ORIGINAL PAPER Effective crop evapotranspiration measurement using time-domain reflectometry technique in a sub-humid region R. K. Srivastava 1 & R. K. Panda 2 & Debjani Halder 3 Received: 27 May 2015 /Accepted: 31 May 2016 /Published online: 18 June 2016 # Springer-Verlag Wien 2016 Abstract The primary objective of this study was to evaluate the performance of the time-domain reflectometry (TDR) technique for daily evapotranspiration estimation of peanut and maize crop in a sub-humid region. Four independent methods were used to estimate crop evapotranspiration (ET c ), namely, soil water balance budgeting approach, energy balance approach—(Bowen ratio), empirical methods ap- proach, and Pan evaporation method. The soil water balance budgeting approach utilized the soil moisture measurement by gravimetric and TDR method. The empirical evapotranspira- tion methods such as combination approach (FAO-56 Penman–Monteith and Penman), temperature-based approach (Hargreaves – Samani), and radiation-based approach (Priestley–Taylor, Turc, Abetw) were used to estimate the ref- erence evapotranspiration (ET 0 ). The daily ET c determined by the FAO-56 Penman-Monteith, Priestley-Taylor, Turc, Pan evaporation, and Bowen ratio were found to be at par with the ET values derived from the soil water balance budget; while the methods Abetw, Penman, and Hargreaves-Samani were not found to be ideal for the determination of ET c . The study illustrates the in situ applicability of the TDR method in order to make it possible for a user to choose the best way for the optimum water consumption for a given crop in a sub- humid region. The study suggests that the FAO-56 Penman– Monteith, Turc, and Priestley–Taylor can be used for the de- termination of crop ET c using TDR in comparison to soil water balance budget. Abbreviations ASW Available soil water (mm) TDR Time domain reflectometry ET Evapotranspiration (mm) ET c Crop evapotranspiration (mm) ET o Reference evapotranspiration (mm) I Net irrigation depth (mm) K c Crop coefficient TAW Total available soil water (mm) θ FC Volumetric soil moisture at field capacity (m 3 m -3 ) θ WP Volumetric soil moisture at wilting point (m 3 m -3 ) θ v Volumetric soil water content (m 3 m -3 ) ρ g Bulk soil density θ g Soil water content by the gravimetric method (m 3 m -3 ) W w Weight of wet (g) W d Dry soil (g) v Velocity (m/s) K a Soil’ s bulk dielectric constant c Speed of light (m/s) Eq Equation A Sum of irrigation and rain (mm) ΔW Variation of soil water (mm) λ Latent heat of vaporization (2.501 MJ kg -1 ) R n Net radiation (W m -2 ) G Soil heat flux (W m -2 ) γ Psychrometric constant (kPa °C -1 ) ΔT Temperature (°C) Δe a Actualsaturation vapor pressure (kPa) U 2 Wind speed (ms -1 ) at 2 m height, Δ Slope of the vapor pressure curve (kPa 0 C -1 ) * R. K. Srivastava rajivkumar@agfe.iitkgp.ernet.in 1 Agricultural and Food Engineering Department, Indian Institute of Technology, Kharagpur, West Bengal 721302, India 2 School of Infrastructure, Indian Institute of Technology, Bhubaneswar 751013, India 3 Department of Agronomy, Uttar Banga KrishiViswavidyalaya, Pundibari, Cooch Behar 736165, India Theor Appl Climatol (2017) 129:1211–1225 DOI 10.1007/s00704-016-1841-7 Content courtesy of Springer Nature, terms of use apply. Rights reserved.