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Digitized by Kansas Correctional Industries

Environmental factors and produce practices influence the microbial quality of produce. The objective of this study was to determine the microbial quality of irrigation water used for the production of fresh produce in Arizona and factors, which may influence this water quality such as canal size, location and rainfall. A total of 117 samples were collected from irrigation canals in Yuma County between June 2001 and March 2003 and 263 water samples were collected in Maricopa County between May 2002 and February 2003. Parameters such as temperature, turbidity, conductivity and pH were recorded for all samples. Water samples were analyzed for microbial indicators which included total coliforms, Escherichia colt, Enterococcus , and Clostridium perfringens. Sampling sites were examined for the presence of Giardia spp., Cryptosporidium spp., Noroviruses, Salmonella spp. and Campylobacter spp. Samples collected in Yuma County showed that 4.3% of the samples were positive for Giardia spp., 19.6% were positive for Cryptosporidium spp., 17.4% were positive for Noroviruses, 20.7% were positive for Salmonella spp. and 55.2% were positive for Campylobacter spp. Overall, results from samples collected in Maricopa County showed that 2.3% of the samples were positive for Cryptosporidium spp, 18.2% were positive for Noroviruses, 28.9% were positive for Salmonella spp. and 68.7% were positive for Campylobacter spp. Giardia spp. were not detected in any samples. One-way ANOVA did not demonstrate any significant difference between microbial indicator concentrations in samples collected from Yuma and Maricopa Counties. Overall, E. colt concentrations correlated strongly with Enterococcus (r=0.858) in samples collected from Maricopa County. Rainfall within 7 days prior to sampling correlated strongly with overall averages for each indicator, the strongest correlation was seen with E. colt (r=0.726). Overall, the main canals tended to have lower microbial numbers than the lateral/drain canals. In Maricopa County, the sampling sites located furthest north and furthest south on each of the main canals tended to have the higher microbial numbers. The sampling points located furthest south tended to be ranked higher in terms of microbial loads. There appeared to be no positive correlation between the levels of microbial indicators and enteropathogens in this study.

No description available.

No description available.

The overabundant proliferation of aquatic weeds in South African water conveyance systems cause a series of operational problems. Filamentous algae, such as Cladophora glomerata and pondweeds impede flow and reduce the capacity of irrigation canals to a significant extent. In worst case scenarios, irrigation scheme managers are faced with situations where they are unable to deliver water at the downstream ends of canal systems. This situation also contributes to water losses, crop losses and structural damage to concrete-lined canals. This dissertation is the product of a research project funded by the Water Research Commission to investigate the possible application of sterile (triploid) grass carp (Ctenopharyngodon idella) as biological control agent on aquatic weeds in concrete-lined irrigation canals. The aims of the project were firstly to investigate the suitability of a concrete-lined irrigation canal as grass carp habitat; secondly to test the efficacy of sterile grass carp as bio-control agent on filamentous algae; thirdly to evaluate the economic feasibility of this biological approach against the current chemical, physical and mechanical control methods; and fourthly to propose a management plan for the operational application of triploid grass carp as bio-control agent in irrigation canals. To achieve the goals set for the project, the Ramah-3 Canal near the town of Orania, was selected to serve as experimental canal. This canal can be regarded as a typical South African concrete-lined canal, and is located in the Orange-Riet River Canal System, downstream of the Vanderkloof Dam. As the majority of local irrigation canals are concrete-lined, skepticism existed amongst local scientists if the fish will be able survive in canals with a presumed high constant flow and low diversity of hydraulic biotopes. It was therefore a priority to establish the suitability of concrete-lined canals as habitat for this herbivorous fish specie. The study found that flow velocities in the Ramah Canal System never exceeded 1 m/s, even under high flow conditions (full capacity and 110% plus conditions) of more than 5 m3/s. It was found that grass carp thrived at flow rates ranging from 0.48 to 0.80 m/s, moving with ease upstream and downstream in a 16 km long experimental section of the Ramah-3 Canal. The sterile grass carp controlled the algal biomass in the Ramah Canal to significant levels. Cladophora was efficiently controlled at stocking rates of 3 to 7 fish per km canal. Triploid grass carp retrieved from the canal system after a six-month experimental period were found to be in an excellent physiological condition and displayed a mean weight increase of more than 300%. An ideal stocking protocol will probably be 10 individuals of 20 – 30 cm in length per kilometer canal, with a 10-15% annual supplementation figure. Civil structures, such as culverts, super-elevated canals and bridges will provide the fish with sufficient protection against possible predators. A few possible adaptations to the existing canal operation regimes should ensure that triploid grass carp could be managed as an effective biological control agent. This should be determined on a site-specific basis and could include additional civil structures such as sanctuary dams and small in-line fishways to ensure free migration throughout the target system. An attempt was made to conduct a brief economic analysis, based on information on expenditures of local irrigation schemes on aquatic weed control in their canals. The outcome of this brief investigation was in line with overseas findings in that biological control with sterile grass carp will be more economical than the currently applied control methods of herbicidal and mechanical or physical control. It can be concluded that the fish adapted to the artificial conditions experienced in a concrete-lined canal and perform their task as bio-control agent with ease. The author is of the opinion that this bio-control technique will contribute to the current Integrated Aquatic Weed Management Programmes (IAWMPs) of the Department of Water Affairs and Forestry. Site-specific conditions for each irrigation scheme will however, dictate a different approach to the aquatic weed problem. It is therefore strongly recommended that suitable qualified specialists should develop all aquatic weed management programmes on a site-specific basis. / Prof. G.J. Steyn

Selected components of the water and energy balances at the surface of a bare clay loam were measured at 57 locations in a 1 ha field. Spatial and temporal variability of these components were also studied. Components included evaporation, irrigation, moisture storage, sensible heat flux and long wave radiation. Sub-studies were conducted on irrigation uniformity under low pressure sprinklers; and, on steel versus plastic microlysimeters (ML) of various lengths. An energy balance model of evaporation, requiring minimal inputs, was developed and validated giving an r$\sp2$ value of 0.78. Model improvements included an easy method of accurately estimating soil surface temperature at many points in a field, and an empirically fitted transfer coefficient function for the sensible heat flux from the reference dry soil. The omission of soil heat flux and reflected shortwave radiation terms was shown to reduce model accuracy. Steel ML underestimated cumulative evaporation compared to plastic ML at 20 and 30 cm lengths. Cumulative evaporation increased with ML length. The 10 and 20 cm ML were too short for use over multiple days but 30 cm ML may not be long enough for extended periods. Daily net soil heat flux for steel ML averaged 44% higher than that for both plastic ML and undisturbed field soil. Christiansen's uniformity coefficient (UCC) was close to 0.83 for each of 3 irrigations when measured by both catch cans and by profile water contents. But UCC for the change in storage due to irrigation averaged only 0.43 indicating than the high uniformity of profile water contents was more due to surface and subsurface redistribution than to the uniformity of application. Profile water contents and catch can depths were time invariant across at least 3 irrigations. Midday soil surface temperatures and daily evaporation were somewhat less time invariant. Variogram plots for evaporation and surface temperature showed mostly random behavior. Relative variograms represented well the spatial variability of both catch can depths and profile water contents. A strong link was demonstrated between the time invariance of a variable and the usefulness of kriging on that variable.

A field study was conducted to determine water and salt distribution patterns in a soil irrigated by pairs of double-chamber, perforated polyethylene tubes. The study consisted of two experiments: a water distribution experiment and a salt distribution experiment. Both experiments were conducted at the same site with experimental plots having two perforated lines 9 m long, spaced 0.60 m. The tubing had outer orifices 0.5 mm in diameter spaced 0.30 m along the tubes. The water distribution experiment consisted of water application to the bare soil for periods of time of 3, 6, 9, and 12 hours. After each test a trench was dug normal to the irrigation tubes and samples were taken to determine soil moisture on a dry weight basis. Moisture profiles are presented for the various tests. The salt distribution experiment was conducted in the Fall of 1973 and repeated in the Spring of 1974. It consisted of four irrigation treatments comprising two irrigation levels and two levels of salt in the irrigation water (327 and 2000 milligrams per liter of salts). Experimental plots were planted with lettuce and soil samples taken after planting and after harvesting the lettuce. Soil samples were analyzed for electrical conductivity of the soil saturation extract, pH, calcium, magnesium, sodium, potassium and nitrates. Saturation extract conductivity profiles in the soil are presented for different treatments. After planting and after harvest concentrations of calcium, magnesium, sodium, potassium, nitrates and pH values are also shown. Seasonal water application and lettuce yields are presented for both trials Water movement in the soil was 2 to 3 times greater in the horizontal than in the vertical direction. Wetted soil volume showed a high positive correlation with both the volume of water applied and with time of application. Salt accumulation occurred mainly at the soil surface between the irrigation tubes and away from the main root zone of the plants. The surface accumulation was followed by a leached zone. There were no significant differences in yield among plots receiving different treatments. Seasonal water application was less than half of the seasonal amount of water normally applied for furrow irrigated lettuce in the Tucson area. It was higher than experimental determinations of seasonal consumptive use for lettuce at Mesa, Arizona. The study indicated that trickle irrigation with water of high salt content is likely to cause a high surface concentration of salts. Application of extra amounts of water by the trickle system, or another method, is recommended to leach the salts to a depth below the crop root zone.

Call number: LD2668 .T4 1986 V57 / Master of Science / Biological and Agricultural Engineering