https://orcid.org/0000-0002-6461-1041
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ABSTRACT
Field lysimetric experiments were conducted on Potato crop grown in a humid sub-tropical agro-climate during 2014–2017 cropping seasons. Reference evapotranspiration (ET0) methods based on limited climatic data were evaluated with the FAO-56 Penman-Monteith (P-M) method. The performance of temperature-based and radiation-based methods was reliable, but evaporation-based methods performed poorly. The best methods in each category viz. Hargreaves-Samani, FAO-24 Radiation, and Snyder along with FAO-56 P-M were considered to estimate the empirical crop evapotranspiration (ETc) using the crop coefficient approach. The empirical ETc was compared with the field ETc obtained through water balance approach. A root water uptake-based numerical model was utilized to simulate the soil moisture dynamics in the crop root zone, wherein ETc is an important input parameter. The model simulated soil moisture was compared with the field observed values. Results indicate that FAO-56 P-M and Hargreaves-Samani-based simulated values presented close agreement with field observed values. FAO-24 Radiation and Snyder-based simulations underestimated and overestimated the field observed soil moisture, respectively. The field soil moisture depletion of 30% corresponds to simulated depletion of 15% (Snyder), 25% (Hargreaves-Samani), 28% (FAO-56 P-M) and 40% (FAO-24 Radiation).
Notations
The following symbols are used in this paper:
| ET0 = | = | Reference evapotranspiration (mm d−1). |
| ETc = | = | Crop evapotranspiration (mm d−1). |
| Kc= | = | Crop coefficient |
| Epan= | = | Pan evaporation (mm d−1) |
| P= | = | Precipitation (mm) |
| ab = | = | Adjustment factor used in FAO-24 Blaney–Criddle method which depends on minimum relative humidity (RHmin) and ratio of actual to possible sunshine Hours (n/N). |
| bb = | = | Adjustment factor used in FAO-24 Blaney–Criddle method which depends on Minimum relative humidity (RHmin), ratio of actual to possible sunshine hours (n/N) and daytime windspeed. |
| c = | = | The FAO-24 Correction (calibration) factor. |
| eo = | = | Actual vapor pressure (kPa). |
| ea = | = | Saturation vapor pressure at daily mean air temperature (mb). |
| ed = | = | Saturation vapor pressure at daily mean dew point (mb). |
| es = | = | Saturation vapor pressure (kPa). |
| F = | = | Upwind fetch of low growing vegetation (m). |
| G = | = | Soil heat flux density (MJ m2 d−1). |
| Kpan = | = | Coefficient of pan. |
| p = | = | Ratio of actual daily day time hours to annual mean daily day time hours (%). |
| RH = | = | Relative humidity (%). |
| RHmean = | = | Mean relative humidity (%). |
| RHmin= | = | Minimum relative humidity (%). |
| Rn = | = | Net radiation at crop surface (MJ m2 d−1). |
| R’n= | = | Net radiation at crop surface (mm d−1). |
| Rs = | = | Incoming solar radiation (MJ m2 d−1). |
| R’s = | = | Incoming solar radiation (mm d−1). |
| Ra= | = | Extra-terrestrial radiation (mm d−1). |
| Tmax = | = | Maximum air temperatures (°C). |
| Tmin = | = | Minimum air temperatures (°C). |
| U = | = | Wind speed at 2 m height (km d−1). |
| u = | = | Wind speed at 2 m height (m s−1). |
| W = | = | A psychrometric weighting function. |
| βp = | = | Priestley–Taylor coefficient. |
| γ = | = | Psychrometric constant (kPa °C−1). |
| ∆ = | = | Slope of vapor pressure versus temperature curve at mean temperature (kPa °C−1). |
| = | Mean air temperature (°C). | |
| J= | = | Annual mean thermal heat index of Thornthwaite’s method. |
| Ksat= | = | Saturated hydraulic conductivity (m d−1) |
| αv= | = | Unsaturated soil hydraulic parameter (m−1) |
| nv= | = | Unsaturated soil hydraulic parameter |
| θr= | = | Residual soil moisture content (cm3 cm−3) |
| θs= | = | Saturated soil moisture content (cm3 cm−3) |
| θfc= | = | Moisture content at field capacity (cm3 cm−3) |
| θpwp= | = | Moisture content at permanent wilting point (cm3 cm−3) |
| I= | = | Average infiltration depth (mm) |
| RO= | = | Runoff (mm) |
| ∆S= | = | Change in soil moisture storage (mm) |
| D= | = | Drainage from the lysimeter (mm) |
| Ir= | = | Irrigation (mm) |
| zr= | = | Root depth (m) |
| hp= | = | Plant height (m) |
| LAI= | = | Leaf area index (m2 m−2) |
| Es= | = | Soil evaporation (mm) |
| Tp= | = | Plant transpiration (mm) |
| ψ= | = | Soil matric potential or pressure head (m) |
| θ= | = | Soil moisture content (mm3 mm−3) |
| K= | = | Unsaturated hydraulic conductivity (m d−1) |
| S= | = | Sink term representing root water uptake (cm3 cm−3 d−1) |
| Ts= | = | Specific transpiration |
| β= | = | Non-linearity coefficient of O-R model. |
| R2= | = | Coefficient of determination. |
Acknowledgments
The authors are thankful to the Civil Engineering Department, National Institute of Technology Hamirpur (India) for providing experimental facilities related to study. The authors would also like to thank the two anonymous reviewers for their positive criticism and valuable suggestions that have contributed to an improved manuscript.
Data availability statement
Some data, models or code used during the study are available from the corresponding author by request.
Disclosure statement
The authors declare no conflict of interest.