Brief Summary of Minutes of Annual Meeting

October 22, 2014 Meeting started by Dr. Dilip Nandwani at 8:40 am Opening remarks by TSU Dean of Extension, Dr. Latif Lighari – Welcomed the group to Nashville and talked about his background as an Ag Engineer in South Dakota with small and large farms with range of irrigation use. Announcements by Dr. Dilip Nandwani and review of agenda – IA symposium in Nov. 2015 in Long Beach, CA and use of project funds to develop products were new items added. Discussion of industry participation – Dr. Freddie Lamm – Dr Lamm led a discussion that the group develop a proposal for industry participation in W-3128 meetings. A subcommittee of the W-3128 group was proposed to discuss possible participation by industry. Naming of the subcommittee was tabled to the W-3128 business meeting. NIFA report by Dr. Steve Loring – Dr. Loring announced to the group that the project has been renewed and the October 2014 meeting constitutes the last meeting of 2128 and first meeting of 3128. He congratulated the group on the Western States Research Directors Award of Excellence, in Reno, NV and national Award for Excellence in Washington in November. He indicated that while W-3128 is a western regional multistate project, it has become a national program because of national scope of irrigation problems. Dr. Loring further indicated that the W-3128 project has great national impact. Dr. Loring suggested that the project must consider a plan to utilize the $15,000 to support for travel to receive awards and products. Recommendations for using the funds were tabled to the business meeting. Dr. Brad Rein (NIFA rep) He led a discussion on the USDA budget problems and discussed some funding opportunities specifically CARE (Critical Agriculture Research and Extension). Dr. Rein went on to indicate the emphasis of NIFA RFP will be water quality and quantity. It was suggested by Dr. Ken Shackel that a subcommittee be established to work with industry to develop proposals to include a critical need and producer involvement. Dr. Dana Porter led a discussion on microirrigation design problems with industry reps including lack of proper designs for small projects was conducted. Standards for minimum specifications including uniformity and management were suggested. It was recommended by the group that the Maintenance of Microirrigation Systems web site (winner of ASABE Blue Ribbon award) should be used as a model for products by the group. State Reports- Dana Porter & Jim Bordovsky – Texas A&M –The Texas A&M group developed a website on irrigation scheduling using ET/soil moisture balance for multiple fields at multiple farms and the Bushland Reference ET calculator for grass and alfalfa, available as phone app. Research project for furrow, low pressure and center pivot systems to develop technology transfer products for stakeholders to promote adoption of microirrigation, including grower meetings was discussed. Clarence Prestwich - NRCS – Dr. Prestwich discussed irrigation system criteria and indicated that EU (emission uniformity) increased to 90% as a minimum for new systems and may be increased further. The importance of water quality testing for irrigation design was discussed. It was observed there exists a wide range of tests and costs and that specific tests to base irrigation system design and management should be established. These comments stimulated a good discussion on uniformity and water savings by proper design and water quality testing Freddie Lamm – Kansas State University – Dr Lamm discussed development of a system to evaluate water quality testing results in Kansas. He suggested a similar system should be developed to evaluate irrigation clogging potential nationally. Discussion by the group indicated that sensors for water quality components should also be evaluated. Conclusion was that standards for agricultural irrigation water samples need to be different than drinking water. The group discussed development of a standard list of tests for agricultural irrigation water that would reduce testing costs to growers. Lunch Mike Bartolo – Colorado State University – Dr. Bartolo discussed challenges to adopting drip irrigation in Colorado. He indicated that cost share of equipment and education were the best tools to increase use of drip irrigation. He also indicated that growers have no incentive to conserve water with drip because if you do not use water you lose it (water rights). Howard Neibling – University of Idaho - Research on nitrate movement with soil depth was discussed. Data indicated that corn silage grown with drip had greater yields and grower acceptance than furrow irrigated corn. Dr. Neibling described the use of cell modem soil moisture loggers and website for irrigation monitoring and scheduling with Washington State University was described. Kelly Morgan – University of Florida – The use of crop water use models by water management districts in Florida was described. Development and use of smartphone irrigation scheduling apps and irrigation water use and irrigation scheduling research projects on citrus infected by Citrus Greening Disease was summarized. Ali Fares – Prairie View A&M – The In-situ water monitoring sensor conference in 2014 was described. Water use and conservation research using soil moisture sensors and water quality measurements using suction lysimeters and the effect of soil organic matter on readings of soil moisture was described. It was also determined that addition of sawdust as a substitute for organic matter in sand had effect on the soil moisture measurement of several commonly used sensors. Manoj Shukla – New Mexico State University – Dr. Shukla described the decline in water table depth from about 10 feet to 25 feet in New Mexico. Research on development of soil moisture sensor calibration, water use, and crop coefficients of greenhouse grown peppers was discussed. A project determining Kc calculated by growing degree day (GDD) was described. Business Meeting Dr. Loring, lead a discussion with the objective of suggesting use of projects funds ($10,000) that must be spent by Sept. 31, 2016. A discussion of the group indicated the products funded should include 1) update of irrigation manual, 2) Development of irrigation kits, 3) Website management charges, 4) Landscape water requirement, and/or 5) Sponsor a microirrigation symposium. Dr. Loring suggested that the group should assign a subgroup of 3-4 people to develop alternatives and communicate with the larger group. The group determined that Dr. Freddie Lamm will head the group. Next meeting location suggestions: Dr. Ken Shackel (next chair) suggested somewhere in California in association with theASABE/ IA symposium in Long Beach, CA scheduled for Nov. 10-12, 2015 so the W3128 would be on Nov. 13, 2015. Adjourned – 5:30 October 23, 2014 – Field Trip to McMinnville, TN Mr. Terry Hines, owner of Hale and Hines Nursery gave us a tour of his irrigation control system. The system provides ET and soil moisture sensor based irrigation on field container grown tree production area with fertigation and line treatment. We then toured the Tennessee State research facility and new Ag biotech building, campus farm tour. TSU facilities were toured on our return to Nashville. October 24, 2014 Meeting opened at 8:30 Business Meeting (con’t) Submission of State Reports - Dr. Loring led a discussion on State Reports. It was agreed by the group that State Reports be due by November 15, 2014 to the secretary using the same format as last year referencing 2128 objectives with goals for coming year using 3128 objectives. Subcommittee on project funding (Freddie Lamm, Ken Shackel, Pete Jacoby, and Clint Shock) reported that the W-3128 group should hold symposium, workshop or webinars with invited speakers may be oriented chemistry of emitter plugging. Review 2013 meeting minutes - Minutes for 2013 meeting were approved. Election of Secretary - Dr. Pete Jacoby was nominated by Freddie Lamm and second by Ken Shackel. The nominations of approved unanimously. Clint Shock suggested that the group recognize Dr. Steve Loring for his work to organize the group and complete the paperwork that resulted in 2138 being recognized in the award. The group voted unanimously supported the recognition. State Report (con’t) Juan Carlos Diaz-Perez – University of Georgia – Dr. Diaz-Perez described research he conducted on establishing ET of vegetable crops to determine crop ET. He has found that 100% crop is not needed with drip irrigation and the Kcs could be reduced. Elvin Roman-Paoli – Puerto Rico – Dr. Roman-Paoli described work on ET estimation for fruit, vegetables and root crops using subsurface drip irrigation management and crop rotation. He further described research conducted to reduce leaching of N in citrus and avocado. Clint Shock – Oregon State University – Dr. Shock conducted studies on E. coli movement in contaminated water in furrow or drip irrigation. Another set of studies looked at N rates in soil solution determining that if soil solution is used to schedule N applications less N is used with similar yields compared to predetermined fertilizer schedules. Dilip Nandwani – Tennessee State University – Dr. Nandwani reported work in Virgin Islands on collection of rainwater for irrigation in reservoirs. He also conducted a study using a water collection kit for drip irrigation using manual pump from a surface rainwater reservoirs. While at TSU, he has established certified organic plots and has produced sweet potato on three types of mulches. Meeting was adjourned at 11:20

Objective 1. Compare irrigation scheduling technologies and develop grower-appropriate scheduling products (CA) Irrigation levels from about 70 to 110 % ETc were imposed on test plots in commercial almond orchards in 3 locations across the central valley of CA in order to develop an almond water production function. Tree water stress (SWP) as well as soil moisture was monitored on an approximately weekly basis from March to October, and other important variables (canopy PAR interception, yield) were recorded. Based on previous studies we did not expect to see a substantial reduction in yield, PAR, or yield/PAR, and only one site showed a statistically significant reduction (15 %) in yield for the lowest irrigation level (70% ET) compared to the control (100% ET). This is the first year that differential irrigation levels have been imposed at these sites, and since many important effects of water stress are carryover effects, only tentative conclusions can be reached. All sites showed a clear increase in stress with reduced irrigation, but even when provided with excess water (110 to 116% of calculated ETc, depending on site) no site exhibited baseline (non-stressed) values of SWP throughout the season. Interestingly, two sites (Kern and Merced counties) showed generally lower SWP values compared to the third site (Tehama county), but had generally higher yields, and all yields were strongly related to crop load. This may be an early indication that under some conditions water stress may have a beneficial effect on almond yields. A mobile sensor suite was developed and evaluated to predict plant water status by measuring the leaf temperature and microclimatic variables in nut crop trees and grape vines. The sensor suite consists of an infrared thermometer to measure leaf temperature along with other relevant sensors to measure microclimatic variables. The sensor suite was successfully evaluated in commercial orchards in central valley of California on three or (ID) A web-based water-budget irrigation scheduling program developed by Dr. Troy Peters, WSU, and a soil sensor based approach with web-based data availability were compared on 6 barley fields in eastern Idaho in 2014. The WSU “Irrigation Scheduler Remote” program used irrigator-selected soil and crop parameters, AgriMet daily estimated crop ET, and rainfall, and irrigator-input irrigation data to evaluate root zone available soil water and depth of irrigation water required to re-fill the root zone on a daily basis. (ID) Watermark sensors were installed at 4 depths (12, 18, 24 and 30 inches) on each field to serve as a daily comparison measurement. Data from the sensors and a tipping bucket rain gage were transmitted by cell phone link to a website at 30-minute intervals. This information, formatted in a user-defined fashion, was available from any mobile device (cell phone, laptop, desktop,...) that could connect with the website. Pre and post-season soil sampling at 6-inch intervals to 5 feet (or rock) depth along with rain gage data provided directly-measured water budget information. (OR) Previously we determined the ideal soil water tension irrigation criteria for the onset of irrigation for drip-irrigated onion. The results were based on assumptions of the ideal plant population to optimize the economic return for onions given US market opportunities. Worldwide onions are often planted at greater plant populations for market opportunities to sell smaller diameter bulbs. Replicated trials indicate that the ideal irrigation criteria for smaller sized onions is drier and less sensitive to very wet irrigation criteria than yield and income optimization for the US market. (OR) Native wildflower seed is needed to restore rangelands of the Intermountain West. Commercial seed production is necessary to provide the quantity of seed needed for restoration efforts but a scientific basis of seed production is lacking for thee species. A major limitation to economically viable commercial of native wildflower seed production is stable and consistent seed productivity over years. In native rangelands, the natural variations in spring rainfall and soil moisture result in highly unpredictable water stress at flowering, seed set, and seed development, which for other seed crops is known to compromise seed yield and quality. By burying drip tapes at 12-inch depth and avoiding wetting the soil surface, we hoped to assure flowering and seed set without undue encouragement of weeds or opportunistic diseases. Irrigation and plant establishment results are now available for over 20 species through this work. (OR) Real time knowledge of soil moisture is helpful to assure crop yields and reduce negative off site effects of irrigation. Manual data retrieval from each field is time consuming and wiring complicates mechanical farming practices. The combined use of soil moisture sensors, a wireless sensor web, and internet communication, could allow growers to view soil moisture data, sensor diagnostics, and other useful information from a computer, smartphone, or tablet. We tested a IRROmesh™ system that used a SensMitWeb™ smartmesh radio platform. The system read soil temperature and soil water tension using three Watermark™ soil moisture sensors in each of twelve fields planted to eight different crops. Real time soil data and graphs of soil water tension trends were easily accessible by smart phone. These preliminary trials using the sensor web showed that this technology holds potential for saving time, increasing accuracy of irrigation scheduling, and assuring yield. (TX) The Texas High Plains ET (TXHPET) Network continued to provide free public access to ET-based crop water demand information (using the ASCE-EWRI Standardized Reference ET model) through the Texas A&M AgriLife Research and Extension Water Management Website (watermgmt.tamu.edu). The TXHPET Network also continued to support research programs with access to their secure database. The Bushland Reference ET Calculator, developed by a team led by Dr. Prasanna Gowda (USDA-ARS-Conservation and Production Laboratory) is now available through the Laboratory website (http://www.cprl.ars.usda.gov/swmru-software-bretc.php) and through the Apple App store. Improvements include broader geographic applicability. The Texas High Plains Water Management Soil Moisture User Profile Tool, available through the Water Management website, is being used in combination with Sentek EnviroSCAN soil moisture probes to manage irrigation treatments in a study comparing subsurface drip irrigation, low pressure center pivot irrigation and furrow irrigation of corn. The Soil Moisture Profile Tool applies ET-based crop water demand and soil moisture balance models to inform in-season irrigation scheduling decisions. Thomas Marek (Senior Research Engineer, Texas A&M AgriLife Research – Amarillo/Bushland) and Dana Porter are co-principal investigators in this work. (FL) Web-based tools that were previously developed had little user-tool interaction and depending largely on the user remembering to return to the website and engage. Smartphone apps provide a different level of engagement with users. Apps allow for notifications and ease of accessibility. The growing use of smartphones and accessibility to weather data has resulted in an ideal situation for implementing smartphone apps for irrigation scheduling. Thus, study objectives were to (1) develop smartphone apps for scheduling irrigation using real-time and forecasted meteorological data and (2) provide users with an irrigation schedule for specific crops developmental phenology based on their site soil and irrigation system characteristics and weather conditions. Field evaluation is encouraging with good user input with suggestions to improve interfaces and outputs. Additional studies have been conducted to improve our understanding of citrus water use by infected with Huanglongbing (HLB) (Candidatus Liberibacter asiaticus). Soil moisture distribution in infected and affected groves is critical for devising appropriate recommendations for optimizing water use and sustaining citrus yields. Thus, the studies described in this report are being conducted to investigate water use patterns and soil moisture movement within groves in central, south-central and southwest Florida. Treatments being evaluated include: 1) daily irrigation (Daily), 2) Institute of Food and Agricultural Sciences (IFAS) recommended scheduling, and 3) irrigation scheduled half the number of days between irrigation recommended by IFAS (Intermediate). The irrigation amounts of the daily and intermediate irrigation schedule are reduced at each irrigation event but provided similar amounts of water to the IFAS recommendation over long periods of time. Preliminary results indicate that water use per unit leaf area ranged from 0.09 to 0.10 oz/ inch2/day at all sites depending on irrigation schedule. Moisture contents were similar among irrigation schedules varying between 5 to 20%, 1 to 14% and 5 to 25% at 6-, 12-, and 18-inch soil depths, respectively. Soil moisture contents increased with depth possibly as a result of uptake in the top 12 inches. These preliminary findings should help in refining limits for available water contents and estimating irrigation demand estimations to sustain citrus productivity of HLB infected trees. Annual water use data were not statistically different among irrigation treatments at any site and were consistent with the goal of this study in that the same amount of water be used for all treatments. Yield data collected in December 2013 indicate that six months (including the rainy season) of the three treatments did not affect yields in the first year of the study. Objective 2. Develop design, management and maintenance recommendations (KS) An oral presentation with written paper entitled “Successful SDI - Addressing the essential issues” was given at several events, regional meetings in Oregon and Colorado, an international conference in Argentina and as a seminar to the Irrigation Association’s technical conference. (KS) The microirrigation maintenance website developed by University of California-Davis, Kansas State University, and Texas A&M University was selected for a ASABE Blue Ribbon award as an education aid in the website category. (KS) Joint technology transfer efforts concerning SDI involving Kansas State University, Texas AgriLife and USDA-ARS were continued in 2014. These efforts included presentations at local, regional and national meetings. (ID) A subsurface drip irrigation (SDI) system was installed in a center pivot corner in May, 2012 using support from a USDA-NRCS Conservation Innovation Grant to determine the suitability of SDI for corn silage production under Idaho soil, climate, and harvest conditions. Three drip tape depths (6, 9, and 12 inches) and 2 tape spacings (30 and 44 inches) were installed. In 2014 corn for silage was planted on Reps 2 and 3 of the trial. Rep 1 was abandoned due to excessive rodent damage. The un-mowed grass and weeds in the fence line and adjacent canal area appeared to provide better habitat for rodents, resulting in greater damage on Rep 1. At harvest, corn ear weight (highly correlated with total crop tonnage and feed value) was measured from all 12 Rep 2 and 3 plots. System performance and crop yield and quality will be measured for a surface drip tape placement in 2015. This site will serve as a demonstration site for this technology, with a field day in June 2015. (TX) Jim Bordovsky and his research team at the Texas A&M AgriLife Research Center at Halfway, Texas, have completed a multi-year study of the effects of varying irrigation capacities on cotton production in the Texas Southern High Plains. In addition to varying irrigation capacities (deficit to full irrigation), Bordovsky’s team has evaluated effects of the timing of irrigation capacity deficits, and the relative responses of the crop to water during different crop growth stages. This work will provide essential knowledge for in-season cotton irrigation recommendations that optimize water value and lint yield in an area with declining irrigation capacity and increasing pumping restrictions. Objective 3. Develop best management practices for application of agrochemicals (KS) A poster presentation related to conjunctive use of water and nitrogen with subsurface drip irrigation for corn production was presented at a field day at Colby, Kansas in August. (KS) Oral presentations of related to conjunctive use of water and nitrogen with subsurface drip irrigation for corn production were made at a regional meeting in Oregon, at the American Society of Biological and Agricultural Engineers (ASABE) in Montreal, Canada, and at international conferences in China and Argentina. (NM) We continued to work with the compensated root water uptake using partial rootzone drying (PRD) techniques. The experiments were conducted using chile plants (NuMex Joe Parker; Capsicum annuum). Results supported our previous observations that chile plants were able to take up more water from less water stressed part of the soil profile while maintaining the plant stress (stem water potential) similar to that in control treatment. Water balance analysis showed that PRD techniques reduced the deep percolation and required the irrigation amounts to 30% less than control. (OR) Improved P and K fertilization of drip-irrigated onion could help to assure yields while using lower levels of inputs. Six different P and K applications strategies are being compared in replicated plots based on information collected by soil analysis, plant tissue analysis, and soil solution sampling. (OR) Weeds like yellow nutsedge are exceedingly difficult to control in onion. Initial work is exploring rates and timings of applying Outlook through drip irrigation for yellow nutsedge control. This method of application is not currently labeled. (OR) Several soil borne diseases attack onion. Preliminary studies are being conducted to examine options to manage these diseases via the application of fungicides through the drip irrigation system. These application methods are not yet labeled. (VI and TN) U.S. Virgin Islands have high rainfall but little irrigation water for farming available for growers. A study conducted using a low pressure irrigation system at the University field on St. Croix. Irrigation kit designed by Proximity Drip Irrigation, CA, containing overhead water collection tank (250gallon) for drip irrigation using a manual pump from a surface rainwater reservoir installed. The system applied to irrigate leafy greens in summer 2013. Quality yields in crops (spinach, bok choy, kale and lettuce) obtained. Data are under analysis. At Tennessee State University, a variety trial on organic sweet potato conducted using drip irrigation and quality yield obtained in three cultivars in various mulches. (TX) The Irrigation for Small Farms manual is in revision, and it will serve as the foundation and primary reference for a series of online presentations (webinars or shortcourses). Work also has been initiated to update and revise the Irrigation Training Program materials. Electronic delivery (via websites) is the primary venue for delivery of these materials to the public. They also provide ready access to materials for sharing among research and outreach programs. The Texas A&M AgriLife Research and Extension Texas High Plains Water Management Website (watermgmt.tamu.edu) provides access to educational materials, research summaries, and other information. Since cotton is the crop most widely irrigated with microirrigation in Texas, cotton-relevant microirrigation research reports and summaries, white papers and Extension fact sheets are available on the Texas A&M AgriLife Extension Service Cotton website (cotton.tamu.edu). Texas Southern High Plains microirrigation research reports are available on the Texas A&M AgriLife Research and Extension Center at Lubbock webpage (Lubbock.tamu.edu). Irrigation scheduling software and research manuscripts are available on the USDA-ARS Conservation and Production Laboratory (Bushland, Texas) website (http://www.cprl.ars.usda.gov/swmru-publications.php). Research and extension presentations, project reports and other information are available on the USDA-ARS Ogallala Aquifer Program website (http://www.ogallala.ars.usda.gov/); Ogallala Aquifer Program projects include research and technology transfer collaborations among faculty and scientists at USDA-ARS-Conservation and Production Laboratory, Kansas State University and Texas A&M AgriLife Research and Extension. Microirrigation research updates and management recommendations are presented in a variety of “face-to-face” venues, including traditional Extension “CEU” meetings for agricultural producers, Master Gardeners, and other end-users. Examples of irrigation workshops and presentations are listed in the Educational Activities section below. Five professional development events (in person and webinars) were conducted for County Extension faculty, with emphasis on the Texas High Plains, Rolling Plains and West Texas where there is most producer interest in microirrigation (especially subsurface drip irrigation). Jim Bordovsky and Dana Porter presented several invited presentations for Regional Water Planning Groups, Groundwater Conservation Districts, Water Conservation Symposia, Commodity Groups, Trade Associations, and International Corporations (Netafim, Bayer, etc.). Examples of these technology transfer activities are listed below. (FL) An experiment to determine differences, if any, in water uptake among infected and non-infected trees is being conducted. Young trees ~3 years old were planted in lysimeters filled with Immokalee fine sand collected from the top 0 to 30 cm of a field at the Southwest Florida Research and Education Center (SWFREC). Twelve Valencia (6 HLB positive and 6 HLB negative) and 12 Hamlin (6 HLB positive and 6 HLB negative) trees were used. The study uses the CR1000 program for monitoring changes in water use using weighing scales and monitoring soil moisture every 30 minutes. The water use was assumed to be the loss in weight between 10:00 am the previous day (maximum lysimeter weight following irrigation) and the weight at 7:30 am the following day (minimum lysimeter weight before next irrigation event is triggered) (Fig. 1). Soil moisture is measured every 30 minutes using TDR probes connected to the same data logger used to collect lysimeter weights. A weather station has been installed to collect weather data for estimating reference evapotranspiration (ETo) and temperature and relative humidity changes in the greenhouse. Stem water potential was measured using a pressure chamber (Model 125 1000, PMS Instrument Co., Corvallis, OR). Consistent readings for the program have been recorded from January 2014. Leaf area index of the trees were collected twice yearly using a Sun Scan LAI meter (Dynamax, Inc.) that measures light transmission through the canopy compared with light reaching the ground away from the tree canopy. The goals of the study are to 1) compare water use between Hamlin and Valencia oranges under greenhouse conditions, and 2) compare water use between HLB positive and HLB negative trees. Preliminary results for trees of similar sizes show similar water use and stem water potential between Valencia and Hamlin and Huanglongbing infected vs non-infected trees, and moisture contents slightly at or above field capacity between 10 and 17% volumetric water content for the period. Leaf area index is a direct measure of canopy density. The canopy had recovered in January and initial LAI measurements were taken, with no significant difference in mean LAI for Hamlin trees compared with Valencia and HLD infected compared with non-infected trees. Data collection continues including monitoring daily water use, soil moisture measurement every 30 minutes and measurement of stem water potential and leaf area index three times a year. Objective 4. Evaluate use of non-potable water through microirrigation (KS) A poster presentation entitled “Application of Biological Effluent with SDI” was given at an SDI Technology Field Day, Colby, Kansas in August. (NM) Salinity responses and salinity-related suppression of budbreak of drip irrigated pecan [Carya illinoinensis (Wangenh.) K. Koch] seedlings under different irrigation water salinity levels were investigated in the pot-in-pot system. No pecan seedlings under the irrigation treatment levels of 5.5 and 7.5 dS/m survived to the end of the 2-year growing period. Paper was published in HortSci. (OR) The FDA has drafted new fresh produce rules due in part to the contamination of fresh water with microorganisms that could spread human diseases. We examined drip vs. furrow irrigation in the movement of soil water carrying E. coli to the base of a vegetable crop using onion as a model. Surface irrigation systems reusing water can deliver bacteria to produce destined for fresh consumption. We tested furrow irrigation using canal water with moderate or high levels of E. coli contamination and drip irrigation using canal water and well water free of E. coli. The four irrigation systems (replicated five times) applied water to onion on silt loam. Water was sampled hourly for E. coli and the lateral movement of E. coli in the soil solution was tracked by soil samples and Sterile Soil Solution Samplers at the end of irrigations. Onions were sampled for E. coli contamination. The most probable numbers of E. coli in water and soil water were determined using IDEXX Colilert® and Colisure®, respectively, +Quanti-Tray/2000®. Furrow irrigation delivered E. coli to the soil immediately adjacent to the onion bulbs. E. coli movement under drip irrigation was mostly confined to near the drip tape. (OR) The delivery of bacteria through irrigation water could contaminate produce destined for fresh consumption. We tested chlorine dioxide at 1 and 3 ppm through drip irrigation to reduce generic E. coli in water delivered to a commercial onion field. Generic E. coli is used as an indicator species for fecal contamination in water. The most probable number of E. coli in water samples was determined using IDEXX Colilert® +Quanti-Tray/2000®. An AgriSystem 2.3 (CH2O, Olympia, WA) utilizing two metering pumps (Model EWC21Y1VC, Walchem, Holliston, MA) mixed 15% sulfuric acid plus additives (Sure Flow F, CH2O) and 15% sodium chloride plus additives (Clean Finish, CH2O) at a 1:1 ratio before the sand media filter station to generate chlorine dioxide. Water was sampled for E. coli at its canal source, after the filter station, and progressively across the field. Chlorine dioxide substantially reduced E. coli counts at all sampled locations and concentrations.