Progress 05/03/11 to 05/02/16
Outputs
Target Audience:Targeted audience included agricultural scientists, extension personnel, and producers in Texas. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?The projects provided opportunities for graduate student training (Ahmed Attia, Sumit Sharma, and Yong Chen). How have the results been disseminated to communities of interest?Project results were disseminated through presentations, abstracts, journal articles, and websites. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Investigate the energy, water, carbon and greenhouse gas fluxes associated with the change in agricultural land use to biofuels-dominated cropping systems in the semi-arid Southwestern U.S. Cotton Belt region and assess the implications of these changes on hydrological and biogeochemical processes. In this project, we established four eddy covariance flux towers in four representative land uses (irrigated cotton, dryland cotton, perennial grasses, and biomass sorghum) in the Southern High Plains region. We also assessed hydrological responses of land use change from cotton to cellulosic bioenergy crops using the SWAT and ArcAPEX hydrology models. Results from field and modeling studies indicate substantial ecosystem benefits if the existing cotton were replaced by perennial grasses and sorghum for bioenergy production. Investigated the effect of 2011 extreme drought on carbon and water dynamics of a grassland in the Southern High Plains. The two years of the project (2010 and 2011) represented extremes in precipitation (mean 48 cm) in this region (2010: 62.2 cm; 2011, the driest year in the past century: 12.6 cm). Energy and carbon flux measurements were made using eddy covariance method on a managed Old World bluestem pasture in the Southern High Plains. The extreme drought of 2011 caused the pasture grass to remain a carbon source throughout the year, and most of the available energy at the surface was converted to sensible heat. With projected increase in drought events in the Southern Great Plains in the coming decades, observations from field experiments such as this are important in understanding the contributions of managed grasslands to regional weather, carbon and hydrologic cycles. Used Cotton2K and DSSAT-CROPGRO-Cotton simulation models for modeling cotton lint yield and water use efficiency responses to irrigation scheduling in the Texas Rolling Plains. Crop growth simulation models, after calibration and validation, offer an excellent tool to compare the responses of crops to management factors and identify optimal management strategies. The models were initially calibrated and validated using field data. Calibrated models were then used to run simulation scenarios. We found that 85% - 90% ET replacement is a promising deficit irrigation strategy for the Texas Rolling Plains. The simulations also demonstrated that adopting deficit irrigation practices under normal weather conditions can conserve water without adversely affecting seed cotton yields. Used DSSAT-CERES-Wheat model to study winter wheat response to irrigation management in the Texas High Plains. Results of simulations using historical weather data for 32 years (1980-2012) showed that a single irrigation of 100 mm at jointing or booting had 35% higher grain yield than dryland while 140 mm at anthesis or grain filling produced 68% higher grain yield compared to dryland. Deficit irrigation at grain filling significantly increased water use efficiency (WUE). Demonstrated tools for improving on-farm irrigation efficiency. Over the years, various methods have been developed for scheduling the irrigation of agricultural crops. This project demonstrated various irrigations scheduling methods for cotton in the Texas Rolling Plains. The irrigation scheduling methods included tensiometers, soil moisture sensors, SmartField sensors, and crop evapotranspiration replacement. Audited the irrigation efficiency of 14 center-pivot irrigation systems in the Texas High Plains. Application efficiencies were in the range of 60-70% for mid-elevation spray application (MESA) systems, 70-80% for low-elevation spray application (LESA) systems, and greater than 90% for low-energy precision application (LEPA) systems. Correction of the small number of defective emitters per system would not realize significant water savings. However, water savings could be realized by switching from MESA or LESA to LEPA, assuming the choice of crop allowed it. Developed and tested a remote sensing based irrigation scheduling tool. This tool was developed based on the theoretical studies Dr. Rajan conducted during her doctoral and post-doctoral programs at Texas Tech University. This tool is designed to use Landsat satellite data for adjusting irrigation recommendations for crops in the Texas High Plains. An online version of the tool is currently being developed. Developed an automated method for identifying the soil line using Landsat satellite data. We developed an automated supervised learning algorithm using relevance vector machine (RVM) for extracting the soil line from Landsat images. The 10-fold cross validation indicated 92% accuracy for distinguishing bare soil and other non-bare soil pixels from an image. The proposed RVM-based procedure successfully incorporated machine-learning algorithms into agricultural remote sensing and eliminated the dependency on empiricism and minimized subjectivity. Evaluated the effects of irrigation methods on growth, lint yield, fiber quality, and spectral reflectance responses of commercial cotton cultivars in the Texas Rolling Plains. Irrigating at 90% evapotranspiration replacement rate produced the greatest lint yield and WUE. Tillage did not significantly affect lint yield, WUE, or fiber quality. Plants exposed to water stress showed significant decrease in leaf area index, normalized difference vegetation index, and normalized difference water index. Compared to dryland, an average 8% increase in fiber length and strength and 10% decrease in micronaire were observed by the high irrigation level. The crop water stress index was negatively correlated with lint yield. Evaluated four irrigation scheduling methods using data from corn fields in the Hale and Floyd counties of Texas. Analysis of four different irrigation scheduling methods (Potential Evapotranspiration/PET, remote sensing, SmartField, and Aquaspy) revealed that the use of any of the four methods is likely to be superior to the use of no objective method, in terms of protecting the crop from stress and avoiding over-irrigation. The PET-based method was the simplest to implement, and would result in little cost to the producer. The remote sensing method should be better at representing the actual water demand of individual fields, and thus may be less likely to result in over-irrigation. The SmartField and Aquaspy methods also appeared to be suitable for practical use in irrigation scheduling, although each would involve a greater investment by the producer. The SmartField sensors (based on canopy temperature) might have some problems dealing with extremely high air temperatures.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2016
Citation:
Shi, Y., J. A. Thomasson, S. C. Murray, N. A. Pugh, W. L. Rooney, S. Shafian, N. Rajan, A. Ibrahim, G. Rouze, C. L.S. Morgan, H. L. Neely, A. Rana, M. V. Bagavathiannan, J. Henrickson, E. Bowden, J. Valasek, J. Olsenholler, M. P. Bishop, R. Sheridan, E. B. Putman, S. Popescu, T. Burks, D. Cope, B. F. Mccutchen, D. D. Baltensperger, R. V. Avant, M. Vidrine, and C. Yang. 2016. Unmanned aerial vehicles for high-throughput phenotyping and agronomic research. Plos One, http://dx.doi.org/ 10.1371/journal.pone.0159781
- Type:
Journal Articles
Status:
Published
Year Published:
2016
Citation:
Attia, A., and N. Rajan. 2016. Within season growth and spectral reflectance of cotton and their relation to lint yield. Crop Science, 56: 2688-2701.
- Type:
Journal Articles
Status:
Published
Year Published:
2016
Citation:
Attia, A., N. Rajan, S. Nair, P. DeLaune, Q. Xue, A. Ibrahim, and D. Hays. 2016. Modeling cotton lint yield and water use efficiency responses to irrigation scheduling using Cotton2K. Agronomy Journal, 108(4):1614-1623.
- Type:
Journal Articles
Status:
Published
Year Published:
2016
Citation:
Chen, Y., S. Ale, and N. Rajan. 2016. Spatial variabilities of biofuel production potentials and hydrologic fluxes of land use change from cotton (Gossypiumhirsutum L.) to Alamo switchgrass (Panicumvirgatum L.) in the Texas High Plains. Bioenergy Research, 9: 1126-1141.
- Type:
Journal Articles
Status:
Published
Year Published:
2016
Citation:
Chen, Y., S. Ale, N. Rajan, C. L. S. Morgan, and J. Park. 2016. Hydrological responses of land use change from upland cotton to cellulosic bioenergy crops in the southern High Plains of Texas. Global Change Biology-Bioenergy, 8(5): 981-999.
- Type:
Journal Articles
Status:
Published
Year Published:
2016
Citation:
Attia, A., N. Rajan, Q. Xue, S. Nair, A. Ibrahim, and D. Hays. 2016. Application of DSSAT-CERES-Wheat model to simulate winter wheat response to irrigation scheduling in the Texas High Plains. Agricultural Water Management, 165: 50-60.
- Type:
Journal Articles
Status:
Published
Year Published:
2016
Citation:
Modala, N. R., S. Ale, D. W. Goldberg, M. Olivares, C. L. Munster, N. Rajan, and R. A. Feagin. 2016. Climate change projections for the Texas High Plains and Rolling Plains. Theoretical and Applied Climatology, DOI 10.1007/s00704-016-1773-2.
- Type:
Journal Articles
Status:
Published
Year Published:
2016
Citation:
Adhikari, P., S. Ale, J. P. Bordovsky, K. R. Thorp, N. R. Modala, N. Rajan, and E. M. Barnes. 2016. Simulating future climate change impacts on seed cotton yields in the Texas High Plains using the CSM-CROPGRO-cotton model. Agricultural Water Management, 164: 317-330.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2016
Citation:
Sharma, S., N. Rajan, and S. Maas. 2016. Effect of potential land use change from cotton to bioenergy crops on carbon dynamics in the Southern Great Plains. Student Research Week, Texas A&M University, 28 March 04 April, College Station, TX.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2016
Citation:
Sharma, S., N. Rajan, and S. Maas. 2016. Effect of potential land use change from cotton to bioenergy crops on carbon dynamics in the Southern Great Plains region. Abstracts, Southern Branch of ASA Annual meeting, Feb 7-9, San Antonio, TX.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2016
Citation:
Chen Y., S. Ale, and N. Rajan. 2016. Land use change from cotton to perennial bioenergy grasses in the Texas High Plains: Implications on water and nitrogen balances. 5th Annual Student Water Conference, March 24-25, Oklahoma State University, Stillwater, OK.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2016
Citation:
Sharma, S., N. Rajan, and S. Maas. 2016. Influence of soil temperature, soil moisture and canopy photosynthesis on diurnal and seasonal dynamics of soil respiration. Abstracts, Southern Branch of ASA Annual meeting, Feb 7-9, San Antonio, TX.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2016
Citation:
Chen, Y., S. Ale, and N. Rajan. 2016. Assessing the impacts of land use change from cotton to cellulosic bioenergy crops on watershed hydrology and water quality in the Texas High Plains, Abstracts, Southern Branch of ASA Annual meeting, Feb 7-9, San Antonio, TX.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2016
Citation:
Murray, S. C., L. Knox, B. Hartley, M. A. M�ndez-Dorado, G. Richardson, J. A. Thomasson, Y. Shi, N. Rajan, H. Neely, M. Bagavathiannan, X. Dong, and W. L. Rooney. 2016. High clearance phenotyping systems for season-long measurement of corn, sorghum and other row crops to complement unmanned aerial vehicle systems. Proc. SPIE 9866, Autonomous Air and Ground Sensing Systems for Agricultural Optimization and Phenotyping, 986607 (May 17, 2016); DOI:10.1117/12.2228323.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2016
Citation:
Rajan, N., and S. Sharma. 2016. Ecosystem evapotranspiration and photosynthesis from eddy covariance. Abstracts, Southern Branch of ASA Annual meeting, Feb 7-9, San Antonio, TX.
|
Progress 10/01/14 to 09/30/15
Outputs
Target Audience:Agricultural scientists, extension personnel, and producers. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?The projects provided opportunities for graduate student training (Ahmed Attia, Sumit Sharma, Diana Zapata and Yong Chen). How have the results been disseminated to communities of interest?Project results were disseminated through presentations, abstracts, journal articles, and websites. What do you plan to do during the next reporting period to accomplish the goals?Field, remote sensing, and modeling work will be continued in all active projects associated with this hatch project for accomplishing the project goals.
Impacts
What was accomplished under these goals?
Objectives 1 and 2: We are investigating the impact of land use change on energy, water, carbon, and greenhouse gas fluxes associated with changes from conventional, continuous cotton systems to second-generation biofuel feedstocks (biomass sorghum and perennial grasses) in the Southern Cotton Belt region. This project is funded by USDA-NIFA. Data were collected in the 2014-2015 growing seasons from four producer fields planted to irrigated cotton, dryland cotton, biomass sorghum, and Old World bluestem (~350 acres) in the Texas High Plains region. Carbon flux, latent heat flux (evapotranspiration), and sensible heat flux between the vegetation and atmosphere was measured using eddy covariance flux method. Other environmental variables measured included air temperature and relative humidity, net radiation, global irradiance, precipitation, soil temperature, and soil moisture. Plant measurements taken include height, leaf area index, biomass, and yield. Our results indicate significant differences in carbon exchange, evapotranspiration, and energy fluxes of cotton compared to biomass sorghum and Old World blue stem. During the year 2014, the biomass sorghum field gained approximately 672 gC m-2y-1. The next highest carbon uptake was recorded for the Old World Bluestem grass field, which was approximately 301 gC m-2y-1. The dominant land use in the region is cotton. While the forage sorghum and grass fields acted as net carbon sinks, the irrigated cotton field acted as a net carbon source to the atmosphere during the same period. The irrigated cotton field exhibited a net carbon loss of approximately 246 gC m-2y-1. In contrast, the dryland cotton field acted as a net carbon sink, with a total uptake of approximately 58 g C m-2y-1. The net primary production of the irrigated cotton field was higher than that of the dryland cotton field, yet the irrigated field was a significant carbon source to the atmosphere. This was due to conventional tillage practices combined with irrigation which enhanced the ecosystem respiration significantly compared to the dryland field. In 2014, an early spring cold front caused poor germination of seeds in the majority of the cotton fields in the region, including the eddy covariance site. This site was re-planted on 9 June, which shortened the growing season for cotton. This was also a contributing factor to this field being a net carbon source. When only seasonal data were considered (i.e, from planting to harvest), the biomass sorghum field was the largest net C sink (-668 g C m-2y-1) followed by the grassland field (-298 g C m-2y-1). Among the two cotton fields, the irrigated cotton field remained a net carbon source (38 g C m-2y-1), while the dryland field was a net carbon sink (-127 g C m-2y-1). We also assessed hydrological responses of land use change from cotton to cellulosic bioenergy crops using the Soil and Water Assessment Tool (SWAT) model. The Double Mountain Fork Brazos watershed (HUC # 12050004) in the Southern Great Plains was selected for hydrologic response analysis. Various land use scenario analyses involving the dominant land use types (cotton and cellulosic bioenergy crops) revealed that around 94% of the water entering this semi-arid watershed through precipitation and irrigation was lost through evapotranspiration regardless of the land use scenario. We estimated an 8% reduction in surface runoff during the 1994-2009 period if the existing cotton were replaced by perennial grasses for bioenergy production. Over the same period, the sorghum hay scenario was associated with an increase in surface runoff of around 5%. We also estimated an increase in average annual water infiltration of 3 to 7% under perennial grass land use. Thus, reduced runoff and increased infiltration allowed the perennial grassland to maintain better soil moisture conditions. In terms of overall production, an additional 4.2 and 8.8 Mg ha-1of biomass could be produced if cotton were replaced by big bluestem and sorghum hay, respectively. Objective 3: A crop growth simulation model called Cotton2K was used with actual 1980-2010 (31-yrs) weather records for the Texas Rolling Plains to estimate cotton yield, water use efficiency (WUE), and economic returns responses to irrigation. The treatments included a combination of six evapotranspiration (ET) replacement levels (40, 60, 80, 100, 120, and 140% ET) and four irrigation durations (4, 6, 8, and 10 wk) compared with dryland production. The model was initially calibrated and validated using field data from the Texas Rolling Plains and then simulation scenarios were performed. Maximum lint yield of 1838 kg ha-1 was obtained by irrigating at 111% ET for 10 wk while maximum WUE of 2.65 kg ha-1 mm-1 was obtained by irrigating at 85% ET for 8 wk or 96% ET for 10 wk. This maximum lint yield required 530 mm of irrigation and 880 mm of total water. Higher irrigation WUE tended to occur at low irrigation rates applied in 8 or 10 wk periods. Maximum economic returns of $1608 ha-1 was obtained with 516 mm of irrigation water. However, if this amount of water was not available for irrigation, deficit irrigation of 85% ET for 8 wk ( ~ 350 mm) produced 1562 kg lint ha-1 and $1235 ha-1 with improved WUE. Scheduling irrigation by considering cotton water requirements could increase lint yield, WUE, and profit in the semi-arid Texas Rolling Plains.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2015
Citation:
Chen, Y., Ale, S., Rajan, N., Morgan, C. L. S., and Park, J. (2015). Hydrological responses of land use change from upland cotton to cellulosic bioenergy crops in the southern High Plains of Texas, Global Change Biology-Bioenergy, DOI: 10.1111/gcbb.12304.
- Type:
Journal Articles
Status:
Published
Year Published:
2015
Citation:
Attia, A., Rajan, N., Ritchie, G., Cui, S., Ibrahim, A., Hays, D., Xue, Q., and Wilborn, J. (2015). Yield, quality, and spectral reflectance responses of cotton under sub-surface irrigation, Agronomy Journal, 107: 1355-1364.
- Type:
Journal Articles
Status:
Published
Year Published:
2015
Citation:
Rajan, N., Maas, S. J., Kellison, R., Dollar, M., Cui, S., Sharma, S., and Attia, A. (2015). Emitter Uniformity and Application Efficiency for Center-pivot Irrigation Systems, Irrigation and Drainage, 64(3): 353-361.
- Type:
Journal Articles
Status:
Published
Year Published:
2015
Citation:
Modala, R., Ale, S., Rajan, N., Munster, C., DeLaune, P., Thorp, K., Nair, S., and Barnes, E. (2015). Evaluation of the CSM-CROPGRO-Cotton Model for the Texas Rolling Plains Region and Simulation of Deficit Irrigation Strategies for Increasing Water Use Efficiency, Transactions of ASABE, 58(3): 685-696.
- Type:
Book Chapters
Status:
Published
Year Published:
2015
Citation:
Guo, W., Cui, S., Torrion, J., and Rajan, N. 2015. Data-Driven Precision Agriculture: Opportunities and Challenges, Chapter 14 In R. Lal, and B. Stewart (eds.), Soil-Specific Farming: Precision Architecture. CRC Press. London. p. 353-371.
- Type:
Journal Articles
Status:
Published
Year Published:
2015
Citation:
Sharma, B., Ritchie, G. L., and Rajan, N. (2015). Near-Remote Green: Red PVI Ground Cover Fraction Estimation. Crop Science, 55:1-10.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2015
Citation:
Attia, A., Rajan, N., Ritchie, G., Ibrahim, A., Hays, D., and Xue, Q. (2015) Effects of varying irrigation on yield, quality, and spectral reflectance responses of cotton. Beltwide cotton conferences, San Antonio, TX. January, 2015.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2014
Citation:
Sharma, S., Rajan, N., and S. Maas. (2014) Measurement of soil carbon dioxide emission from a cotton cropping system using LI-8100. Abstracts, ASA-CSSA-SSSA Annual Meeting, Long Beach, CA. November, 2014.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2014
Citation:
Rajan, N., Sharma, S., and S. Maas. (2014) Ecosystem-scale carbon fluxes and evapotranspiration of bioenergy crops compared to conventional cotton cropping systems. Abstracts, ASA-CSSA-SSSA Annual Meeting, Long Beach, CA. November, 2014.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2014
Citation:
Attia, A., Rajan, N., Ritchie, G., Barnes, E., Cui, S., Ibrahim, A., Hays, D., and Xue, Q. (2014) Cotton yield, fiber quality, water use efficiency, and spectral reflectance responses to irrigation and tillage management in the Texas Rolling Plains. Abstracts, ASA-CSSA-SSSA Annual Meeting, Long Beach, CA. November, 2014.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2014
Citation:
Attia, A., Rajan, N., Xue, Q., Ibrahim, A., and Hays, D. (2014) Application of CSM-CERES-Wheat model for irrigation management of winter wheat in the Texas High Plains. Abstracts, ASA-CSSA-SSSA Annual Meeting, Long Beach, CA. November, 2014.
- Type:
Theses/Dissertations
Status:
Published
Year Published:
2014
Citation:
Attia, A. 2014. Modeling cotton and winter wheat growth and yield responses to irrigation management in the Texas high Plains and Rolling Plains. PhD dissertation, Texas A&M University, College Station, TX.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2015
Citation:
Modala, R., Ale, S., Rajan, N., Munster, C., DeLaune, P., Thorp, K., Nair, S., and Barnes, E. 2015. Simulating the impacts of future climate variability and change on cotton production in the Texas Rolling Plains. In Proc. of the Beltwide cotton conferences, San Antonio, TX.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2015
Citation:
N. Rajan. (2015) The Cotton 2K plant growth simulation model. Beltwide cotton conferences Precision Group Meeting, San Antonio, TX. January, 2015.
|
Progress 10/01/13 to 09/30/14
Outputs
Target Audience: Agricultural scientists, extension personnel, and producers in the Texas High Plains and Rolling Plains regions. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided? The projects provided opportunities for graduate student training (Ahmed Attia, Sumit Sharma, and Yong Chen). How have the results been disseminated to communities of interest? Project results were disseminated through presentations, abstracts, journal articles, and websites. What do you plan to do during the next reporting period to accomplish the goals? Field, remote sensing, and modeling work will be continued in all active projects associated with this hatch project for accomplishing the project goals.
Impacts
What was accomplished under these goals?
Objectives 1 and 2: We investigated the impact of the 2011 severe drought on summer evapotranspiration (ET) and energy partitioning of a managed Old World bluestem grassland in the Southern Great Plains and compared the results with those from 2010, a hydrologically wet year. Measurements of CO2, latent heat (LE), and sensible heat (H) fluxes were made using an eddy covariance flux tower. In 2010, the total precipitation received during the summer months (June-August) was 82% above the 9-yr average precipitation and in 2011, it was only 8% of the 9-yr average precipitation. The amount of net radiation (Rn) available at the surface was higher in the wet year (54.3% of the incident radiation) compared with the drought year( 41.1% of the incident radiation). In 2010, LE consumed the majority of available energy resulting in a high evaporative fraction (EF). In 2011, less energy was converted to LE as soil moisture remained low, which also resulted in reduced plant growth. Thus, the energy partitioning in 2011 was dominated by H. Significant differences in bulk canopy conductance (Gs) were also observed between the two years. In both years, Gs was linearly correlated with soil volumetric water content in the top 4 cm of the soil profile. The gross primary production (GPP) was linearly correlated to ET. The water use efficiency (WUE) was 2.63 g C Kg-1 of water in 2010 and 0.69 g C Kg-1 of water in 2011. Results from this study showed that, in semi-arid grasslands, the ET and energy balance are strongly affected by water availability. We are investigating the impact of land use change on energy, water, carbon, and greenhouse gas fluxes associated with changes from conventional, continuous cotton systems to second-generation biofuel feedstocks (biomass sorghum and perennial grasses) in the Southern Cotton Belt region. This project is funded by USDA-NIFA. Data were collected in the 2014 growing season from four producer fields planted to irrigated cotton, dryland cotton, biomass sorghum, and Old World bluestem (~350 acres) in the Texas High Plains region. Carbon flux, latent heat flux (evapotranspiration), and sensible heat flux between the vegetation and atmosphere was measured using eddy covariance flux method. Other environmental variables measured included air temperature and relative humidity, net radiation, global irradiance, precipitation, soil temperature, and soil moisture. Plant measurements taken include height, leaf area index, biomass, and yield. Our results indicate significant differences in carbon exchange, evapotranspiration, and energy fluxes of cotton compared to biomass sorghum and Old World blue stem. Surface energy balance closure was approximately 90% in biomass sorghum and perennial grassland sites. In the cotton field, the closure was approximately 100%. In the cotton field, most of the available energy (Rn) was used for evapotranspiration. In the biomass sorghum field, approximately 50 - 80% of available energy was used for evapotranspiration. In the perennial grassland, this ranged between 20-50% depending on the soil moisture conditions. The Bowen ratio, which indicates the partitioning of Rn between LE and H, varied between project sites. High Bowen ratio indicates significant amount of energy being converted to sensible heat. The Bowen ratio was highest in the perennial grass field. The biomass sorghum field had higher Bowen ratio compared to the cotton field. This indicates significant evaporative cooling of the cotton field. Daily net ecosystem carbon exchange (NEE) observed during the growing season of 2014 showed a net carbon dioxide uptake (negative NEE) on most days. As C4 plants, biomass sorghum and perennial grasses such as Old World Bluestem are adapted to surviving the hot, semi-arid climatic conditions of the Southwestern Cotton Belt region. The low C uptake in the grass field was primarily due to lack of irrigation. However, during the peak growing season of the grass, its C uptake was similar to the cotton field. Objective 3: The growth, yield, WUE, and spectral reflectance responses of cotton under different irrigation and tillage treatments was investigated in 2012 and 2013. A split-split plot design with three replications was used with irrigation as the main plot (dryland, 45% evapotranspiration replacement, 90% evapotranspiration replacement, and irrigation based on a remote sensing method developed by researchers in the current study), tillage (conventional and minimum) as the sub plot, and varieties (PHY499, DP1044, PHY375, and FM9170) as the sub-sub plot. Plant height, lint yield, WUE, and fiber quality were significantly affected by irrigation and irrigation-by-variety interaction. Increasing irrigation level resulted in a linear increase in lint yield and WUE. The irrigation-by-variety interaction showed that the 90% evapotranspiration (ET) replacement treatment involving PHY375 produced the greatest lint yield and WUE. Tillage did not significantly affect lint yield, WUE, and fiber quality. Increasing irrigation resulted in a linear increase in fiber length and strength, and a linear decrease in fiber micronaire. Two vegetation indices, Normalized Difference Vegetation Index (NDVI) and Normalized Difference Water Index (NDWI) were calculated using spectral reflectance measurements in this study. During the peak growing season, NDWI performed better compared to NDVI as no saturation problems were observed. We suggest further investigation on using NDWI for irrigation management for cotton in the Texas Rolling Plains. The Cotton2K model was calibrated and validated using data from field studies conducted at the Texas AgriLife Research-Chillicothe Research station on an Abilene clay loam soil (fine, mixed, superactive, thermic Pachic Agriustolls) from 2009 to 2012. Lint yield response to ET-based irrigation using weather data from 1980 to 2010 was simulated using the calibrated model. The ET replacement treatments included in the simulation study were dry land, 40%, 60%, 80%, 100%, 120%, and 140% ET replacements. General cultural practices in the region were applied to the model. The yield response was estimated using a quadratic polynomial regression model. Yield response to irrigation treatments indicated that deficit irrigation below 300 mm significantly reduced the yield. The maximum simulated lint yield was 1277 kg ha-1 with an application of 569 mm of irrigation water.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2014
Citation:
Rajan, N., Puppala, N., Maas, S., Payton, P., and Nuti, R. 2014. Aerial remote sensing of peanut ground cover. Agronomy Journal 106(4):1358-1364.
- Type:
Journal Articles
Status:
Published
Year Published:
2014
Citation:
Rajan, N., and Maas, S. 2014. Spectral crop coefficient for estimating crop water use. Advances in Remote Sensing 106(4):1536-1544.
- Type:
Journal Articles
Status:
Published
Year Published:
2014
Citation:
Thorp, K. R., Ale, S., Bange, M., Barnes, E., Hoogenboom, G., Lascano, R., McCarthy, A., Nair, S., Paz, J., Rajan, N., Reddy, R., Wall, G., and White, J. 2014. Development and Application of Process-based Simulation Models for Cotton Production: A Review of Past, Present, and Future Directions. Journal of Cotton Science 18:10-47.
- Type:
Journal Articles
Status:
Published
Year Published:
2014
Citation:
Cui, S., Rajan, N., Maas, S. J., and Youn, E. 2014. An automated soil line identification method using relevance vector machine. Remote Sensing Letters 5: 205-212.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2014
Citation:
Rajan, N., Sharma, S., and Maas, S. 2014. Ecosystem-scale carbon fluxes and evapotranspiration of bioenergy crops compared to conventional cotton cropping systems. Abstracts, ASA-CSSA-SSSA Annual Meeting, November 2-5, Long Beach, CA.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2014
Citation:
Sharma, S., Rajan, N., and Maas, S. 2014. Measurement of soil carbon dioxide emission from a cotton cropping system using LI-8100. Abstracts, ASA-CSSA-SSSA Annual Meeting, November 2-5, Long Beach, CA.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2014
Citation:
Sharma, S., Rajan, N., and Maas, S. 2014. Ecosystem-scale carbon fluxes and evapotranspiration of bioenergy crops compared to conventional cotton cropping systems. Abstracts, ASA-CSSA-SSSA Annual Meeting, November 2-5, Long Beach, CA.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2014
Citation:
Attia, A., Rajan, N., Ritchie, G., Barnes, E., Cui, S., Ibrahim, A., Hays, D., and Xue, Q. 2014. Cotton yield, fiber quality, water use efficiency, and spectral reflectance responses to irrigation and tillage management in the Texas Rolling Plains. Abstracts, ASA-CSSA-SSSA Annual Meeting, November 2-5, Long Beach, CA.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2014
Citation:
Attia, A., Rajan, N., Xue, Q., Ibrahim, A., and Hays, D. 2014. Application of CSM-CERES-Wheat model for irrigation management of winter wheat in the Texas High Plains. Abstracts, ASA-CSSA-SSSA Annual Meeting, November 2-5, Long Beach, CA.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2014
Citation:
Attia, A., Rajan, N., Ritchie, G., Barnes, E., Cui, S., Ibrahim, A., Hays, D., and Xue, Q. 2014. Deficit irrigation and tillage effects on lint yield and profitability of four cotton cultivars in the Texas Rolling Plains. Beltwide cotton conferences, January 6-8, New Orleans, LA.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2014
Citation:
Sharma, S., Rajan, N., and Maas, S. 2014. Carbon dynamics of biofuel cropping systems compared to conventional cotton cropping systems. Annual Meeting of the Southern Branch of the American Society of Agronomy, February 2-4, Dallas, TX.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2014
Citation:
Sharma, S., Rajan, N., and Maas, S. 2014. Land use change from cotton to biofuel crops: Implications on evapotranspiration and energy fluxes. Annual Meeting of the Southern Branch of the American Society of Agronomy, February 2-4, Dallas, TX.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2014
Citation:
Attia, A., Nair, S., Rajan, N., and Ritchie, G. 2014. Optimization of deficit irrigation using the Cotton2K crop growth simulation model. Beltwide cotton conferences, January 6-8, New Orleans, LA.
- Type:
Other
Status:
Published
Year Published:
2014
Citation:
Rajan, N. 2013. An Integrated Approach to Enhance Water Use and Drought Tolerance in Texas Cotton Production (12-196TX). Final project report submitted to the Texas State Support Committee (Cotton Inc.).
- Type:
Other
Status:
Published
Year Published:
2014
Citation:
Rajan, N. 2013. Improving Cotton2K model performance through variety specific calibration (13-734). Final project report submitted to Cotton Incorporated.
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Progress 01/01/13 to 09/30/13
Outputs
Target Audience: Targeted audience included agricultural scientists, extension personnel, and producers in the Texas High Plains and Rolling Plains regions. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided? The projects provided opportunities for post-doctoral and graduate student training. Post-doctoral research associate Dr. Song Cui has accepted an Assistant Professor position at Middle Tennessee State University in August 2013. The projects also provided opportunities for dissertation research for three Ph.D. graduate students (Ahmed Attia, Sumit Sharma, and Naga Modala). How have the results been disseminated to communities of interest? Project results were disseminated through presentations, abstracts, journal articles, and websites. What do you plan to do during the next reporting period to accomplish the goals? Field, remote sensing, and modeling work will be continued in all active projects associated with this Hatch project for accomplishing the project goals.
Impacts
What was accomplished under these goals?
Objectives 1 and 2: The impact of the 2011 mega-drought on seasonal changes in net CO2 exchange of a WW-B. Dahl Old World bluestem [Bothriochloa bladhii (Retz) S.T. Blake] pasture in the Texas High Plains was investigated. The results were compared with those from 2010, a hydrologically wet year. Our results indicate that net ecosystem exchange, ecosystem respiration, and gross primary production for this agroecosystem were strongly affected by environmental variables and grazing. During the period of measurement in 2010 (Days of the Year 152–365), the pasture accumulated 164 g C m–2 and was a net C sink. During the same period in 2011, the severe drought changed the dynamics of the pasture from a C sink to a source, with a net cumulative loss of 142 g C m–2. Ecosystem respiration was an exponential function of soil temperature in both years. When extreme water-limiting days were excluded, the exponential model explained 90% of the variation in ecosystem respiration in 2011 and 92% of the variation in ecosystem respiration in 2010. Field studies were conducted to study greenhouse gas emissions associated with conventional and minimum tillage soil management conditions and nitrogen fertilizer treatments in winter wheat at the Chillicothe Research Station. Greenhouse gas measurements were made using static chambers along with in-situ soil and water measurements. Results from these studies are currently being analyzed. We are investigating the impact of land use change on energy, water, carbon, and greenhouse gas fluxes associated with changes from conventional, continuous cotton systems to second-generation biofuel feedstocks (biomass sorghum and perennial grasses) in the Southern Cotton Belt region. This project is funded by USDA-NIFA. Eddy covariance and ancillary data were collected in the 2013 growing season from producer fields planted to cotton, biomass sorghum, and Old World bluestem. Eddy covariance flux measurements of carbon dioxide, water and components of the energy balance showed considerable variation among the sites. Other environmental variables measured include air temperature and relative humidity, net radiation, global irradiance, precipitation, soil temperature, and soil moisture. Plant measurements collected include height, leaf area index, biomass, and yield. Concurrent with the field studies, ArcAPEX is being evaluated for the study region. A Ph.D. student (Sumit Sharma) was hired to study land use change implications on evapotranspiration, carbon, and energy fluxes from cotton to biofuel crops. Another Ph.D. student (Yong Chen) was hired to expand the field-based results to the regional scale using spatial interpolation based on remote sensing, along with regional simulations using the geospatial model ArcAPEX. Objective 3: Crop water use (CWU) was estimated from three farmers' fields in the Texas High Plains using the spectral crop coefficient (Ksp) approach. In this approach, CWU was evaluated from standard weather observations from operational weather observing networks and readily available medium-resolution multispectral satellite imagery (Landsat). The results were compared to observed values of CWU obtained from eddy covariance measurements. The average absolute error (AAE) between estimated and observed CWU values was 0.69 mm/day. The AAE for CWU estimates for the combined data from all fields was 0.62 mm/day suggesting that, on average, estimates of CWU produced by the approach should have sub-mm accuracy. These results suggest that the Ksp approach could be effectively used in applications such as operational irrigation scheduling, where its field-specific nature could minimize over-irrigation and support water conservation. Variable rate irrigation according to different irrigation scheduling methods (Tensiometer, 75% ET based on crop coefficient, soil moisture, and SmartField) were demonstrated in a project established in subsurface drip-irrigated cotton field plots at the Chillicothe Research Station near Vernon, TX. The greatest amount of irrigation was applied using the SmartField sensors at 100% ET replacement level in both years (23.40 inches in 2011 and 16.39 inches in 2012). In 2011, similar amounts of irrigation were applied based on the 75% ET and soil moisture-based methods (21 inches), while the least amount of irrigation was applied using tensiometer-based irrigation scheduling (19 inches). In 2012, the amount of irrigation applied based on the 75% ET method was 12.50 inches which was one inch lower than the tensiometer-based application (13.55 inches). The least amount of irrigation was applied using soil moisture-based irrigation scheduling in 2012 (11.60 inches). Some of the differences in performance of soil moisture sensors and tensiometers in 2011 and 2012 might be attributed to the placement of sensors relative to the drip emitters. The Cotton2K model was calibrated and validated using data from field studies conducted at the Texas AgriLife Research-Chillicothe Research station on an Abilene clay loam soil (fine, mixed, superactive, thermic Pachic Agriustolls) from 2009 to 2012. Lint yield response to ET-based irrigation using weather data from 1980 to 2010 was simulated using the calibrated model. The ET replacement treatments included in the simulation study were dry land, 40%, 60%, 80%, 100%, 120%, and 140% ET replacements. General cultural practices in the region were applied to the model. The yield response was estimated using a quadratic polynomial regression model. Yield response to irrigation treatments indicated that deficit irrigation below 300 mm significantly reduced the yield. The maximum simulated lint yield was 1277 kg ha-1 with an application of 569 mm of irrigation water. Participants: Principal Investigator: Nithya Rajan, Assistant Professor, Texas AgriLife Research; Collaborators: Srinivasulu Ale, Paul DeLaune, Soeng Park, Qingwu Xue and Kenneth Casey, Texas AgriLife Research; Stephen Maas, Glen Ritchie, and Dick Auld, Texas Tech University.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2013
Citation:
Rajan, N., S. J. Maas and S. Cui. 2013. Extreme drought effects on carbon dynamics of a semi-arid pasture. Agronomy Journal 105(6):1749-1760.
- Type:
Journal Articles
Status:
Published
Year Published:
2013
Citation:
Snowden, C., G. Ritchie, J. cave, W. Keeling, and N. Rajan. 2013. Multiple irrigation levels affect boll distribution, yield, and fiber micronaire in cotton. Agronomy Journal 105(6):1536-1544.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2013
Citation:
Rajan, N., S. J. Maas and G. Ritchie. Field Evaluation of a remote sensing based irrigation scheduling tool. Abstracts, 2013 Beltwide Cotton Conference, January 7-10, San Antonio, TX.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2013
Citation:
Auld, D., G. Ritchie, C. Trostle, S. Angadi, D. Malinowski, N. Rajan, D. Baltensperger, R. Imel, B. Hendon, L. Davis, and T. Witt. A New Generation of Desert Crops for the Lower Great Plains, USA. 11th Desert Technologies Conference, November 19-22, San Antonio, TX.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2013
Citation:
Park, S., T. Wang, N. Rajan, S. Bevers and S. Amosson. Life cycle analysis on cropping and rangeland systems in the Texas High Plains and Rolling Plains. Abstracts, 2013 SAEA Annual Meeting, February 2-5, Orlando, FL.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2013
Citation:
Modala, N.R., S. Ale, N. Rajan, K. R. Thorp and C. Munster 2013. Studying the effects of climate change on cotton production in the Texas High Plains using the DSSAT-CROPGRO-Cotton model. ASABE Annual Meeting Paper No. 131612145. St. Joseph, MI: ASABE.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2013
Citation:
Rajan, N., S. J. Maas, S. Ale, and K.D. Casey. 2013. Impacts of biofuel induced land use change on energy, water, carbon and greenhouse gas balances of the Southwest U.S. cotton belt region. Abstracts. The Association for the Advancement of Industrial Crops Annual Meeting, September 13-19, Washington D.C.
- Type:
Other
Status:
Published
Year Published:
2013
Citation:
Rajan, N., S. Ale, P. B. DeLaune, Q. Xue, and S. Maas. 2013. Development and evaluation of technologies for improving crop production and formulating decision management tools. Report submitted to the Texas AgriLife Research Cropping Systems Program.
- Type:
Other
Status:
Published
Year Published:
2013
Citation:
Rajan, N., S. Ale, and P. B. DeLaune. 2013. Demonstrating tools for improving on farm irrigation efficiency (TWDB Contract No. 1103581253). Final project report submitted to the Texas Water Development Board. p.91. http://www.twdb.state.tx.us/publications/reports/contracted_reports/doc/1103581253.pdf
- Type:
Websites
Status:
Published
Year Published:
2013
Citation:
Rajan, N. Irrigation scheduling tools. http://people.tamu.edu/~nrajan /IrrigationSchedulingTools.html
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Progress 01/01/12 to 12/31/12
Outputs
OUTPUTS: Objective 1: Field studies were conducted to study GHG emissions associated with conventional and minimum tillage soil management conditions and nitrogen fertilizer treatments in wheat and grain sorghum cropping systems at the Chillicothe Research Station. Greenhouse gas measurements were made using static chambers along with in-situ soil and water measurements. Results from these studies were presented at producer and scientific meetings. Objective 2: A project was initiated to study the impact of land use change on energy, water, carbon and GHG fluxes associated with changes from a conventional, continuous cotton system to second-generation biofuel feedstocks (biomass sorghum and perennial grasses). Eddy covariance flux towers are currently being installed in six selected producer sites in the Texas High Plains and Rolling Plains regions. A Ph.D. student (Zach Langford) was hired to expand the field-based results to the regional scale using spatial interpolation based on remote sensing, along with regional simulations using the geospatial model ArcAPEX. Objective 3: Field studies were conducted to determine the effect of irrigation on cotton yield and quality. Irrigation treatments included crop water demands estimated using the standard crop coefficient approach and remote sensing-based spectral crop coefficient approach. One of these studies also evaluated two additional treatments, tillage (conventional and minimal tillage) and cultivars (PHY499, DP1044, PHY375, FM9170). Field-based remote sensing data were collected to assess LAI using spectral vegetation indices such as the normalized difference vegetation index (NDVI) and perpendicular vegetation index (PVI). Results from these studies were presented at producer and scientific meetings. PARTICIPANTS: Principal Investigator: Nithya Rajan, Assistant Professor, Texas AgriLife Research; Post-doctoral Research Associate: Song Cui. Graduate students: Zach Langford and Ahmed Attia. Collaborators: Srinivasulu Ale, Paul DeLaune, Soeng Park, Qingwu Xue and Kenneth Casey, Texas AgriLife Research; Stephen Maas, Francisco Padilla and Glen Ritchie, Texas Tech University. TARGET AUDIENCES: Agricultural scientists; Producers in the Texas High Plains and Rolling Plains regions. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
(1) Irrigation and rain events triggered higher emissions of greenhouse gases (CO2 and N2O). Conventional tillage and N fertilizer applications also increased greenhouse gas emissions. Very low to negligible methane fluxes were observed from all treatment plots. (2) No significant differences in cotton yields were observed due to conventional and minimum tillage practices. Irrigation scheduling at 90% evapotranspiration level using the conventional crop coefficient method and irrigation based on the spectral crop coefficient method has resulted in similar application of irrigation water amounts and no significant differences in cotton yield were observed. The spectral crop coefficient-based irrigation scheduling program is currently available as an executable program that can be installed on a computer. Producers can use this program for estimating irrigation water demand using the spectral crop coefficient method. Based on the yield results, all cotton varieties (PHY499, DP1044, PHY375, FM9170) tested in the Texas Rolling Plains could be considered acceptable cultivars for the climatic conditions of this region. (3) Soil background brightness significantly affected NDVI-based estimation of cotton LAI when the ground cover was less than 50%. Cotton LAI estimation using PVI was minimally affected by soil background brightness conditions.
Publications
- Rajan, N., Roy, M., Maas, S. J. and Padilla, F.M. 2012. Soil Background Effects On Reflectance-Based Estimates of Leaf Area Index of Cotton. Abstracts, Annual Meetings, Amer. Soc. Agronomy. October 21 - 24, Cincinnati, OH.
- Roy, M., Rajan, N., Casey, K.D., Padilla, F.M. and Sharma, P. 2012. Greenhouse Gas Emissions From Cotton and Grain Sorghum Cropping Systems Under Different Nitrogen and Tillage Treatments. Abstracts, Annual Meetings, Amer. Soc. Agronomy. October 21 - 24, Cincinnati, OH.
- Rajan, N and Maas, S. J. 2012. Inter-Annual Variation In Carbon Dioxide and Water Fluxes From a Grazed Pasture In the Semi-Arid Texas High Plains. Abstracts, Annual Meetings, Amer. Soc. Agronomy. October 21 - 24, Cincinnati, OH (Invited).
- Roy, M and Rajan, N. 2012. Leaf Area Index Mapping of Cotton Using Remote Sensing Data. Abstracts, ASABE, July 28-August 1, Dallas, TX
- Rajan, N. 2012. Potential of precision agriculture in the Texas High Plains. Third International Symposium on Precision Aerial Application. College Station, TX, USA, August 1-3, 2012 (Invited).
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Progress 01/01/11 to 12/31/11
Outputs
OUTPUTS: Objective 1: The greenhouse gas emissions (carbon dioxide and nitrous oxide) associated with conventional and slow-release nitrogen fertilizer applications in wheat under conventional and no-tillage soil management conditions are currently being assessed in a study at the Chillicothe Research Station. A post-doctoral research associate (Mimi Roy) has been hired to perform research activities in this project. Objective 2: Sustainable production practices are currently being evaluated through various studies initiated in 2011. Objective 3: (a) A study has been established at the Chillicothe Research Station for demonstrating irrigation scheduling methods for cotton. Amounts of irrigation applied were varied based on irrigation scheduling method. Plant height, leaf area index, biomass, spectral reflectance, yield, and lint quality were measured and recorded. This study will be continued in 2012. (b) Crop water demands were calculated for corn based on the standard crop coefficient and remotely sensed spectral coefficient methods. Seasonal crop water demands estimated using the remotely sensed spectral crop coefficient method for corn was about 30% lower than the seasonal crop water demands estimated using the standard crop coefficient method. PARTICIPANTS: Principal Investigator: Nithya Rajan, Assistant professor, Texas AgriLife Research; Collaborators: Srinivasulu Ale, Paul DeLaune, Soeng Park, and Kenneth Casey, Texas AgriLife Research; Stephen Maas, Texas Tech University TARGET AUDIENCES: Agricultural scientists; Producers in the Texas High Plains and Rolling Plains regions. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Demonstration and evaluation of irrigation scheduling methods provide producers in the Texas High Plains and Rolling Plains with knowledge and familiarity in the use of these methods for irrigating their crops. Irrigation based on a scheduling strategy could conserve water compared to the use of no objective method.
Publications
- Rajan, N., Ale, S. and DeLaune, P.B. 2011. On-farm evaluation of irrigation management options for cotton in the Texas Rolling Plains. Abstracts, Annual Meetings, Amer. Soc. Agronomy. October 16 - 19, San Antonio, TX.
- Maas, S. J. and Rajan, N. 2011. Satellite-based irrigation scheduling. Abstracts, Annual Meetings, Amer. Soc. Agronomy. October 16 - 19, San Antonio, TX.
- Rajan, N. and Maas, S. J. 2011. Comparison of carbon, water and energy fluxes between grassland and agricultural ecosystems. Abstracts, Annual Meetings, Amer. Soc. Agronomy. October 16 - 19, San Antonio, TX.
- Maas, S. J. and Rajan, N. 2011. Determining crop water use in the Texas Alliance for Water Conservation Demonstration Project. UCOWR/NIWR Annual Conference, July 11-14, Boulder, CO.
- Maas, S. J. and Rajan, N. 2011. 2011. Seasonal ground cover for crops in the Texas High Plains. 108th Annual Meeting of the Southern Association of Agricultural Scientists, February 6-8, Corpus Christi, TX.
- Ale, S., Chaudhuri, S., DeLaune, P. B., Rajan, N. and Gowda, P. H. 2011. Evaluation of strategies to improve ground water quality in the Texas Rolling Plains using APEX model. Abstracts, American Geophysical Union Fall Meeting, December 5-9, San Francisco, CA.
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