Many problems of management of irrigated soils require a knowledge of the soil moisture status and its relationship to plant growth before they can be solved.

The purpose of this thesis was to compare the tensiometer and climatic methods of scheduling irrigation of potatoes under field conditions. Tensiometers were placed in a 160 acre field to maintain the crop within the optimum moisture range and schedule irrigations. An automatic solid set system was used to apply water to the potato crop. Instrumentation was used to determine daily input for the climatological method. Daily evapotranspiration (Et) was computed and Et (tensiometer) was comPared with Et (climatic). The results showed total variation of the climatic method from the tensiometer method of .62 inches or less than 5 per cent. The study indicated that the climatological method would have under irrigated the potato crop by . 62 inches during the 48 day study. Variations are also shown for each irrigation interval. Results indicated that a combination of both methods would allow the most feasible approach to scheduling irrigation of potatoes.

The mountainous areas in the Intermountain West (IMW) of the North America are considered as the major water reservoir for the Western US. Summer evapotranspiration (ET) and soil moisture are key factors affecting the annual water yield in the montane region of the IMW. This research estimated ET of four common vegetation types (aspen, conifer, grass, and sage) and areal soil moisture in an advanced instrumentation site located at the T.W. Daniel Experimental Forest (TWDEF). Among instrumented forest research sites worldwide, TWDEF is one of a few with triplicate measures of meteorological parameters, radiation, and soil moisture within four common vegetation types in the IMW. This unique dataset enables study and understanding of the ecological and hydrological responses to climate change in Utah and the IMW region. In a second phase of this study, summer water uses from the four common vegetation types were simulated using a numerical simulation model, Hydrus-1D. The simulation was informed by soil moisture measurements at three depths (0.1 m, 0.25 m, and 0.5 m) and by ET measured from an eddy covariance tower. The results confirmed the value of numerical simulations as a viable alternate method to estimated ET where no direct ET measurements are available. It also provided comparison of water use by these vegetation species including both high and low water years. In the third phase of this study, a comparison was made between the intermediate-scale areal soil moisture measured by a Cosmic-ray neutron probe (CRNP) and the in situ TDT soil moisture network at the TWDEF site. Improved correlations were obtained, especially after shallow rainfall events, by including numerically simulated soil moisture above 0.1 m where no measurements were available. The original CRNP calibration exhibited a dry bias during spring/early summer, leading to the need for a site-specific enhanced calibration, which improved the accuracy of the CRNP soil moisture estimate at the TWDEF site.

1v. (various paging) : / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (D.Sc.)--University of Adelaide, Dept. of Botany, 1978

Thesis (M.S.)--University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (February 7, 2007) Includes bibliographical references.

Thesis (M.S.)--University of Delaware, 2006. / Principal faculty advisor: Tracy DeLiberty, Dept. of Geography. Includes bibliographical references.

The overarching goal of this dissertation project was to address several fundamental aspects of applying site-specific crop management for fiber quality in cotton production. A two-year (2005 and 2006) field study was conducted at the IMPACT Center, a portion of the Texas A&M Research farm near College Station, Texas, to explore the spatial variability of cotton fiber quality and quantify its relationship with in-season soil moisture content. Cotton samples and in-situ soil moisture measurements were taken from the sampling locations in both irrigated and dry areas. It was found that generally low variability (CV < 10%) existed for all of the HVI (High Volume Instrument) fiber parameters under investigation. However, an appreciable level of spatial dependence among fiber parameters was discovered. Contour maps for individual fiber parameters in 2006 exhibited a similar spatial pattern to the soil electrical conductivity map. Significant correlations (highest r = 0.85) were found between most fiber parameters (except for micronaire) and in-season soil moisture in the irrigated areas in 2005 and in the dry area in 2006. In both situations, soil moisture late in the season showed higher correlation with fiber parameters than that in the early-season. While this relationship did not hold for micronaire, a non-linear relationship was apparent for micronaire in 2006. This can be attributed to the boll retention pattern of cotton plants at different soil moisture levels. In addition, a prototype wireless- and GPS-based system was fabricated and developed for automated module-level fiber quality mapping. The system is composed of several subsystems distributed among harvest vehicles, and the main components of the system include a GPS receiver, wireless transceivers, and microcontrollers. Software was developed in C language to achieve GPS signal receiving, wireless communication, and other auxiliary functions. The system was capable of delineating the geographic boundary of each harvested basket and tracking it from the harvester basket to the boll buggy and the module builder. When fiber quality data are available at gins or classing offices, they can be associated with those geographic boundaries to realize fiber quality mapping. Field tests indicated that the prototype system performed as designed. The resultant fiber quality maps can be used to readily differentiate some HVI fiber parameters (micronaire, color, and loan value) at the module level, indicating the competence of the system for fiber quality mapping and its potential for site-specific fiber quality management. Future improvements needed to make system suitable for a full-scale farming operation are suggested.

Wilting during shelf life is a major cause of postharvest shrink for bedding plants shipped long distances from production greenhouses to retail outlets. The objective of this research was to determine if irrigation at lower, constant substrate moisture content (SMC) during greenhouse production would be a feasible way to acclimate plants for reduced shrinkage during shelf life, while potentially conserving irrigation water. Rooted plugs of Angelonia angustifolia 'Angelface Blue' were grown in greenhouse production until a marketable stage in substrates irrigated at SMC levels of 10, 20, 30, and 40% using a controlled irrigation system. At the end of the greenhouse production stage, plants were irrigated to container capacity and subjected to a simulated shipping environment, in shipping boxes in the dark for two days. After shipping, plants were placed back in the greenhouse and watered minimally to simulate a retail environment. Data was taken at the end of each stage i.e. greenhouse production, simulated shipping, and simulated retail. Parameters measured at the end of the production stage were fresh and senesced flower number, stem number, pre-dawn and mid-day water potential, SPAD meter readings (Experiment 2), and plant height and node number segmented into vegetative, flowering, and bud area. Plant quality was observed and rated. At the end of the simulated retail stage, the same data was taken, along with fresh and dry shoot and root weight. Results indicated that as SMC decreased from 40 to 10%, plants were shorter in height, but had proportional flowering sections (Experiment 1) or more compact flowering sections (Experiment 2). The volume of water received by the 40% SMC plants was three times greater (Experiment 1) and 12 times greater (Experiment 2) than the 20% SMC plants during greenhouse production, and two times greater (Experiment 1) and nine time greater (Experiment 2) during simulated retail. Additionally, the 40% SMC plants used 15 liters (Experiment 1) and 38 liters (Experiment 2) of water during greenhouse production compared to the 20% SMC plants using only three liters in both experiments. During simulated retail the 40% SMC plants used six liters (Experiment 1) and nine liters (Experiment 2) of water while the 20% SMC plants used five liters (Experiment 1) and three liters (Experiment 2) of water. During production, mid-day water potentials decreased as the SMC levels decreased, but at the end of the simulated retail (Experiment 1), the mid-day water potentials were all the same, suggesting plants that were drought stressed during production area were acclimated to lower water levels experienced in retail settings. Overall, the 20% SMC treatment produced the best postharvest quality plant due to reduced plant height without detrimental effects on flowering. The results demonstrate that while conserving water, controlled irrigation at a medium-low SMC can produce high quality plants that have equal shelf life to those that are irrigated at high levels.

Sandy soils are among the least productive soils because of their inability to store adequate water for plant growth. Their high percolation rate not only allows water to move quickly beyond the root zone, but also washes nutrients below the reach of plant roots. High evaporation occurs from the soil surface. Many acres of these soils around the world are left out of crop production. This study is a contribution to bring these soils into production by increasing their ability to hold more water in the root zone. Several promising methods of enhancing these soils were simulated, surface mulch, buried barrier layer, and a combination of both. The effects of varying texture and thickness of these layers and varying evaporative demand were investigated. The impact of such modifications on solute distribution in the soil was also simulated. A simulation model of water and solute transport in layered soils was developed for this purpose. The Richards equation for one-dimensional water transport in unsaturated soils was modified to account for the water jump between the layers. The solute transport equation was also modified by implementing the same theory of water infiltration in layered soil to the solute convective transport. The Crank-Nicolson scheme was used to solve the transport equations with the help of the Newton-Raphson iteration method. The results of the simulation show that the proposed methods increase water content in the sandy soil by up to 45%. The combination of barriers, which decreases leaching and evaporation was the most effective in conserving water. Most of the contribution came from the influence of the mulch layer in suppressing water losses by evaporation. The combination method traps solute in the root zone, and this decreased solute leaching from the soil may limit plant growth in saline soils. / Graduation date: 1993

Graduation date: 1994