Subsurface Drip Irrigation for Vegetables Using Effluent in Arid Lands
Investigators (most current known information)
Proposal Abstract
The present study was conducted to compare two different irrigation systems, subsurface drip irrigation (SDI) and furrow irrigation (FI), in terms of viral contamination and survival and water use efficiency (WUE) when tertiary effluent is used for irrigation water in arid and semi-arid regions. The water use efficiency (WUE) of the SDI system was higher than that of the FI system, which is consistent with previous research results. Since the SDI system supplies water lose to the root zone, the crop can use water more efficiently, while furrow-irrigated water has a greater chance of evaporation. The effluent was injected with bacteriophages of PRD1 and MS2. A greater number of PRD1 and MS2 were recovered from the lettuce in the SDI plots as compared to those in the FI plots. This was due to the direct contact of the lettuce leaves with the irrigation water, which penetrated the soil surface. The loose soil structure was caused by field plowing in the first year and by incomplete displacement of the preferential water paths during the second year. To estimate viral persistency in terms of heat units, the cumulative degree days required for 99.9 % viral die-off were calculated as a combination of the inactivation rates of viruses and average degree days, which is the cumulative degree days divided by the duration of the experiment. Greater heat units were required in the subsurface while fewer cumulative heat units were necessary for the same viral reduction on the surface of the lettuce. MS2 seemed to be more persistent in humid conditions than in dry conditions, in contrast to PRD1, which showed greater persistency in dry conditions. PRD1 was more tolerable at higher temperatures than MS2 and showed overall greater heat unit requirements to realize 99.9 % die-off. Although temperature as a single factor cannot sufficiently explain virus survival patterns, the average heat unit can be an effective parameter for reflecting the effect of daily temperature changes. Results from this study suggest that deeper installation of drip tapes and/or frequent irrigations as alternative practices are appropriate in order to minimize soil surface wetting in SDI plots and reduce potential contamination.
Outcome
Articles in Journals
Choi, C.Y., S. Stine, J. Song, C.P. Pimentel, C. Gerba and A. Tamimi. 2004. "Role of irrigation and wastewater reuse in the viral contamination of iceberg lettuce." IWA Water Science and Technology.
Presentations
Choi, C.Y., J. Pimentel and C. Gerba. 2003. "Role of Irrigation and wastewater reuse: Comparison of subsurface irrigation and furrow irrigation." Presented, IWA 4th international symposium on wastewater reclamation and reuse in waste science, technology, and water supply. Mexico City.
Stine S., I. Song, J. Pimentel, C.Y. Choi and C. Gerba. 2002. "Comparison of subsurface and furrow irrigation in the viral contamination of iceberg lettuce." Presented, International Association of Food Safety annual conference. San Diego CA.
Song, I., S. Stine, J. Pimentel, C.Y. Choi and C. Gerba. 2003 "Comparison of subsurface drip irrigation and furrow irrigation." Presented, ASAE annual international meeting. Las Vegas NV.
Ph.D. Dissertation
Song, I. 2004. Subsurface drip irrigation with wastewater and the effects of environmental factors on microbial survival. Ph.D. Dissertation. The University of Arizona. Tucson AZ. (in press).