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United States Department of Agriculture

Agricultural Research Service

Research Project: Improving Water Productivity and New Water Management Technologies to Sustain Rural Economies

Location: Soil and Water Management Research

2012 Annual Report


1a.Objectives (from AD-416):
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.


1b.Approach (from AD-416):
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.


3.Progress Report:
This project, Improving Water Productivity and New Water Management Technologies to Sustain Rural Economies, is new, beginning January 26, 2012, and replacing 6209-13000-013-00D, Sustaining Rural Economies Through New Water Management Technologies. Progress was made on all objectives in the research plan for the project. Research addresses objectives related to three of the four problems areas in NP211:.
1)Effective Water Management in Agriculture;.
3)Improving Conservation Effectiveness; and.
4)Improving Watershed Management and Ecosystem Services in Agricultural Landscapes. ARS scientists continued to cooperate with scientists from numerous other ARS locations, Texas A&M AgriLife Research and Extension Service, Colorado State University, Kansas State University, Texas Tech University, West Texas A&M University to meet program objectives. The project has numerous international collaborative efforts. This research project includes the Ogallala Aquifer Program, a research and education consortium consisting of the ARS laboratories in Bushland and Lubbock, Texas, Kansas State University, Texas A&M AgriLife Research and Extension Service, Texas Tech University, and West Texas A&M University. Research is led by ARS scientists and is coordinated through an annual workshop and annual reporting effort. Frequent meetings, teleconferences and emails occur among the leadership team, and participating scientists. Research plans are reviewed annually to keep the team focused on critical issues. The Ogallala Aquifer Program manager serves as the ARS PI for the four associated Specific Cooperative Agreements, and provides leadership for the coordination and oversight activities. The research project is associated with additional agreements including two CRADAs, one Specific Cooperative Agreement, one reimbursable agreement, one trust agreement, land use agreements and memorandums, and one non-funded cooperative research agreements to facilitate accomplishment of the project's objectives. ARS PIs for these agreements monitor progress through frequent emails, phone calls and occasional meetings. Further details regarding progress towards research objectives and agreement management can be found in the annual reports for these subordinate projects.


4.Accomplishments
1. New soil water sensor guides better for determining crop water use efficiency. Knowledge of soil water content is key for irrigation and farm management, development of new drought-tolerant and water-efficient crop varieties and hybrids, and for watershed and environmental management. USDA-ARS scientists on the Texas High Plains at Bushland, Texas, cooperated with a private company to invent a new, accurate, automatic system for simultaneous measurement of soil water content and bulk electrical conductivity, for which a patent application was filed. The new system can be installed to depths greater than 10 feet in 8-inch sensor segments to cover only as much of the crop root zone as needed for irrigation management, or to measure the complete soil profile from the surface to well below the root zone. The additional ability to measure soil bulk electrical conductivity enables better management of salt-affected soils and monitoring of environmental contamination.

2. Evaporation and drift losses from sprinkler irrigation determined. During sprinkler irrigation, wind drift and evaporation losses can be large and can decrease irrigation application efficiency. These losses are not well understood and may decrease the crop water use through a reduction in crop transpiration from humidifying the air and wetting the leaf surfaces. The gross evaporation, drift losses and net crop water use were measured simultaneously in two adjacent alfalfa plots in Spain by scientists from ARS (Bushland, Texas) and Consejo Superior de Investigaciones Científicas (CSIC). One field was irrigated and the other one was not. Net sprinkler evaporation losses were 6.6% of the total applied water and were mainly influenced by the wind speed. The combined wind drift and evaporation losses contributed to the humidification of the air and decreased transpiration during sprinkler irrigation, especially for daytime irrigation events. This information aids in improved sprinkler irrigation system designs and management to avoid excessive devlopment of water losses.

3. Soil temperatures distort crop irrigation needs. Irrigation of crops is important to maintain abundant food for a growing population; however, crop irrigation requires large amounts of water and energy, both of which are becoming less available and more expensive. Irrigation scheduling methods based on crop canopy temperature measured by infrared thermometers (IRT) are being developed to better manage water and energy. When the crop does not completely cover the soil, the soil temperature beneath the crop will influence the crop temperature that is measured by IRT. In order to get accurate estimates of the rate of crop water use, the influence of the soil temperature must be taken into account. ARS scientists from Bushland, Texas, and Beltsville, Maryland, and a scientist from the Agricultural Research Organization-Volcani Center in Israel developed a new mathematical model that more accurately accounts for the influence of soil temperature on IRT measurements. This model was tested against actual measurements of crop water use, and the model greatly improved the accuracy of crop water use estimated by IRT. This improved the usefulness of using crop temperatures for irrigation management and will help farmers continue to produce crops for a growing population, while using less water and energy.

4. Improving evapotransporation calculations. As availability of Ogallala Aquifer water for irrigation declines, farmers on the Southern High Plains will need new water management technologies, like using evapotranspiration (ET) data to calculate crop water needs, to maximize crop production from the irrigation water applied. Reference ET is a useful parameter that can be accurately computed from meteorological data recorded from weather stations that are properly sited and instrumented with calibrated sensors. In this study, scientists from ARS (Bushland, Texas), University of Nebraska and Texas A&M AgriLife Research and Extension Service determined the relative effects of measurement errors in climate data on the accuracy of calculated reference ET values. Results indicated that reference ET was most sensitive to measurement of wind speed and air temperaturefollowed by solar radiation. These results indicate that accurate measurements of air temperature and wind speed are essential for calculating reference ET.

5. Planting and irrigation strategies reduce evaporation, improve yields. Use of groundwater from the Ogallala Aquifer for irrigation has transformed the High Plains into one of the largest and most productive agricultural regions in the United States. The decrease in profits from pumping from greater depths has led producers to look for alternative practices. Evaporation from the soil surface is a significant component of the water balance, but does not contribute to crop yield. ARS scientists from Bushland, Texas, and Beltsville, Maryland, and scientists from the Agricultural Research Organization-Volcani Center, Israel, and Colorado State University studied methods to measure evaporation losses and its relationship to crop row direction, crop height and time since irrigation. They found that orienting crop rows at right angles to the direction of the winds decreased evaporation by 20%. Applying larger irrigations and increasing the interval between irrigations also decreased evaporation losses. Planting and irrigation application strategies based on these findings could increase crop production per unit of applied water.

6. Weather-based methods improve crop water use estimates. Farmers aim to schedule crop irrigations so that crop water needs are met without over irrigating, thus saving water and pumping costs. To schedule irrigation based on estimates of crop water needs from weather data, state and U.S. governmental agencies have developed weather station networks in the most heavily irrigated portions of western states. The equations used to estimate water use from weather data are not completely accurate, however. Scientists from two USDA-ARS laboratories (Bushland and Lubbock, Texas) collaborated to assess the possibility of more accurate ways to estimate water use. Two methods were developed and tested against both measured water use and water use estimated using the current best method. All three methods estimated crop water use well, with one of the newly developed methods showing some improvement over the other two. A crop-related parameter used in all three methods was shown to be inaccurate in some circumstances. Recommendations were made for improving the values assigned to that parameter

7. Automated crop water stress index to better irrigate sorghum. As water availability from the Ogallala Aquifer for irrigation declines, farmers on the High Plains will need new water management technologies to maximize crop production from the irrigation water applied. ARS scientists (Bushland, Texas) used an integrated Crop Water Stress Index (CWSI) based on data from leaf temperature sensors to assess its effectiveness as a trigger for irrigating grain sorghum. The completely automatic CWSI method produced similar results to irrigation scheduling using a neutron probe to measure soil water depletion. Over two years, yields and irrigation water use efficiencies were as good using the automatic CWSI method as those obtained using the time-consuming manual soil water depletion measurements. Because it is time consuming, farmers do not typically use a neutron probe to take soil water measurements. They are more likely to invest in moving sprinkler systems that are outfitted with sensor networks for automated control as a means to manage irrigations.

8. Better sorghum irrigation with Time Temperature Threshold (TTT) method. As water availability from the Ogallala Aquifer for irrigation declines, farmers on the High Plains will need new water management technologies to maximize crop production from the irrigation water applied. The automated Time Temperature Threshold (TTT) method may be one technology to help schedule irrigation with reduced management time. ARS scientists at Bushland, Texas, compared yields of sorghum irrigated using the TTT method to those from irrigation based on soil moisture depletion using neutron probe measurements. Sorghum leaf temperatures were remotely monitored by wireless infrared thermometers located on a pivot lateral. Irrigation was applied, when the sorghum leaf temperature was greater than a threshold value for more than 315 minutes during a 24-hour period. Grain yields using the TTT were similar to those irrigated using data from neutron probe over a range of total water applications. These results indicate that sorghum irrigation can be automated via TTT, saving producer management time and money.

9. Stay-green sorghum did better during drought of 2011. Recent results from the Ogallala Aquifer Program's Economic Assessment and Impact Team indicate the development and use of cultivars that use less water can reduce withdrawals from the aquifer while enhancing farm and community economic outlook. The stay-green trait may be one way to increase grain yields of sorghum grown under deficit irrigation. Growth and yields of a stay green variety were compared to that of a non-stay-green (senescent) variety by ARS scientists at Bushland, Texas, under limited irrigation using four soils common to the Southern High Plains. The weather during the two-years of the study was quite different, with the drought conditions being more severe in 2011 than in 2010. In 2010, the senescent variety produced significantly greater yields compared with the stay-green variety. In the extreme drought conditions of 2011, the stay-green variety produced significantly greater grain yield. These results indicate that the stay-green trait may impart a competitive advantage to sorghum grown under extreme water stress.

10. Fine-scale mapping of evapotranspiration. As water availability from the Ogallala Aquifer declines, the resource will need to be managed more closely to ensure that maximum benefits are derived from the water used. Maps of evapotranspiration (ET) can assist the management of groundwater use for irrigation and municipal uses. Remote-sensing-based ET models are presently most suited for mapping ET at regional scales, but water management at smaller scales (county, fields, etc.) would benefit from such information. In this study, scientists from ARS-Bushland, Texas, Kansas State University, and Utah State University evaluated a surface energy model for its ability to estimate ET from high-resolution remote sensing data in the Texas High Plains. These analyses suggested improvements in smaller scale ET mapping are possible, but additional research is needed.

11. Sunflower yields lower in the Texas High Plains. Sunflower is a drought-adapted crop whose short growing season reduces irrigation requirements, thus making it ideal for regions with limited irrigation water supplies like the Texas High Plains. However, best management practices and yield potential are poorly defined for the region. ARS scientists at Bushland, Texas, evaluated sunflower grown under full and limited irrigation using four soils (clay loam, silt loam, sandy loam, and fine sand) common to the Southern High Plains. At the lowest irrigation levels, the crops grown in the fine sand and sandy loam soils had the greater yields. Irrigation increased the seed yield of the crops in the fine sand more than that of the crops in the silt loam and clay loam. When comparing yields in this study to those from around the world, these yields were as much as 30% lower, even at the greater irrigation levels. Smaller yields are probably due to the region's hot, dry conditions. Although sunflower appears to be suited to the Texas High Plains, it is best suited to the areas with sandier soils.

12. Keeping crop residue in place improves rain storage. Storing rain in the soil during fallow is crucial for good dryland wheat and grain sorghum crops on the Southern High Plains, and the presence of crop residues usually promotes rain storage. To learn how tillage, residue, and crop rotation affect the efficiency of rain storage during fallow, scientists from Bushland, Texas, quantified infiltration of rain into no-tilled or stubble-mulch tilled in long-term continuous wheat and wheat-sorghum-fallow sites that were either bare or straw covered. Infiltration increased with straw cover for any combination of tillage or crop rotation. Infiltration into bare sites did not vary with tillage. The continuous wheat rotation improved aggregates, increased infiltration, and reduced soil loss over the wheat-sorghum-fallow rotation. Results suggest more intensive rotations that keep residue in place can improve rain storage during fallow periods by increasing infiltration.

13. BMR sorghums higher in forage quality. With the increasing presence of dairies on the Southern High Plains and declining water availability from the Ogallala Aquifer, there is a greater interest in the use of sorghum for forage production. Best management practices need to be defined for the region. Clear yield and forage quality tendencies were observed between different classes of sorghums in tests conducted by ARS (Bushland, Texas) and Texas A&M AgriLife Research and Extension Service. The sorghum-sudan crosses with photoperiod sensitivity class had the greatest forage yield. The non-brown midrib (non-BMR) classes consistently yielded more than those with the brown midrib (BMR) trait. Sorghum classes with the BMR trait consistently were greater in forage quality. Lodging was not increased in BMR cultivars compared to the non-BMR cultivars when harvested at the soft-dough stage. These results provide knowledge for best management practices for forage production with sorghum on the Southern High Plains.

14. Lower water storage in Lake Meredith (Texas) associated with decreases in annual rainfall. Dams were created along the Canadian River in New Mexico and Texas during the 20th century to supply water for irrigation, and municipal and industrial uses. In recent years, demand has exceeded the ability of these reservoirs to supply water. ARS scientists from Bushland and Lubbock, Texas, examined trends in rainfall, stream flow and reservoir levels in the Canadian River throughout the New Mexico-Texas region from 1940 to 2009. Water stored in Eagle Nest Lake, Conchas Lake, Ute Lake, and Lake Meredith was less than the long-term averages between 2000 and 2009, which was associated with less than average stream flows. The decline in water storage in Lake Meredith between 1990 and 2009 was associated with decreased annual rainfall in almost the entire upstream watershed. The results indicate that a small decrease in annual rainfall had a disproportionate effect on water availability from the Canadian River and may increase the reliance of towns on the Ogallala Aquifer as a water source.

15. Higher irrigation linked to streamflow in eastern New Mexico watershed. Dams were created along the Canadian River in New Mexico and Texas during the 20th century to supply water for irrigation, municipal, and industrial uses. In recent years, demand has exceeded supplies. ARS scientists from Bushland and Lubbock, Texas, examined trends in stream flow, and irrigation in the Revuelto Creek watershed, a tributary of the Canadian River in eastern New Mexico. Annual total outflow from the Revuelto Creek Watershed was positively related to the amount of irrigation water available to a water district within the watershed. The Soil Water Assessment Tool, a hydrologic model for agricultural watersheds, adequately predicted outflow from Revuelto Creek when historical values for irrigation were used. These results indicate the potential positive effects that irrigation can have on stream flow in a semi-arid watershed.

16. New water policies in southwest Kansas will extend contribution of Ogallala Aquifer to egional economy. As water available for irrigation from the Ogallala Aquifer decreases, water planners and policy makers will need information on the socio-economic impacts of proposed conservation measures. Scientists and economists from Kansas State University estimated the economic impact of three groundwater-use scenarios and two weather scenarios when evaluating stakeholder proposed reductions in groundwater use. The results suggest that new water policies may lead to economic benefits for both the farmers and rural economies. However, the proposed reductions in groundwater use will not prevent the groundwater resource from being exhausted.

17. Irrigation affects soil carbon concentrations, not greenhouse gas emissions. Although there is a great interest in soils as a buffer against the increasing atmospheric carbon dioxide, data on the effects of crop management on carbon storage in soils and the potential of soils to emit greenhouse gases (carbon dioxide, nitrogen oxide and methane) are scarce. Scientists from Kansas State University compared changes in soil carbon concentrations and soil gas emissions at several levels of limited irrigation under no-till cropping systems on two soils, one at Garden City, Kansas, and the other at Tribune, Kansas. The soil organic carbon concentrations in the top 4 inches increased with the amount of applied irrigation water at the Garden City site, but not at the Tribune site; however, the two irrigation regimes at Tribune were greater than those at Garden City. Irrigation levels had no significant effects on soil gas emissions in the short term.

18. Methods developed to produce maps of daily evapotranspiration for the Texas High Plains. As water from the Ogallala Aquifer for irrigation decreases, farmers will need tools to use the available water as efficiently as possible. One method to increase the efficiency by which irrigation water is converted into crops is scheduling irrigation based on evapotranspiration (ET) rates. Scientists from ARS (Bushland, Texas) and Texas A&M AgriLife Research and Extension Service developed graphical representation of ET and daily weather parameters from the Texas High Plains Evapotranspiration (TXHPET) Network weather station data. Daily generated maps can be viewed on the TXHPET Network website to give users a much needed graphical representation of the ET for rapid visual analysis and interpretation purposes. These representation maps are particularly beneficial to agricultural producers who have off-site ET network and multiple, widespread field locations. Although the TXHPET is currently restricted to researcher use, plans are to implement this methodology to the related and publicly available Texas A&M AgriLife water management site.

19. Weekly irrigation by subsurface drip does not reduce cotton yields. As water available for irrigation from the Ogallala Aquifer declines, farmers on the Texas High Plains will need new water conservation technologies, like subsurface drip irrigation (SDI), to maximize crop production from the irrigation water applied. Irrigation intervals as frequent as every 8 hours have been advocated by SDI service providers in an attempt to reduce severe water stress where irrigation capacity is limited. Negative aspects of high-frequency, drip irrigation include non-uniform water distribution and potential increases in mineral concentrations in the smaller wetted volumes adjacent to the drip lateral. A field study was conducted by scientists from Texas A&M AgriLife Research and Extension Service, Texas Tech University and ARS in Lubbock, Texas, with the objective of determining cotton response to SDI application intervals of 0.25, 2, and 7 days. Lint yields, seasonal irrigation water use efficiencies, and loan values of the 7-day irrigation interval treatments were equal to or greater than the 0.25- and 2-day treatments. Longer irrigation intervals with SDI on cotton could simplify irrigation control systems and lower initial installation costs, thereby helping the transition to more water-efficient delivery methods.

20. Crop canopy temperatures are useful to verify crop water needs. As water available for irrigation from the Ogallala Aquifer declines, farmers on the Southern High Plains will need new water conservation technologies to maximize crop production from the irrigation water applied. Using crop canopy temperatures to schedule irrigations appears to have potential as a deficit irrigation management tool but such practices have not been tested at production scales. In a 3-year study of deficit irrigation in a production environment, scientists from ARS (Lubbock, Texas), Texas Tech University, and Texas A&M AgriLife Research found that canopy temperature data were useful to identify which irrigations in the deficit treatments were in excess of the target amounts. These results provide further indications that canopy temperatures can be used to schedule water applications under deficit irrigation regimes for cotton.

21. Potato production possible with reduced irrigation applications in the Texas Panhandle. Increased concerns about water use for agricultural irrigation on the Southern High Plains warrant examination of alternatives to traditionally grown high-water-use crops. Scientists from Texas A&M AgriLife Research and Extension Service, ARS (Bushland, Texas) and West Texas A&M University investigated the response of potatoes to varying levels of irrigation, from 50 to 100% of evapotranspiration. There was no difference in tuber yield or quality among the irrigation treatments, indicating that potatoes may be grown with less water than other crops. However, the heavy clay soils of the Amarillo area are probably less than ideal for optimum potato production.

22. Beef carcass chilling can use water more efficiently. Although water use by agricultural processing industries located on the Southern High Plains is relatively small in terms of volume compared to irrigation, water conservation by these industries can improve their profitability. Scientists from West Texas A&M University studied means by which water can be saved in beef packing plants when chilling carcasses. For water-chilled carcass halves, considerable weight savings is achieved by increasing the spray force, and not always by increasing the water volumetric flow rate. Cooling effectiveness significantly increases as the spray droplet size increases due to the weakening in spray drift inside the meat chiller. These results provide insights into how meat packing plants can conserve water.


Review Publications
Samui, P., Gowda, P., Oommen, T., Howell, T.A., Marek, T.H., Porter, D.O. 2012. Statistical learning algorithms for identifying contrasting tillage practices with landsat thematic mapper data. International Journal of Remote Sensing. 33(18):5732-5745.

Howell, T.A., Evett, S.R., O'Shaughnessy, S.A., Colaizzi, P.D., Gowda, P. 2012. Advanced irrigation engineering: Precision and Precise. Journal of Agricultural Science and Technology. 2(1A):1-9.

Evett, S.R., Schwartz, R.C., Casanova, J.J., Heng, L.K. 2012. Soil water sensing for water balance, ET, and WUE. Agricultural Water Management. 104:1-9.

O'Shaughnessy, S.A., Evett, S.R., Colaizzi, P.D., Howell, T.A. 2012. A crop water stress index and time threshold for automatic irrigation scheduling of grain sorghum. Agricultural Water Management. 107:122-132.

Hernandez, J.E., Gowda, P., Howell, T.A., Steiner, J.L., Mojarro, F., Nunez, E.P., Avila, J.R. 2012. Modeling groundwater levels on the Calera Aquifer Region in Central Mexico using ModFLow. Journal of Agricultural Science and Technology. 2(1B):52-61.

Tolk, J.A., Howell, T.A. 2012. Sunflower water productivity in four Great Plains soils. Field Crops Research. 120(1):120-128.

Gowda, P., Westra, J.V., Petrolia, D.R., Dalzell, B.J., Mulla, D.J. 2011. Impact of targeted removal of residue cover on water quality in the sand creek watershed. Journal of Environmental Hydrology. 19(25):1-12.

Casanova, J.J., Evett, S.R., Schwartz, R.C. 2012. Design of access-tube TDR sensor for soil water content: Theory. IEEE Sensors Journal. 12(6):1979-1986.

Colaizzi, P.D., Evett, S.R., Howell, T.A., Gowda, P., O'Shaughnessy, S.A., Tolk, J.A., Kustas, W.P., Anderson, M.C. 2012. Two source energy balance model: Refinements and lysimeter tests in the Southern High Plains. Transactions of the ASABE. 55(2):551-562.

Evett, S.R., Lascano, R.J., Howell, T.A., Tolk, J.A., O'Shaughnessy, S.A., Colaizzi, P.D. 2012. Single- and dual-surface iterative energy balance solutions for reference ET. Transactions of the ASABE. 55(2):533-541.

O'Shaughnessy, S.A., Evett, S.R., Colaizzi, P.D., Howell, T.A. 2012. Grain sorghum response to irrigation scheduling with the time-temperature threshold method and deficit irrigation levels. Transactions of the ASABE. 55(2):451-461.

Tuppad, P., Santhi, C., Wang, X., Williams, J.R., Srinivasan, R., Gowda, P. 2010. Simulation of conservation practices using the APEX model. Applied Engineering in Agriculture. 26(5):778-779.

Casanova, J.J., Evett, S.R., Schwartz, R.C. 2012. Design of access-tube TDR sensor for soil water content: Testing. IEEE Sensors Journal. 12(6):2064-2070.

Baumhardt, R.L., Johnson, G.L., Schwartz, R.C. 2012. Residue and long-term tillage and crop rotation effects on simulated rain infiltration and sediment transport. Soil Science Society of America Journal. 76(4):1370-1378.

Lamm, F.R., Bordovsky, J.P., Schwankl, L.J., Grabow, G.L., Enciso-Medina, J., Peters, T.R., Colaizzi, P.D., Trooien, T.P., Porter, D.0. 2012. Subsurface drip irrigation: Status of the technology in 2010. Transactions of the ASABE. 55(2):483-491.

Schwartz, R.C., Dao, T.H., Bell, J.M. 2011. Manure and mineral fertilizer effects on seasonal dynamics of bioactive soil phosphorus fractions. Agronomy Journal. 103(6):1724-1733.

Halvorson, A.D., Schlegel, A.J. 2012. Crop rotation effect on soil carbon and nitrogen stocks under limited irrigation. Agronomy Journal. 104(5):1265-1273.

Villarreal, C.J., Zartman, R., Hudnall, W., Gitz, D.C., Rainwater, K., Smith, L.M. 2012. Spatial distribution and morphology of sediments in Texas Southern High Plains playa wetlands. Texas Water Journal. 3(1):1-4.

Schlegel, A.J., Stone, L.R., Dumler, T.J., Lamm, F.R. 2012. Managing diminished irrigation capacity with preseason irrigation and plant density for corn production. Transactions of the ASABE. 55(2):525-531.

Steward, D.R., Yang, X., Staggenborg, S.A., MacPherson, G.L., Welch, S.M. 2011. From precipitation to groundwater baseflow in a native prairie ecosystem: A regional study of the Konza LTER in the Flint Hills of Kansas, USA. Hydrology and Earth System Sciences. 15:3181-3194.

Casanova, J.J., Evett, S.R., Schwartz, R.C. 2012. Design and field tests of an access-tube soil water sensor. Applied Engineering in Agriculture. 28(4):603-610.

Peterson, J. 2012. Comparing the cost-effectiveness of water conservation policies in a depleting aquifer:A dynamic analysis of the Kansas High Plains. Journal of Agricultural and Applied Economics. 44(2):222-234.

Bordovsky, J.P., Mustian, J.T. 2012. Cotton response to crop row offset and orientation to subsurface drip irrigation laterals. Applied Engineering in Agriculture. 28(3):367-376.

Guerrero, B., Johnson, J., Amosson, S., Johnson, P., Segarra, E., Surles, J. 2011. Ethanol production in the Southern High Plains of Texas: Impacts on the economy and scarce water resources. The Journal of Regional Analysis & Policy. 41(1):22-32.

Unger, P.W., Blanco-Canqui, H. 2011. Conservation tillage. In: Huang, P.M., Li, Y., Sumner, M.E., editors. Handbook of Soil Sciences: Resource Management and Environmental Impacts, 2nd Edition. CRC Press, Boca Raton, Florida. p. 25-1--25-31.

Tolk, J.A., Evett, S.R. 2012. Lower limits of crop water use in three soil textural classes. Soil Science Society of America Journal. 76(2):607-616.

Colaizzi, P.D., Evett, S.R., Howell, T.A., Li, F., Kustas, W.P., Anderson, M.C. 2012. Radiation model for row crops: I. Geometric view factors and parameter optimization. Agronomy Journal. 104(2):225-240..

Colaizzi, P.D., Schwartz, R.C., Evett, S.R., Howell, T.A., Gowda, P., Tolk, J.A. 2012. Radiation model for row crops: II. Model evaluation. Agronomy Journal. 104(2):241-255.

Avila-Carrasco, J.R., Mojarro, F.D., Moriasi, D.N., Gowda, P., Bautista-Capetillo, C., Echavarria-Chairez, F.G., Garbrecht, J.D., Steiner, J.L., Howell, T.A., Kanemasu, E.T., Verser, J.A., Wagner, K., Hernandez, J. 2012. Calibration of SWAT2009 using crop biomass, evapotranspiration, and deep recharge: Calera watershed in Zacatecas, Mexico case study. Journal of Water Resource and Protection. 4:439-450.

Last Modified: 11/28/2014
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