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Title: Using eddy covariance and flux partitioning to assess basal, soil, and stress coefficients for crop evapotranspiration models

item Anderson, Raymond - Ray
item Alfieri, Joseph
item Gartung, Jimmie
item McKee, Lynn
item Tirado-Corbala, Rebecca
item Prueger, John
item Wang, Dong
item Kustas, William - Bill

Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 7/28/2015
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Current approaches to scheduling crop irrigation using reference evapotranspiration (ET0) recommend using a dual-coefficient approach using basal (Kcb) and soil (Ke) coefficients along with a stress coefficient (Ks) to model crop evapotranspiration (ETc), [e.g. ETc=(Ks*Kcb+Ke)*ET0]. However, independently determining Ks, Kcb, and Ke from the combined single coefficient (Kc) is challenging, particularly for Ke, and a new method is needed to more rapidly determine crop coefficients for novel cultivars and cultivation practices. In this study, we partition Eddy Covariance ET observations into evaporation and transpiration components using correlation structure analysis at multiple irrigated agricultural sites with minimal growing season precipitation. These include a C4 photosynthetic-pathway species (sugarcane – Sacharum officinarum L.) and a C3 pathway species (peach - Prunus persica) under sub-surface drip and furrow irrigation, respectively. Both sites showed high overall Kc consistent with their height (>4 m) and full canopy cover. However, the results showed differences in Ke, with the drip-irrigated sugarcane having a Ke that was ~30% of the peach Ke. There was no significant relationship (r2<0.05) between root zone soil moisture in sugarcane, and observed Kcb*Ks, indicating that there was no stress (Ks=1). Comparison of shallow soil moisture and soil diurnal temperature variation with Ke in Peach showed a significant relationship that could be used to constrain model estimates of Ke. Partitioning of Kc into Kcb and Ke resulted in a stronger regression (r=0.65) between the Normalized Differential Vegetation Index (NDVI) and Kcb in sugarcane than between NDVI and Kc (r=0.41). The results indicate the strong potential for correlation structure flux partitioning to improve crop ET coefficient determination and its relationship with both satellite and soil observations. However, further work on this method is needed to reduce the uncertainty in the partitioning and to assess the validity of partitioned fluxes and coefficients against independent evaporation and transpiration observations.