

Basic

(N/A)

Applied

(N/A)

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
102	0210	1020	60%
132	0210	2050	20%
132	0899	2050	20%

Knowledge Area
102 - Soil, Plant, Water, Nutrient Relationships; 132 - Weather and Climate;

Subject Of Investigation
0210 - Water resources; 0899 - Wildlife and natural fisheries, general/other;

Field Of Science
2050 - Hydrology; 1020 - Physiology;

Keywords

evapotranspiration

energy flux

energy balance

bowen ratio

eddy covariance system

penman-monteith

microclimate

Goals / Objectives
1. The fundamental premise of the NEBFLUX is to measure continuous and long-term (at least ten complete annual cycles for each surface) exchange of water vapor and energy fluxes for various vegetation surfaces/cropping systems. The measurements will include evapotranspiration, sensible heat, soil heat flux, net radiation, incoming shortwave radiation, soil temperature, precipitation, wind speed and directions, air temperature and humidity gradients, actual vapor pressure, soil water content (every 0.30 m up to 1.8 m on an hourly basis throughout the year), soil properties, plant height, leaf area index, yield and/or dry matter (biomass) production, irrigation applications, fertilizer, herbicide, pesticide, and insecticide applications, and other management practices. All variables will be used to quantify water use and its interactions with various management practices and environmental variables for different land use types. 2. Measure nocturnal period evaporative losses for all cropping systems/vegetation surfaces. 3. Quantify water re-charge for each vegetation surface. 4. Measure/update crop coefficient (Kc) values for maize, soybean, winter wheat, grassland, and alfalfa. NEBFLUX data from all sites will be used to develop updated Kc values for various cropping systems. 5. Measure and develop techniques to predict evaporative losses during the non-growing season. Because all NEBFLUX systems are operated on an hourly basis and continuously throughout the year, the annual water use rates of surface will be measured. Expected Outputs: All the flux systems are, and will continue, providing extremely valuable data and information to state water regulatory agencies for their designing, planning, and management of water resources infrastructures. The evapotranspiration datasets will be used to make policy and regulatory decisions by the state agencies. The datasets will be used by growers and crop consultants to make better irrigation management decisions. From NEBFLUX datasets, progress, and functions, we will organize educational and outreach programs to disseminate the project findings for community/public education. Educators, students from different disciplines, and faculty members will be given exposure to the project through field tours to visit experimental setups and other forms of educational outreach such as workshops and seminars. The project will be carried out based on science and engineering principles. The project results will be disseminated through several outlets: (i) program results will be analyzed, summarized, written in manuscript format, and published in refereed scientific journals, (ii) education and outreach publications will be developed to reach a large audience of educators, general public, public school teachers, state and federal agency personnel, and (iii) presentations will relate project findings to interested parties at local, state, and professional national meetings. Internet will be utilized to share the results of the program on the worldwide web.

Project Methods
PROCEDURES NEBFLUX site descriptions All aforementioned objectives will be accomplished simultaneously by utilizing the measured evapotranspiration, sensible heat, radiation envelopes, soil heat flux, and other supporting climatic, soil and plant physiological parameters as all objectives rely on these measurements. The NEBFLUX vegetation surfaces include both rainfed and irrigated and tilled and untilled croplands, irrigated and rainfed grasslands, and riparian vegetation comprised of Phragmites (Phragmites australis)-dominated cottonwood (Populus deltiodes var. occidentalis) and willow stand (Willow salix) plant community. The locations of ten BREBSs and one eddy covariance system (ECS) are presented in Figure 1 of the proposal. Depending on the availability of resources, the future plans for the NEBFLUX include expanding the sites for additional vegetation surfaces towards the western (drier) parts of the state. Detailed location information on Bowen ratio energy balance system (BREBS) (BREBS-1 through BREBS-10) and eddy covariance system (ECS-1) data year, latitude, longitude, elevation, and vegetation type is given in Table 1 of the proposal. The systems are installed on large fields and the fetch distance was adequate for each BREBS site Instrumentation for Bowen ratio energy balance systems The surface energy balance components, including ETa, microclimatic variables, at each site are measured using a deluxe version of a Bowen ratio energy balance system (BREBS) (Radiation and Energy Balance Systems, REBS, Inc., Bellevue, WA). At all NEBFLUX sites, identical BREBSs are used so the data will be intercomparable between the sites. Because significant procedures and field research and many measurement details and other functions are involved, the primary instrumentation, procedures, and measurement details of the NEBFLUX are provided in tabular format. The summary of specifications of the sensors/instruments used to measure fluxes, microclimatic variables, soil moisture, and plant physiological parameters for various vegetation surfaces at all the NEBFLUX sites are presented in Table 1, 2, and 3 of the proposal. At all NEBFLUX sites, the deluxe version of the BREBS uses an automatic exchange mechanism that physically exchanges the air temperature (Ta) and relative humidity (RH) sensors at two heights above the canopy, which is a critical part of the BREBS theory for good quality data collection. A BREBS that does not exchange the Ta and RH units will result in faulty data. Ta and RH sensors are exchanged during the last two minutes of each 15-minute interval. The upper exchanger tube that houses the Ta and RH probes is driven down in the 1st and 3rd 15-minute periods of each hour, and the bottom tube is driven up in the 2nd and 4th 15-minute periods of each hour. All variables are sampled every 60 sec and are averaged and recorded every hour for energy balance calculations using a Model CR10X datalogger and AM416 Relay Multiplexer (Campbell Scientific, Inc., Logan, UT). All system components are powered by a solar panel and a 12-V, 140-AMP marine battery.

Progress 08/01/10 to 07/31/15

Outputs
Target Audience:State and federal water management agency personnel (including Department of Natural Resources, Natural Resources Districts), agricultural producers, irrigation district personnel, crop consultants. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Program progress and accomplishements have been shared in numerous national and international conferences, meetings, etc. How have the results been disseminated to communities of interest?Program progress and accomplishements have been disseminated in various local, regional, national and international conferences/meetings. What do you plan to do during the next reporting period to accomplish the goals?I will prepare a new Hatch Project Proposal that will be primarily a continuation of the NEBFLUX project. The NEBFLUX project has been established to be a long-term (at least 10 years) process to be able to collect sufficient data under various climatic conditions and management setttings to be able to capture variations in environmental conditions impact(s) on evaporative losses and crop coefficients.

Impacts
What was accomplished under these goals? -NBEFLUX towers continue to measure surface energy and water vapor fluxes, including evapotranspiration, sensible heat flux, soil heat flux, radiation envelopes, microclimatic variables, plant physiological parameters, soil water content, surface characteristics, and their interactions for various vegetation surfaces ranging from irrigated and rainfed and tilled and untilled croplands to Phragmites-dominated invasive vegetation surfaces. The information from all these extensive field projects continue to be disseminated (and used) for enhancing water resources assessment and management. -The NEBFLUX project continue to operate10 Bowen ratio energy balance systems in various parts of NE.The Network is measuring and transferring the information to the state and federal agencies and farmers and crop consultants for improved water balance and crop water use analyses. -The NEBFLUX project is also providing valuable data to state agencies (irrigation districts, NRDs, and DNR) for their designing, planning, and management of water resources and related infrastructures. The datasets are also being used by growers and crop consultants to make better irrigation management decisions. Data from the towers are also being used to develop improved evapotranspiration and transpiration crop coefficients for irrigation management. -Two new flux towers (one over surface drip-irrigated vineyard and another one over center pivot-irrigated black turtle bean and popcorn field) were installed and data collection has been started. -Information and data have been continued to be shared with citizens and stakeholders in various programs.

Publications

• Type: Conference Papers and Presentations Status: Accepted Year Published: 2015 Citation: Irmak, S. February 3, 2015. Long-term research on irrigation-yield production functions and evapotranspiration-yield production functions for full and limited-irrigated and rainfed corn. Holdrege Water Conference. Holdrege, NE. 150 people.
• Type: Conference Papers and Presentations Status: Accepted Year Published: 2015 Citation: Irmak, S. March 5, 2015. Comparative analyses of measured evapotranspiration for various land surfaces. 5th Interagency Conference on the Research in the Watersheds. March 2-5, 2015. Charleston, SC. 35 people.
• Type: Conference Papers and Presentations Status: Accepted Year Published: 2015 Citation: Irmak, S. April 15, 2015. Science and research integration into Extension and outreach programs for enhancing crop water productivity. Global Food Security Consortium (invited). Iowa State University. Ames, IA. 200 people.
• Type: Conference Papers and Presentations Status: Accepted Year Published: 2015 Citation: Irmak, S. April 21, 2015. Agricultural engineering and agricultural science and research and Extension programs for irrigation/water management crop productivity. UNL IANR and COE Osher Lifelong Learning Institute Lecture Series. Lincoln, NE. 20 people.
• Type: Conference Papers and Presentations Status: Accepted Year Published: 2015 Citation: Irmak, S. June 10, 2015. Irrigation engineering and water management fundamentals. North Central Region Water Management Network Capacity Building Training Workshop. Lincoln, NE. 25 people.
• Type: Conference Papers and Presentations Status: Accepted Year Published: 2015 Citation: Irmak, S. October 12, 2015. Change in climate variables impacts on water resources and agricultural productivity. UNL Extension Workshop on Climate Change. Lincoln, NE. 50 people.
• Type: Conference Papers and Presentations Status: Accepted Year Published: 2015 Citation: Irmak, S. December 2, 2015. Soil and water resources and irrigation engineering, evapotranspiration and impact(s) of change in climate variables on agricultural productivity and water resources: research, science and education programs. BSE Colloquium. Lincoln, NE. 50 people.
• Type: Conference Papers and Presentations Status: Accepted Year Published: 2015 Citation: Irmak, S. December 11, 2015. Advances and practical applications in soil water status measurement technologies. Nebraska Agribusiness Association (invited). Lincoln, NE. 80 people.

Progress 10/01/13 to 09/30/14

Outputs
Target Audience: Natural Resources Districts; Department of Natural Resourcees; Natural Resources Conservation District; Irrigation Districts; Farmers; Extension Educators; Crop consultants; Scientists; Students. Changes/Problems: I do not anticipate any major changes in our research and education directions with NEBFLUX and I do not anticipate any major issues/problems. What opportunities for training and professional development has the project provided? The NEBFLUX functions have been presented in various regional, national, and international professional conferences, meetings, and programs by myself and by my research team members which provided excellent professional development opportunities for all my team members involved. The NEBFLUX functions have also been presented to Extension Educators and state and federal water management agency personnel through various educational programs that provided them professional development opportunities as well. How have the results been disseminated to communities of interest? The results have been disseminated to all targeted audiance through numerous local, regional, national and international presentations. What do you plan to do during the next reporting period to accomplish the goals? Continue to enhance NEBFLUX functios and ensure quality data collection -Continue to conduct research and educational programs on irrigation and fertigation best management practices for agronomical crops under center pivot, subsurface drip irrigation, and gravity irrigation systems. -Continue on researching new generation water management practices, including innovative underground wireless sensor development and researching fundamentals of variable rate irrigation.

Impacts
What was accomplished under these goals? The fundamental premise of the NEBFLUX is to measure continuous and long-term (at least ten complete annual cycles for each surface) exchange of water vapor and energy fluxes for various vegetation surfaces/cropping systems. The measurements include evapotranspiration, sensible heat, soil heat flux, net radiation, incoming shortwave radiation, soil temperature, precipitation, wind speed and directions, air temperature and humidity gradients, actual vapor pressure, soil water content (every 0.30 m up to 1.8 m on an hourly basis throughout the year), soil properties, plant height, leaf area index, yield and/or dry matter (biomass) production, irrigation applications, fertilizer, herbicide, pesticide, and insecticide applications, and other management practices. All variables are used to quantify water use and its interactions with various management practices and environmental variables for different land use types. 2. Measure nocturnal period evaporativelosses for all cropping systems/vegetation surfaces. 3. Quantify water re-charge for each vegetation surface. 4. Measure/update crop coefficient (Kc) values for maize, soybean, winter wheat, grassland, and alfalfa. NEBFLUX data from all sites are used to develop updated Kc values for various cropping systems. 5. Measure and develop techniques to predict evaporative losses during the non-growing season. Because all NEBFLUX systems are operated on an hourly basis and continuously throughout the year, the annual water use rates of surface are measured. Expected Outputs: All the flux systems are providing, and will continue to provide, extremely valuable data and information to state water regulatory agencies for their designing, planning, and management of water resources infrastructures. The evapotranspiration datasets are used to make policy and regulatory decisions by the state agencies. The datasets are used by growers and crop consultants to make better irrigation management decisions. From NEBFLUX datasets, progress, and functions, we organized educational and outreach programs to disseminate the project findings for community/public education. Educators, students from different disciplines, and faculty members are given exposure to the project through field tours to visit experimental setups and other forms of educational outreach such as workshops and seminars. The project are carried out based on science and engineering principles. The project results are disseminated through several outlets: (i) program results are analyzed, summarized, written in manuscript format, and published in refereed scientific journals, (ii) education and outreach publications are developed to reach a large audience of educators, general public, public school teachers, state and federal agency personnel, and (iii) presentations relate project findings to interested parties at local, state, and professional national meetings. Internet is utilized to share the results of the program on the worldwide web.

Publications

• Type: Journal Articles Status: Published Year Published: 2014 Citation: Irmak, S., L.O. Odhiambo, J.E. Specht, and K. Djaman. 2013. Hourly and daily single and basal evapotranspiration crop coefficients as a function of growing degree days, days after emergence, leaf area index, fractional green canopy cover, and plant phenology for soybean. Transactions of the ASABE 56(5):1785-1803. Rudnick, D.R., and S. Irmak. 2014. Spatial and temporal maize soil-water extraction (depletion) dynamics: Part I. Development and evaluation of a soil-water extraction model. Transactions of the ASABE 57(2):431-444. Mutiibwa, D., A. Kilic, and S. Irmak. 2014. The effect of land cover/land use changes on the regional climate of the U.S.A. High Plains. Climate 2(3):153-167 doi:10.3390/cli2030153. Rudnick, D.R., and S. Irmak. 2014. Spatial and temporal maize soil-water extraction (depletion) dynamics: Part II. Impact of water and nitrogen management strategies on soil-water extraction. Transactions of the ASABE 57(2):445-462. Rudnick, D.R., and S. Irmak. 2014. Impact of nitrogen fertilizer on maize evapotranspiration crop coefficients under fully-irrigated, limited irrigation, and rainfed settings. J. Irrigation and Drainage Engineering, ASCE 10.1061/(ASCE)IR,1943-4774.0000778,0401403. Rudnick, D.R., and S. Irmak. 2014. Implementation of soil water extraction model on a spatial domain using field capacity and apparent electrical conductivity relationships. Transactions of the ASABE 57(5):1359-1373.

Progress 10/01/12 to 09/30/13

Outputs
Target Audience: Natural District Personnel; Department of Natural Resourcees; Natural Resources District; Irrigation Districts personnel; producers; Extension Educators; crop consultants; scientists; students. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? The NEBFLUX functions have been presented in various regional, national, and international professional conferences, meetings, and programs by myself and by my research team members which provided excellent professional development opportunities for all my team members involved. The NEBFLUX functions have also been presented to Extension Educators and state and federal water management agency personnel through various educational programs that provided them professional development opportunities as well. How have the results been disseminated to communities of interest? The results have been disseminated to all targeted audiance that was mentioned previously. What do you plan to do during the next reporting period to accomplish the goals? -Continue to conduct research and educational programs on irrigation and fertigation best management practices for agronomical crops under center pivot, subsurface drip irrigation, and gravity irrigation systems. -Continue on researching new generation water management practices, including innovative underground wireless sensor development and researching fundamentals of variable rate irrigation.

Impacts
What was accomplished under these goals? -The main objectives of the NEBFLUX is to measure surface energy and water vapor fluxes, including evapotranspiration, microclimatic variables, plant physiological parameters, soil water content, surface characteristics, and their interactions for various vegetation surfaces ranging from irrigated and rainfed and tilled and untilled croplands to Phragmites-dominated invasive vegetation surfaces. The information from all these extensive field projects continue to be disseminated (and used) to the clientele, including federal and state water agencies. -The NEBFLUX project currently operates 11 Bowen ratio energy balance and eddy covariance systems in various parts of NE. It is the largest and most comprehensive network of its kind that is operated by a single research laboratory in the United States. The Network is measuring and transferring the information to the state and federal agencies and farmers and crop consultants. -The NEBFLUX project is providing extremely valuable data to state agencies (irrigation districts, NRDs, and DNR) for their designing, planning, and management of water resources and related infrastructures. The request by the state agenacies of data/information from this project has been increeasing significantly. The evapotranspiration datasets that my research team measure are also being used to make policy and regulatory decisions by the state agencies. The datasets are also being used by growers and crop consultants to make better irrigation management decisions. All the NEBFLUX components are vital to better understand and manage state's water resources. In 2012 and 2013, more than 7 refereed journal articles related to this project have been published and numerous educational programs have been conducted to inform/educate public and state agency personnel.

Publications

• Type: Journal Articles Status: Published Year Published: 2013 Citation: Irmak, S., I. Kabenge, I., D. Rudnick, S. Knezevic, D. Woodward, and M. Moravek. 2013. Evapotranspiration crop coefficients for mixed riparian plant community and transpiration crop coefficients for phragmites, cottonwood and peach-leaf willow in the Platte River Basin, Nebraska-USA. Journal of Hydrology 481:177-190.
• Type: Journal Articles Status: Published Year Published: 2013 Citation: Mutiibwa, D., and S. Irmak. 2013. AVHRR-NDVI-based crop coefficients for analyzing long-term trends in evapotranspiration in relation to changing climate in the USA High Plains. Water Resources Research 49(1):231-244. doi:10.1029/2012WR012591
• Type: Journal Articles Status: Published Year Published: 2013 Citation: Payero, J.O., and S. Irmak. 2013. Daily energy fluxes, evapotranspiration and crop coefficients of soybean. Agric. Water Management 129:31-43. http://dx.doi.org/10.1016/j.agwat.2013.06.018
• Type: Journal Articles Status: Published Year Published: 2013 Citation: Mutiibwa, D., and S. Irmak. 2013. Transferability of Jarvis-type models developed/re-parameterized for specific crops to estimate stomatal resistance for other crops: Analyses on model calibration, validation, performance, sensitivity, and elasticity. Transactions of the ASABE 56(2):409-422
• Type: Journal Articles Status: Published Year Published: 2013 Citation: Kabenge, I., S. Irmak, G.E. Meyer, J.E. Gilley, S. Knezevic, T.J. Arkebauer, D. Woodward, and M. Moravek. 2013. Evapotranspiration and surface energy balance of a common reed-dominated riparian system in the Platte River Basin, central Nebraska, USA. Transactions of the ASABE 56(1):135-153

Progress 10/01/11 to 09/30/12

Outputs
OUTPUTS: The main objectives of the NEBFLUX is to measure surface energy and water vapor fluxes, microclimatic variables, plant physiological parameters, soil water content, surface characteristics, and their interactions for various vegetation surfaces ranging from irrigated and rainfed and tilled and untilled croplands to Phragmites-dominated invasive vegetation surfaces. The information from all these extensive field projects will be disseminated to the clientele, including federal and state water agencies. The NEBFLUX project which measures evapotranspiration and other surface energy fluxes, crop coefficients, soil moisture, plant physiological parameters and their interactions for many different vegetation surface currently operates 11 Bowen ratio energy balance systems and one eddy covariance system. It is the largest and most comprehensive network of its kind that is operated by a single research laboratory in the United States. The Network is measuring and transferring the information to the state and federal agencies and farmers and crop consultants on: -evapotranspiration for growing and non-growing (dormant) seasons -providing supporting data to estimate recharge -continuous (hourly) soil moisture every 12 in up to 6 ft -measuring nighttime evaporative losses -measuring plant physiological parameters and their interactions with microclimate/climate PARTICIPANTS: Academic, farmers, crop consultants, Natural District Districts, Department of Natural District, Irrigation Districts, USDA, NRCS TARGET AUDIENCES: Academic, farmers, crop consultants, Natural District Districts, Department of Natural District, Irrigation Districts, USDA, NRCS, students PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
The NEBFLUX project is providing extremely valuable data to state agencies (irrigation districts, NRDs, and DNR) for their designing, planning, and management of water resources and related infrastructures. The evapotranspiration datasets that my research team measure are also being used to make policy and regulatory decisions by the state agencies. The datasets are also being used by growers and crop consultants to make better irrigation management decisions. All the NEBFLUX components are vital to better understand and manage state's water resources. So far, more than 10 refereed journal articles related to this project have been either submitted or published and numerous educational programs have been conducted to inform/educate public and state agency personnel.

Publications

• Sharma, V., and S. Irmak. 2012. Mapping spatially-interpolated precipitation, reference evapotranspiration, actual crop evapotranspiration, and net irrigation requirements: Part I. Precipitation and reference evapotranspiration. Transactions of the ASABE 55(3): 907-921.
• Sharma, V., and S. Irmak. 2012. Mapping spatially-interpolated precipitation, reference evapotranspiration, actual crop evapotranspiration, and net irrigation requirements: Part II. Actual crop evapotranspiration and net irrigation requirements. Transactions of the ASABE 55(3): 923-936.
• Djaman, K., and S. Irmak. 2012. Soil water extraction patterns and crop-, irrigation-, and evapotranspiration water use efficiency of maize under full and limited irrigation and rainfed settings. Transactions of the ASABE 55(4):1223-1238.
• Skaggs, K.E., and S. Irmak. 2012. Analysis of microclimate data measured over grass and soybean canopy and their impacts on Penman-Monteith grass and alfalfa-reference evapotranspiration. J. Irrigation and Drainage Engineering, ASCE 138(2): 120-134 .
• Odhiambo, L.O., and S. Irmak. 2012. Evaluation of the impact of surface residue cover on single and dual crop coefficient methods for estimating soybean actual evapotranspiration. Agricultural Water Management 104:221-234.

Progress 10/01/10 to 09/30/11

Outputs
OUTPUTS: Continuous measurements of long-term (at least ten complete annual cycles for each surface) exchange of water vapor and energy fluxes for various vegetation surfaces/cropping systems, Measurements of nocturnal period evaporative losses for all cropping systems/vegetation surfaces, Measurement/updating crop coefficient (Kc) values for maize, soybean, winter wheat, grassland, and alfalfa PARTICIPANTS: S. Irmak, K. Skaggs, B. Rathje, D. Mutiibwa, S. Chatterjee, Central Platte Natural Resources District. TARGET AUDIENCES: Satate and federal water agencies, farmers, crop consultants, university colleagues and students. PROJECT MODIFICATIONS: Not relevant to this project.

Impacts
All the flux systems are, and will continue, providing extremely valuable data and information to state water regulatory agencies for their designing, planning, and management of water resources infrastructures. The evapotranspiration datasets will be used to make policy and regulatory decisions by the state agencies. The datasets will be used by growers and crop consultants to make better irrigation management decisions.

Publications

• Lagos, L.O., D.L. Martin, S.B. Verma, S. Irmak, A. Irmak, D.E. Eisenhauer, and A. Suyker. 2011. Surface energy balance model of transpiration and evaporation from residue-covered or bare-soil systems: Model evaluation. Irrigation Science, Aug. 2011. DOI10.1007/s00271-011-0298-9.
• Irmak, S. 2011. On the dynamics of nocturnal, day-time, and sum-of-hourly evapotranspiration and other surface energy fluxes over a non-stressed maize canopy. J. Irrigation and Drainage Engineering, ASCE 137(8):475-490.
• Irmak, S., L.O. Odhiambo, and D. Mutiibwa. 2011. Assessing the impact of daily net radiation models on grass and alfalfa-reference evapotranspiration estimated using Penman-Monteith equation in a sub-humid and arid climate. J. Irrigation and Drainage Engineering ASCE 137(2):59-72.
• Mutiibwa, D., and S. Irmak. 2011. On the scaling up soybean leaf level stomatal resistance to canopy resistance for one-step estimation of actual evapotranspiration. Transactions of the ASABE 54(1):141-154.

Progress 10/01/09 to 09/30/10

Outputs
OUTPUTS: The fundamental premise of the NEBFLUX is to measure continuous and long-term (at least ten complete annual cycles for each surface) exchange of water vapor and energy fluxes for various vegetation surfaces/cropping systems. The outputs include The measurements will include evapotranspiration, sensible heat, soil heat flux, net radiation, incoming shortwave radiation, soil temperature, precipitation, wind speed and directions, air temperature and humidity gradients, actual vapor pressure, soil water content (every 0.30 m up to 1.8 m on an hourly basis throughout the year), soil properties, plant height, leaf area index, yield and/or dry matter (biomass) production, irrigation applications, fertilizer, herbicide, pesticide, and insecticide applications, and other management practices. All variables will be used to quantify water use and its interactions with various management practices and environmental variables for different land use types. PARTICIPANTS: Post-doctoral research associates, Research assistant professor, graduate students, and research technician. TARGET AUDIENCES: State and federal water agency personnel, university personnel, growers and crop consultants, educators PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
The NEBFLUX project will provide good quality flux and other extensive supportive data on plant physiology [leaf area index, stomatal resistance, within-canopy radiation parameters, productivity (yield and/or biomass), and plant height], soil characteristics, soil water content, and surface characteristics to the micrometeorology, water resources engineering, and science community on broad spectrum of agro-ecosystems. At the completion of this project, state water regulatory agencies, growers, and decision/policymakers will have improved and continuous evapotranspiration, re-charge and other water balance datasets that will enable them to enhance water resources assessments and planning decisions; better manage irrigations, and also will have a better handle on water balance calculations not only for the growing season, but also on an annual basis for various cropping systems and watersheds. These will aid in better managing state's water resources. In addition to the scientific and research functions, information/data dissemination to educate the general public and youth is another important objective and output of the network.

Publications

• Irmak, S., and D. Mutiibwa. 2010. On the dynamics of canopy resistance: Generalized-linear estimation and its relationships with primary micrometeorological variables. Water Resources Research 46:1-20, W08526, doi: 10.1029/2009WR008484.
• Irmak, S. 2010. Nebraska Water and Energy Flux Measurement, Modeling, and Research Network (NEBFLUX). Transactions of the ASABE 53(4):1097-1115.
• Irmak, S., D. Mutiibwa, and J.O. Payero. 2010. Net radiation dynamics: Performance of 20 daily net radiation models as related to model structure and intricacy in two climates. Transactions of the ASABE 53(4):1059-1076.
• Irmak, A., P. Ranade, D. Marx, S. Irmak, K.G. Hubbard, G. Meyer, and D.L. Martin. 2010. Spatial interpolation of climate variables in Nebraska. Transactions of the ASABE 53(6):1759-1771.
• Irmak, S., J.M. Rees, G.L. Zoubek, B.S. VanDeWalle, W.R. Rathje, R. DeBuhr, D. Leininger, D.D. Siekman, J.W. Schneider, and A.P. Christiansen. 2010. Nebraska Agricultural Water Management Demonstration Network: Integrating Research and Extension/Outreach. Applied Engineering in Agriculture 26(4):599-613.
• Hay, C.H., and S. Irmak. 2010. Recursive and explicit combination-based energy balance equations for calculating reference evapotranspiration in relation to Bowen ratio measurements. Transactions of the ASABE 53(6):1799-1810.
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