Surface renewal measurements in roughness sublayer for water management in irrigated orchards
Abstract
Irrigation scheduling is often based on evapotranspiration (ET); however, the ET rates are affected by several factors including tree pruning, planting density, row orientation, crop phenology, irrigation system, cultivar and rootstock, soil type, topography, evaporative demand, and management . These variables affect crop coefficient (Kc) values and crop evapotranspiration (ETc=ETo×Kc), where ETo is reference evapotranspiration, which characterizes evaporative demand. We suggest using the surface renewal (SR) method to determine sensible heat flux and use it with net radiation (Rn) and ground heat flux at the surface (G) to estimate latent heat flux (LE) as the residual of the energy balance. This is a semi-direct measurement method for ETc that is low maintenance, affordable, and simple - which means higher spatial monitoring possibilities. We installed combination surface renewal-eddy covariance stations over three sweet cherry orchards with different planting densities, row orientations, rootstocks, and irrigation systems to measure ETc and estimate Kc values using locally measured ETo. All orchards were well-watered and grown under typical farming practices in California's San Joaquin Valley. Sensors include sonic anemometers and fine-wire thermocouples for measuring H, net radiometers for Rn, and soil heat flux plates together with soil temperature and humidity sensors to estimate G. The self-calibrating SR method (CastellvÍ, 2004) was used to measure sensible heat flux (H). Since H, Rn, and G were measured, LE was computed from the residual of the energy balance equation and it was converted to ETc. We compared H values from SR and eddy covariance (EC) and found good agreement (R2~0.9); however, some SR values overestimated EC up to 30 %. In well-watered fields, H is small relative to LE, therefore the H overestimation of SR values compared to EC had little effect on ETC with R2~0.98 and 8% underestimation. In conclusion, the reliability and affordability from using thermocouples and the SR method provides an excellent alternative to using a sonic anemometer.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B31L2465S
- Keywords:
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- 0402 Agricultural systems;
- BIOGEOSCIENCES;
- 0495 Water/energy interactions;
- BIOGEOSCIENCES;
- 1842 Irrigation;
- HYDROLOGY;
- 1855 Remote sensing;
- HYDROLOGY