BASELINE GROUNDWATER COMPOSITION AND QUALITY BELOW IRRIGATED ALMOND AND WALNUT ORCHARDS IN DURHAM, CA, USA. Candace A. Gallion This study investigated groundwater quality in the Durham, California, USA area. The goal of the study was to determine baseline groundwater quality for the study area, whether crop type or time of year influenced groundwater quality, whether groundwater quality was significantly different among sample sites, and if groundwater quality test factors were correlated, and if any limiting factors for irrigation were present. Groundwater samples were collected and analyzed from eleven wells in almond (A2, A4, A5, A6, A7 and A8) and walnut (W1, W2, W3, W4 and W5) orchards and samples were sent to a laboratory to be analyzed for calcium (Ca), magnesium (Mg), potassium (K), sodium (Na), sulfate (SO4), bicarbonate (HCO3), iron (Fe), chloride (Cl), and nitrate (NO3) concentrations, total dissolved solids (TDS), hardness, pH, electrical conductivity (EC), and sodium adsorption ratio (S.A.R.). Groundwater samples were collected in September 2008, March 2009, May 2009 and September 2009. Results were analyzed using One-Way ANOVA testing and a correlation analysis, both at alpha levels equal to 0.05. Not many differences were discovered among sampling times or between tree types. Potassium was the only factor significantly different between the almond (0.98 ppm) and walnut (0.73 ppm) sites, a trend possibly resulting from greater usage of potassium fertilizer in almond orchards as compared to walnut orchards. Sodium adsorption ratio was greater in March 2009 (0.35) and May 2009 (0.34) than either September sample (both 0.26) due to leaching of sodium into groundwater following rain events. Mean potassium concentration was greater in March 2009 (1.49 ppm) than in May 2009 (0.69 ppm), September 2008 (0.75 ppm) or September 2009 (0.63 ppm), also due to leaching of potassium into groundwater during the rainy winter months. Many differences were found among the sampling sites. In general, W1, W3, W5, A2, A4, A6 and A8 had lower concentrations of the test factors, and therefore purer groundwater, than W2, W4, A5 and A7. The majority of the test factors had significant, positive correlations with other test factors, with the exception of pH; pH had primarily significant negative correlations with the other test factors. Test factors were not present in groundwater at levels to cause any severe irrigation restrictions. Slight-to-moderate limitation levels were found for HCO3 (all sample sites), TDS and EC (W2, W4, A5, and A7), and NO3 (W1, W2, W3, W4, A4, A5, and A7). Overall, groundwater at the sampled sites was suitable for use as irrigation water, not many tree type or temporal differences in groundwater quality were discovered, many differences were found among sample sites, and many correlations were present among test factors. The information gathered and interpreted in this study will be useful for making management decisions regarding use of the tested groundwater for irrigation. Keywords: groundwater quality, irrigation suitability

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Tomato fruit have been associated with numerous outbreaks of salmonellosis in recent years. Trace back suggests tomato fruit may become contaminated during pre-harvest, however exact routes are unclear. The objective of this study was to determine the potential for Salmonella enterica serotype Newport to be associated with the roots, leaves, stems, and ultimately fruit of red round tomato plants through contaminated irrigation water, at various stages of plant development, when grown under controlled environmental conditions. Tomato plants were individually root irrigated with 250 or 350 ml (depending on growth stage) of 7 log CFU/ml S. Newport contaminated irrigation water every seven days. Presence of the pathogen in plant tissue was evaluated at five growth stages; 14 days post transplant, early fruit, mid fruit, full fruit, and terminal stages. At each stage, roots, stems, leaves, and two tomato fruit, if present, from four S. Newport and four water irrigated (negative control) tomato plants were sampled for S. Newport contamination. Association of S. Newport was detected in tomato roots and stems using both conventional plating and molecular techniques. Twenty-four samples were confirmed positive for S. enterica using PCR. Sixty-five percent of the roots, 40% of the stems, 5% of the leaves and 5% of the fruit sampled were confirmed to contain S. enterica. Overall, there was significant difference in the presence of S. Newport according to tissue sampled (roots > stems > leaves and fruit) (P > 0.05). There was no correlation between growth stage and presence of S. Newport in tissues (P > 0.05). Ultimately, irrigation with S. Newport has a low probability of contaminating tomato fruit. / Master of Science

La Californie est la plus grande région productrice de fraise en Amérique du nord et cette production ne serait pas possible sans irrigation. Toutefois, les ressources en eau sont limitées dans cette région et la qualité des eaux souterraines est menacée par le lessivage des nitrates. Dans ce contexte, il est essentiel d’optimiser la gestion de l’irrigation afin d’économiser l’eau et de limiter le lessivage tout en maintenant le même niveau de productivité. Des travaux antérieurs ont démontré que le rendement était maximal avec une gestion humide par tensiométrie avec un seuil de -10 kPa, mais l’efficacité d’utilisation de l’eau (EUE) n’est pas maximisée. Des gains d’efficacité pourraient être obtenus en utilisant un seuil plus sec lorsque les besoins en eau de la plante sont plus faibles. Le premier volet de cet ouvrage consistait à comparer différentes stratégies d’irrigation de déficit à une gestion humide et à une gestion conventionnelle de l’irrigation. Des augmentations significatives de l’EUE ont été obtenues avec l’irrigation de déficit sans diminution de rendement significative comparativement à la gestion humide. Toutefois, ces régies tendaient à diminuer le rendement de 0 à 3 % et comme le prix du produit est élevé, il serait pertinent dans des travaux futurs de vérifier si cette tendance de baisse du rendement se confirme. De plus, la gestion par tensiométrie a diminué le lessivage comparativement à la gestion conventionnelle puisque cette technologie permet un ajustement plus précis du temps d’irrigation afin de limiter la perte d’eau et de nutriments au-delà de la zone racinaire. Le deuxième volet visait à mesurer l’impact de différentes régies d’irrigation sur la salinité du sol et à vérifier si la conductivité électrique (CE) de la solution du sol était un indicateur fiable pour suivre la concentration de nitrate dans le sol. Différentes régies d’irrigation basées sur le potentiel matriciel du sol ont été comparées à des régies basées sur l’évapotranspiration et à la régie conventionnelle du producteur. Aucune différence significative n’a été observée sur les deux sites, tous les traitements ont subi une hausse de salinité pendant la saison, mais les pluies hivernales ont été suffisantes pour lessiver cette accumulation de sels. La régie d’irrigation de déficit par tensiométrie ne présente donc pas de risque d’augmentation de salinité dans le sol comparativement à une gestion humide. De plus, la CE du sol s’est avérée inefficace pour estimer la concentration en nitrate du sol puisque la contribution de l’ion nitrate est très faible comparativement à d’autres ions naturellement présents dans le sol. / California is the largest strawberry producing region in North America and this productionwould not be possible without irrigation. However, water resources are limited in thisregion and the water quality has become an issue in some growing areas due to nitrateleaching. Therefore, it appears essential to optimize the irrigation management to savewater and to limit the leaching of nutrients without decreasing fruit productivity. Previousworks have shown that maximum yield is obtained under wet irrigation managementconditions (i.e. irrigation being initiated when a soil matric potential threshold of -10 kPawas exceeded), but the water use efficiency (WUE) is not maximized. WUE could beimproved by using drier thresholds when the water need of the plant is lower.The first chapter aimed to compare different deficit irrigation strategies to wet managementand to conventional grower management. Significant increases in WUE were obtainedusing deficit irrigation compared to wet management (-10 kPa) without any significantimpact on fruit yield. However, deficit irrigation tended to decrease fruit yield by 0 to 3 %and given the high value of the strawberry product, it would be relevant to verify whetherthis trend of yield loss is confirmed. Moreover, using a predetermined soil water potentialthreshold to manage irrigation more efficiently could reduce the water leaching comparedwith conventional grower management as this technology allows a finer adjustment ofirrigation period and therefore limits the loss of water and nutrients beyond the root zone.The second chapter aimed to measure the impact of different irrigation strategies on soilsalinity and to determine whether the electrical conductivity (EC) of the soil solution was anappropriate indicator to follow the concentration of nitrates in the soil. Different irrigationmanagements based on soil water potential were compared with irrigation managementbased on evapotranspiration (ET) and with conventional grower management. Nosignificant difference was observed among treatments on both sites, as all five irrigationstrategies resulted in a salinity build-up over the season, but winter rainfalls were sufficientto leach the salt accumulation from the root zone. Thus, tension-based deficit irrigationmanagement does not represent a risk of increasing the soil salinity. Furthermore, the ECof the soil turned out to be inadequate to assess the nitrate concentration in the soil sincethis ion did not have a great impact on the soil salinity compared with other ions naturallypresent in the soils investigated.

Le transport de solutés est gouverné par le flux de l’eau dans la zone non saturée du sol. Ces substances chimiques peuvent migrer jusqu’à atteindre la nappe phréatique et contaminer les ressources en eau disponibles. De ce fait, l’application de l’eau et des fertilisants aux cultures doit se faire de manière à minimiser ses répercussions sur l’environnement. La modélisation numérique constitue un outil puissant pour optimiser les régimes hydriques et nutritifs dans le sol en production agricole. L’objectif de ce travail est de comprendre les processus de transport des solutés induits par l’irrigation de surface et dans les sols sableux à fort drainage des champs de canneberges. Il veut aussi simuler différentes conditions climatiques et tester leurs influences sur le transport des solutés.Trois expériences de transport de KBr ont été menées de manière similaire en laboratoire, dans un simulateur de drainage. Des lysimètres à succion et des tensiomètres installés à différentes profondeurs dans le simulateur ont permis respectivement de collecter les lixiviats et de mesurer le potentiel de l’eau du sol. Un modèle analytique de fonction de transfert convectif lognormale et le modèle numérique Hydrus-2D ont été utilisés pour analyser les données mesurées. Les modèles fournissent de très bonnes performances pour la simulation du transport de bromure avec des valeurs de R! > 0,70 et des erreurs de simulation acceptables en termes de RMSE. Le modèle de fonction de transfert indique qu’environ 230 mm d’eau est nécessaire pour déplacer un front de bromure de la surface du sol jusqu’à une profondeur de 100 cm. Le modèle Hydrus-2D a pu simuler avec succès les différents scénarios climatiques et montre que les scénarios les plus humides influencent beaucoup plus la migration des solutés. Pour tous les scénarios testés, aucun cas de lessivage n’a été enregistré hors du profil de sol. / Solutes transport is governed by the flow of water in the unsaturated zone of the soil. These chemicals can migrate to the water table and contaminate available water resources.Therefore, the application of water and fertilizers to crops must be done in a reasonable manner in order to minimize its impact on the environment. Mathematical modeling is a powerful tool for optimizing water and nutrient regimes of the soils in agricultural production. The objective of this work is to understand the solute transport processes induced by surface irrigation in sandy soils with high drainage of cranberry fields. A second objective is to simulate different climatic conditions and test their influences on the transport of solutes. Three KBr transport experiments were carried out in a similar way in the laboratory, in a drainage simulator. Suction lysimeters and tensiometers installed at different depths in the simulator made it possible respectively to collect the leachate and to measure the potential of the water soil water. A lognormal convectif transfer function analytical model and the Hydrus-2D numerical model were used to analyze the measured data. The models provide very good performance for the simulation of bromide transport with values of R! > 0.70 and acceptable simulation errors in terms of RMSE. The transfer function model indicates that approximately 230 mm of water is required to displace abromide front from the soil surface to a depth of 100 cm. The Hydrus-2D model was able to successfully simulate the different climate scenarios and shows that the wet test scenarios have a much greater influence on the migration of solutes. For all the scenarios tested, no case of leaching was recorded outside the soil profile.

Call number: LD2668 .T4 1985 M49 / Master of Science