Corn (Zea mays L.) is a major irrigated crop in the Texas High Plains (THP). Inadequate precipitation, declining groundwater resources, and inevitable seasonal drought in the area have led to a greater number of studies on crop hybrids, water regimes, and other yield-enhancing techniques. A four-year field study was conducted to investigate the effect of foliar fungicide timing on corn grain yield, grain moisture, and grain test weight under different irrigation regimes. A fungicide containing QoI + DMI was applied to four to six corn hybrids each year at various growth stages (V5, R1, and V5 + R1). For all years, corn plants were grown under three irrigation regimes to meet the seasonal evapotranspiration (ET) requirements of 50% (I50), 75% (I75), and 100% (I100). Hybrid response to the timing of fungicide application and irrigation regime was not consistent over the years. However, in 2 of the 4 years, timing of fungicide application resulted in yield differences among the hybrids, especially at I75 and L100. For those years, the fungicide applied at R1 resulted in a higher grain yield, grain moisture, and grain test weight followed by the fungicide applied at V5 + R1. Results showed that hybrids reacted differently to the foliar fungicide based on the availability of water under disease-free conditions. This study further revealed that irrigation water could be reduced from I100 to I75 with a limited (5.6% in 2011, 11.3% in 2012, 1.3% in 2013, and 0.3% in 2014) yield penalty in the THP region.

Highlights Losses for MESA and LESA were comparable on the day of irrigation and oftentimes greater for the subsequent day. Losses were greater due to incomplete canopy conditions for both MESA and LESA on both days. Evaporative losses from irrigation extended to at least the subsequent day following irrigation in most cases. Losses over two days accounted for as much as 39.5% and 28.0% of irrigation depth for MESA and LESA, respectively. Abstract. Effective irrigation systems that increase crop water productivity by minimizing evaporative losses are paramount for extending the longevity of finite groundwater resources in the semi-arid U.S. Southern High Plains (SHP). Although subsurface drip irrigation (SDI) acreage has increased in recent years, center-pivot sprinkler systems still account for greater than 85% of the irrigated area in the SHP. Modern sprinkler configurations are typically classified according to application height as either mid-elevation spray application (MESA) or low-elevation spray application (LESA). While application drift and evaporative losses are easily measured under fallow conditions, quantifying evaporative losses under cropped conditions is difficult. Lysimeter-derived daily evapotranspiration (ET) values for SDI-irrigated and sprinkler-irrigated fields planted to corn in 2016 (MESA) and 2018 (LESA) near Bushland, TX, were compared for days when sprinkler irrigation events occurred and for subsequent days, when possible. Differences (extra ET) were attributed to evaporative losses associated with MESA and LESA irrigation. Average daily extra ET values for both sprinkler irrigation methods were similar on the day of irrigation, although MESA was slightly larger than LESA at 1.4 and 1.2 mm, respectively. The average daily extra ET values for incomplete canopy conditions were 2.2 mm for MESA and 1.9 mm for LESA, while values were identical for both methods at 0.6 mm for full canopy conditions. Average daily extra ET values were also expressed as a percentage of daily standardized grass reference ET (ETos) values. Average values for MESA and LESA were 20.1% and 13.5%, respectively, for the season, with similar findings of 29.3% and 19.4% for incomplete canopy conditions. Average extra ET/ETos values for incomplete canopy conditions were similar at 7.5% and 7.7% for MESA and LESA, respectively. Evaporative irrigation losses, calculated as the percentage of extra ET to irrigation depth, were slightly larger overall for the day of irrigation for MESA (5.4%) than LESA (5.2%). Losses of 7.9% and 7.0% were observed for incomplete canopy conditions for MESA and LESA, respectively. Average losses for LESA (3.5%) under full canopy conditions were greater than those for MESA (1.9%). A comparison of extra ET values for days following irrigation revealed that evaporative losses from irrigation events extended beyond the day of irrigation. MESA extra ET values for the day following irrigations increased by 57.1% (2.2 mm) overall, 13.6% (2.5 mm) for incomplete canopy conditions, and 150.0% (1.5 mm) for full canopy conditions. The same was true for LESA, with increases of 125.0% (2.7 mm) overall, 78.9% (3.4 mm) for incomplete, and 216.7% (1.9 mm) for full canopy conditions. Summing of extra ET values for the day of irrigation and the subsequent day yielded average values more than double those for the day of irrigation only, at 3.9 and 4.3 mm for MESA and LESA, respectively. Similarly, values for extra ET as a percentage of irrigation depth were also more than double those for the day of irrigation only, with the greatest loss values of 39.5% for MESA and 28.0% for LESA. These findings suggest that although LESA appears to mitigate evaporative losses marginally more in corn than MESA on the day of irrigation, considerably more evaporative losses occurred for both methods during the subsequent day, with slightly increased losses for LESA, resulting in little difference between overall losses over the two days. This may in part be explained by the temporary cooling effect of the irrigation inside the canopy on the day of irrigation, which is diminished by the second day. A greater discrepancy between evaporative losses for MESA and LESA is likely to be observed for crops having shorter stature or lower leaf density, such as cotton, although more study is needed to corroborate this claim. Knowledge of these findings provides useful information for both producers and water managers when considering irrigation management and water planning strategies. Keywords: Evaporation, Evapotranspiration, LESA, MESA, Semi-arid, Sprinkler Irrigation, Subsurface Drip Irrigation, Transpiration, Weighing Lysimeters.

Highlights Soil profile water content derived from Acclima TDR-315™ sensors approximated those from NMM measurements. Soil profile water content from Campbell Scientific SoilVUE™10 sensors grossly underestimated those from the NMM. VWC values from SoilVUE10 sensors were consistently less than those reported by the TDR-315 sensors at all depths. These findings do not support SoilVUE10 use for irrigation scheduling in clay loam soils. Abstract. A field study was performed to evaluate the efficacy of two commercially available time domain reflectometry (TDR) soil water sensors for irrigation scheduling in a clay loam soil near Bushland, Texas. SoilVUE10 (Campbell Scientific Inc., Logan, Utah) and TDR-315 (Acclima Inc., Meridian, Idaho) sensors were installed within 30 cm of neutron moisture meter (NMM) access tubes in a research field planted to corn (Zea mays L) in 2020 and irrigated by a center pivot sprinkler system. Irrigation treatments included 50%, 75%, and 100% of evapotranspiration (ET) replacement with two access tubes installed in each plot, totaling six sensor evaluation sites. Semiweekly measurements with a field-calibrated NMM were used to monitor soil water status and schedule irrigation throughout the growing season. Soil profile water content values integrated over the surface to 1.1-m depth range were derived from SoilVUE10 and vertically distributed arrays of Acclima TDR-315 sensors installed at equivalent depths and were compared with those from NMM data. Average profile soil water contents from the TDR-315 sensors trended well with those from the NMM having mean bias difference (MBD) values of -9.8, -3.1, and 8.4 mm for the 50%, 75%, and 100% treatments, respectively. In contrast, soil profile water content values from the SoilVUE10 sensors grossly underestimated those from the NMM for all irrigation treatments with MBD values of -54.4, -70.5, and -89.8 mm for the 50%, 75%, and 100% treatments, respectively. Comparisons of volumetric water content (VWC) at each of the nine depths common to both electromagnetic sensor types revealed that values from the SoilVUE10 sensors were consistently less than TDR-315 values for all irrigation treatments. Underestimation at the near surface (5 and 10 cm depths) was attributed to loss of soil to electrode contact possibly associated with clay shrinkage during periodic drying following irrigation. Although soil to electrode contact can be problematic at greater depths, the explanation for chronic underestimation of VWC was less obvious except to note that underestimation occurred immediately after installation, which indicated poor electrode-soil contact after installation despite use of manufacturer guidelines and tools. Other possible reasons include challenges for accurate estimation of soil permittivity for a measured permittivity that includes the plastic sensor body. Results from this study suggest vertically distributed arrays of TDR-315 sensors can provide profile water content values adequate for monitoring soil water status for irrigation scheduling in a clay loam soil. The chronic underestimation observed for the SoilVUE10 sensors does not support their use for water resources research and irrigation management and could lead to over irrigation. Additionally, the relatively short 1 m length is less than the rooting depth of many regional crops and thus not capable of determining percolation below the root zone. Keywords: Acclima TDR-315, Campbell Scientific SoilVUE, Irrigation scheduling, Neutron moisture meter, Semi-arid, Soil water sensors, Time domain reflectometry, Volumetric water content.

The southern Ogallala Aquifer continues to deplete due to decades of irrigation with minimal recharge. Recently enacted regulations limiting groundwater withdrawals and the potential for farm profitability with cotton production systems indicate driving forces for increased cotton production acreage in the Northern High Plains of Texas (NHPT). This study focused on evaluating the land-use change from corn or winter wheat to cotton under irrigation and dryland conditions in the Palo Duro watershed (PDW) in the NHPT using an improved Soil and Water Assessment Tool (SWAT) model. Land-use change from irrigated corn to irrigated cotton led to reductions in average (2000–2014) annual irrigation, actual evapotranspiration (ETa), and surface runoff by 21%, 7%, and 63%, respectively. Nevertheless, the replacement of irrigated wheat with irrigated cotton caused irrigation and ETa to increase by 46% and 18%, respectively. Land-use conversion from dryland wheat to dryland cotton showed 0.1% and 15% decreases in ETa and surface runoff, respectively. More than 40% reductions in simulated cotton yields were found when the cotton planting area was moving northward to the cooler NHPT. The ongoing change in land use provided an option to lengthen the water availability of the southern Ogallala Aquifer for irrigation.

Deficit irrigation (DI) is an effective way to save irrigation water while maintaining sustainable yield in irrigated crops. However, limited information is available related to canopy structure and solar radiation use under DI condition. In this study, our objective was to assess maize hybrids for leaf development, photosynthetically active radiation (PAR) interception and water use under DI condition. Field experiments were conducted in 2016 and 2017 in four maize hybrids at well-watered (I-100, referring to 100% evapotranspiration [ET] requirement) and DI (I-75, referring to 75% ET requirement) water regimes. Compared to I-100, I-75 did not reduce maize biomass and grain yield. Although DI reduced the leaf appearance rates (1.5% in 2016 and 7.6% in 2017) and resulted in greater variations in leaf area index (LAI) among hybrids, the amount of PAR interception was not affected during the growing season. DI significantly reduced the seasonal ET in both years (19.8% in 2016 and 26.6% in 2017). All the hybrids extracted more soil water (29 mm in 2016 and 27 mm in 2017) at I-75 than at I-100. Maize plants at I-75 had greater water use efficiency (WUE) (1.68 kg m(-3)) than those at I-100 (1.41 kg m(-3)). However, DI did not affect radiation use efficiency (RUE). In conclusion, DI at I-75 maintained grain yield through improved soil water extraction and WUE but stable canopy radiation interception and RUE.

Drought is an enduring abiotic constraint to stable and consistent maize productivity under climate change, especially for low rainfall regions with limited irrigation. One adaptation for severe drought is using drought-tolerant (DT) hybrids. Here, we characterize differences between conventional and DT hybrids in terms of yield and water-use efficiency under drought conditions at a regional scale of the Texas High Plains (THP). Using a validated version of APSIM-Maize, we simulated yields of conventional and DT hybrids across 11 water regimes and 25 counties in THP from 1984 to 2018. When irrigation amounts were constrained to 90%, 80%, 70%, 60% and 50% of total irrigation used for the baseline scenario (BS; a simulated scenario of conventional hybrid under full irrigation), DT hybrids showed lower yield penalties under drought stress relative to conventional hybrids. This improved total production by 19%, 24%, 26%, 26%, and 21% for each of the above irrigation levels. When the yield-target was set as 90%, 80%, 70%, and 60% of BS, total regional irrigation applied to DT hybrid could be saved more than that to the conventional hybrid, and therefore reduced more 17%, 16%, 15%, and 15% of BS irrigation, respectively. We showed that DT hybrids had greater yield gain and water savings through improved water productivity under deficit irrigation, highlighting the potential of deficit irrigation for increasing yield for the adoption of DT hybrid. Our quantitative evaluation of the yield advantage and water saving potential associated with DT hybrids also highlighted the regional benefits associated with adoption of drought adaptive hybrids.

As crop production has become more mechanized and complex, and as sensors and data have become more accessible, limitations of production managers to effectively use the data and the need for automated integration of information into useful management decisions with automated controls have become more apparent. In this article, a double deep Q-learning technique based module for irrigation and chemigation control is proposed and evaluated. This module is designed to maximize net return at harvest by automatically managing the irrigation and chemigation scheduling processes during the crop growing season. Using this approach, the proposed module can automatically select the optimal or near-optimal irrigation and chemigation amount and application schedule. The proposed module is evaluated on various crops, climate conditions, and soil types. The results show that the proposed module can achieve an average of 50% higher net return compared to traditional strategies.

Sustaining irrigated corn (Zea mays L.) production under changing climate and reduced irrigation water availability presents a key challenge for producers in the Northern High Plains (NHP) of Texas. We assessed climate change impacts on corn production at Bushland in the NHP region using the CERES-Maize model under 36 future climate scenarios. These scenarios included nine global climate models (GCMs), two representative concentration pathways (RCPs) 4.5 and 8.5, and two future time periods 2050s (2036–2065) and 2080s (2066–2095). Simulated grain corn yield decreased, under all scenarios in the future, by approximately 31 % on average in the 2050s and by approximately 55 % in the 2080s, under RCP 8.5, mainly due to reduced unit grain weight and biomass, and shorter crop cycle. Seasonal irrigation water use was simulated to either increase or decrease in the future depending on the rainfall projection of a GCM. Adaptation strategies considered in this study included using ideotypes with a longer maturity, higher yield potential, and greater heat tolerance than the reference cultivar, and shifting of planting dates. The ideotypes were created by modifying thermal times from emergence to end-of-juvenile phase, thermal time from silking to maturity, maximum kernel number per plant, radiation use efficiency (RUE), and optimum and failure temperature thresholds during relative grain filling. The planting dates considered were 16 April, 1 May, 16 May (reference), 1 June, and 16 June. By increasing the reproductive period by 13 days, grain yield could increase by 40 %, but that could increase seasonal irrigation water requirement by 10 %. Grain corn yield increased by 13 % on average when the maximum number of kernels per plant or RUE were increased by 15 %, with minor changes in seasonal irrigation water requirement. Heat tolerant ideotypes showed yield advantage over the reference cultivar without much change in irrigation. Delayed planting increased grain yield in the future. Overall, grain yield could decline under climate change without adaptation. Ideotypes with greater silking to maturity period, potential number of kernels per plant, RUE, and heat tolerance during grain filling, showed yield benefits in the future.

Corn (Zea mays L.) was grown under full and deficit irrigation in two research field locations near Bushland, TX, in 2018 to compare seasonal water use of two irrigation management approaches. Full irrigation was achieved in both fields by allowing no more than 55% depletion of plant available soil water. However, irrigation depth and frequency were different in each field. The USDA-ARS Conservation and Production Research Laboratory (CPRL) weighing lysimeter fields were generally irrigated twice weekly using irrigation depths ranging from 19 to 32 mm. The Texas A&M AgriLife Research Emeny field was irrigated only once per week, having greater application depths ranging from 35 to 42 mm. Deficit irrigation treatments of 75% of full irrigation were also performed in both research fields. Yield and crop water productivity values for the 100 and 75% lysimeter field irrigation treatments were greater than corresponding values for the Emeny field. Emeny field yields may have been slightly reduced by heat stress incurred between irrigations during early grain fill whereas more frequent irrigations on the lysimeter fields may have reduced heat stress during that period. Results from this study suggest that evaporative losses associated with the more frequent, smaller application depth irrigations on the lysimeter fields did not contribute to appreciably lower CWP values, as losses were likely mitigated by the rapid development of the corn canopy. These findings suggest that corn yield is principally dependent upon seasonal water inputs and losses from frequent, smaller depth irrigations are minimal outside of incomplete canopy conditions.

A calibrated SWAT model equipped with an improved auto-irrigation function was used to evaluate the impacts of agricultural production practices on water balances and crop yields of corn, sorghum, and winter wheat for the Palo Duro watershed located in the Texas High Plains (THP). Fourteen scenarios were simulated including alternative irrigation application depths of 12.7 mm and 38.1 mm for irrigated corn, sorghum, and wheat and with different planting dates for irrigated corn, sorghum, wheat, and dryland wheat. Results indicated the greater irrigation depth (38.1 mm) led to reductions in seasonal irrigation requirements and crop evapotranspiration (ETc) when compared to the baseline scenarios using an irrigation depth of 25.4 mm for corn, sorghum, and wheat. However, soil water content, surface runoff, and percolation were increased. The opposite was observed for simulations of the same hydrologic variables but with an irrigation depth of 12.7 mm. Crop yields associated with the alternative irrigation depths were similar to those achieved with the baseline. Delayed planting of corn and sorghum resulted in the decrease of all the studied hydrologic parameters relative to the baseline. By contrast, the early planting scenarios showed the increase in those variables generally. Simulated corn yields were relatively stable, but a 3.7% reduction in irrigated sorghum yield was found with late planting. Notably, the early planting of wheat resulted in a clear increase in both irrigated and dryland yields of 11.2% and 13.5%, respectively. However, the yields of irrigated and dryland wheat were reduced by 28.8% and 2.7%, respectively, for the late planting. These findings suggest the greater irrigation application depth is promising for maintaining crop yields and reducing groundwater use from the Ogallala Aquifer. Also, the late planting of corn may benefit water conservation. Nevertheless, the early planting of wheat might be warranted to enhance yield in the THP.

Simulating the impacts of future climate change on water footprints and crop production allows for selecting alternative crops for mitigating climate change effects. In this study, climate change impacts on irrigated grain corn, grain sorghum, winter wheat, and dryland (rainfed) winter wheat in the Palo Duro watershed of the Texas High Plains were assessed using an improved Soil and Water Assessment Tool (SWAT) model with an enhanced irrigation representation of management allowed depletion (MAD) irrigation scheduling. Climate change analyses in this study used the Coupled Model Intercomparison Project Phase 5 (CMIP5) climate projections of 11 General Circulation Models (GCMs) under four Representative Concentration Pathway (RCP) emission scenarios of RCP2.6, 4.5, 6.0, and 8.5 during two 30-year periods of the middle (2040-2069) and end (2070-2099) of the 21st century to compare to a baseline period of 1970-1999. For the irrigated summer crops of corn and sorghum, all 11 GCMs predicted the reductions of future irrigation, crop evapotranspiration (ETc), and yields compared to the baseline period. According to an ensemble of 11 GCMs, the simulated reductions in average annual irrigation, ETc, and yield for the irrigated corn were 63%, 34%, and 13%, respectively, at the end of the 21st century under the severe emission scenario of RCP8.5. Those values were 80%, 34%, and 34% under the irrigated sorghum land use. As for the irrigated winter wheat, the decreases in future irrigation and ETc were also identified in all GCMs relative to the baseline period. However, irrigated wheat yields were increased in the future climate. The changes in dryland wheat ETc were consistent with the rainfall variation under all climate change scenarios. Generally, the future climate could benefit the dryland wheat yields. A large uncertainty was found for the surface runoff simulations under both irrigated and dryland wheat according to various GCMs.

Declining enrollments in a declining number of university degree programs in irrigation engineering are generating concern about the future of irrigation engineering expertise.Technical degree and certificate programs offer options for professionals in irrigation careers, especially those in landscape irrigation careers requiring licensure.Extension programs are evolving to include more on-demand internet-based and social media-based information delivery, as audiences have become more accustomed to these platforms.Addressing workforce and expertise needs in irrigation engineering is critically important, and it will involve equipping future professionals to address national and international challenges in agriculture.Abstract. Irrigation continues to be economically important in the U.S. and internationally, yet there is concern about future accessibility to appropriate expertise and the engineering preparation of irrigation professionals for both public and private sectors. Recent and impending retirements of academic and industry leaders, losses of some important academic programs (curricula/degree programs, research, and extension) in irrigation engineering, and reduced numbers of students threaten to significantly limit irrigation engineering capacity, especially in agricultural irrigation. Some of the challenges can be met through opportunities afforded by development of distance education programs; expansion of multi-state, multi-agency, multi-university collaborations; and increasing public-private partnerships, as well as through vigorous recruitment efforts. Recruitment can be strengthened by improving the competitiveness of salaries to be commensurate with other engineering disciplines, and by demonstrating and better explaining the abilities of the irrigation engineering profession to meet future challenges related to food, fiber, fuel, and ecosystem demands of a rapidly growing global population. While access to irrigation engineering expertise, especially domestic expertise, has declined, the need for such technical support and information for practitioners has not decreased. In fact, in many cases, technical advancements from public and industry developments have greatly outpaced the capacity for applied research and extension programs to robustly evaluate technologies and deliver objective, science-based recommendations. Growing knowledge gaps and time lags have exacerbated restlessness among some audiences, increasing the opportunities for promotion of unsubstantiated claims for some products that remain unchallenged, and further confusing appropriate selection from a growing array of available technologies. Keywords: Continuing education, Distance education, Extension, Irrigation engineering, Public-private partnerships, Technical support.

The SWAT model is a well-documented hydrologic model. However, some studies report that the existing SWAT auto-irrigation methods are unable to represent actual irrigation management, particularly in intensively irrigated regions. In the U.S. Great Plains, the SWAT model does not reproduce the management allowed depletion (MAD) irrigation scheduling commonly used by researchers and producers. To this purpose, the SWAT source code has been modified to include the MAD auto-irrigation function. This study evaluated the performance of the soil water content (SWC), corrected soil water content (CSWC), plant water demand (PWD), and MAD auto-irrigation methods in streamflow and irrigation simulations by comparison with observed data. The CSWC and MAD methods performed the best in streamflow simulations with NSE > 0.75 and PBIAS within ±11%. Comparisons of simulated irrigation with the field irrigation also indicated the CSWC and MAD methods outperformed other methods with the NSE > 0.75 and PBIAS within ±5%.

Presented at the 2006 Central Plains irrigation conference on February 21-22 in Colby, Kansas.

Agricultural production in the Texas High Plains (THP) relies heavily on irrigation and is susceptible to drought due to the declining availability of groundwater and climate change. Therefore, it is meaningful to perform an overview of possible climate change scenarios to provide appropriate strategies for climate change adaptation in the THP. In this study, spatio-temporal variations of climate data were mapped in the THP during 2000–2009, 2050–2059, and 2090–2099 periods using 14 research-grade meteorological stations and 19 bias-corrected General Circulation Models (GCMs) under representative concentration pathway (RCP) scenarios RCP 4.5 and 8.5. Results indicated different bias correction methods were needed for different climatic parameters and study purposes. For example, using high-quality data from the meteorological stations, the linear scaling method was selected to alter the projected precipitation while air temperatures were bias corrected using the quantile mapping method. At the end of the 21st century (2090–2099) under the severe CO2 emission scenario (RCP 8.5), the maximum and minimum air temperatures could increase from 3.9 to 10.0 °C and 2.8 to 8.4 °C across the entire THP, respectively, while precipitation could decrease by ~7.5% relative to the historical (2000–2009) observed data. However, large uncertainties were found according to 19 GCM projections.

As groundwater levels continue to decline in the Ogallala Aquifer, stakeholders, policymakers, and producers encourage the adoption of new irrigation technology in an effort to conserve groundwater, extend the economic life of the aquifer, and enhance profitability. One such technology currently receiving attention in the Central Ogallala region is the mobile drip irrigation (MDI) application system. This study compares MDI to low elevation spray application irrigation by evaluating the changes in variable cost per hectare to calculate the payback period for a MDI system under three levels of investment cost for grain and fiber crops representing three levels of water use while holding yield constant. Using a 3% discount rate, under the medium level of investment cost ($371 per hectare), a discounted payback period of 4.9, 9.0, and 6.3 years is required for corn, cotton, and sorghum/wheat, respectively. As the cost per hectare to convert an existing center pivot drops to $185 per hectare, the payback period also drops to 2.3, 4.2, and 3.0 years, respectively. Thus, producers growing higher water use crops are able to recover the costs of the conversion to MDI through increased water use efficiency quicker than producers growing medium and lower water use crops.

Highlights Irrigation scheduling using accurate ET network data can conserve energy and water. ET networks can be a valuable, cost effective, and feasible management tool in water policy. The Texas High Plains ET Network saved irrigated producers an estimated $US 22M dollars annually. ET network benefits and use extend beyond the agricultural sector. Abstract . Evapotranspiration (ET) networks have been developed and used to support weather and related ET information needs of U.S. agricultural production for nearly half a century, but many networks have been affected by inherent problems associated with sustaining operations. Consequently, these challenges have led to the discontinuation of network service in many cases. Most ET networks have been impacted by inadequate financial support compounded by inadequate public awareness and understanding of their usefulness and value in irrigation management, water conservation and water planning, and policy activities. Data accuracy is vital to usefulness, yet network data quality is often degraded when limited resources result in reduced equipment maintenance and data QA/QC. A discussion of ET network requirements and associated costs is presented. Estimates of the value and pumping reduction using the Texas High Plains ET networks are presented documenting the improvements of crop water use estimates and the impact associated with these improvements on irrigation groundwater withdrawal. Keywords: ET network, Evapotranspiration network, Irrigation scheduling, Irrigation value, Water management tools, Water savings.

HighlightsDaily maximum crop coefficient (Kc) values were similar for legacy hybrids and a modern drought-tolerant (DT) hybrid.Later planting dates for a DT hybrid resulted in average season lengths ~25 days shorter than those of legacy hybrids.Results illustrated the effects of environment, planting date, interannual variation in temperature, and the importance of climate-specific Kc functions.DT hybrids may be more effective at reproductive growth during periods of heat stress in semi-arid environments, although additional data are needed to support this conclusion.Abstract. Corn (Zea mays L.) is a major irrigated crop grown in the Southern High Plains including the Texas Panhandle. Irrigation from the Ogallala Aquifer is required to sustain profitable corn production in the region by supplementing inadequate and erratic rainfall. Effective irrigation scheduling works to extend limited groundwater resources by avoiding water losses associated with runoff and/or percolation below the root zone. The use of crop coefficient (Kc) and reference evapotranspiration (ETo) values to estimate daily crop water use (ETc) remains an effective scheduling tool that can complement other irrigation scheduling approaches. Both Food and Agriculture Organization (FAO-56) piecewise and curvilinear Kc values for corn are found in the literature. However, advances in corn genetics have led to questions about the applicability of Kc values developed using legacy corn hybrids to irrigation of modern drought-tolerant (DT) hybrids. Lysimeter-derived Kc values for legacy corn hybrids grown in large weighing lysimeter fields at the USDA-ARS Conservation and Production Research Laboratory at Bushland, Texas, were compared with those derived from a modern DT corn hybrid recently grown in the same fields. Results indicated that although midseason daily Kc values were similar for all hybrids, average season length was ~25 days shorter for the modern DT hybrid, characterized by a shortened initial growth period followed by more rapid increase of Kc during the development period. However, plots of Kc over thermal time illustrated that the differences in season length were likely attributable to later planting dates associated with the DT corn hybrids. Average seasonal water use was 730 and 811 mm for the legacy and modern DT hybrids, respectively (three years each), with corresponding average yields of 1.2 and 1.4 kg ha-1. Results suggest that published Kc and Kcb values developed with legacy corn hybrids remain largely applicable to modern DT corn hybrids when used with accurate estimates of effective canopy-based growth stages and climate-specific Kc functions. Keywords: Crop coefficients, Drought-tolerant, Evapotranspiration, Maize, Weighing lysimeters.