Charles A Sanchez

Interests

Teaching

Soil Fertility

Research

Develop and conduct an applied research program to solve problems of commercial growers in the low desert region of the southwestern United States. Also develop and conduct extension support program to complement research program. Research may include plant nutrient utilization, soil and water management, salinity, and fate and transport of agriculturally derived chemicals and environmental toxins. This program should complement other research activities at the University and also be responsive to the needs of commodity groups, associated governmental agencies, and commercial and industrial interests. Cooperative research and outreach programs should be coordinated with research and extension faculty throughout Arizona and the lower Colorado River area including California’s Imperial and Coachella Valleys.

Courses

Scholarly Contributions

Chapters

• Zerihun, D., & Sanchez, C. (2012). Using mathematical models to improve the performance of surface irrigation systems. In Handbook of Environmental Fluid Mechanics. Taylor and Francis Group.
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  Editor(s): Fernando, FJ

Journals/Publications

• Sanchez, C. A., Dhungel, R., Andersen, R., French, A., Saber, M., Skaggs, T. R., & Scudiero, E. (2023).

  Early season irrigation detection and evapotranspiration modeling of winter vegetables based on Planet satellite using water and energy balance algorithm in lower Colorado basin. Irrig. Sci. https://doi.org/10.1007/s00271-023-00874-7

  . Irrigation Science.
• Sanchez, C. A., French, A., Wirth, T., Scott, A., Shields, J. W., Sabor, M., Gohardoust, M. R., & Bautista, E. (2023).

  Remote sensing of evapotranspiration for irrigated crops at Yuma, Arizona, USA.  Agric. Water Management. (http/doi.org1-:1-16/j.agwat.2023.108582).

  . Agriculture Water Management.
• Sanchez, C. A., Zerihun, D., & French, A. N. (2023). Derivation of the Penman-Monteith equation with the thermodynamic approach, I. A review and theoretical development. J. Irrig. Drain Eng. 149 (5); https://doi.org/10.1061/JIDEDH.IRENG-9887.. Irrig. Drainage Engineering.
• Sanchez, C. A., Zerihun, D., & French, A. N. (2023). Derivation of the Penman-Monteith equation with the thermodynamic approach, II. Numerical solutions and evaluation.J. Irrig. Drain Eng. 149 (5). https://doi.org/10.1061/JIDEDH.IRENG-9888.
  . Irrig. Drainge Engineering..
• Sanchez, C. A., Zerihun, D., Williams, C., & Rock, C. (2023).

  Modeling solute transport in sprinkler irrigation laterals. J. Irrig. Drain Eng. 150: https://doi.org/10.1061/JIDEDH.IRENG-10176

  . ASCE Irrigation and Drainage.
• Sanchez, C. A., & Zerihun, D. (2022). Software for Hydraulic Analysis of Linear-Move and Center-Pivot Irrigation Systems: LincSys, I. User Interface and Computational Module.. Irrig. Drain. Sys. Eng., 11(3).
• Sanchez, C. A., & Zerihun, D. (2022). Software for Hydraulic Analysis of Linear-move and Center Pivot Irrigation Systems: LincSys, II. Application Examples and Model Evaluation  . Irrig. Drain. Sys. Eng, 11(3).
• Sanchez, C. A., Dhungel, R., Anderson, R. G., French, A. N., Saber, M., & Scudiero, E. (2022). Assessing evaporation in lettuce crops with a two-source energy balance model.  . Irrigation Science. doi:https://doi.org/10.1007/s00271-022-00814-x
• Sanchez, C. A., Dhungel, R., French, A. N., Anderson, R. G., Skaggs, T. H., Saber, M., & Scudiero, E. (2022). Remote sensing-based energy balance for lettuce in an arid environment: influence of management scenarios on irrigation and evapotranspiration modeling
  . Irrigation Science.
• Sanchez, C. A., Zhu, X., Yang, T., Hamilton, J. M., & Fonseca, J. M. (2022). Nutrition by Design: Boosting selenium content and fresh matter yields of salad greens with pre-harvest light intensity and selenium applications. Frontiers in Nutrition, 5. doi:https://doi.org/10.3389/fnut.2021.787085
• Sanchez, C. A., Kazemi, H., Sadraddini, A. A., & Nazemi, A. H. (2021). Moment Analysis for Modeling Soil Water Distribution in Furrow Irrigation: Variable vs. Constant Ponding Depths. Water, 13(10), 1415.
• Sanchez, C. A., Fonseca, J. M., Nolte, K. D., Ravishankar, S., & Park, E. (2020). Assessing the Food Safety Risk Posed by Birds Entering Leafy Greens Fields in the US Southwest.. Int J Environ Res Public Health, 17(23).
• Sanchez, C. A., French, A. N., Hunsaker, D. J., Anderson, R., Sabor, M., & Gonzalez, J. (2020). Satellite-based NDVI crop coefficients and evapotranspiration with eddy covariance validation for multiple durum wheat fields in the US Southwest.. Agriculture Water Management., 239. doi:https://doi.org/10.1016/j.agwat.2020.106266
• Sanchez, C. A., & Zerihun, D. (2019). Hydraulics of Linear-Move Sprinkler Irrigation Systems, II: Model Development. Irrigation Drainage System Engineering, Volume 8: 236..
• Sanchez, C. A., & Zerihun, D. (2019). Hydraulics of Linear-move Sprinkler Irrigation Systems, I. System Description, Assumptions, and Definition of the Hydraulic Simulation Problem. Irrigation Drainage System Engineering, Volume 8 • Issue 2 • 1000235.
• Sanchez, C. A., & Zerihun, D. (2019). Pressure Head Profile of Linear-Move Sprinkler Irrigation Laterals: Analysis, Equation and Profile Patterns. Irrigation Drainage System Engineering, Volume 8 • Issue 3 • 1000239.
• Sanchez, C. A., Zerihun, D., Thorp, K. R., & Hagler, M. J. (2019). Hydraulics of Linear-Move Sprinkler Irrigation Systems, III: Model Evaluation. Irrigation Drainage System Engineering, Volume 8 • Issue 2 • 1000237.
• Frisvold, G. B., Sanchez, C. A., Gollehon, N., Megdal, S. B., & Brown, P. W. (2018). Evaluating Gravity-Flow Irrigation with Lessons from Yuma, Arizona. Sustainability, 10(5), 27. doi:https://doi.org/10.3390/su10051548
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  Frisvold, G., Sanchez, C., Gollehon, N., Megdal, S.B., and Brown, P., (2018) Evaluating Gravity-Flow Irrigation with Lessons from Yuma, Arizona, Sustainability 10(5), 1548; https://doi.org/10.3390/su10051548
• Sanchez, C. A., Zerihun, D., & Bautista, E. (2018). Slope Effects on the Pressure Head Profile Patterns of Sprinkler Irrigation Laterals, I. Theoretical Analysis.. Irrigat Drainage Sys Eng, 7(3), 14. doi:doi: 10.4172/2168-9768.1000
• Sanchez, C. A., Zerihun, D., & Bautista, E. (2018). Slope Effects on the Pressure Head Profile Patterns of Sprinkler Irrigation Laterals, II. Evaluation Based on Simulation.. Irrigat Drainage Sys Eng, 7(3), 13. doi:doi: 10.4172/2168-9768.1000222
• Sanchez, C. A., & Zerihun, D. (2017). Irrigation lateral hydraulics with the gradient method. Journal of Irrigation and Drainage Engineering, J. Irrig. Drain. Eng., 10.1061/(ASCE)IR.1943-4774.0001195, 04017023..
• Sanchez, C. A., Zerihun, D., Subramani, J., Badaruddin, M., & Bronson, K. (2017). Fertigation uniformity under sprinkler irrigation: evaluation and analysis. Irrigation and Drainage Engineering systems, Irrig Drain Sys Eng. 10.4172/2168-9768.1000177..
• Sanchez, C. A., Zerihun, D., & Warrick, A. W. (2016). Sprinkler Irrigation Droplet Dynamcis. I. Review and Theoretical Development. J. Irrigation and Drainage Engineering (ACCE), 16. doi:10.1061/(ASCE)IR.1943-4774.0001003
• Sanchez, C. A., Zerihun, D., & Warrick, A. W. (2016). Sprinkler Irrigation Droplet Dynamics. II. Numerical Solution and Model Evaluation. J. Irrigation and Drainage Engineering (ASCE), 18.
• Sanchez, C. A., Zerihun, D., & Warrick, A. W. (2016). Sprinkler Irrigation Droplet Dynamics. I:Review and Theoretical Development. J. Irrig. Drain Eng.. doi:10.1061/(ASCE)IR.1943-4774.0001003
• Sanchez, C. A., Zerihun, D., & Warrick, A. W. (2016). Sprinkler Irrigation Droplet Dynamics. II: Numerical Solution and Model Evaluation. J. Irrig. Drain Eng.. doi:10.1061/(ASCE)IR.1943-4774.0001004
• Sanchez, C. A., Zerihun, D., Lazarovitch, N., Warrick, A. W., Clemmons, A. J., & Bautista, E. (2014). Modelling Flow and Solute Transport in Irrigation Furrows. Irrigation and Drainage System Engineering, 3.
• Zerihun, D., & Sanchez, C. A. (2014). A field-scale sprinkler irrigation system hydraulic model, II: hydraulic simulation. Journal of Irrigation and Drainage Engineering, 140(7).
• Zerihun, D., Sanchez, C. A., & Nolte, K. (2014). A field-scale sprinkler irrigation system hydraulic model, I: Hydraulic characterization.. Journal of Irrigation and Drainage Engineering, 140(7).
• Sanchez, C. A., Valencia, J., Lares-Sanchez, J., Marsh, E., Dorneles, L., Santos, M., Sanchez, D., Winter, A., Murphy, S., Cox, J., Trzaska, M., Metler, J., Kozic, A., Facanha, A., Schachtman, D., Sanchez, ., & Gaxiola, R. (2013). Enhanced H+-PPase Activity Improves Nitrogen Use Efficiency in Romaine Lettuce. Plant Physiology, 161, 1557–1569.
• Gaxiola, R., Sanchez, C., Paez-Valencia, J., Ayre, B., & Elser, J. (2012). Genetic manipulation of a vacuolar H+-PPase: from salt tolerance to yield enhancement under phosphorus-deficient soils. Plant Physiology, 159, 3-11.
• Jones-Lepp, T. L., Sanchez, C., Alvarez, D. A., Wilson, D. C., & Taniguchi-Fu, R. (2012). Point sources of emerging contaminants along the Colorado River Basin: Source water for the arid Southwestern United States. Science of the Total Environment, 430, 237-245.
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  PMID: 22684090;Abstract: Emerging contaminants (ECs) (e.g., pharmaceuticals, illicit drugs, personal care products) have been detected in waters across the United States. The objective of this study was to evaluate point sources of ECs along the Colorado River, from the headwaters in Colorado to the Gulf of California. At selected locations in the Colorado River Basin (sites in Colorado, Utah, Nevada, Arizona, and California), waste stream tributaries and receiving surface waters were sampled using either grab sampling or polar organic chemical integrative samplers (POCIS). The grab samples were extracted using solid-phase cartridge extraction (SPE), and the POCIS sorbents were transferred into empty SPEs and eluted with methanol. All extracts were prepared for, and analyzed by, liquid chromatography-electrospray-ion trap mass spectrometry (LC-ESI-ITMS). Log D OW values were calculated for all ECs in the study and compared to the empirical data collected. POCIS extracts were screened for the presence of estrogenic chemicals using the yeast estrogen screen (YES) assay. Extracts from the 2008 POCIS deployment in the Las Vegas Wash showed the second highest estrogenicity response. In the grab samples, azithromycin (an antibiotic) was detected in all but one urban waste stream, with concentrations ranging from 30ng/L to 2800ng/L. Concentration levels of azithromycin, methamphetamine and pseudoephedrine showed temporal variation from the Tucson WWTP. Those ECs that were detected in the main surface water channels (those that are diverted for urban use and irrigation along the Colorado River) were in the region of the limit-of-detection (e.g., 10ng/L), but most were below detection limits. © 2012.
• Fonseca, J. M., Fallon, S. D., Sanchez, C. A., & Nolte, K. D. (2011). Escherichia coli survival in lettuce fields following its introduction through different irrigation systems. Journal of Applied Microbiology, 110(4), 893-902.
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  Abstract: Aims: This study aimed to assess the contamination risk of Escherichia coli in commercial lettuce grown under three different irrigation systems (overhead sprinkler, subsurface drip and surface furrow). Methods and Results: Three replicated field trials were conducted. In an initial trial, we consistently observed higher mesophilic bacteria counts under sprinkler irrigation but visual quality was found to be dependent on the water potential of leaves at harvest. Further, in the other two trials, E. coli K-12 strains LMM1010 and ATCC 25253, was injected into the water stream of the different irrigation systems to determine survival in the field. Results showed that product samples were positive for E. coli up to 7days when using sprinkler irrigation, whereas only one product sample was found positive for E. coli when using other irrigation methods. Survival of bacteria in soil persisted longer in furrow-irrigated areas, ranging from an estimated 17days in winter months to 5days during the warmer summer periods. This finding combined with results from a parallel 3-year survey of canal waters indicate that while highest risk of finding E. coli in irrigation water is in warmer months, the survival in soil is lower during the same time period. Conclusions: Our results in a study set under common commercial conditions confirmed the enhanced risk of E. coli contamination when using sprinkle irrigation. Furthermore, E. coli persistence in furrow-irrigated soil validates the importance of an early irrigation termination for both sprinkler and furrow methods. Significance and Impact of the Study: Stringent monitoring and in-field food safety controls should be emphasized during the last few days before harvest. © 2011 The Authors. Journal of Applied Microbiology © 2011 The Society for Applied Microbiology.
• Jones-Lepp, T. L., Sanchez, C. A., Moy, T., & Kazemi, R. (2010). Method development and application to determine potential plant uptake of antibiotics and other drugs in irrigated crop production systems. Journal of Agricultural and Food Chemistry, 58(22), 11568-11573.
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  PMID: 20964347;Abstract: Studies have shown the detection of emerging contaminants (ECs), of which pharmaceuticals are a subset, in surface waters across the United States. The objective of this study was to develop methods, and apply them, to evaluate the potential for food chain transfer when EC-containing waters are used for crop irrigation. Greenhouse experiments were performed in which select food crops were irrigated with water spiked with three antibiotics. Field experiments, at two different sites, were conducted. Select crops were irrigated with wastewater effluent known to contain ECs, EC-free well water, and Colorado River water containing trace-level ECs. The results of the greenhouse studies show the potential for uptake of one or more of the antibiotics evaluated, albeit at very low levels. In those food crops watered with wastewater effluent, only an industrial flavoring agent, N,N'-dimethylphenethylamine (DMPEA), was consistently found. None of the evaluated contaminants were found in crops irrigated with Colorado River water. © 2010 American Chemical Society.
• Sanchez, C. A., Barraj, L. M., Blount, B. C., Scrafford, C. G., Valentin-Blasini, L., Smith, K. M., & Krieger, R. I. (2009). Perchlorate exposure from food crops produced in the lower Colorado River region. Journal of Exposure Science and Environmental Epidemiology, 19(4), 359-368.
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  PMID: 18506207;Abstract: The Colorado River shows low levels of perchlorate derived from aerospace- and defense-related fuel industries once located near the Las Vegas Wash. At sufficiently high dosages perchlorate can disrupt thyroid function by inhibiting uptake of iodide. The Colorado River is the primary source of irrigation water for most food crops grown in Southern California and Southwestern Arizona. The objective of this study was to evaluate potential perchlorate exposure from food crops produced in the lower Colorado River region (LCRR). The major food commodities produced in the region were sampled and perchlorate levels were determined by ion chromatography followed by detection using either conductivity or tandem mass spectrometry, depending on analyte levels. The Monte Carlo module of the Dietary Exposure Evaluation Model (DEEM) was used to derive an estimate of the 2-day average perchlorate intakes. Data were derived assuming that individuals residing in the LCRR get their fruits and vegetables from within the LCRR as well as from other areas in the United States, or assuming individuals living in the LCRR get their fruits and vegetables from the LCRR only. Perchlorate exposure estimates derived in this study are comparable to exploratory estimates by the US Food and Drug Administration. For infants and children, over 50% of the estimated perchlorate exposure was from milk. The relative impact of vegetables and fruit toward perchlorate exposure increased by age through adulthood. Cumulative perchlorate exposure estimates based on this hypothetical analysis could approach or exceed the NAS reference dose (RfD) for some population groups as drinking water levels exceeded 6 g/l. However, few individuals are exposed to perchlorate in drinking water at levels above 4 g/l in the United States and very few would be exposed to perchlorate levels exceeding the RfD, whether consuming food crops from within or outside the LCRR. © 2009 Nature Publishing Group.
• Sanchez, C. A., Fonseca, J. M., Blount, B. C., & Krieger, R. I. (2009). Hypochlorite treatments are not a significant source of perchlorate Exposure in lettuce. Journal of Agricultural and Food Chemistry, 57(6), 2320-2323.
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  PMID: 19245207;Abstract: Leafy vegetables, such as lettuce (Lactuca sativa L), have been identified as a potential source of perchlorate exposure to humans. Perchlorate is of concern because excessive amounts may impair thyroid function by inhibiting iodide uptake by the sodium iodide symporter. Perchlorate has been identified as an oxidation product in sodium hypochlorite. Dilute hypochlorite solutions are widely used on lettuce as a preservative and as a treatment to reduce microbial food risks. However, the potential of hypochlorite to be a source of human perchlorate exposure from lettuce had not been evaluated. Studies were conducted with lettuce collected in the San Luis Valley of southern Colorado and in the lower Colorado River Valley of southwestern Arizona to represent conditions under which hypochlorite is applied to lettuce in the field and in salad processing facilities. We used spray and dipping solutions that were dilutions of concentrated sodium hypochlorite that would contain from 12000 and 120000 μg/L perchlorate. The perchlorate content of iceberg and romaine lettuce averaged 6.2 and 7.2 μg/kg fw in southern Colorado and 14.0 and 56.7 μg/kg fw in southwestern Arizona and there were no significant (P > 0.05) increases in the perchlorate content of lettuce due to hypochlorite treatments. Because of the relatively low concentrations of perchlorate present after dilution and the low volumes applied to lettuce, hypochlorite solutions do not appear to be a significant source of the perchlorate levels found in lettuce. © 2009 American Chemical Society.
• Sanchez, C. A., Zerihun, D., & Farrell-Poe, K. (2009). Management guidelines for efficient irrigation of vegetables using closed-end level furrows. Agricultural Water Management, 96(1), 43-52.
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  Abstract: Closed-end level furrows are commonly used to irrigate vegetables in the Lower Colorado River region (LCRR). The application efficiency of furrow irrigation in this area is often low. The objective of this study is to develop management tools and guidelines for the efficient irrigation of vegetables using closed-end level furrows. The study consisted of field experiment and modeling (model calibration, model verification, and the development of management tools by simulation). Field experiments were performed over a period of 27 months. Infiltration parameters were estimated for four soil textural groups (i.e., moderately coarse textured, medium textured, moderately fine textured, and fine textured soils) using a two-point method modified for closed-end level furrows. Model verification shows that the surface irrigation hydraulic model used in this study (SRFR) is capable of simulating the furrow irrigation process with acceptable levels of accuracy. Results of the study also indicate that adequate and efficient irrigations can be achieved using closed-end level furrows through the proper selection of unit inlet flow rate, Qo, and cutoff time, tco. However, given the soil and crop combinations in the LCRR, sometimes significant increases in irrigation efficiency, compared to present levels, can be attained only if furrow lengths are shorter than the typical size currently in use in the LCRR. Limitations of the proposed management tools and on-going research to address these limitations are briefly discussed. © 2008 Elsevier B.V. All rights reserved.
• Niblack, M., & Sanchez, C. A. (2008). Automation of surface irrigation by cut-off time or cut-off distance control. Applied Engineering in Agriculture, 24(5), 611-614.
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  Abstract: An automated surface irrigation system is described that demonstrates control by either cut-off time or cut-off distance using off-the-shelf commercial products. The cut-off time control uses a standard commercial sprinkler controller to operate the gates. The cut-off distance system uses commercial radio transmitters and transceiver-relays commonly used to operate security systems or industrial processes. These systems were each installed in four irrigation basins in a 7-ha surface irrigation research facility. Over 15 irrigation events have been performed satisfactorily with minimal maintenance. While the immediate impetus for automation is likely to be the growing labor shortage, it is anticipated that water conservation benefits will be realized as well. Future research and development needs include logic control based upon variations in flow rate and soil intake rate. © 2008 American Society of Agricultural and Biological Engineers.
• Sanchez, C. A., Blount, B. C., Valentin-Blasini, L., Lesch, S. M., & Krieger, R. I. (2008). Perchlorate in the feed-dairy continuum of the Southwestern United States. Journal of Agricultural and Food Chemistry, 56(13), 5443-5450.
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  PMID: 18553887;Abstract: Perchlorate has the potential to cause thyroid dysfunction by inhibiting iodide uptake by the sodium iodide symporter. Perchlorate-contaminated waters may lead to human exposure through drinking water and food chain transfer in crops by way of irrigation water. Perchlorate has been found in dairy milk collected nationally and internationally. This study was conducted to evaluate perchlorate in the feed-dairy continuum in the southwestern United States. All feed products collected at dairies in this study had detectable levels of perchlorate as analyzed by ion chromatography-tandem mass spectrometry. The calculated total perchlorate intake across dairies ranged from 1.9 to 12.7 mg/cow per day. The variation in total perchlorate intake across dairies was largely associated with variation in forage and silage products. Alfalfa products were the single most important source of perchlorate intake variability among dairies. The estimated perchlorate intake from drinking water ranged from 0.01 mg per cow per day and was generally less than 2% of the total perchlorate intake. The perchlorate content of milk ranged from 0.9 to 10.3 μg/L and was similar to levels reported by the Food and Drug Administration's Total Diet Study. The perchlorate content of milk was significantly related to the presence of perchlorate in feed but the variation of perchlorate in milk could not be explained by feed intake alone. © 2008 American Chemical Society.
• Sanchez, C. A., Zerihun, D., Strelkoff, T. S., Clemmens, A. J., & Farrell-Poe, K. L. (2008). Development of management guidelines for efficient irrigation of basins on sandy soils. Applied Engineering in Agriculture, 24(2), 215-224.
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  Abstract: Level and graded-basins are widely used to irrigate citrus (Citrus sp.) and alfalfa (Medicago sativa L.) crops grown on sandy soils of the Yuma Mesa Irrigation and Draniange Districts (YMIDDs) of southwestern Arizona. Historically, irrigation application efficiencies in the YMIDDs have been low (generally
• Zerihun, D., Bautista, E., Strelkoff, T. S., Sanchez, C. A., Clemmens, A. J., & Niblack, M. (2008). Evaluation of basin inflow cutoff criterion in the irrigation districts of southwest Arizona. World Environmental and Water Resources Congress 2008: Ahupua'a - Proceedings of the World Environmental and Water Resources Congress 2008, 316.
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  Abstract: Low irrigation efficiencies persist in irrigated areas near Yuma, Arizona due to poorly designed irrigation systems, poor condition of existing systems, inaccurate delivery of flow rates, and inadequate criteria for determining irrigation cutoff to individual basins. In farms where growers lack adequate control over the water supplied to individual basins, conventional irrigation cutoff criteria, based on precise measurement of inflow rates, are ineffective. A joint research project, involving the USDA-ARS-ALARC, University of Arizona, and the USBR, is exploring the management of these systems using the time of advance to half the field length as a criterion for cutoff when inflow rates are not know accurately. Preliminary simulation studies have shown the potential benefits and limitations of such a strategy. This strategy is being tested in the field, to assess its sensitivity to uncertain system properties. This article describes the general research methodology and some of the initial simulation and field results. © 2008 ASCE.
• Zerihun, D., Furman, A., Sanchez, C. A., & Warrick, W. A. (2008). Development of simplified solutions for modeling recession in basins. Journal of Irrigation and Drainage Engineering, 134(3), 327-340.
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  Abstract: In irrigation basins the decrease in the gradient of the water-surface elevation following inflow cutoff often leads to reduced rate of convergence, increased computational time, and reduced robustness of the numerical solutions of the recession phase. As the water surface levels off, the underlying physical problem simplifies, thus allowing the use of highly accurate yet simple alternate solutions to the full-numerical solution of the zero-inertia equations. For level basins, the simplification involves treating the stream as a static pool, in which water level only falls in response to infiltration. Graded basins may require partitioning the stream into a flowing and static pool, before water-surface eventually levels off over the entire stream length. Implementation of these solutions enhances computational efficiency and robustness of surface irrigation models without a concomitant loss of accuracy. This paper discusses numerical problems related to the recession phase computation in basins and proposes simplified and robust, yet highly accurate solutions. A comparison of the recession trajectories and final infiltration profiles predicted by the full-numerical solution of the zero-inertia equations, obtained by using double-precision floating-point arithmetic, and the simplified alternate solutions, which is robust enough to be implemented over a range of hardware-software capabilities, show that the two approaches yield essentially identical results. Finally, the general validity of the proposed solutions is tested by comparing predictions of recession trajectories and infiltration profiles with those obtained using a surface irrigation hydraulic model, SRFR. © 2008 ASCE.
• Sanchez, C. A., Blount, B. C., Valentin-Blasini, L., & Krieger, R. I. (2007). Perchlorate, thiocyanate, and nitrate in edible cole crops (Brassica sp.) produced in the lower Colorado River region. Bulletin of Environmental Contamination and Toxicology, 79(6), 655-659.
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  PMID: 17962898;Abstract: The Colorado River is contaminated with low levels of perchlorate. Perchlorate has the potential to disrupt thyroid function by inhibiting the uptake of iodide. Brassica are rich sources of thiocyanate and nitrate, also inhibitors of iodide uptake. This study was conducted to estimate potential human exposure to perchlorate, thiocyanate, and nitrate from Brassica sp. irrigated with Colorado River water. Results indicate that Brassica sp. irrigated with Colorado River water do accumulate trace levels of perchlorate. However, the levels of perchlorate observed are low relative to the nitrate and thiocyanate naturally present in these species and low relative to the reference dose recommended by the NAS and the USEPA. © 2007 Springer Science+Business Media, LLC.
• Furman, A., Warrick, A. W., Zerihun, D., & Sanchez, C. A. (2006). Modified kostiakov infiltration function: Accounting for initial and boundary conditions. Journal of Irrigation and Drainage Engineering, 132(6), 587-596.
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  Abstract: The effect of specific initial and boundary conditions is generally not considered when applying the Kostiakov infiltration functions. A methodology is developed to account for changes in water levels and initial soil moisture. First, Richards' equation is solved numerically to generate a database of one-dimensional infiltration values, with varying initial (water content or pressure head) and boundary (ponding depth) conditions for three contrasting soils. These are then used to calibrate corresponding coefficients for modified Kostiakov models and, by considering linear regressions, to obtain simple correction factors. Results show that the correction factors are not universally valid, and only the correction to the Kostiakov k parameter shows statistically consistent applicability. However, examples demonstrate potentially significant improvement in the accuracy of irrigation models by correcting the Kostiakov equation to account for initial and boundary conditions. © 2006 ASCE.
• Sanchez, C. A., Krieger, R. I., Khandaker, N. R., Valentin-Blasini, L., & Blount, B. C. (2006). Potential perchlorate exposure from Citrus sp. irrigated with contaminated water. Analytica Chimica Acta, 567(1 SPEC. ISS.), 33-38.
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  PMID: 17723376;Abstract: Citrus produced in the southwestern United States is often irrigated with perchlorate-contaminated water. This irrigation water includes Colorado River water which is contaminated with perchlorate from a manufacturing plant previously located near the Las Vegas Wash, and ground water from wells in Riverside and San Bernardino counties of California which are affected by a perchlorate plume associated with an aerospace facility once located near Redlands, California. Studies were conducted to evaluate the uptake and distribution of perchlorate in citrus irrigated with contaminated water, and estimate potential human exposure to perchlorate from the various citrus types including lemon (Citrus limon), grapefruit (Citrus paradise), and orange (Citrus sinensis) produced in the region. Perchlorate concentrations ranged from less than 2-9 μg/L for Colorado River water and from below detection to approximately 18 μg/L for water samples from wells used to irrigate citrus. Destructive sampling of lemon trees produced with Colorado River water show perchlorate concentrations larger in the leaves (1835 μg/kg dry weight (dw)) followed by the fruit (128 μg/kg dw). Mean perchlorate concentrations in roots, trunk, and branches were all less than 30 μg/kg dw. Fruit pulp analyzed in the survey show perchlorate concentrations ranged from below detection limit to 38 μg/kg fresh weight (fw), and were related to the perchlorate concentration of irrigation water. Mean hypothetical exposures (μg/person/day) of children and adults from lemons (0.005 and 0.009), grapefruit (0.03 and 0.24), and oranges (0.51 and 1.20) were estimated. These data show that potential perchlorate exposures from citrus in the southwestern United States are negligible relative to the reference dose recommended by the National Academy of Sciences. © 2006 Elsevier B.V. All rights reserved.
• Sanchez, C. A., Krieger, R. I., Valentin-Blasini, L., Blount, B. C., & Khandaker, N. R. (2006). Perchlorate accumulation and potential exposure from durum wheat irrigated with Colorado River water. Journal of ASTM International, 3(7).
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  Abstract: The Colorado River is contaminated with low levels of perchlorate derived from aerospaceand defense-related fuel industries once located near the Las Vegas Wash. At sufficiently high doses, perchlorate can disrupt thyroid function by inhibiting uptake of iodide. Researchers have reported on the presence of perchlorate in lettuce (Lactuca sativa L.) grown in the lower Colorado River region. Recent work has demonstrated the potential for wheat (Triticum aestivum L.) to accumulate perchlorate when irrigated with perchlorate contaminated irrigation water in Texas. Over 45 000 ha of durum wheat (Triticum turgidum var. durum) are irrigated with Colorado River water in Arizona and California for the national and international pasta industries. Studies were conducted to determine perchlorate accumulation of wheat irrigated with Colorado River water. Perchlorate did accumulate in the above-ground plant components (982 to 3924 μg/kg dry weight (dw)) and roots (96 to 650 μg/kg dw) of immature durum wheat. For mature wheat, concentrations were greater in the stalk (490 μg/kg dw) compared to the spike (80 μ/kg dw). Most of the detectable perchlorate in the spike was in the rachis (125 μ/kg dw) and glumes (236 μ/kg dw). A majority of grain samples collected had perchlorate concentrations below levels of quantification by ion chromatography with tandem mass spectrometry (IC/MS/MS) (25
• Moore, R. C., Gasser, M., Awwad, N., Holt, K. C., Salas, F. M., Hasan, A., Hasan, M. A., Zhao, H., & Sanchez, C. A. (2005). Sorption of plutonium(VI) by hydroxyapatite. Journal of Radioanalytical and Nuclear Chemistry, 263(1), 97-101.
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  Abstract: The sorption of Pu(VI) by synthetic hydroxyapatite was determined in NaClO4 media. Pu(VI) sorption was determined to be rapid with equilibrium attained in 2 hours. Equilibrium experiments indicated sorption to be pH dependent with distribution constants, log Kd values, ranging from 4.11 at pH 6 to 5.92 at pH 8.5. Data collected at pH 8.0 with varying total Pu(VI) were fit to the Langmuir isotherm and yielded Langmuir constants of Ca = 0.0147 mole/mole and/C= 1.71·108l/mole. Although varying ionic strength did not have an effect on Pu(VI) sorption, a decrease in sorption was evident at high calcium and phosphate concentrations. © 2005 Akadémiai Kiadó.
• Sanchez, C. A., Crump, K. S., Krieger, R. I., Khandaker, N. R., & Gibbs, J. P. (2005). Perchlorate and nitrate in leafy vegetables of North America. Environmental Science and Technology, 39(24), 9391-9397.
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  PMID: 16475313;Abstract: In previous studies trace levels of perchlorate were found in lettuce (Lactuca sativa L.) irrigated with Colorado River water, which is contaminated with low levels of perchlorate from aerospace and defense related industries. In this paper, we report the results of a survey conducted across North America to evaluate the occurrence of perchlorate in leafy vegetables produced outside the lower Colorado River region, and evaluate the relative iodide uptake inhibition potential to perchlorate and nitrate in these leafy vegetables. Conventionally and organically produced lettuce and other leafy vegetable samples were collected from production fields and farmers' markets in the central and coastal valleys of California, New Mexico, Colorado, Michigan, Ohio, New York, Quebec, and New Jersey. Results show that 16% of the conventionally produced samples and 32% of the organically produced samples had quantifiable levels of perchlorate using ion chromatography. Estimated perchlorate exposure from organically produced leafy vegetables was approximately 2 times that of conventional produce, but generally less than 10% of the reference dose recommended by the National Academy of Sciences. Furthermore, the iodide uptake inhibition potential of perchlorate was less than 1% of that of the nitrate present. These data are consistent with those of other reported perchlorate survey work with lettuce, bottled water, breast milk, dairy milk, and human urine, and suggest a wide national presence of perchlorate. © 2005 American Chemical Society.
• Sanchez, C. A., Krieger, R. I., Khandaker, N., Moore, R. C., Holts, K. C., & Neidel, L. L. (2005). Accumulation and perchlorate exposure potential of lettuce produced in the lower Colorado River region. Journal of Agricultural and Food Chemistry, 53(13), 5479-5486.
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  PMID: 15969537;Abstract: The Colorado River is contaminated with perchlorate concentrations of 1.5-8 μg/L, an anion linked to thyroid dysfunction. Over 90% of the lettuce (Lactuca sativa L.) consumed during the winter months in the United States is produced in the Lower Colorado River region. Studies were conducted in this region to survey the potential for lettuce perchlorate accumulation and estimate potential human exposure to perchlorate from lettuce. Total uptake of perchlorate in the above-ground plant of iceberg lettuce was approximately 5 g/ha. Exposure estimates ranged from 0.45 to 1.8 μg/day depending on lettuce types and trimming. For all lettuce types, hypothetical exposures were less than 4% of the reference dose recommended by the National Academy of Sciences. Results show the relative iodide uptake inhibition potential because of lettuce nitrate was 2 orders of magnitude greater than that associated with the corresponding trace levels of perchlorate. These data support the conclusion that potential perchlorate exposures from lettuce irrigated with Colorado River water are negligible relative to acute or long-term harmful amounts. © 2005 American Chemical Society.
• Warrick, A. W., Zerihun, D., Sanchez, C. A., & Furman, A. (2005). Infiltration under variable ponding depths of water. Journal of Irrigation and Drainage Engineering, 131(4), 358-363.
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  Abstract: Cumulative infiltration was computed as a function of time-varying ponded water depths using a Green and Ampt analysis. The input water depths were field-measured values from two irrigation events on Superstition sand, one from a basin and one from a border. For both types of irrigation, the computed cumulative infiltration at a given measuring station was nearly the same whether using a variable head input or a constant (average) head during the time of opportunity. As an example, at the first measurement station for the basin event, the ponded depth went from a 0 to 9 cm depth over the 2-12 min. from the time water was introduced into the basin; this was followed by a decrease to a depth of 4 cm at 60 min. The computed infiltration using the depth hydrograph was 14.3 cm compared to 14.1 cm when using an average depth. A smaller value of 13.7 cm is found using the appropriate time of opportunity with a field averaged depth and a considerably smaller value of 12.4 cm was found when a zero-depth boundary is considered. Basin and border uniformities were also computed based on variable and different constant depths and the results were found to be reasonably robust whether infiltration is computed using a variable or an appropriate constant ponded depth. © ASCE.
• Zerihun, D., Furman, A., Warrick, A. W., & Sanchez, C. A. (2005). Coupled surface-subsurface flow model for improved basin irrigation management. Journal of Irrigation and Drainage Engineering, 131(2), 111-128.
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  Abstract: The availability of a process-based coupled surface-subsurface model can lead to improved surface irrigation/fertigation management practices. In this study, a one-dimensional zero-inertia model is coupled with a one-dimensional unsaturated zone water-flow model: HYDRUS-1D. A driver program is used to effect internal iterative coupling of the surface and subsurface flow models. Flow depths calculated using the surface-flow model are used as Dirichlet boundary conditions for the subsurface-flow model, and infiltration amounts calculated by the subsurface model are in turn used in surface-flow mass balance calculations. The model was tested by using field data collected at the University of Arizona, Yuma Mesa, research farm. The maximum mean absolute difference between field-observed and model-predicted advance is 2 min. Applications of the coupled model in improved irrigation management are highlighted. In addition, the significance of the effects of soil moisture redistribution on irrigation water availability to crops and the capability of the coupled model in tracking those changes in soil water status over time are discussed using examples. © ASCE.
• Zerihun, D., Furman, A., Warrick, A. W., & Sanchez, C. A. (2005). Coupled surface-subsurface solute transport model for irrigation borders and basins. I. Model development. Journal of Irrigation and Drainage Engineering, 131(5), 396-406.
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  Abstract: Surface fertigation is widely practiced in irrigated crop production systems. Lack of design and management tools limits the effectiveness of surface fertigation practices. The availability of a process-based coupled surface-subsurface hydraulic and solute transport model can lead to improved surface fertigation management. This paper presents the development of a coupled surface-subsurface solute transport model. A hydraulic model described in a previous paper by the writers provided the hydrodynamic basis for the solute transport model presented here. A numerical solution of the area averaged advection-dispersion equation, based on the split-operator approach, forms the surface solute transport component of the coupled model. The subsurface transport process is simulated using HYDRUS-1D, which also solves the one-dimensional advection-dispersion equation. A driver program is used for the internal coupling of the surface and subsurface transport models. Solute fluxes calculated using the surface transport model are used as upper boundary conditions for the subsurface model. Evaluation of the model is presented in a companion paper. Journal of Irrigation and Drainage Engineering © ASCE.
• Zerihun, D., Sanchez, C. A., Furman, A., & Warrick, A. W. (2005). Coupled surface-subsurface solute transport model for irrigation borders and basins. II. Model evaluation. Journal of Irrigation and Drainage Engineering, 131(5), 407-419.
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  Abstract: The development of a coupled surface-subsurface solute transport model for surface fertigation management is presented in a companion paper (Part I). This paper discusses an evaluation of the coupled model. The numerical solution for pure advection of solute in the surface stream was evaluated using test problems with steep concentration gradients. The result shows that the model can simulate advection without numerical diffusion and oscillations, an important problem in the solution of the advection-dispersion equation in advection dominated solute transport. In addition, a close match was obtained between the numerical solution of the one-dimensional advection-dispersion equation and a simplified analytical solution. A comparison of field data and model output show that the overall mean relative residual between field observed and model predicted solute breakthrough curves in the surface stream is 16.0%. Excluding only two outlier (in the graded basin data) reduces the over all mean relative residual between field observed and model predicted breakthrough curves to 5.2%. Finally, potential applications of the model in surface fertigation and salinity management are highlighted. Journal of Irrigation and Drainage Engineering © ASCE.
• Moore, R. C., Sanchez, C., Holt, K., Zhang, P., Huifang, X. u., & Choppin, G. R. (2004). Formation of hydroxyapatite in soils using calcium citrate and sodium phosphate for control of strontium migration. Radiochimica Acta, 92(9-11), 719-723.
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  Abstract: 90Sr contamination is a major problem at several U.S. sites. At some sites, 90Sr has migrated deep underground making site remediation difficult. In this paper, we describe a novel method for precipitation of hydroxyapatite, a strong sorbent for 90Sr, in soil. The method is based on mixing a solution of calcium citrate and sodium phosphate in soil. As the indigenous soil microorganisms mineralize the citrate, the calcium is released and forms hydroxyapatite. Soil, taken from the Albuquerque desert, was treated with a sodium phosphate solution or a sodium phosphate/calcium citrate solution. TEM and EDS were used to identify hydroxyapatite with CO32- substitutions, with a formula of (Ca4.8Na0.2)[(PO4)2.8(CO 3)0.2](OH), in the soil treated with the sodium phosphate/calcium citrate solution. Untreated and treated soils were used in batch sorption experiments for Sr uptake. Average Sr uptake was 19.5, 77.0 and 94.7% for the untreated soil, soil treated with sodium phosphate, and soil with apatite, respectively. In desorption experiments, the untreated soil, phosphate treated soil and apatite treated soil released an average of 34.2, 28.8 and 4.8% respectively. The results indicate the potential of forming apatite in soil using soluble reagents for retardation of radionuclide migration.
• Zerihun, D., Sanchez, C. A., & Farrell-Poe, K. (2004). Modified two-point method for closed-end level-bed furrows. Proceedings of the 2004 World Water and Environmetal Resources Congress: Critical Transitions in Water and Environmetal Resources Management, 1680-1688.
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  Abstract: The two-point method is a simple, compact, and relatively accurate inverse solution technique widely used to estimate the parameters of the Kostiakov-Lewis infiltration function. However, the applicability of the method is limited to sloping free-draining furrows. In this paper, the two-point method is modified to extend its application to close-end level-bed furrows. The modifications deal with the calculation of the basic intake rate and the inlet flow cross-sectional area during the advance phase. With the modified method, basic intake rate is calculated as the quotient of the change in volumetric surface storage between two selected time lines during the steady state period and the product of the furrow length and related time interval. In addition, the inlet flow cross-sectional area can be calculated as a function of flow depth at the inlet or using the Manning equation and an assumed linear flow depth gradient. The proposed approach was tested by comparing advance trajectories computed by SRFR, on the basis of infiltration parameter estimates by the modified two-point method, with field observed advance. A satisfactory agreement was obtained between SRFR predicted and field observed advance.
• Moore, R. C., Holt, K., Zhao, H., Hasan, A., Awwad, N., Gasser, M., & Sanchez, C. (2003). Sorption of Np(V) by synthetic hydroxyapatite. Radiochimica Acta, 91(12), 721-727.
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  Abstract: The sorption of Np(V) to synthetic hydroxyapatite was determined in batch experiments in a 0.1 M NaClO4 solution. The hydroxyapatite used was of high purity as determined by SEM, EDS, XRD, FT-IR and ICP-MS analysis. Results from kinetic experiments with an initial Np(V) concentration of 1 × 10-7 to 1 × 10-6 indicate the sorption process is relatively fast with more than 90% of the Np(V) being sorbed in approximately 3 hours. Equilibrium experiments performed over the pH range of 6 to 11 indicated sorption is strongly pH dependent with distribution coefficients, Kd values (mL/g), increasing from 123 L/mole at pH 6 to 69 200L/mole at pH 8.5. Kd values are observed to decrease as pH further increases. Data points over a range of Np(V) concentrations were collected at pH 8 and fitted to the Langmuir isotherm model for simple adsorption. The Langmuir equation gave an excellent representation of the data. Langmuir parameters were determined to be Ca = 0.032 mole/mole and K = 1.22 × 106 L/mole, indicating the high affinity of hydroxyapatite for Np(V) adsorption.
• Zerihun, D., Sanchez, C. A., Farrell-Poe, K., Adamsen, F. J., & Hunsaker, D. J. (2003). Performance indices for surface N fertigation. Journal of Irrigation and Drainage Engineering, 129(3), 173-183.
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  Abstract: The application of N fertilizers mixed with a surface irrigation stream (surface N fertigation) is widely practiced in the southwestern United States. Procedures for the optimal design and management of surface N fertigation systems are needed. The purpose of this work is to identify and define a set of performance indices that can be used to assess the relative merits of alternative design and management scenarios. Equations and solutions for quantifying the performance indices are proposed. Sample performance calculations are presented for a fertigation field experiment in which bromide ion was used as a tracer to simulate the movement of nitrate on the surface and through the soil profile.
• Rice, R. W., Datnoff, L. E., Raid, R. N., & Sanchez, C. A. (2002). Influence of vesicular-arbuscular mycorrhizae on celery transplant growth and phosphorus-use efficiency. Journal of Plant Nutrition, 25(8), 1839-1853.
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  Abstract: Elevated phosphorus (P) levels present in Everglades Agricultural Area (EAA) stormwater runoff are an environmental concern for adjoining wetlands in South Florida. A regulatory program requires EAA growers to adopt best management practices that reduce P in farm drainage water. Given the prevailing regulatory climate, P fertilization practices are under scrutiny, and a premium is placed on identifying management practices that improve crop P-use efficiency. By enhancing root P uptake, vesicular-arbuscular mycorrhizae (VAM) can potentially reduce P inputs to celery (Apium graveolens L.) without compromising crop yields. The initial objective of this study was to determine whether celery infection by Glomus intraradices was feasible. Subsequent objectives included the assessment of plant growth response to VAM inoculation during the transplant production phase and quantification of VAM effects on P-use efficiency in celery. Pre-germinated celery seeds were direct-seeded into flats containing VAM-amended potting mix at concentrations of 0, 200, 500, and 1000 chlamydospores (30-mL mix)-1, for treatments V-0, V-200, V-500, and V-1000, respectively. Following 90 days growth, root colonization under low VAM amendments (V-200) ranged from 87.1% (Experiment #1) to 92.7% (Experiment #2), far exceeding the non-inoculated control (V-0; 0 to 3.7%). Relative to V-0, celery plants infected with VAM averaged 21.7 to 57.0% greater shoot dry matter, were 22.9 to 42.7% taller, supported 9.5 to 15.5% more petioles, and shoots had 8.6 to 23.0% greater P concentrations. Overall P-use efficiency, represented by top-growth P uptake, was 33.0 to 94.2% greater than the control. Under high VAM (V-1000) amendments, P uptake exceeded V-0 by 61.7 to 102.5%. Time-trend analyses indicate that shoot dry matter accumulation and P uptake trends over the 90-day growing period generally ranked as follows: V-1000 > (V-500 = V-200) > V-0. These results document successful VAM colonization in celery. Additionally, VAM confers improved growth performance and P-use efficiencies during celery transplant growth.
• Silvertooth, J. C., Navarro, J. C., Norton, E. R., & Sanchez, C. A. (2001). Division S-8 - Notes: Evaluation of a nitrogen-15 microplot design in furrow-irrigated cotton. Soil Science Society of America Journal, 65(1), 247-250.
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  Abstract: Information is needed regarding an appropriate microplot design for use in furrow-irrigated row crop systems. Field experiments were conducted at two locations in Arizona, Maricopa in 1991 (Casa Grande sandy loam) and Marana in 1995 (Pima clay loam). The purposes of the experiments were to evaluate the dimensions of an 15N microplot design used in a furrow irrigated row crop system. The experiments each utilized ammonium sulfate fertilizer with 5 atom% 15N enrichment applied at a rate of 56 kg N/ha in a simulated side-dress band application during the early bloom stage of development of Upland cotton (Gossypium hirsutum L.). At each location, microplots were four, 1.02-m rows wide and 1.00 m in length. Whole plant samples were collected at specific locations within and near the microplots. Collection of plant materials at a minimum distance of 25 cm from the microplot borders provided uniform 15N enrichment levels for determining fertilizer N uptake and recovery. Microplots with the dimensions of those used in this study are sufficient for collecting plant materials from a 1-m2 area, consisting of two, 50-cm segments from the interior two rows of the four row microplot.
• Zerihun, D., Sanchez, A. C., & Farrell-Poe, K. (2001). Analysis and design of furrow irrigation systems. Journal of Irrigation and Drainage Engineering, 127(3), 161-169.
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  Abstract: Application efficiency is the primary criterion for furrow irrigation system design and management. In this study, the application efficiency function of a furrow irrigation system is analyzed. The application efficiency function is unimodal with respect to inlet flow rate and furrow lenght. Optimality conditions are derived for the cases in which application efficiency is a function of either furrow length or flow rate. Simple and sufficiently accurate equations and design and management rules are developed.
• Sanchez, C. A. (2000). Response of lettuce to water and nitrogen on sand and the potential for leaching of nitrate-N. HortScience, 35(1), 73-77.
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  Abstract: The low desert region of Arizona is the major area of lettuce (Lactuca sativa L.) production in the United States during the winter. Lettuce is commonly grown on the loam, clay loam, and clay soils of the alluvial river valleys. There is some interest in moving a portion of the vegetable production onto the sandy soils of the terraces (mesa) above the alluvial river valley to partially relieve the intensive production pressure being placed on lands in the valley. Of major concern in these sandy soils is water and N management. Studies were conducted during two seasons to evaluate the response of crisphead lettuce to sprinkler irrigation and N fertilizer and to evaluate the potential for leaching of nitrate-N on a coarse-textured soil Lettuce yields increased in response to water and N, and were maximized by 55 cm of water and 271 kg · ha-1 N in 1991-92 and 76 cm water and 270 kg · ha-1 N in 1992-93. These water and N rates exceeded those typically required on finer-textured alluvial valley soils. At N and water rates required for maximum yields, 88% and 77% of the applied N was not recovered in the aboveground portions of the plant during the 1991-92 and 1992-93 seasons, respectively. Overall, data for the amount of N fertilizer not recovered, estimates of nitrate-N leaching determined during one growing season, and analysis of soil samples collected after harvest indicate the potential for large N leaching losses on this coarse-textured soil. Alternative production methods that enhance water and N use efficiencies, such as drip irrigation and/or the use of controlled-release fertilizers, should be considered on this sandy soil.
• Zerihun, D., Sanchez, C. A., & Farrell-Poe, K. (2000). Maximization of application efficiency of furrow irrigation: Simplified analysis. 2000 ASAE Annual Intenational Meeting, Technical Papers: Engineering Solutions for a New Century, 2, 1787-1797.
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  Abstract: Application efficiency is the primary criteria for furrow irrigation system design and management. In this study, optimality conditions are derived for the cases in which application efficiency is a function of either furrow length or furrow inflow rate. The optimality conditions have been evaluated by comparing their output with the output of a surface irrigation simulation model.
• Zerihun, D., Sanchez, C. A., & Farrell-Poe, K. (2000). Optimal design of furrow irrigation system using an enumeration algorithm. 2000 ASAE Annual Intenational Meeting, Technical Papers: Engineering Solutions for a New Century, 2, 1749-1753.
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  Abstract: A furrow irrigation system design problem has been formulated in a minimum cost design setting. The design problem has been formulated as a function of three integer valued decision variables. A simple exhaustive enumeration based model has been used to solve the design problem. The model is simple (requires only about 40 lines of code), robust, and capable of finding a globally optimal solution to the design problem.
• Sanchez, C. A. (1999). Wetlands and horticulture: Problems and solutions: Introduction to the workshop. HortScience, 34(1), 26-.
• Sanchez, C. A., & Doerge, T. A. (1999). Using nutrient uptake patterns to develop efficient nitrogen management strategies for vegetables. HortTechnology, 9(4), 601-606.
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  Abstract: Nitrogen (N) in a soil that is not immediately taken up by a crop is subject to leaching, denitrification and other mechanisms of loss. Nitrogen uptake studies identify the total amount of N accumulated by the crop and the period of peak demand. This information can be used to devise management strategies aimed at supplying N preceding anticipated uptake. Split sidedress application, fertigation, and use of controlled release fertilizers (CRN) are all viable options for N management, depending on the crop production scenario and available infrastructure. Soil and plant tissue testing can be useful feedback tools for adjusting N applications for soil contributions of N and unexpected N losses. Efficient irrigation is of paramount importance in achieving efficient N fertilization regardless of management practice.
• Silvertooth, J. C., Navarro, J. C., Norton, E. R., & Sanchez, C. A. (1999). Uptake and recovery of N-15 labeled fertilizer as a function of time of application. Proceedings of the 1999 Beltwide Cotton Conference, January 1999, Orlando, Florida, USA, 1263-.
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  Abstract: Attaining the highest level of efficiency associated with the application of fertilizer N in an irrigated cotton (Gossypium hirsutum L.) production system is important agronomically, economically, and environmentally. The objective of this project was to evaluate the affect of time of application on the uptake and recovery of fertilizer N in a furrow irrigated cotton. Field experiments were conducted using Upland cotton at the University of Arizona Maricopa and Marana Agricultural Centers on a Casa Grande sandy loam soil (Typic Natrargid) and a Pima clay loam (Typic Torrifluvent). Three treatment regimes consisted of varied application timings (preplant, early bloom, and peak bloom) of 15N labeled fertilizer as (15NH4)2SO4 with 5 atom % 15N at a rate of 56 kg N/ha/application. At maturity, entire plants were collected and analyzed for fertilizer N uptake. In general, uptake and recovery of fertilizer N increased with later dates of application, coinciding with higher periods of N demand. However, uptake and recovery estimates of fertilizer N and lint yields were not significantly different as a function of time of application. Therefore, applications of fertilizer N between pinhead square and peak bloom stages of growth are capable of achieving equal levels of efficiency in an irrigated cotton production system.
• Palumbo, J. C., Kerns, D. L., Engle, C. E., Sanchez, C. A., & Wilcox, M. (1996). Imidacloprid formulation and soil placement effects on colonization by sweetpotato whitefly (Homoptera: Aleyrodidae): Head size and incidence of chlorosis in lettuce. Journal of Economic Entomology, 89(3), 735-742.
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  Abstract: The effects of imidacloprid formulation and soil placement on colonization by sweetpotato whitefly, Bemisia tabaci (Gennadius), at 3 plant growth stages of lettuce, Lactuca sativa L., were evaluated in experimental and commercial lettuce plots in 1993-1994. We also evaluated the effects of imidacloprid treatments on yield response and incidence of chlorosis associated with sweetpotato whitefly control. Imidacloprid placement had a significant effect on sweetpotato whitefly colonization in lettuce throughout the experimental period. Sweetpotato whitefly densities on lettuce varied at each plant stage relative to depth of placement within the lettuce seed bed. Applications made to the soil surface and at 4.0-cm subseed furrow, followed by irrigation, provided the most consistent control of sweetpotato whitefly nymphs in small plots and in on-farm lettuce plots. These imidacloprid soil treatments also prevented reductions in head size and incidence of leaf chlorosis associated with sweetpotato whitefly colonization in lettuce. Our data suggest that incorporation of imidacloprid into the upper 3-4 cm of soil below the seed furrow is optimal for absorption and translocation by lettuce roots. Imidacloprid soil treatments may provide a more environmentally suitable and effective alternative to control of sweetpotato whiteflies in lettuce than is currently possible with foliar insecticide treatments.
• Sanchez, C. A., Roth, R. L., Gardner, B. R., & Ayer, H. (1996). Economic responses of broccoli and cauliflower to water and nitrogen in the desert. HortScience, 31(2), 201-205.
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  Abstract: Field studies were conducted to develop water and N response surface models for broccoli and cauliflower (Brassica oleracea L., Botrytis Group) produced in the low desert of the southwestern United States and to estimate profit maximizing combinations of water and N over a range of realistic price situations. Marketable broccoli and cauliflower yields were increased by water and N inputs in all experiments. Generalized response equations indicate maximum broccoli yields with 43 cm of water and N at 267 kg·ha-1 and maximum cauliflower yields with 65 cm of water and N at 338 kg·ha-1. Least-cost combinations of water and N changed with the costs of these inputs for yield levels below the economic maximum. However, profit maximizing N and water rates changed little regardless of input or crop prices investigated.
• Alvarez, J., & Sanchez, C. A. (1995). Agro-economic research results and environmental regulations: phosphorus applications in sweet corn and lettuce in the Everglades. Journal of Sustainable Agriculture, 7(2-3), 15-24.
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  Abstract: This paper confirms the negative impact of environmental constraints on farm profitability, and also demonstrates that results from agro-economic research can lead to the discovery of practices that could be both environment-protecting and productivity-enhancing. Phosphorus applications on sweet corn and lettuce in the Everglades Agricultural Area are used as a case study. -Authors
• Capone, L. T., Izuno, F. T., Bottcher, A. B., Sanchez, C. A., Coale, F. J., & Jones, D. B. (1995). Nitrogen concentrations in agricultural drainage water in south Florida. Transactions of the American Society of Agricultural Engineers, 38(4), 1089-1098.
• Izuno, F. T., Bottcher, A. B., Coale, F. J., Sanchez, C. A., & Jones, D. B. (1995). Agricultural BMPs for phosphorus reduction in south Florida. Transactions - American Society of Agricultural Engineers, 38(3), 735-744.
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  Abstract: Four sets of eight or twelve 0.7 ha plots, designed for soil and hydraulic uniformity, were used to screen potential "Best Management Practices' (BMPs) for reducing total phosphorus (TP) concentrations and loadings in the Everglades Agricultural Area (EAA) of south Florida. The four production systems and their alternatives (treatments) studied were: (1) sugarcane (interspecific hybrids of Saccharum sp.) versus drained fallow plots; (2) fast versus slow drainage rates for sugarcane; (3) rise (Oriza sativa L.) in rotation following radishes to serve as a P filter crop versus traditional flooding fallow; and (4) banding phosphorus (P) fertilizer at 50% of the soil-test recommendation rate for cabbage (Brassica oleracea L.) versus full-rate broadcast applications. All treatment TP loadings leaving the plots in drainage water were close in magnitude to TP loadings to the plots, even under heavy fertilization. This indicates that the EAA system is currently a net assimilator of P. -from Authors
• Palumbo, J. C., & Sanchez, C. A. (1995). Imidacloprid does not enhance growth and yield of muskmelon in the absence of whitefly. HortScience, 30(5), 997-999.
• Roth, R. L., Sanchez, C. A., & Gardner, B. R. (1995). Growth and yield of mature 'Valencia' oranges converted to pressurized irrigation systems. Applied Engineering in Agriculture, 11(1), 101-105.
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  Abstract: A study was conducted during four seasons to evaluate the performance of mature 'Valencia' orange trees converted to pressurized irrigation systems. Trees irrigated by trickle, bubbler, spray, and sprinkler systems were compared to trees irrigated by the traditional border-flood irrigation method used in the southwestern Arizona desert region. During the first year only trees irrigated by the sprinkler system grew significantly less than trees irrigated by border-flood. During the second year after conversion, trees irrigated by border-flood grew significantly more than trees irrigated by any of the pressurized systems. However, there were no differences in tree growth during the third and fourth years, suggesting that the trees adapted to the new irrigation systems. Effects of irrigation treatments on leaf concentrations of N, P, Fe, Zn, Mn, and Cu were minimal. There were significant differences in orange yields from trees among the different irrigation treatments within years. However, average or total tree yields over the four-year period did not vary due to irrigation treatment. Similarly, there were no consistent differences in fruit or juice quality. Overall, results from this study indicate that mature 'Valencia' orange trees can be converted to pressurized irrigation systems with minimal effects on fruit yield and quality. Under the conditions imposed in the studies, 33% less irrigation water was utilized with the pressurized systems compared to border-flood. © 1995 American Society of Agricultural Engineers.
• Sanchez, C. A., Roth, R. L., & Gardner, B. R. (1994). Irrigation and nitrogen management for sprinkler-irrigated cabbage on sand. Journal of the American Society for Horticultural Science, 119(3), 427-433.
• Shrefler, J. W., Dusky, J. A., Shilling, D. G., Brecke, B. J., & Sanchez, C. A. (1994). Effects of phophorus fertility on competition between lettuce (Lactuca sativa) and spiny amaranth (Amaranthus spinosus). Weed Science, 42(4), 556-560.
• Espinoza, L., Sanchez, C. A., & Schueneman, T. J. (1993). Celery yield responds to phosphorus rate but not phosphorus placement on histosols. HortScience, 28(12), 1168-1170.
• Larson, K. D., Schaffer, B., Davies, F. S., & Sanchez, C. A. (1992). Flooding, mineral nutrition and gas exchange of mango trees. Scientia Horticulturae, 52(1-2), 113-124.
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  Abstract: Two-year-old cultivar 'Peach' mango trees (Mangifera indica L.) were grown in containers with (+Fe) or without (-Fe) chelated iron in limestone soil for 7 months and exposed to one of three flooding regimes: non-flooded (control) and 10 or 20 days of flooding. Prior to the imposition of flooding, and about 80 days later, total leaf chlorophyll content (Chl) and foliar concentrations of N, P, K, Ca, Mg, Fe, Mn, Cu and Zn were determined. Initially, Chl and foliar Fe and Mn concentrations were higher, but foliar K, Ca and Mg concentrations were lower, in the +Fe trees than in the -Fe trees. After the imposition of flooding treatments, significant interactions were observed between iron fertilization and flooding treatments with regard to Chl and certain foliar nutrient concentrations. Therefore, the effect of flooding on mineral nutrition was analysed separately for each iron fertilization regime. For +Fe trees, Chl was unaffected by flooding treatment, but for -Fe trees Chl increased with increased flooding duration. For both iron fertilization regimes, foliar Mn increased with flooding and tended to be greatest with increased flooding duration. For both iron fertilization regimes, there was no effect of flooding on foliar N, Fe or Zn concentrations, and no clear effect of flooding on foliar Cu concentration. For +Fe trees, foliar P concentration was reduced in trees flooded for 20 days, but there was no effect of flooding on foliar P concentration in -Fe trees. Flooding resulted in reductions in foliar K concentration in -Fe trees, but not in +Fe trees. For both iron fertilization regimes, flooding resulted in a reduction in foliar Ca concentration. For +Fe trees, flooding for 20 days resulted in increased foliar Mg concentration, but there was no effect of flooding on foliar Mg in -Fe trees. Prior to flooding, net CO2 assimilation (A) was greater for +Fe trees than for -Fe trees. Six months after the imposition of flooding, A of flooded -Fe trees was similar to that of +Fe trees. The results of this study indicate that short-term flooding may reduce certain micronutrient deficiencies in mango trees grown in limestone soils. © 1992.
• Rechcigl, J. E., Payne, G. G., & Sanchez, C. A. (1992). Comparison of various soil drying techniques on extractable nutrients. Communications in Soil Science & Plant Analysis, 23(17-20), 2347-2363.
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  Abstract: The effects of drying and storage techniques (air, microwave, oven-drying, and frozen) on the levels of Mehlich-I-extractable nutrients were evaluated in six diverse soils. Drying and freezing caused large changes in the levels of extractable nutrients in all soils. The effects of drying were dependent on drying intensity and the initial physical and chemical properties of the soil. Many of the changes in the levels of extractable nutrients resulting from drying the soil appear to be associated with the oxidation of organic matter and changes in hydration state and redox states of different soil components. Results from this study also indicate that microwave drying of soils has potential for rapid drying of soil samples prior to analyses. -from Authors
• Rezaian, S., Hanlon, E. A., Sanchez, C. A., & Cornell, J. A. (1992). Optimization of solution:soil ratio and shaking times of the Mehlich- III soil test on Histosols. Communications in Soil Science & Plant Analysis, 23(17-20), 2247-2259.
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  Abstract: Recent research at the University of Florida Everglades Soil Testing Laboratory at Belle Glade has suggested that the Mehlich-III soil test has potential for use on Histosols. A laboratory study with shaking times (SHs) ranging from 1 to 29 min and solution:soil ratios (RAs) ranging from 8 to 22 was conducted using four Florida Histosols. Across the four soils, the amounts of extracted P and K in this study were increased at high levels of RAs and SHs. Extracted P and K levels for all soils were well above the lower limits for standard analytical procedures. Within each soil, the models for P data predicted a higher coefficient of determination than did the models for K. Since no optimum RA and SH combinations were found, the published values appear to be acceptable for Florida Histosols to minimize laboratory analytical time and chemical waste or costs. -from Authors
• Izuno, F. T., Sanchez, C. A., Coale, F. J., Bottcher, A. B., & Jones, D. B. (1991). Phosphorus concentrations in drainage water in the everglades agricultural area. Journal of Environmental Quality, 20(3), 608-619.
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  Abstract: Phosphorus in drainage water leaving the Everglades Agricultural Area (EAA) in southern Florida is alleged to be contributing to the accelerated eutrophication of Lake Okeechobee and the degradation of the Water Conservation Areas and the Everglades National Park ecosystems. Agricultural ''best management practices'' (BMPs) offer a means for achieving reductions in P in drainage water. Prior to developing and implementing BMPs, it is necessary to establish baseline EAA P concentrations. Baseline total P (TP) and total dissolved P (TDP) concentrations for various crop and field conditions in the EAA were determined. Thirty-six 0.7-ha plots were installed at four locations. Average TP and TDP concentrations were derived from 6 to 30 drainage events for each of five conditions between November 1988 and December 1989: sugarcane (Saccharum spp.), radish (Raphanus sativus L.), and cabbage (Brassica oleracea L.) production fields, flooded fallow fields, and drained fallow fields. Baseline TP and TDP concentrations for main farm canals and rainfall were also determined. Average TP concentrations ranged from 0.25 mg L-1 for radishes to 1.03 mg L-1 during the drain-down of flooded fallow plots. Total dissolved P concentrations ranged from 48 to 80% of TP. Main farm canal TP concentrations averaged 0.16 mg L-1. Total P concentrations in rainfall averaged 0.07 mg L-1. Total P in drainage water during 1989 for sugarcane, cabbage, and drained fallow fields were 0.72, 1.38, and 0.59 kg ha-1, respectively. During the radish season, drainage water TP loading was 0.8 kg ha-1. Flooded fallow fields after radishes yielded a TP loading rate of 3.82 kg ha-1. Total P loading to the fields from rainfall averaged 0.70 kg ha-1. Total dissolved P loading rates ranged from 25 to 60% of TP. Potential areas for BMP development and implementation for P concentration and loading reduction in the EAA include drainage rate, volume, and timing management, fertilizer use reduction, and enhanced crop rotation strategies.
• Jansson, R. K., Leibee, G. L., Sanchez, C. A., & Lecrone, S. H. (1991). Effects of nitrogen and foliar biomass on population parameters of cabbage insects. Entomologia Experimentalis et Applicata, 61(1), 7-16.
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  Abstract: The effects of different nitrogen (N) fertilization rates (0, 45, 90, and 168 kg N/ha), plant nitrogen concentration, and plant biomass on abundance and population growth of diamondback moth, Plutella xylostella (L.), cabbage looper, Trichoplusia ni (Hübner), cabbage budworm, Hellula phidilealis (Walker), imported cabbageworm, Artogeia rapae (L.), and cross-striped cabbageworm, Evergestis rimosalis (Guenée), were investigated in Homestead and Sanford, Florida in 1987. The effects of these factors on the parasitization of P. xylostella were also examined. In Homestead, abundance of most insect pests and parasitized P. xylostella increased with an increase in the level of N applied and with an increase in plant biomass. Similar results were found in Sanford, although results were not consistently significant. Abundance of most insect pests was significantly positively correlated with plant N concentration. Multiple regression analyses indicated that foliar biomass was significantly more important than N fertilization rate and subsequent plant N concentration at predicting abundance of insect pests and parasitized P. xylostella on cabbage. © 1991 Kluwer Academic Publishers.
• Sanchez, C. A., Porter, P. S., & Ulloa, M. F. (1991). Relative efficiency of broadcast and banded phosphorus for sweet corn produced on histosols. Soil Science Society of America Journal, 55(3), 871-875.
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  Abstract: Histosols used extensively for crop production are often hydrologically linked to environmentally sensitive wetlands, making it imperative that management strategies be developed to improve the efficiency of fertilizer P. Furthermore, sweet corn (Zea mays L.) produced on Florida Histosols is grown in rotation with sugarcane (Saccharum spp.), which responds negatively to high P. Reduction of the P rates applied to sweet corn would increase the compatibility of this common crop rotation. Studies were conducted across six site-seasons during 1988 and 1989 to evaluate the relative efficiency of broadcast and banded P for sweet corn. Broadcast and banded P rates were 0, 25, 50, 75, and 100 kg P ha-1. Broadcast P was surface applied and disked into the soil before planting. Banded P was applied ≈ 3 cm below the corn seeds in bands mixed with soil in an approximate diameter of 5 cm. Sweet corn responded to P when soil-test P levels were below 1.2 g m-3. Total marketable yields, yield of U.S. Fancy, and quality parameters of sweet corn ears were increased by P rate and affected by placement in four of the six site-seasons. Band placement reduced the amount of P required for a specified sweet corn yield and also appeared to result in higher total yield. The relative efficiency of banded to broadcast P depended on soil-test P level. The relative efficiency was greater than 3:1 (band/broadcast) when soil-test P was
• Sanchez, C. A., & Blackmer, A. M. (1987). METHOD FOR APPLICATION OF NITROGEN-15-LABELED ANHYDROUS AMMONIA TO SMALL PLOTS.. Soil Science Society of America Journal, 51(1), 259-261.
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  Abstract: A method is described that permits precise application of anhydrous ammonia in bands to plots of the size often used in **1**5N-tracer studies. This method involves placing a stainless-steel capillary tube in the soil where the ammonia is to be banded, attaching this tube to a cylinder of ammonia, and then pulling the tube through the soil with deposition of ammonia as an even band. The procedure has marked advantages over previously described methods because it can be used with mixtures of anhydrous ammonia and nitrification inhibitors and because the soil environment at the point of application is representative of the soil environment found when a conventional applicator is used.

Proceedings Publications

• Sanchez, C. A., & Andrade, P. (2023, March).

  Variable Rate N and P Management for high-value Vegetable Cropping Systems

  . In Western Nutrient Management Conference.
• Sanchez, C. A., & Zerihun, D. (2023).

  Optimizing Fertigation for High Value Crops 

  . In Western Nutrient Management Conference.

Presentations

• Sanchez, C. A., & Brown, P. (2019, Summer). Prospects of Using Water to Mitigate Challenges of a Warming Climate in the Lower Colorado River Region Vegetable Cropping Systems. American Society of Horticulture Annual Conference. Las Vegas: ASHS.
• Sanchez, C. A., French, A., & Guillevie, P. (2019, Winter). Earth Observations and models to support agricultural water resources management. AGU Fall Meeting. San Francisco, CA: AGU.
• Sanchez, C. A., French, A., & Williams, C. (2019, Summer). Water and Salt Balance in Desert Cool Season Vegetable Cropping Systems. American Society of Horticulture Annual Conference. Las Vegas: ASHS.
• Sanchez, C. A., French, A., Saber, M., Gonzales, J., & Hunsaker, D. (2019, Fall). Bridging the gap between satellite and ground-based temperature observations with UAV data over Yuma, Arizona Vegetable crops. Tri-Societies. San Antonio, TX: ASA.
• Sanchez, C. A., French, A., Saber, M., Gonzales, J., Hunsaker, D., & Andersen, R. (2019, Winter). Remote Sensing of ET over US Southwest Irrigated Agriculture. AGU Fall Meeting. San Francisco, CA: AGU.
• Sanchez, C. A., French, A., Sabor, M., Gonzales, J., & Hunsaker, D. (2019, Fall). Using remote sensing to monitor and forecast water use by durum wheat in Arizona. Tri-Societies. San Antonio, TX: ASA.
• Sanchez, C. A., & Gaxiola, R. (2014, October). Exploring the Potential of Transgenic Crops for Improved Fertilizer Use Efficiency. FREP/WPHA Conference. Modesto.
• Sanchez, C. A., Ellison, E., & Tindall, T. (2014, July). Controlled Release N Fertilizer for Irrigated Arid-land Vegetable Crops: A Decade of Research. American Soceity of Horticultural Sciences Annual Conference.
• Sanchez, C. A. (2013, Summer 2013). Teaching Soil Fertility and Plant Nutrition in an Off-Campus 2+2 Degree Program. Cutting Edge Teaching Workshop. Teaching Hydrogeology, Soils, and Low-T Geochemistry in the 21st Century. Albuquerque: NSF.
• Sanchez, C. A., & Gaxiola, R. (2013, Summer 2013). Response of AVP1-OX Romaine Lettuce to Phosphorus. American Society for Horticultural Science Annual Conference. Palm Desert, CA: American Society for Horticultural Science.
• Sanchez, C. A., Naugler Klassen, T., & Froehlich, D. (2013, fall). Evaluation of Struvite as a P Fertilizer Source for Irrigated Vegetables in the Arid Southwestern U.S.. American Society of Agronomy Annual Meeting.
• Sanchez, C. A. (2011, November). Phosphorus Managment. FREP Annual Conference. Tulare, CA.

Poster Presentations

• Sanchez, C. A., & Gaxiola, R. (2014, June). Enhanced Phosphorus Use Efficiency in AVP-OX Romaine Lettuce. World Biotechnology Conference. Boston.
• Sanchez, C. A., Ellison, E., & Tindall, T. (2014, July). Using Heat Unit Models to Predict N Release from Controlled Release Fertilizers for Vegetable Production. American Soceity of Horticultural Sciences Annual Conference. Orlando: ASHS.
• Sanchez, C. A., Froelich, D., & Naugler Klassen, T. (2014, July). Struvite as a P Fertilizer Source for Irrigated Vegetables on Calcareous Soils. American Society of Horticultural Sciences Annual Conference. Orland.
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  Presentation
• Sanchez, C., Fonseca, J., Ravishankar, S., Zhu, L., & Fallon, S. (2011, July). Factors affecting the area of contamination due to the presence of animal feces in overhead sprinkler irrigated lettuce fields. Society of Applied Microbiology meetings. Dublin, Ireland.

Case Studies

• Brown, P. W., Nolte, K. D., & Sanchez, C. A. (2015. Chapter 3. Irrigation Management in Yuma County(p. 108).

Others

• Sanchez, C. A., & French, A. (2023, September). Quantitative Assessments of Water and Salt Balance for Cropping Systems in the Lower Colorado River Region. YCEDA. https://desertagsolutions.org/sites/desertagsolutions.org/files/attachment/Quantitative%20Assessments%20Report%20on%20water%20and%20salt%20balance_eread.pdf
• Artiola, J. F., Chief, K., Beamer, P., Wilkinson, S. T., Maier, R. M., Rock, C. M., & Sanchez, C. A. (2016, April). The Gold King Mine Spill: Can it Impact Water Users below Lake Powell Reservoir and Yuma Farmers?. University of Arizona, College of Agriculture & Life Sciences, Cooperative Extension. http://arizona.openrepository.com/arizona/bitstream/10150/607717/1/az1698-2016.pdf
• Chief, K., Artiola, J. F., Beamer, P., Wilkinson, S. T., Maier, R. M., Rock, C. M., & Sanchez, C. A. (2015, August). Understanding the Gold King Mine Spill. CALS publications Website. http://superfund.pharmacy.arizona.edu/info-material/gold-king-mine
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  This bulletin was produced in response to questions arising about the Gold King Mine spill.
• Chief, K., Artiola, J. F., Beamer, P., Wilkinson, S. T., Maier, R. M., Rock, C. M., & Sanchez, C. A. (2015, August). Understanding the Gold King Mine Spill. web. http://superfund.pharmacy.arizona.edu/info-material/gold-king-mine
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  This bulletin was produced in response to questions arising about the Gold King Mine spill.