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Location: Soil and Water Management Research

2014 Annual Report

The long-term goal of this project is to prolong the economic activity derived from the Ogallala Aquifer by providing knowledge, tools, and technologies for water conservation and scientifically sound water use policies. Specifically, during the next five years, we will focus on: Objective 1. Improve the management of the Ogallala Aquifer by developing tools and knowledge of hydrological properties and water budget components. Subobjective 1.A: Improve the characterization of the Ogallala Aquifer including locations and rates of recharge. Subobjective 1.B: Integrate remotely-sensed data into water resource monitoring and decision support tools. Objective 2. Improve the efficiency by which agriculture converts water into food, feed, fuel and fiber. Subobjective 2.A: Improve irrigation scheduling technologies, strategies, and practices. Subobjective 2.B: Develop improved design, performance and management of irrigation control and application systems. Subobjective 2.C: Determine best management practices (BMP) for water-limited production of crop, fuel and forage in a semi-arid region. Subobjective 2.D: Improve knowledge of crop water demand and productivity at field, region and aquifer scales. Objective 3. Facilitate the adoption of water conservation practices by providing estimates of the socio-economic impacts of various water management activities and policies. Objective 4. Provide data, knowledge, and decision support systems to farmers, ranchers, water-policy makers, and the general public.

This cooperative project between the ARS (Bushland and Lubbock, Texas), Kansas State University, Texas A&M University, Texas Tech University, and West Texas A&M University, elucidates innovative management technologies appropriate for the Ogallala Aquifer region of the U.S. to enhance and sustain rural economies. The results are applicable to other areas in which there is increasing demands on the water supply. The in-research program addresses issues related to water management practices in cropping and integrated crop-livestock systems, and irrigation management and automation for increased water use efficiency (WUE). Knowledge of the processes affecting soil water content during a growing season will facilitate refinement of models to simulate water balance and assist in assessing the merits of alternative practices. Longer-term studies will be used to quantify effects of reduced tillage on crop yield, WUE, and soil physical characteristics for wheat-sorghum-fallow crop rotations and alternative cropping sequences. Several experiments focusing on different hydrological aspects and time scales will investigate management effects on soil water and availability to crops utilizing watershed, remote sensing, and meteorological networks. Research approaches related to irrigation management include determinations of crop water use by weighing lysimeters, neutron scattering methods, etc. Experiments include variations in irrigation methods, irrigation amount, tillage, and/or crop and crop rotation. Automatic irrigation systems based on sensing of crop water status are being engineered and tested. Remote sensing approaches to water use prediction are expected to improve their utility in decision making by farm managers, irrigation projects or water districts, and policy makers. University partners have critical roles in supporting the above activities as well as providing additional expertise in technology transfer, hydrology and economic assessments of existing and future water conservation technologies and policies. Support from cooperating university is evaluated annually. Work plans are developed for each project describing research to be conducted during a 2-year period. Yearly workshops are held with stakeholders and cooperating scientists; these workshops are used to review progress, re-define or clarify research priorities, and inform stakeholders, project leaders and administrators. Annual and final reports are used to document progress of the research.

Progress Report
To date, 90% of the milestones in the project's research plan (2012 to 2017) have been successfully completed. The severe drought from August 2010 to April 2014 had severely depleted soil moisture by the fall of 2013, resulting in failure of dryland wheat planted early FY2014 and making preparations for the summer crops in the spring of 2014 difficult. Between the last week of May and the first week of June in 2014, 25 cm (10 inches) of rain fell at Conservation and Production Research Laboratory in Bushland, Texas. The cold, wet conditions and hail severely damaged the emerging cotton, and many cotton experiments had to be either abandoned or modified. The loss of cotton plantings may either delay or prevent the successful completion of milestones in future years. Despite these complications from the prolonged drought, cold wet conditions in May and June of 2014, and declining well yields for irrigation, significant progress has been made in the development of energy/water balance models, automation of center pivot irrigation systems, and reliable and accurate soil profile moisture sensors. Early in FY2014, the former Research Leader (RL) position was abolished due to a lack of discretionary funding per SY. An internal recruitment resulted in one of the Unit's SY's duties being accrued to include those of the RL. Later in FY2014, the project's base funding was increased to include additional $290,000 for extramural agreements associated with the project's Ogallala Aquifer Project (OAP) and an additional $130,000 for the in-house research efforts. Increases for the in-house program were insufficient to increase discretionary funding levels per SY to a level that would justify hiring an additional SY. The project's OAP, a research-education consortium seeking solutions to problems arising from declining water availability from the Ogallala Aquifer on the Southern High Plains that is led by the ARS locations in Bushland and Lubbock, Texas, and includes scientists from Kansas State University, Texas A&M AgriLife Research and Extension Service, Texas Tech University and West Texas A&M University, was recognized by the Secretary of Agriculture for its efforts in sustaining rural communities in the face of drought and declining water availability in December 2013. There are five Specific Cooperative Agreements associated with the OAP (partners being Colorado State University, Kansas State University, Texas A&M AgriLife Research and Extension Service, Texas Tech University, and West Texas A&M University) that expired FY2014. Cooperative OAP research with Kansas State University, Texas A&M AgriLife Research and Extension Service, Texas Tech University, and West Texas A&M University will continue for at least another two years under the remaining four Specific Cooperative Agreements. University cooperators published 22 peer reviewed journal articles during FY2014 (10 for Kansas State University, 8 from Texas Tech University, and 4 from Texas A&M AgriLife), including an article in the Proceedings of the National Academy of Sciences (PNAS). In addition, scientists from West Texas A&M University co-authored several extension publications with other members of the OAP team determining the value of Ogallala Aquifer water on various sectors of the agricultural economy. Six publications resulting from OAP support were published in 2014 by ARS scientists at the Lubbock location. The project has associated with it three CRADA and one grant. Objective of one of the three CRADA projects is to develop an accurate and economical profile soil water content measurement system capable of discrete depth-interval water content measurement. ARS scientists working with this CRADA partner completed the objective's related SBIR Phase II project on which ARS is a subcontractor. Redesigned sensors were manufactured by ARS and the CRADA partner, and field testing in November 2013 revealed need for further design changes. A major design revision resulted in a sensor with sufficient strength for insertion into the soil to required depths, but manufacturing costs were too high. These circumstances resulted in another design cycle in spring and summer 2014. The new design will make the sensor more flexible since it can be operated in two modes: 1) as a replacement for the neutron probe with manual operation and movement of the sensor electronics from one access tube to another; and 2) as an autonomous, automatically logging wireless sensor meant for long-term unattended operation. Four journal articles and a proceedings article were published, and 16 presentations were made in FY2014. The CRADA was extended to 9/30/2015 in order to complete design revisions and field testing. The objective of the second CRADA is to commercialize an economical wireless narrow field-of-view infrared thermometer. A new exterior housing and circuit board with lower power consumption and a smart charging circuit were designed. Four prototype IRTs were tested against a commercial blackbody in a controlled temperature chamber. The sensors were also deployed under a six-span center pivot to test the transmission distance and the reliability of wireless data throughput. Sensor temperature readings were as expected and data capture rate at the maximum distance tested, 600 feet, was greater than 99%. A commercial graphical user interface was developed to capture and store data to a network host device. The CRADA was extended until 6/1/2015 with the expectation of testing prototype IRTs that function with Digimesh firmware. The third CRADA completed of a two-year study that used the Irrigation Scheduling and Supervisory Control and Data Acquisition System (ISSCADAS) to develop dynamic prescription maps and control irrigation scheduling of cotton based on a plant feedback system. Results from the study demonstrated that it was possible to integrate the ISSCADAS with a commercial variable rate irrigation (VRI) system. A new researcher hired with CRADA funds has modified the software that operates the ISSCADAS to make it easier to apply the system to irrigation systems of different sizes with different sizes of management zones. These modifications enhance the robustness of the code and ensure proper functionality over a wide range of conditions. To date, the revised software effectively controls the commercial VRI system and accommodates specific field information that can be easily entered by a producer or crop adviser. Furthermore, the software can automatically generate prescription maps based on the plant feedback system and the inputs provided by the user, such as the number of management zones, their angles and constituent sprinkler banks, and the location of non-arable areas such as pivot roads. This new version of software is currently being tested in the 2014 summer field experiments. A scientist in the project contributes to the efforts of a grant from National Institute for Food and Agriculture (NIFA/USDA) titled "Resilience and vulnerability of beef cattle production in the Southern Great Plains under changing climate, land use and markets", which entered its second year of five late in FY2014. Progress has been made in developing evapotranspiration maps from Landsat images.

1. Early maturing sorghum hybrids are more water efficient than later maturing hybrids. Water resources for crop production are limited, and rainfall amounts and timing are unpredictable on the Southern High Plains. Sorghum is drought tolerant relative to corn, making it a better crop where water availability is limited; however, the rain patterns can make it difficult for producers to determine type of hybrid, planting date, and irrigation strategy. In this study, ARS scientists at Conservation and Production Research Laboratory (Bushland, Texas) compared yields and water use efficiency between a later maturing sorghum hybrid planted early in the growing season with an early maturing hybrid planted in June. The advantage to using the early maturing hybrid in years of moderate drought was that water use efficiency was greater than for the later maturing hybrid. During exceptional drought, both hybrids were only able to produce expected yields if irrigation was applied at 80% of evapotranspiration. These results are of interest to sorghum growers in planning hybrid selections and irrigation strategies.

2. Predictions of La Nina mean more water needed for cotton on the Southern High Plains. The falling Ogallala Aquifer level under the U.S. Southern High Plains prompts farmers to improve water use and use more water-smart crops like cotton; however, new tools and management are needed to decrease dependence on the Ogallala Aquifer for irrigation water. The El Nino-Southern Oscillation (ENSO) causes likely weather patterns on the Southern High Plains that could be used when making irrigation decisions. The goal of this research was to optimize cotton yield under various scenarios during La Nina, neutral, and El Nino years. ARS scientists from the Conservation and Production Research Laboratory (Bushland, Texas) and Cropping Systems Research Laboratory (Lubbock, Texas) found that La Nina years had less rain during the growing season than neutral and El Nino phases. Cotton crop models predict yields increase with greater irrigation for drier La Nina growing seasons. These results indicate that farmers need to plan for greater irrigation demand during a predicted La Nina growing season.

3. Groundwater conserved today will increase Ogallala Aquifer's life cycle crop production. As water available from the Ogallala Aquifer declines, water policy makers will need information regarding the possible consequences of their policies. Scientists from Kansas State University in ARS' Ogallala Aquifer Program evaluated past and future trends in agricultural production and water withdrawals from the Ogallala Aquifer. Results indicated that 30% of the groundwater under the Kansas High Plains has already been depleted and an additional 39% will be withdrawn by 2060 under current practices. Results also indicated that groundwater conserved today will yield more crops in the future because of the continued increases in crop yields. These results indicate that overall agricultural productivity and possibly farm income can be increased by conserving groundwater today.

4. Simple energy balance can be used to develop evapotranspiration maps to guide water use. Evapotranspiration (ET) maps for large irrigated regions are essential for developing and evaluating irrigation management strategies. The operational Simplified Surface Energy Balance (SSEBop) approach was developed for this purpose; however, the SSEBop is not evaluated for its ability to derive ET fluxes from Landsat satellite datasets. In this study, the performance of the SSEBop for estimating daily and seasonal ET was evaluated as compared with lysimeter-measured crop ET under dryland and irrigation management practices by scientists from Conservation and Production Research Laboratory (Bushland, Texas), U.S. Geological Survey, and Texas A&M AgriLife Research. Results demonstrated that the SSEBop can produce quick and accurate ET maps that can be used for managing water resources at regional scales. These results may lead to methods for both farmers and water district managers to partition limited available water for irrigation.

5. Determining level of compensation for farmers not to irrigate will be difficult. Water conservation practices will hopefully extend the longevity of the Ogallala Aquifer on the Southern High Plains; however, the economics of potential conservation practices are not known. Scientists from ARS, Kansas State University, Texas A&M AgriLife Research and Extension Service, Texas Tech University, and West Texas A&M University tried to determine the amount that farmers should be paid not to irrigate. The results indicated that determining such a compensation level will be difficult because many factors will need to be considered, including well capacity, suitable crops for an area, and commodity prices. These results are particularly important to farmers, and water policy makers in Texas because of a recent state court ruling that farmers should be compensated when water policies reduce their ability to maximizing water withdrawals and irrigated crop income.

6. Wheat prefers to follow fallow rather than oil seed crops. Dryland and minimally irrigated cropping systems on the Southern High Plains typically include a summer fallow period to capture rainfall for the succeeding crop. However, these production systems do not generate income every year. Alterative cropping systems without a fallow period were compared to the profitability of wheat-fallow in western Kansas. Replacing the summer fallow with an oil seed crop like soybeans or sunflowers decreased the yields of succeeding wheat, resulting in decreased returns relative to continuous wheat or wheat-fallow systems. These results by Kansas State University scientists working in the ARS-led Ogallala Aquifer Program indicate that wheat rotations with oils seed crops are not as economically suitable as wheat and wheat-fallow systems.

7. Climate variability may affect land prices for irrigated acres more than for dryland and rangeland acres. One of the major factors affecting the relative prosperity of agricultural communities is the price for farm land. There is little information on the effects of possible climate change and declining water availability from the Ogallala Aquifer on land prices on the Southern High Plains in Texas. Scientists from Texas Tech University in the ARS-lead Ogallala Aquifer Program evaluated land prices for irrigated and dryland crop acreages, and rangeland from 1991 to 2030 under different climate scenarios. The results indicated that the price of irrigated acres would be more affected by changing climate than would dryland acres or rangeland. These results are of particular interest to water and farming policy makers.

8. Processing data from large weighing lysimeters. As the world's population grows, the scarcity of fresh water for different uses will increase, creating an environment in which agriculture must be water efficient. Evapotranspiration (ET) is the major use of irrigation water and rain. The ET estimation methods can be tested against ET measured using weighing lysimeters. Global interest in ET has resulted in an increased number of lysimeters and measured ET data; however, limited information is available on the proper collection and processing of these data. ARS researchers from Conservation and Production Research Laboratory (Bushland, Texas) developed guidelines and processing methods designed to minimize errors in lysimeter ET data. These results are of interest to other ET researchers and stakeholders who use data derived from such instruments.

9. New program to determine soil moisture more accurately. Accurate soil moisture measurements are required for efficient irrigation management and making decisions about dryland cropping practices. Time domain reflectometry (TDR) is a standard method used to measure soil water content that requires the evaluation of the signals recorded by instruments, and the current computer programs to interpret waveforms can cause large errors. User input of program parameters is often necessary. Research objectives were to develop a new computer program that requires no user input, and reduces water content errors. ARS scientists from the Conservation and Production Research Laboratory (Bushland, Texas) created a new adaptive computer program that yielded consistent evaluation of water contents, and required no user intervention. This program and the underlying principles will be of interest to soil scientists and landowners making decisions regarding water management.

10. Improved crop water use model developed. As water availability from the Ogallala Aquifer declines, farmers will need to implement both irrigation and dryland farming strategies that maximize crop water use, i.e., transpiration, and minimize evaporation from the soil. Evaporation and transpiration are difficult to measure. Therefore, crop water use models are needed that calculate evaporation and transpiration. Scientists from ARS' laboratories in Bushland, Texas, and Beltsville, Maryland, and Ben-Gurion University of Negev found that a commonly used crop water use model overestimated evaporation and underestimated transpiration. A revised model was created, which did a better job of calculating evaporation and transpiration. This knowledge and use of the model will help researchers create new management practices that will reduce evaporation losses from crops, and thus sustain or increase crop production in areas where water is limiting.

11. Feed grain is multi-billion dollar industry on the Southern High Plains. As water availability from the Ogallala Aquifer on the Southern High Plains declines, water policy makers and other water users will need information on the economic productivity used by various sectors of the agricultural economy. Scientists from ARS, Kansas State University, Texas A&M AgriLife Research and Extension Service, Texas Tech University, and West Texas A&M University analyzed data to determine the value of the region's feed grain industry. The feed grain industry (crop production and processing, but not consumption by livestock) was estimated to generate $2,400 per acre foot of water used, totaling $9 billion annually. These returns per acre foot of water used doubled the returns per water use for irrigated crop production. Water use planners and policy makers need knowledge of the returns per unit of water used by various agricultural industries so that decisions regarding water allocations from the Ogallala Aquifer can have optimal effects on regional economies.

12. Central High Plains growing season is increasing. Recent assessments indicated that agriculture on the Southern U.S. Great Plains is particularly vulnerable to projected changes in climate, and frost days can be indicative of changes in climate over time. In this study, scientists from Kansas State University and ARS (Bushland, Texas) developed frost indices for Kansas. Results indicated that there was a general increase in minimum air temperature and length of the growing season. Detailed geographical and temporal variations of the frost indices revealed in this study can be beneficial for updating management decisions and planting date recommendations for local and regional agricultural productions.

13. Method developed to estimate solar radiation where data are limited. Solar radiation plays an important role in hydrological processes. The lack of observed solar radiation data in developing countries and remote areas of developed countries, including the U.S., limited the ability to estimate future solar radiation scenarios for climate change impact studies. There are no clear guidelines to derive future solar radiation scenarios for regions where data are either measured sparsely or not at all. In this study, scientists from India and ARS (Bushland, Texas) developed guidance to estimate future solar radiation scenarios under different circumstances. Results are of interest to climatologists, agronomists and hydrologists to better understand hydrological processes where data are not robust.

Review Publications
Casanova, J.J., Schwartz, R.C., Evett, S.R., Anderson, S.K. 2013. Directly coupled vs conventional time domain reflectometry in soils. Applied Engineering in Agriculture. 29(5):771-777.
O'Shaughnessy, S.A., Evett, S.R., Colaizzi, P.D., Howell, T.A. 2014. Wireless sensor network effectively controls center pivot irrigation of sorghum. Applied Engineering in Agriculture. 29(6):853-864.
Moorhead, J.E., Gowda, P., Marek, T.H., Porter, D.O., Howell, T.A., Singh, V.P., Stewart, B. 2014. Use of crop-specific drought indices for determining irrigation demand in the Texas High Plains. Applied Engineering in Agriculture. 29(6):905-916.
Schwartz, R.C., Casanova, J.J., Bell, J.M., Evett, S.R. 2013. A reevaluation of time domain reflectomery propagation time determination in soils. Vadose Zone Journal. 13(1):1-13, doi:10.2136/vzj2013.07.0135.
Price, J.A., Simmons, A.R., Rashed, A., Workneh, F., Rush, C.M. 2014. Winter wheat cultivars with temperature sensitive resistance to wheat streak mosaic virus do not recover from early season infections. Plant Disease. 98(4):525-531.
Liu, L., Klocke, N., Yan, S., Rogers, D., Schlegel, A., Lamm, F., Chang, S.I., Wang, D. 2013. Impact of deficit irrigation on maize physical and chemical properties and ethanol yield. Cereal Chemistry. 90(5):453-462.
Liu, L., Maier, A., Klocke, N.L., Yan, S., Rogers, D.H., Tesso, T., Wang, D. 2013. Impact of deficit irrigation on sorghum physical and chemical properties and ethanol yield. Transactions of the ASABE. 56(4):1541-1549.
Baker, J.T., Mahan, J.R., Gitz, D.C., Lascano, R.J., Ephrath, J.E. 2013. Comparison of deficit irrigation scheduling methods that use canopy temperature measurements. Plant Biosystems. 147(1):40-49.
Mittal, A., Gampala, S.S., Ritchie, G.L., Payton, P.R., Burke, J.J., Rock, C.D. 2014. Related to ABA-Insensitive3(ABI3)/Viviparous1 and AtABI5 transcription factor coexpression in cotton enhances drought stress adaptation. Plant Biotechnology Journal. 12(5):578-589.
Nelson, J.R., Lascano, R.J., Booker, J.D., Zartman, R.E., Goebel, T.S. 2013. Evaluation of the precision agricultural landscape modeling system (PALMS) in the semiarid Texas Southern High Plains. Open Journal of Soil Science. 3:169-181.
Bulatewicz, T., Andresen, D., Auvenshine, S., Peterson, J., Steward, D.R. 2014. A distributed data component for the open modeling interface. Journal of Environmental Modeling and Software. 57:138-151.
Steward, D.R., Bruss, P.J., Yang, X., Staggenborg, S.A., Welch, S.M., Apley, M.D. 2013. Tapping unsustainable groundwater stores for agricultural production in the High Plains Aquifer of Kansas, projections to 2110. Proceedings of the National Academy of Sciences. 110(37):E3477-E3486.
Bechere, E., Auld, D.L. 2014. Registration of a tufted-naked seed upland cotton germplasm. Journal of Plant Registrations. 8(1):63-67.
Patel, J.D., Wright, R.J., Auld, D., Chandnani, R., Goff, V.H., Ingles, J., Pierce, G.J., Torres, M.J., Paterson, A.H. 2014. Alleles conferring improved fiber quality from EMS mutagenesis of elite cotton genotypes. Theoretical and Applied Genetics. 127(4):821-830.
Puig-Bargues, J., Lamm, F.R. 2013. Effect of flushing velocity and flushing duration on sediment transport in microirrigation driplines. Transactions of the ASABE. 56(5):1821-1828.
Harmoney, K.R., Lamm, F.R., Johnson, S.K., Aboukheira, A.A. 2013. Reducing water inputs with subsurface drip irrigation may improve alfalfa nutritive value. Forage and Grazinglands. 11(1)8 p. doi:10.1094/FG-2013-117-01-RS.
Torrion, J.A., Maas, S.J., Guo, W., Bordovsky, J.P., Cranmer, A.M. 2014. A three-dimensional index for characterizing crop water stress. Remote Sensing. 6:4025-4042.
Snowden, M.C., Ritchie, G.L., Simao, F.R., Bordovsky, J.P. 2014. Timing of episodic drought can be critical in cotton. Agronomy Journal. 106(2):452-458.
Reddy, S., Liu, S., Rudd, J.C., Xue, Q., Payton, P.R., Finlayson, S.A., Mahan, J.R., Akhunova, A., Holalu, S.V., Lu, N. 2014. Physiology and transcriptomics of water-deficit stress responses in wheat cultivars TAM 111 and TAM 112. Journal of Plant Physiology. 171(14):1289-1298.
Aiken, R.M., O'Brien, D.M., Olson, B.L., Murray, L. 2013. Replacing fallow with continuous cropping reduces crop water productivity of semiarid wheat. Agronomy Journal. 105(1):199-207.
Xue, Q., Rudd, J.C., Liu, S., Jessup, K.E., Devkota, R.N., Mahan, J.R. 2014. Yield determination and water-use effenciency of wheat under water-limited conditions in the U.S. Southern High Plains. Crop Science. 54(1):34-47.
Niu, G., Rodriguez, D., Dever, J., Zhang, J. 2013. Growth and physiological responses of five cotton genotypes to sodium chloride and sodium sulfate saline water irrigation. Journal of Cotton Science. 17(3):233-244.
Klocke, N.L., Currie, R.S., Holman, J.D. 2013. Alfalfa response to irrigation from limited water supplies. Transactions of the ASABE. 56(5):1759-1768.
Tewari, R., Johnson, J., Hudson, D., Wang, C., Patterson, D. 2013. Does climatic variability influence agricultural land prices under differing uses? The Texas High Plains case. Natural Resources. 4(8):506-513.
Holman, D., Sridharan, M., Porter, D., Gowda, P., Howell, T.A., Moorhead, J.E., Marek, T. 2014. Gaussian process models for reference ET estimation from alternative meteorological data sources. Journal of Hydrology. 517:28-35.
Colaizzi, P.D., Agam, N., Tolk, J.A., Evett, S.R., Howell, T.A., Gowda, P., O'Shaughnessy, S.A., Kustas, W.P., Anderson, M.C. 2014. Two source energy balance model to calculate E, T, and ET: Comparison of Priestly-Taylor and Penman-Monteith formulations and two time scaling methods. Transactions of the ASABE. 57(2):479-498.
Simao, F.R., Ritchie, G.L., Bednarz, C.W. 2013. Cotton physiological parameters affected by episodic irrigation interruption. Journal of Agricultural Science and Technology A. 3(6):443-454.
Narayanan, S., Aiken, R.M., Prasad, P., Xin, Z., Paul, G., Yu, J. 2014. A simple quantitative model to predict leaf area index in sorghum. Agronomy Journal. 106(1):219-226.
Steward, D.R., Allen, A.J. 2013. The analytic element method for rectangular gridded domains, benchmark comparisons and application to the High Plains Aquifer. Advances in Water Resources. 60:89-99.
Goldstein, J.C., Tarhule, A., Brauer, D.K. 2014. Simulating the hydrologic response of a semiarid watershed to switchgrass cultivation. Hydrology Research. 45(1):99-114.
Moriasi, D.N., Gowda, P., Arnold, J.G., Mulla, D.J., Ale, S., Steiner, J.L., Tomer, M.D. 2013. Evaluation of the Hooghoudt and Kirkham tile drain equations in SWAT to simulate tile flow and nitrate-nitrogen. Journal of Environmental Quality. 42:1699-1710.
Mauget, S.A., Leiker, G.R., Nair, S. 2013. A web application for cotton irrigation management on the US Southern High Plains. Part I: Crop yield modeling and profit analysis. Computers and Electronics in Agriculture. 99:248-257.
Mauget, S.A., Leiker, G.R., Nair, S. 2013. A web application for cotton irrigation management on the US Southern High Plains. Part II: Application design. Computers and Electronics in Agriculture. 99:258-264.
Baker, J.T., Gitz, D.C., Payton, P.R., Broughton, K.J., Bange, M.P., Lascano, R.J. 2014. Carbon dioxide control in an open system that measures canopy gas exchanges. Agronomy Journal. 106(3):789-792.
Goebel, T.S., Lascano, R.J. 2014. Time for cotton to uptake water of a known isotopic signature as measured in leaf petioles. Agricultural Sciences. 5(2): 170-177.
Acosta Martinez, V., Waldrip, H. 2014. Soil enzyme activities as affected by manure types, application rates and management practices. In: He, Z. and Zhang, H., editors. Applied Manure and Nutrient Chemistry for Sustainable Agriculture and Environment. New York, NY: Springer Science+Business Media Dordrecht. p. 99-122.