Evaluation of Water Use Efficiency Algorithms for Flux Variance Similarity‐Based Evapotranspiration Partitioning in C<sub>3</sub> and C<sub>4</sub> Grain Crops
Pradeep Wagle, Todd H. Skaggs, Prasanna H. Gowda, Brian K. Northup, James P. S. Neel, Ray G. Anderson
Abstract
Abstract Despite the high sensitivity of Flux Variance Similarity (FVS) partitioning to leaf‐level water use efficiency (WUE), relatively little work has been done comparing WUE algorithms. We evaluated four intercellular CO 2 concentration parameterizations (constant_ppm, constant_ratio, and linear and square root functions of vapor pressure deficit) and one optimized WUE approach using eddy covariance data for three C 3 (wheat – Triticum aestivum L., canola – Brassica napus L., and soybean – Glycine max L.) and two C 4 (maize – Zea mays L. and sorghum – Sorghum bicolor L. Moench) grain crops. The different data requirements of the WUE models resulted in discrepancies in the number of partitioned outputs among WUE algorithms. The transpiration:evapotranspiration (T:ET) ratios found with the five WUE algorithms varied by 6%–8% for soybean and maize, 12%–13% for wheat and canola, and 22% for sorghum. The crops producing larger variations in computed T:ET also tended to have higher estimated WUE magnitudes. The constant_ppm and constant_ratio parameterizations showed better potential to partition ET in all crops, except soybean. The linear and square root WUE models failed to produce reduced T:ET ratios during wet periods in all crops, except soybean. The optimized WUE approach has potential as a benchmark for comparing other WUE algorithms for C 3 crops. The applicability of the linear and optimized WUE approaches was uncertain in C 4 crops. Agreement and disagreement among the five WUE algorithms in multiple crops provide new perspectives for applying FVS partitioning to a range of biomes and climate conditions.