Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/9/2018
Publication Date: 4/17/2018
Citation: Anapalli, S.S., Green, T.R., Reddy, K.N., Gowda, P., Sui, R., Fisher, D.K., Moorhead, J.E., Marek, G.W. 2018. Application of an energy balance method for estimating evapotranspiration in cropping systems. Agricultural Water Management. 204:107-117.
Interpretive Summary: Accurate estimate of water requirements of crops (evapotranspiration) from planting through harvest is critical for managing limited water resources for crop irrigation. Scientists at the USDA's Agricultural Research Service, Crop Production Systems Research Unit, Stoneville, MS, in collaboration with scientists at the Conservation and Production Research Laboratory, Bushland, TX, and Forage and Livestock Production Research Unit, El Reno, OK, developed and applied a land-crop surface energy balance method for estimating water requirements of corn (Zea mays L.) at Stoneville, Mississippi in the lower Mississippi Delta region. The corn water requirement information developed in this study will be useful for farmers in managing the limited water available for irrigating their crops. The instrumentation used in this method is portable, unlike other traditional lysimeter-based measurements. This method provides a timely, viable alternative for quantification of crop water requirements in cropping systems across soils and climates cost-effectively.
Technical Abstract: Accurate quantification of evapotranspiration (ET, consumptive water use) from planting through harvest is critical for managing the limited water resources for crop irrigation. Our objective was to develop and apply an improved land-crop surface residual energy balance (EB) method for quantifying ET and use it for estimating ET from corn (Zea mays L.) at Stoneville, Mississippi in the lower Mississippi Delta region. In the EB method, actual ET is estimated (ETe) as the residual term of the energy balance equation from measurements of net solar irradiance (Rn) and computing energy losses due to sensible heat (H) and ground heat (Go) fluxes. The H was computed from measurements of the air and crop canopy temperature differential and modeling the aerodynamic resistance (ra) to heat and water transport in the turbulent atmospheric boundary layer above the canopy. The computed H was further corrected for atmospheric stability and wind effects. The Go was estimated measuring heat flux at 8 cm depth and accounting for heat storage in the soil layer above it. The developed EB procedure was tested for accuracy in computed ET using simultaneous measurements of EB data and lysimetric ET in a cotton (Gossypium hirsutum L.) field at Bushland, TX, in 2008. The lysimeter measured ET compared well with the computed ETe under cotton (RMSE of daily ET = 0.11 cm, and seasonal ET within 1% error). Further, we used the developed EB procedure, for computing irrigated corn ET in a silt loam soil at Stoneville, MS in 2016. Average maximum corn plant height was 190 cm and LAI 5.5, and average harvested grain yield was 10,467 kg ha-1. Computed seasonal values of ETe were more than short grass reference ET (ETo) by 2.7 cm and less than alfalfa reference crop ET (ETr) by 8.0 cm. The instrumentation used in the EB method is portable, and the estimated ET is comparable with lysimeter measured ET, as such, this method provides a timely, viable alternative for quantification of ET in cropping systems cost-effectively.