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In the Texas High Plains, variable climatic conditions prevail between and within growing seasons. As this area continues to experience drought conditions and water resources for irrigation become more limited, sorghum [Sorghum bicolor (L.) Moench] production may become a more popular choice to sustain profitable crop water productivity with limited water. Regional sorghum production functions are helpful in strategizing adaptation methods for coping with climatic variability, but new varieties often exhibit new production functions. This article compares sorghum responses of grain yield, evapotranspiration (ET), water use efficiency (WUE), and irrigation water use efficiency (IWUE) of a late maturing (LM) and early maturing (EM) hybrid during three recent growing years exhibiting climatic variability (2009-2011). The hybrids were irrigated at levels of 80%, 55%, 30%, and 0% replenishment of soil water depletion to field capacity (FC). Mean maximum daily air temperatures and mean daily reference evapotranspiration (grass) for the 2009 (28.2°C, 6.5 mm d-1) and 2010 (28.6°C, 6.4 mm d-1) growing seasons were similar; in 2011, these parameters were considerable greater (32.6°C and 8.8 mm d-1, respectively). For both hybrids, dry grain yields were greatest in 2009 in the I80% treatment at 9.80 and 8.04 Mg ha-1 for the LM and EM hybrids, respectively. For irrigation treatment amounts of 80% replenishment of soil water to FC, grain yields in the LM hybrid were always greater compared with the EM hybrid. However, WUE in the EM hybrid in 2009 and 2011 was 27% and 29% greater, respectively, than in the LM hybrid. Grain yield responses in both hybrids were most sensitive to the exceptional drought year of 2011 where irrigation applied at less than 80% replenishment of soil water to FC greatly reduced grain yields. Irrigation applied at less than 55% replenishment produced minimal to no grain yields. [ABSTRACT FROM AUTHOR]

In agriculture, evapotranspiration (ET) is a major consumptive use of irrigation water and precipitation on cropland. Global interest in sustainable management of limited freshwater supplies to meet increased food demand has resulted in increased reporting of ET measurement and modeling methods in the literature. Direct measurements of ET by large weighing lysimeters are commonly used to test other ET measurement and estimation methods. Numerous studies have emphasized the importance of proper lysimeter design and management for accurate ET measurement. However, equally important and noticeably absent from the literature are guidelines for data collection, processing, analysis, and quality assurance and quality control (QA/QC) measures. Omission and/or inadequate attention to these processes can have significant impacts on the accuracy of ET derived from large weighing lysimeters. Improper processing of rainfall, irrigation, snowfall, dew and frost accumulation, wind, and management events can also lead to substantial errors. In this study, we present data processing strategies and techniques for ET datasets measured using large weighing lysimeters. Measurements from two large lysimeters built and managed by the USDA-ARS Conservation and Production Laboratory (CPRL) in Bushland, Texas, were used for this purpose. Examples used in the study demonstrate that indiscriminate application of smoothing functions, misidentification, and misinterpretation of changes in lysimeter mass can lead to significant errors and erroneous conclusions. Comprehensive record keeping is paramount in documenting lysimeter status and operations. Errors associated with data processing are dataset specific, corresponding to the magnitude, duration, and frequency of occurrences of the aforementioned events. Understanding and prudent application of the presented techniques and QA/QC procedures can help to minimize errors in processing lysimeter datasets. [ABSTRACT FROM AUTHOR]

The two-source energy balance (TSEB) model calculates the energy balance of the soil-canopy-atmosphere continuum, where transpiration is initially determined by the Priestley-Taylor equation. The TSEB was revised recently using the Penman-Monteith equation to replace the Priestley-Taylor formulation, thus better accounting for the impact of large and varying vapor pressure deficits (VPD) typical of advective, semiarid climates. This study is a comparison of the Priestley- Taylor and Penman-Monteith versions of the TSEB (termed TSEB-PT and TSEB-PM, respectively). Evaporation (E), transpiration (T), and evapotranspiration (ET) calculated by the TSEB-PT and TSEB-PM versions were compared to measurements obtained with microlysimeters, sap flow gauges, and weighing lysimeters, respectively, for fully irrigated cotton (Gossypium hirsutum L.) at Bushland, Texas. Radiometric surface temperature (TR) was used to calculate E, T, and ET in both TSEB versions in 15 min intervals and summed to intervals coinciding with times of measurements. In addition, a one-time-of-day TR measurement was used (9:45, 11:15, 12:45, 14:15, or 15:45 CST), and E, T, and ET were calculated for the appropriate measurement interval (i.e., daytime, nighttime, and 24 h) using the time scaling methods based on reference ET (TSCET) and reference temperature (TSCTEMP). Measured average values of E, T, and ET during the study period were 0.94 mm (24 h), 6.9 mm (7:00 to 22:00 CST), and 7.2 mm (24 h), respectively. The TSEB-PT consistently overestimated E and underestimated T, with RMSE/MBE of up to 2.8/1.8 mm and 4.1/-3.9 mm, respectively. In comparison, the TSEB-PM greatly reduced discrepancies between calculations and measurements, with respective RMSE/MBE for E and T of only up to 1.5/0.79 mm and 1.3/ ±0.76 mm, respectively. For 24 h ET, the TSEB-PT resulted in maximum RMSE/MBE of 3.2/-1.9 mm, and the TSEB-PM had maximum RMSE/MBE of 1.7/0.95 mm. Daytime ET model agreement was very similar for both model versions (RMSE/MBE usually <1.1/< ±1.0 mm). However, the TSEB-PT consistently calculated negative nighttime ET of up to - 2.0 mm. Summed 15 min calculations generally had better agreement with measurements than did the TSCET or TSCTEMP methods, and results did not greatly differ for TSCET or TSCTEMP. Both time scaling methods were not very sensitive to the TR measurement time used, although morning (9:45 CST) TR measurement times did not perform as well as the other times. [ABSTRACT FROM AUTHOR]