Other Civil and Environmental Engineering Commons^™

Soybean Crop Coefficients Under Different Seeding Rates And Full And Limited Irrigation And Rainfed Management, Suat Irmak, Rupinder Sandhu

Biological Systems Engineering: Papers and Publications

The effects of soybean seeding rates on evapotranspiration (ET_c) and grassand alfalfa-reference crop coefficients (K_co and K_cr) were investigated under five seeding rates (185,250, 247,000, 308,750, 370,500 and 432,250 seeds ha^-1) (62, 82, 103, 124 and 144% of the recommended seeding rate of 300,000 seeds ha^-1 in the experimental region) and different irrigation strategies (i.e. full irrigation treatment [FIT], limited irrigation of 75% FIT and 50% FIT and rainfed treatment). K_co and K_cr values were developed for each soybean growth stage. The seasonal ET_c ranged from 460 mm for …

Toward Automated Irrigation Management With Integrated Crop Water Stress Index And Spatial Soil Water Balance, Sandeep Bhatti, Derek M. Heeren, Susan A. O’Shaughnessy, Christopher M. U. Neale, Jacob Larue, Steve Melvin, Eric Wilkening, Geng Bai

Biological Systems Engineering: Papers and Publications

Decision support systems intended for precision irrigation aim at reducing irrigation applications while optimizing crop yield to achieve maximum crop water productivity (CWP). These systems incorporate on-site sensor data, remote sensing inputs, and advanced algorithms with spatial and temporal characteristics to compute precise crop water needs. The availability of variable rate irrigation (VRI) systems enables irrigation applications at a sub-field scale. The combination of an appropriate VRI system along with a precise decision support system would be ideal for improved CWP. The objective of this study was to compare and evaluate two decision support systems in terms of seasonal applied …

Toward Automated Irrigation Management With Integrated Crop Water Stress Index And Spatial Soil Water Balance, Sandeep Bhatti, Derek M. Heeren, Susan A. O’Shaughnessy, Christopher M. U. Neale, Jacob Larue, Steve Melvin, Eric Wilkening, Geng Bai

Biological Systems Engineering: Papers and Publications

Decision support systems intended for precision irrigation aim at reducing irrigation applications while optimizing crop yield to achieve maximum crop water productivity (CWP). These systems incorporate on-site sensor data, remote sensing inputs, and advanced algorithms with spatial and temporal characteristics to compute precise crop water needs. The availability of variable rate irrigation (VRI) systems enables irrigation applications at a sub-field scale. The combination of an appropriate VRI system along with a precise decision support system would be ideal for improved CWP. The objective of this study was to compare and evaluate two decision support systems in terms of seasonal applied …

The Effect Of Relative Humidity On Eddy Covariance Latent Heat Flux Measurements And Its Implication For Partitioning Into Transpiration And Evaporation, Weijie Zhang, Martin Jung, Mirco Migliavacca, Rafael Poyatos, Diego G. Miralles, Tarek S. El-Madany, Marta Galvagno, Arnaud Carrara, Nicola Arriga, Andreas Ibrom, Ivan Mammarella, Dario Papale, Jamie R. Cleverly, Michael Liddell, Georg Wohlfahrt, Christian Markwitz, Matthias Mauder, Eugenie Paul-Limoges, Marius Schmidt, Sebastian Wolf, Christian Brümmer, M. Altaf Arain, Silvano Fares, Tomomichi Kato, Jonas Ardö, Walter Oechel, Chad Hanson, Mika Korkiakoski, Sébastien Biraud, Rainer Steinbrecher, Dave Billesbach, Leonardo Montagnani, William Woodgate, Changliang Shao, Nuno Carvalhais, Markus Reichstein, Jacob A. Nelson

Biological Systems Engineering: Papers and Publications

While the eddy covariance (EC) technique is a well-established method for measuring water fluxes (i.e., evaporation or 'evapotranspiration’, ET), the measurement is susceptible to many uncertainties. One such issue is the potential underestimation of ET when relative humidity (RH) is high (>70%), due to low-pass filtering with some EC systems. Yet, this underestimation for different types of EC systems (e.g. open-path or closed-path sensors) has not been characterized for synthesis datasets such as the widely used FLUXNET2015 dataset. Here, we assess the RH-associated underestimation of latent heat fluxes (LE, or ET) from different EC systems for 163 sites in …

The Combined Impact Of Redcedar Encroachment And Climate Change On Water Resources In The Nebraska Sand Hills, Yaser Kishawi, Aaron R. Mittelstet, Zablon Adane, Nawaraj Shrestha, Paolo Nasta

Biological Systems Engineering: Papers and Publications

The Nebraska Sand Hills (NSH) is considered a major recharge zone for the High Plains Aquifer in the central United States. The uncontrolled expansion of the eastern redcedar (Juniperus Virginiana) under climate warming is posing threats to surface water and groundwater resources. The combined impact of land use and climate change on the water balance in the Upper Middle Loup River watershed (4,954 km²) in the NSH was evaluated by simulating different combination of model scenarios using the Soil Water Assessment Tool (SWAT) model. A total of 222 climate models were ranked according to the aridity …

Behavior Of Completely Automated Evapotranspiration Estimation (Eemetric), Atiqullah Atif

Department of Civil and Environmental Engineering: Dissertations, Theses, and Student Research

Evapotranspiration (ET) is the second-largest component in the water balance equation, globally consuming 70% of the earth’s annual precipitation. Accurate and consistent estimation of ET is essential for ensuring water resources sustainability, proper management, planning, and regulations of water resources. Though a 100% accurate estimation of ET may not be feasible with the current technology, there are proven techniques that give us estimates of ET we can heavily rely on. Mapping Evapotranspiration at High Resolution with Internalized Calibration (METRIC) is a widely used surface energy balance model that produces relatively accurate ET maps utilizing remote sensing data and requires skilled …

Dynamics Of Crop Evapotranspiration Of Four Major Crops On A Large Commercial Farm: Case Of The Navajo Agricultural Products Industry, New Mexico, Usa, Koffi Djaman, Komlan Koudahe, Ali T. Mohammed

Biological Systems Engineering: Papers and Publications

Crop evapotranspiration (ETa) is the main source of water loss in farms and watersheds, and with its effects felt at a regional scale, it calls for irrigation professionals and water resource managers to accurately assess water requirements to meet crop water use. On a multi-crop commercial farm, different factors affect cropland allocation, among which crop evapotranspiration is one of the most important factors regarding the seasonally or annually available water resources for irrigation in combination with the in-season effective precipitation. The objective of the present study was to estimate crop evapotranspiration for four major crops grown on the Navajo Agricultural …

Crop Response To Thermal Stress Without Yield Loss In Irrigated Maize And Soybean In Nebraska, Sandeep Bhatti, Derek M. Heeren, Steven R. Evett, Susan A. O'Shaughnessy, Daran Rudnick, Trenton E. Franz, Yufeng Ge, Christopher M.U. Neale

Biological Systems Engineering: Papers and Publications

Thermal sensing provides rapid and accurate estimation of crop water stress through canopy temperature data. Canopy temperature is highly dependent on the transpiration rate of the leaves. It is usually assumed that any reduction in crop evapotranspiration (ET) leads to crop yield loss. As a result, an increase in canopy temperature due to a decrease in crop ET would indicate crop yield loss. This research evaluated the hypothesis that crop water stress could be detected using canopy temperature measurements (increased leaf temperature) from infrared thermometers (IRTs) before incurring crop yield loss. This would be possible in a narrow range when …

Real-Time Irrigation Scheduling Of Maize Using Degrees Above Non-Stressed (Dans) Index In Semi-Arid Environment, Hope Njuki Nakabuye, Daran Rudnick, Kendall C. Dejonge, Tsz Him Lo, Derek M. Heeren, Xin Qiao, Trenton E. Franz, Abia Katimbo, Jiaming Duan

Biological Systems Engineering: Papers and Publications

Irrigation scheduling methods have been used to determine the timing and amount of water applied to crops. Scheduling techniques can include measurement of soil water content, quantification of crop water use, and monitoring of crop physiological response to water stress. The aim of this study was to evaluate the performance of a simplified crop canopy temperature measurement (CTM) method as Irrigation Principles. Soil and Water Conservation Engineera technique to schedule irrigation for maize. Specifically, the Degrees Above Non-Stressed (DANS) index, which suggests water stress when canopy temperature exceeds the non-stressed canopy temperature (T_cns), was determined by estimating T …

Site-Specific Irrigation Management In A Sub-Humid Climate Using A Spatial Evapotranspiration Model With Satellite And Airborne Imagery, Sandeep Bhatti, Derek M. Heeren, J. Burdette Barker, Christopher M. U. Neale, Wayne Woldt, Mitchell S. Maguire, Daran Rudnick

Biological Systems Engineering: Papers and Publications

Variable Rate Irrigation (VRI) considers spatial variability in soil and plant characteristics to optimize irrigation management in agricultural fields. The advent of unmanned aircraft systems (UAS) creates an opportunity to utilize high-resolution (spatial and temporal) imagery into irrigation management due to decreasing costs, ease of operation, and reduction of regulatory constraints. This research aimed to evaluate the use of UAS data for VRI, and to quantify the potential of VRI in terms of relative crop and water response. Irrigation treatments were: (1) VRI using Landsat imagery (VRI-L), (2) VRI using UAS imagery (VRI-U), (3) uniform (U), and (4) rainfed (R). …

Actual Evapotranspiration And Crop Coefficients Of Irrigated Lowland Rice (Oryza Sativa L.) Under Semiarid Climate, Koffi Djaman, Daran R. Rudnick, Yonnelle D. Moukoumbi, Abdoulaye Sow, Suat Irmak

Biological Systems Engineering: Papers and Publications

Lowland irrigated rice is the predominant crop produced in the Senegal River Valley characterized by very low annual rainfall, high temperatures, and low relative humidity. The Senegal River is shared by Senegal, Mali, Mauritania, and Guinea, and serves as the main source of irrigation water for the adopted double rice cropping system. Developing appropriate resource management strategies might be the key factor for the sustainability of rice production in the region. This study aims to estimate rice seasonal evapotranspiration (ETa), irrigation water requirement, and to develop rice growth stage specific crop coefficients (Kc) to improve rice water productivity. Field experiments …

Evaluation Of Variable Rate Irrigation Using A Remote-Sensing-Based Model, John Burdette Barker, Derek M. Heeren, Christopher M.U. Neale, Daran Rudnick

Biological Systems Engineering: Papers and Publications

Improvements in soil water balance modeling can be beneficial for optimizing irrigation management to account for spatial variability in soil properties and evapotranspiration (ET). A remote-sensing-based ET and water balance model was tested for irrigation management in an experiment at two University of Nebraska-Lincoln research sites located near Mead and Brule, Nebraska. Both fields included a center pivot equipped with variable rate irrigation (VRI). The study included maize in 2015 and 2016 and soybean in 2016 at Mead, and maize in 2016 at Brule, for a total of 210 plot-years. Four irrigation treatments were applied at Mead, including: VRI based …

Crop Evapotranspiration, Irrigationwater Requirement And Water Productivity Of Maize From Meteorological Data Under Semiarid Climate, Koffi Djaman, Michael O'Neill, Curtis K. Owen, Daniel Smeal, Komlan Koudahe, Margaret West, Samuel Allen, Kevin Lombard, Suat Irmak

Biological Systems Engineering: Papers and Publications

Under the semiarid climate of the Southwest United States, accurate estimation of crop water use is important for water management and planning under conservation agriculture. The objectives of this study were to estimate maize water use and water productivity in the Four Corners region of New Mexico. Maize was grown under full irrigation during the 2011, 2012, 2013, 2014 and 2017 seasons at the Agricultural Science Center at Farmington (NM). Seasonal amounts of applied irrigation varied from 576.6 to 1051.6 mm and averaged 837.7 mm and the total water supply varied from 693.4 to 1140.5 mm. Maize actual evapotranspiration was …

Spatial And Temporal Changes In Maize And Soybean Grain Yield, Precipitation Use Efficiency, And Crop Water Productivity In The U.S. Great Plains, Meetpal S. Kukal, S. Irmak

Biological Systems Engineering: Papers and Publications

Sustainable agricultural utilization of the limited water resources demands improvements in understanding the changes in crop water productivity (CWP) in space and time, which is often presented as a potential solution to relieve the growing pressure on fresh water resources. In addition, crop yield needs to be studied in relation to precipitation received annually and during the growing season for its contribution to reduce irrigation water requirements, which is quantified through precipitation use efficiency (PUE). Hence, systematic quantifications, mapping, and analyses of large-scale CWP and PUE levels are needed. This study aims to quantify long-term (1982-2013) information on grain yield, …

Trend Analysis In Rainfall, Reference Evapotranspiration And Aridity Index In Southern Senegal: Adaptation To The Vulnerability Of Rainfed Rice Cultivation To Climate Change, Komlan Koudahe, Koffi Djaman, Ansoumana Bodian, Suat Irkmak, Mamadou Sall, Lamine Diop, Alpha B. Balde, Daran Rudnick

Biological Systems Engineering: Papers and Publications

Rainfall and evapotranspiration are two vital elements for food production under rainfed agriculture. This study aims at investigating the combined changes in these variables in the form of aridly index in the southern Senegal. The temporal trends in annual and monthly (from May to October) aridity index, rainfall and evapotranspiration are examined and adaptation strategies to the vulnerability of rainfed rice cultivation to the changes are developed. The results show a significant decreasing trend in annual rainfall at all study locations for the period 1922-2015. When analyzing the trends in sub-periods, there are two clear patterns in the annual rainfall …

Long-Term Patterns Of Air Temperatures, Daily Temperature Range, Precipitation, Grass-Reference Evapotranspiration And Aridity Index In The Usa Great Plains: Part I. Spatial Trends, Meetpal S. Kukal, Suat Irmak

Biological Systems Engineering: Papers and Publications

Due to their substantial spatio-temporal behavior, long-term quantification and analyses of important hydrological variables are essential for practical applications in water resources planning, evaluating the water use of agricultural crop production and quantifying crop evapotranspiration patterns and irrigation management vs. hydrologic balance relationships. Observed data at over 800 sites across the Great Plains of USA, comprising of 9 states and 2,307,410 km² of surface area, which is about 30% of the terrestrial area of the USA, were used to quantify and map large-scale and long-term (1968-2013) spatial trends of air temperatures, daily temperature range (DTR), precipitation, grass-reference evapotranspiration (ET …

Vulnerability Of Crops And Native Grasses To Summer Drying In The U.S. Southern Great Plains, Naama Raz-Yaseef, Dave P. Billesbach, Marc L. Fischer, Sebastien C. Biraud, Stacey A. Gunter, James A. Bradford, Margaret S. Torn

Biological Systems Engineering: Papers and Publications

The Southern Great Plains are characterized by a fine-scale mixture of different land-cover types, predominantly winter-wheat and grazed pasture, with relatively small areas of other crops, native prairie, and switchgrass. Recent droughts and predictions of increased drought in the Southern Great Plains, especially during the summer months, raise concern for these ecosystems. We measured ecosystem carbon and water fluxes with eddy-covariance systems over cultivated cropland for 10 years, and over lightly grazed prairie and new switchgrass fields for 2 years each. Growing-season precipitation showed the strongest control over net carbon uptake for all ecosystems, but with a variable effect: grasses …

Surface Energy Balance, Evapotranspiration, And Surface Coefficients During Non-Growing Season In A Maize-Soybean Cropping System, Lameck O. Odhiambo, Suat Irmak

Biological Systems Engineering: Papers and Publications

Surface energy balance components, including actual evapotranspiration (ET), were measured in a reducedtill maize-soybean field in south central Nebraska during three consecutive non-growing seasons (2006/2007, 2007/2008, and 2008/2009). The relative fractions of the energy balance components were compared across the non-growing seasons, and surface coefficients (K_c) were determined as a ratio of measured ET to estimated alfalfa (ET_r) and grass (ET_o) reference ET (ET_ref). The non-growing season following a maize crop had 25% to 35% more field surface covered with crop residue as compared to the non-growing seasons following soybean crops. Net …

Improved Simulation Of Evapotranspiration For Land Use And Climate Change Impact Analysis At Catchment Scale, Ann Van Griensven, Samita Maharjan, Tadesse Alemayehu

International Congress on Environmental Modelling and Software

Evapotranspiration is not only one of the major components of the hydrological cycle, it also controls impacts of drivers such as climate and land use changes. One of the widely used simulation tools for climate and impact studies is the Soil and Water Assessment Tool {SWAT). This study evaluates the evapotranspiration processes in SWAT in the Kenyan Mau forest within the Mara basin that drains to Lake Victoria. The study reveals that typical SWAT applications have flaws as in the implementation or parameterisation of tropical forests.

To improve the use of SWAT for land use and climate change studies, the …

Soybean Yield, Evapotranspiration, Water Productivity, And Soil Water Extraction Response To Subsurface Drip Irrigation And Fertigation, Suat Irmak, James E. Specht, Lameck O. Odhiambo, J. M. Rees, K. G. Cassman

Biological Systems Engineering: Papers and Publications

Soybean [Glycine max (L.) Merr.] yield, irrigation water use efficiency (IWUE), crop water use efficiency (CWUE), evapotranspiration water use efficiency (ETWUE), and soil water extraction response to eleven treatments of full, limited, or delayed irrigation versus a rainfed control were investigated using a subsurface drip irrigation (SDI) system at a research site in south-central Nebraska. The SDI system laterals were 0.40 m deep in every other row middle of 0.76 m spaced plant rows. Actual evapotranspiration (ET_a) was quantified in all treatments and used to schedule irrigation events on a 100% ET_a replacement basis in all but …

Impact Of Water And Nitrogen Management Strategies On Maize Yield And Water Productivity Indices Under Linear-Move Sprinkler Irrigation, Daran Rudnick, Suat Irmak

Biological Systems Engineering: Papers and Publications

With uncertainty in future irrigation water availability and regulations on nutrient application amounts, experimentally determined effects of “controllable” management strategies such as nitrogen (N), water, and their combination on crop water productivity (CWP, also known as crop water use efficiency) and actual evapotranspiration (ET_a) are essential. The effects of various N application rates (0, 84, 140, 196, and 252 kg ha^-1) under fully irrigated (FIT), limited irrigation (75% FIT), and rainfed conditions on maize (Zea mays L.) yield and various CWP indices were investigated in 2011 and 2012 growing seasons under linear-move sprinkler irrigation in south …

Evapotranspiration And Surface Energy Balance Of A Common Reed-Dominated Riparian System In The Platte River Basin, Central Nebraska, Isa Kabenge, Suat Irmak, John E. Gilley, George E. Meyer, Stevan Z. Knezevic, Timothy J. Arkebauer, Duane Woodward, Milton Moravek

Biological Systems Engineering: Papers and Publications

Quantifying actual evapotranspiration (ET_a) of riparian zones is important for more robust water balance analyses that will enable better planning, managing, and allocating of water resources as well as developing strategies to protect delicate riparian ecosystem functions. The ET_a, sensible heat flux (H), net radiation (R_n), soil heat flux (G), meteorological variables (air temperature, T_a; incoming shortwave radiation, R_s; wind speed, u₃; relative humidity, RH; vapor pressure deficit, VPD; precipitation, etc.), and albedo were measured on an hourly time step, and leaf area index (LAI) and plant height …

Maize Evapotranspiration, Yield Production Functions, Biomass, Grain Yield, Harvest Index, And Yield Response Factors Under Full And Limited Irrigation, Koffi Djaman, Suat Irmak, William R. Rathje, Derrel L. Martin, Dean E. Eisenhauer

Biological Systems Engineering: Papers and Publications

South-central Nebraska is one of the most extensively irrigated areas in the U.S., with over 65,000 active irrigation wells, and maize is the major agronomical crop produced. Maize production in this region requires supplementary irrigation for maximum productivity. Effective on-farm implementation of full and limited irrigation practices for potential improvements of crop productivity requires knowledge of locally developed crop yield response to water functions. In this study, the effects of full and limited irrigation practices on maize (Zea mays L.) plant height, leaf area index (LAI), grain yield and biomass production, actual crop evapotranspiration (ET_a), yield production functions, …

Development And Evaluation Of Ordinary Least Squares Regression Models For Predicting Irrigated And Rainfed Maize And Soybean Yields, Vivek Sharma, Daran R. Rudnick, Suat Irmak

Biological Systems Engineering: Papers and Publications

Understanding the relationships between climatic variables and soil physical and chemical properties with crop yields on large scales is critical for evaluating crop productivity to make better assessments of local and regional food security, policy, land and water resource allocation, and management decisions. In this study, ordinary least squares(OLS) regression models were developed to predict irrigated and rainfed maize and soybean yields at the county level as a

function of explanatory variables [precipitation (P), actual crop evapotranspiration (ETa), organic matter content (OMC), cation exchange capacity (CEC), clay content (CC), and available soil water capacity (ASW)] of the dominant soil type …

Large-Scale On-Farm Implementation Of Soil Moisture-Based Irrigation Management Strategies For Increasing Maize Water Productivity, Suat Irmak, Michael J. Burgert, Haishun Yang, Kenneth G. Cassman, Daniel T. Walters, William R. Rathje, Jose O. Payero, Patricio Grassini, Mark S. Kuzila, Kelly J. Brunkhorst, Dean E. Eisenhauer, William L. Kranz, Brandy Vandewalle, Jennifer M. Rees, Gary L. Zoubek, Charles A. Shapiro, Gregory J. Teichmeier

Biological Systems Engineering: Papers and Publications

Irrigated maize is produced on about 3.5 Mha in the U.S. Great Plains and western Corn Belt. Most irrigation water comes from groundwater. Persistent drought and increased competition for water resources threaten long-term viability of groundwater resources, which motivated our research to develop strategies to increase water productivity without noticeable reduction in maize yield. Results from previous research at the University of Nebraska-Lincoln (UNL) experiment stations in 2005 and 2006 found that it was possible to substantially reduce irrigation amounts and increase irrigation water use efficiency (IWUE) and crop water use efficiency (CWUE) (or crop water productivity) with little or …

Do Invasive Riparian Woody Plants Affect Hydrology And Ecosystem Processes?, Julie Huddle, Tala Awada, Derrel Martin, Xinhua Zhou, Sue Ellen Pegg, Scott Josiah

Great Plains Research: A Journal of Natural and Social Sciences

© 2011 Copyright by the Center for Greot Plains Studies, University of Nebraska-Lincoln

Performance Of Extended Shuttleworth‐Wallace Model For Estimating And Partitioning Of Evapotranspiration In A Partial Residue‐Covered Subsurface Drip‐Irrigated Soybean Field, Lameck O. Odhiambo, Suat Irmak

Biological Systems Engineering: Papers and Publications

Estimation of actual evapotranspiration (ET), especially its partitioning into plant transpiration (T) and soil evaporation (E), in agricultural fields is important for effective soil water management and conservation and for understanding the interactions between ET, T, and E with the management practices. Direct field measurements of ET, T, and E rates are difficult and costly; hence, mathematical models are used for estimating them. The objective of this study was to evaluate the practical applicability of the Shuttleworth‐Wallace (S‐W) model to estimate and partition ET in a subsurface drip‐irrigated soybean (Glycine max L. Merr.) field with partial residue cover. While its …

Nebraska Water And Energy Flux Measurement, Modeling, And Research Network (Nebflux), Suat Irmak

Biological Systems Engineering: Papers and Publications

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 understand the behavior and dynamics involved with the flux transfer so that robust models can be developed …

Impact Of Microclimatic Data Measured Above Maize And Grass Canopies On Penman‐Monteith Reference Evapotranspiration Calculations, Suat Irmak, Lameck O. Odhiambo

Biological Systems Engineering: Papers and Publications

Estimation of reference evapotranspiration (ET_ref) using measured microclimatic data and the Penman‐Monteith (PM) method provides a powerful means of quantifying actual plant evapotranspiration (ET_a) needed for use in various disciplines. When applying the PM method to estimate ET_ref, it is desirable to measure the required microclimatic data over a reference grass or alfalfa surface rather than above non‐reference surfaces. However, in reality, establishing and maintaining a reference surface for long periods of time is a difficult task. Other surface energy balance systems, such as the Bowen ratio energy balance system (BREBS), eddy covariance system, …

Evaluation Of Methods For Estimating Daily Reference Crop Evapotranspiration At A Site In The Humid Southeast United States, R. E. Yoder, Lameck O. Odhiambo, Wesley C. Wright

Biological Systems Engineering: Papers and Publications

Estimated daily reference crop evapotranspiration (ET_o) is normally used to determine the water requirement of crops using the crop factor method. Many ET_o estimation methods have been developed for different types of climatic data, and the accuracy of these methods varies with climatic conditions. In this study, pair−wise comparisons were made between daily ET_o estimated from eight different ET_o equations and ET_o measured by lysimeter to provide information helpful in selecting an appropriate ET_o equation for the Cumberland Plateau located in the humid Southeast United States. Based on the standard error of the …