Call number: LD2668 .T4 1960 B35

Call number: LD2668 .T4 1961 M67

Call number: LD2668 .T4 1985 Y67 / Master of Science

This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

The thesis numerically models and investigates the effect of a variable water table on the soil moisture content. The modelling is done using COMSOL and Richards' equation. The temporal variation plots can be used to find the capillarity of the soil and its impact on other phenomenon such as vapor intrusion and infiltration.

The objective of the study was to determine if and how grain sorghum hybrids (Sorghum bicolor (L.) Moench) of different maturity dates compete with one another when planted in adjacent rows under different moisture levels. Five sorghum varieties differing in their maturity were used: Taylor Evans Y-101-G coming to mid-bloom in 71 days, RS 610, Asgrow Corral, DK 64 and DK 69 coming to mid-bloom in 56.9 days, 61 days, 69.3 days and 75.6 days respectively. Six agronomic characters were measured to determine the effect and extent of competition. They included the number of days to mid-bloom, tiller ratio, grain yield, grain test weight and 300-seed weight. According to the results, adjacent row competition took place due to differences in maturity date for grain yield and 300-seed weight. An almost equilibrium appeared between loss or gain of border rows compared to the loss or gain of the middle row. Also the length of time between day to mid-bloom of the border rows hybrids and the center row genotype was important in the extent of competition effects.

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

An investigation into the flux of soil water under the influence of a thermal gradient was conducted in closed soil systems in the laboratory. A thermal gradient was imposed across the sandy loam soil columns and measured continuously for the duration of the experiment. The movement of soil water was monitored periodically using a gamna ray attenuation device until the columns reached an apparent steady state condition with no net flow. Imposition of boundary conditions enabled delineation and evaluation of the system parameters. Values of net water flux in soil columns were analyzed using the Taylor-Cary irreversible thermodynamic and the Philip-de Vries theory of water movement. Application of the Taylor-Cary equation to describe the flow reveals that for initial time periods the flow is slightly overestimated, however, this small difference may be within the realm of experimental error. The flow predicted by the Taylor-Cary equation for the succeeding time periods greatly exceeded the measured flow rates. The Philip-de Vries theory of soil-water movement predicted greater net water movement than was observed in soil columns with a temperature gradient of 2.67 ° C/cm and with an average soil water content of 10.5 to 11.5 cm³/cm³. The following conclusions were reached after analyzing the data for the sandy loam soil material. Water content and temperature influence the diffusion transfer coefficient, β*, in a closed soil system. Thus the transfer coefficient is not an independent entity. Hysteresis is present in the wetter part of the system, although the magnitude of hysteresis involved is unknown. The β* coefficient can be evaluated only in regions where hysteresis is not present. The transfer of soil water was greater in a leached soil with no air gap than in an unleached soil with no air gap. There was supporting evidence that liquid water continuity did not exist throughout the column since there was no appreciable solute transport. The observed change in soil water content distribution at 18.0 cm³/cm³ to the imposed temperature gradient was not significant for the sandy loam soil material. The observed soil water flux increased in response to the imposed temperature gradient as soil water content decreased from 18.0 to 10.5 cm³/cm³. No analytical procedure is presently available that will describe thermally induced flow under all conditions. The approach of Philip and de Vries requires that the physical properties of the soil must be known accurately so that correct estimates can be made of the individual diffusivities. This approach has been found to predict the flow with some success on relatively dry soils, however, it possibly would be in error when estimating thermally induced flow in regions where liquid continuity exists and up through to a saturated system. The Taylor and Cary equation may be adequate for describing water flow to predict trends or obtain comparative values, however, much additional work needs to be done before it will adequately describe the flow for transient conditions or steady state conditions where nonuniform water content distributions are present.

Sampling and analysis of the soil moisture distribution and the overall water balance in an irrigated area are the central topics of this work. An experimental study was made in a 14-ha, border-irrigated, alfalfa field near Coolidge, in Final County, Arizona, during the summer/fall 1983. The water stored in the soil profile and its change with time were normally distributed, with coefficients of variation of about 10 and 25 percent, respectively. Temporal correlations were significant for storage (about .60), but absent in the other. Variograms were calculated to show the spatial structure of the distributions. An analogous statistical description was presented for the alfalfa yield. Also shown is a methodology to infer errors due to the field calibration of the neutron probe. Another task was to assess a methodology to minimize sample numbers for soil-water storage. Following the ideas of Vachaud and co-workers in France, it was verified that rankings of the measurements were approximately time-preserved. As a consequence, only a few key locations need to be sampled to evaluate the mean in those circumstances. Included also is an approximation to predict confidence intervals for estimating the mean, when such "representative sites" are used. Using irrigation inflow and rainfall, a procedure is defined to make use of the soil moisture data to evaluate irrigation efficiency and uniformity. Evapotranspiration (ET) distribution can also be assessed by soil moisture measurements, but only conditionally. For example, adaptation of the "field capacity" concept in the field study led to average daily ET rates in the range of 3-11 mm day⁻¹. ET and potential ET (PET) were also determined from weather data. Crop temperature was required in the ET calculation. Such a model, developed by Hatfield and co-workers, was judged satisfactory in our application, but not the Penman PET estimates. It is concluded that the ET model is promising, particularly if remote sensing of the temperatures is successful in the future. Also shown as a possibility is the use of plant temperature and pan evaporation data to infer crop water stress.

Ultra low-k dielectric films are expected to widely replace SiO2 as the interlayer dielectric for the next-generation microelectronic devices. A challenge facing the integration of these dielectrics in manufacturing is their interactions with gaseous contaminants, such as moisture and isopropanol, and the resulting change in their properties. Moisture retained in the film not only has detrimental effect on the k value of the film but also causes reliability and adhesion problems due to gradual outgassing. The physical and chemical interactions of moisture with porous spin-on and chemical vapor deposited (CVD) dielectrics are investigated using temperature- and concentration-programmed exposure and purge sequence together with trace moisture analysis, using atmospheric pressure ionization mass spectrometry.The model compounds in this study are porous Methylsilsesquioxane and Black Diamond II films, deposited and treated under typical manufacturing conditions. Transmission Electron Microscope (TEM) studies showed that etching and ashing processes resulted in the formation of two layers, a damaged layer and non-damaged layer, which significantly changed moisture interaction properties.Moisture sorption and desorption studies showed that as compared to SiO2 these films not only have a higher uptake capacity but also a slower and more activated moisture removal process. This could be a significant problem in successful integration of these films in IC manufacturing process.A process model was developed that provided information on the mechanism and kinetics of moisture uptake and release in thin porous films. The model elucidated the effect of film properties on the contamination uptake as well as outgassing. The model is a valuable tool for designing an optimum process for contamination control and removal in porous films.Another concern in IC manufacturing is the outgassing of impurities of electropolished stainless steel (EPSS) surfaces used in UHP gas distribution system. Moisture interaction with EPSS surface is studied in sub ppb range. A fundamental model was developed to study the mechanism and kinetics of moisture uptake and release from EPSS. The model developed would be a valuable tool for designing an optimum process for contamination control and to predict the moisture dry down performance of large-scale, systems.