The Soil and Water Assessment Tool (SWAT) is one of the most widely used watershed models for simulating hydrology in response to agricultural management practices. However, limited studies have been performed to evaluate the SWAT model's ability to estimate daily and monthly evapotranspiration (ET) in semiarid regions. ET values were simulated using ArcSWAT 2012 for a lysimeter field managed under dryland conditions at the USDA‐ARS Conservation and Production Research Laboratory at Bushland, Texas, and compared with measured lysimeter values from 2000 to 2010. Two scenarios were performed to compare SWAT's performance: (1) use of default plant leaf area index (LAI) values in the embedded plant database and (2) adjusted LAI values. Scenario 1 resulted in an “unsatisfactory” Nash‐Sutcliffe efficiency (NSE) of 0.42 and 0.38 for the calibration and validation periods, respectively. Scenario 2 resulted in a “satisfactory” NSE value for the calibration period while achieving a “good” NSE of 0.70 for the validation period. SWAT generally underestimated ET at both the daily and monthly levels. Overestimation during fallow years may be due to the limitations of the pothole function used to simulate furrow diking. Users should be aware of potential errors associated with using default LAI parameters. Inaccuracies in ET estimation may also stem from errors in the plant stress functions, particularly when evaluating water management practices for dryland watersheds.

No abstract

Core Ideas No‐till residue management during fallow consistently increased storage of precipitation as available soil water. The annualized storm water runoff during our 30‐yr experimental record was greater for no‐till residue management than for stubble‐mulch tillage. Sustainable semiarid dryland cropping systems are critically dependent on evaporation control to provide water for crop production that is increased through no‐till residue management. Semiarid dryland crop yields with no‐till (NT) residue management are often greater than stubble‐mulch tillage (SM) because of improved soil conditions and water conservation, but information on long‐term tillage effects on field hydrology and sustained crop production are needed. Our objective was to quantify the effects of NT and SM on stored soil water, runoff, and deep drainage through a clay loam soil in relation to crop growth and yield. Wheat (Triticum aestivum L.) and grain sorghum [Sorghum bicolor (L.) Moench] were grown in paired tillage treatments using a 3‐yr wheat–sorghum–fallow (WSF) rotation from 1983 to 2013. We measured crop growth and yield factors, precipitation, runoff, and Cl concentration in variable increments to a 14.0‐m depth. Cumulative runoff during the fallow periods after wheat and sorghum averaged 57 mm for NT compared with 33 mm under SM. Annual deep drainage averaged ∼ 2 mm for SM and 14 mm for NT dryland crop production based on Cl displacement compared with no drainage below the root zone of adjacent native rangeland. Despite greater runoff and drainage, plant available soil water for the 1.8‐m profile at wheat and sorghum planting averaged 194 mm for NT compared with 166 mm for SM because of reduced evaporation. Although wheat growth and grain yield did not vary with tillage, sorghum grain yield was 17% greater under NT, averaging 3420 versus 2920 kg ha–1 under SM. We attributed the greater sorghum yield with NT to increased crop water use.

Abstract. Water scarcity due to drought and groundwater depletion has led to increased interest in deficit irrigation strategies that reduce irrigation requirements while maintaining profitable yields. This has resulted in an increase in the number of modeling studies aimed at evaluating crop response to limited irrigation strategies. However, the ability of widely used crop simulation models to accurately represent responses to limited irrigation has not been thoroughly evaluated. The primary objective of this study was to determine the efficacy of DSSAT-CERES-Maize (ver. 4.6.1.0) to simulate leaf area index (LAI), crop evapotranspiration (ET), and yield response to full (100%) and limited (75% and 50%) irrigation regimes for two corn varieties. Comparisons of simulated and measured data from full and limited irrigation treatments of` two drought-tolerant corn hybrids (DuPont Pioneer AQUAmax P1151HR and Pioneer 33D49) grown in the Texas Panhandle in 2013 and 2014 were evaluated. Simulated in-season daily crop ET values for P1151HR grown in 2013 were also compared to those measured by precision large weighing lysimeters at Bushland, Texas. Additionally, a comparison of simulated and measured soil water content (SWC) within the root zone was performed for P1151HR grown in 2013. Simulated LAI for fully irrigated treatments approximated measured values reasonably well, although manipulation of plant genetic parameters failed to match measured LAI during the period between maximum LAI and the beginning of crop senescence in the 50% irrigation treatments. Similarly, simulated yield values approximated measured values for the fully irrigated treatments, while considerable overestimation of yield occurred in the limited irrigation treatments for both varieties. However, consistent overestimation of both LAI and yield for the limited irrigation treatments suggests a functional relationship between LAI and yield. Further, DSSAT overestimated crop ET by 16% for fully irrigated P1151HR and by 40% for limited irrigation treatments in 2013 as compared to measured lysimeter values. Corresponding underestimations of SWC were also observed in neutron probe measurements for both treatments. Overestimation of ET and yield and corresponding underestimation of SWC in limited irrigation treatments were mainly due to overestimation of LAI in those treatments, indicating a potential deficiency in the water stress algorithms. Additional comparisons of agronomic and lysimeter-based water balance data are needed to corroborate the findings of this study. Further investigations into the calculation of reference evapotranspiration (ETo), crop coefficients, and water stress functions in DSSAT are needed in order to provide suggestions for model improvement. Keywords: TCERES-Maize, Crop modeling, DSSAT, Evapotranspiration, Limited irrigation, Lysimeters, Maize, Semi-arid, Sprinkler irrigation, Weighing lysimeters.