Master of Science / Department of Agronomy / Loyd R. Stone / Corn (Zea mays L.) yields are often reduced by limited pumping capacity of irrigation wells drawing from the High Plains Aquifer. As a result of decreased well capacities in this region, many irrigation systems no longer have the ability to meet peak irrigation (water) needs during the growing season. The purpose of this study was to measure easily identifiable plant characteristics of corn hybrids and relate those characteristics with the ability to maintain yield under water-limited conditions. This study involved measuring several plant characteristics of 18 corn hybrids grown under irrigated and dryland conditions near Tribune, KS during the growing seasons of 2005, 2006, and 2007. During each year, hot and dry conditions occurred during silking which resulted in large differences, and many poor yields, in the dryland plots. The number of days and growing degree days (GDD) to initiation of silking were the variables most strongly correlated with grain yield in the dryland environment. The shorter the time it took to reach initiation of silking the greater the grain yield. The number of days, or the GDD, to initiation of silking in irrigated environments did not have a significant correlation with corn grain yield. Other characteristics including canopy temperature, PAR (photosynthetically active radiation), color, leaf angle, number of internodes, number of leaves, and leaf N had no significant correlation with corn grain yield for either dryland or irrigated environments in 2005 and 2006. In this study using hybrids with maturity ratings between 98 and 118 d, there were no significant differences in grain yield in the irrigated environment. In the dryland environment, the hybrids used (98 – 118 d) in this study resulted in a decrease in grain yield with an increase in maturity. By considering the maturity of a hybrid, a producer will potentially be able to better select a variety that will perform well in a growing season with potential or likely severe water cutbacks as a result of limited water supply or reduced well capacity.

The transfer of prey resources between ecosystems can have dramatic consequences for both recipient and donor systems by altering food web stability and the likelihood of trophic effects cascading across the ecosystem boundary. Landscape-scale factors influence the importance, direction and magnitude of energy flows, but may also alter the ability of consumer organisms to respond to spatio-temporal changes in allochthonous prey availability. Here, I used flood and drying disturbance gradients to investigate interactions between these two processes on populations of a riparian fishing spider Dolomedes aquaticus (Pisauridae). The abundance of aquatic insects with a winged adult stage, a major component of the diet of D. aquaticus, was markedly higher at less flood-prone rivers and declined with increasing flood disturbance. It was expected that spider populations would be largest at these stable rivers where the aquatic prey abundance was highest. However, a habitat (loose, unembedded riverbank rocks) manipulation revealed that the lack of scouring floods at these sites led to habitat-limited populations, preventing response to the increased prey resource. In fact a peak shaped relationship of spider biomass and abundance was found, with the largest spider populations at intermediately disturbed rivers. In addition, patchy habitat availability was the most likely cause of the small scale (4 m2) aggregation of spiders seen at the most stable and disturbed rivers. These patterns were also associated with strong interactions between the spiders. Stable isotope analysis of field collected spiders and an experimental manipulation of spider densities and food availability indicated that cannibalism rates were likely to be significantly higher at stable and disturbed rivers than those intermediate on the disturbance gradient. Differences in D. aquaticus population size structure and life history traits across the flood disturbance gradient were driven by interactions between resource availability, environmental stability and cannibalism rates. To separate the effects of habitat availability and aquatic prey abundance I used drying rivers, as the amount of aquatic insect prey alters as the water recedes. Desiccation mortality and low aquatic prey biomass most likely caused the spiders' spatial distribution and size class structure to alter in drying river reaches, potentially also leading to differences in cannibalism rates. Overall, cross-ecosystem transfers of prey had large impacts on the distribution, cannibalism rates and life history traits of D. aquaticus but their effects were modified by the nature of the ecosystem boundary. Thus river flow regime controlled the magnitude of the subsidy and its use by a consumer. Hence, cross-ecosystem subsidies will not always lead to larger consumer populations and consumer responses will depend on interactions between large-scale processes.

Current global population growth and economic development accelerates the land cover conversion in many parts of the world and compromises the natural environment. However, the impacts of this land cover change on the hydrologic cycle at local to regional scales are poorly understood. The thesis presented here investigates the hydrologic implications of land use conversion in two different settings using two different approaches. The first study focuses in Southeast Asia and the expansion of rubber monocultures in a middle-sized basin. Field measurements suggest rubber has distinct dynamics compared to the area's native vegetation, depleting and exhausting the local water balance more than native vegetation. A phenology based evapotranspiration function is developed and used in a hillslope based hydrologic model to predict the implications of rubber expansion at a basin scale. The second study is centered in the semi-arid southwestern United States. This study challenges the traditional assumption that deforestation increases water yield at regional scales. Observations of water yield in basins affected by a regional piñon pine die-off show a decline in water yield during several years after die-off. These results suggest an increase in landscape sensitivity to vegetation disruption in semi-arid ecosystems as scale increases. Consequences of both studies have important implications for land and water managers in these different ecosystems.

11 pp. / This publication contains information about browse utilization by ruminant animals. It provides information about the rangelands in Arizona, the nutritional quality of browse, effects of drought and tannin and how to overcome them.

This study sought to determine the effects of reselection on the adaptation of a grain sorghum (Sorghum bicolor (L.) Moench) population to heat and drought. A random-mating population, NP9BR, was subjected to selection under heat and moisture stress for nine generations to improve its resistance to drought. One hundred single plants selected from the original (C₀) and the reselected (C₉) population were grouped by maturity and evaluated for drought resistance by measuring morphological and agronomic characters under wet (normal irrigation) and dry (restricted irrigation) conditions at the University of Arizona, Marana Agricultural Center, Arizona. Eighty of the selections were grown under a sprinkler irrigation gradient system at Yuma Mesa Agricultural Center, Arizona. Selection under drought conditions reduced plant height, head exsertion, leaf width and length, and seed weight of the population. Blooming was evened out from predominantly early in C₀ to early, medium and late maturing in C₉. Moisture stress reduced grain yield by an overall 16%. The medium maturing selections suffered less yield reduction than the early and late. Although C₉ progenies showed a greater reduction in grain yield, several of them produced equal yields in wet and dry treatments. Leaf width and length were significantly correlated (p = .1%) with yield under dry conditions in all maturity groups. Most selections with very short narrow leaves had small heads and low yields. Some with medium leaf width and length out-yielded broad-leaved ones especially under dry conditions. Forty percent of the selections from C₉ had good head production characteristics under the irrigation gradient system, compared to only 20% from C₀. There were four times as many selections in C₀ unable to produce heads under the system as there were in C₉. The majority of genotypes with good head production in both populations came from the early maturing group. The highest grain yields came from C₀ selections but some C₉ selections with comparable yields were observed. This study indicates that phenotypic selection may still have potential for isolating high-yield genotypes from random-mating populations but may be inadequate for separating differences in drought tolerance among genotypes.

The effect of water stress on the growth, landscape performance, and plant-water relations of four ornamental ground cover species (gray santolina, Santolina chamaecyparissus; dwarf rosemary, Rosemarinus officinalis; Chihuahuan Desert lantana, Lantana velutina; and prostrate germander, Teucrium chamaedrys) was investigated for a twoyear period. Plants were established in a drip irrigated field and subjected to four soil moisture regimes (-1, -5, -10, and -15 bars), monitored by neutron probe. While water stress reduced vegetative covers, shoot growths, heights, and fresh and dry weights of the plants, species response to water deficit varied greatly. Minimum amounts of water required for growing each species were determined. Germander was found to be the most drought tolerant, followed by santolina, rosemary, and lantana in decreasing order. In earlier treatment period, adequately watered plants showed better aesthetic appeal and landscape performance than the plants grown under a high soil moisture tension. However, the effect of water stress on plants' landscape performance was less evident as plants became more established. In all species tested, with an exception of germander, leaf water, osmotic, and turgor potentials of nonstressed plants were higher than those of severely stressed plants. Using the pressure-volume technique, apoplastic water was found to contribute a significant proportion of the total tissue water content. The dilution of symplastic water by apoplastic water during osmotic potential determinations was found to be the major cause of the frequently observed negative turgidity. Methods for correcting for these apoplastic dilution effects were suggested. Osmotic potentials at full and zero turgor, symplastic water contents, changes in water, osmotic, and turgor potentials relative to changes in cell water content (Blifler diagrams), and cell wall elasticity varied significantly with species and treatments. Water stress caused a reduction in total chlorophyll and carotenoids concentrations and in the chlorophyll/ carotenoids ratio, without changing chlorophyll a/chlorophyll b ratio in plant tissues. Leaf reflectances to incident light as measured at 400 to 700 nm were found to differ substantially by species but not by treatments. No consistent correlations were found to exist between leaf pigment content and each of dominant wavelength, brightness, and the purity of leaf color.

Long-lived trees and excellent preservation of remnant wood allow examination of late-Holocene climate variability and its relation to woodland tree demography and populations of prehistoric agriculturalists in northeastern Utah using dendrochronological methods. Tree-ring chronologies are developed from Douglas-fir (Psuedotsuga menziesii) and Colorado pinyon (Pinus edulis) on the Tavaputs Plateau covering the last 2,300 years. The climate reconstructions fill an important temporal and spatial gap in our understanding of moisture related climate variability in the region. We investigate the relationships between climate and woodland demography by constructing a 1,500-year record of pinyon establishment and death. Twentieth-century expansion and infill of pinyon/juniper woodlands and more recent widespread die-offs in the early 21st century heighten the importance of understanding these relationships. The climate reconstruction is analyzed in light of the archaeological record of Fremont agriculturalists between approximately AD 550 and 1300, and provides the first glimpse of climate variability throughout the Fremont era in this region.Results of the hydroclimate reconstructions show that multidecadal droughts unlike any observed in the instrumental record occur regularly over the last 2,000 years. Droughts in the mid 12th century and late 13th century are synchronous those found in numerous other records across the southwestern United States. A drought in the early 6th century is especially severe. Analysis of pinyon demography indicates rates of tree establishment, release, and death are highly variable over the last 1,500 years. Broad peaks in tree establishment occur in the 7th and 8th centuries, the 12th and 13th centuries, and again in the 18th, 19th and 20th centuries. Higher tree death rates are related to dry periods, but tree establishment is only weakly associated with wetter periods. Instead, cohorts of suppressed young trees established over decades tend to synchronously experience rapid growth rate increases during wet periods following droughts. Stands appear more susceptible to population turnover as semi-dominant cohorts of trees age and decline. Two critical periods in Fremont archaeology in the region, coincide with significant changes in moisture conditions. These changes follow longer periods of stability suggesting that changes in the predictability of climate conditions may have impacted Fremont agriculturalists in the region.

Water security is becoming an increasing concern for communities in the southwestern United States. Projected decreases in water availability due to climate change combined with increased demands from a rapidly growing population have many concerned about the sustainability of the water supply in coming years. As water availability becomes an increasing concern, greater efficiencies must be made to increase the resilience of the water supply system. This dissertation analyzes the efforts of Tucson, Arizona households to conserve water during the hottest and driest decade in the city's recorded history, between 2000 and 2009. This study utilizes survey data to statistically examine the motivations for household adoption of five conservation methods: rainwater harvesting systems, graywater systems, xeriscaping, high-efficiency devices and volunteerism for public water conservation projects. Following the statistical analysis, interviews were conducted with participants to provide further context for analyzing the results. This mixed method approach reveals that drought alone did little to directly encourage household water conservation over the decade. However, public water conservation initiatives that were launched during the decade made a significant contribution to increasing household water conservation. Households consistently cited a desire for more information about the implications of the current drought status as well as additional information about their individual household's water use.

No description available.

The yield of UK’s commercial oilseed rape (Brassica napus) crops has not increased over the last three decades, while a significant increase in yield has been found in trials that test new varieties before they enter the market. It has been suggested that oilseed rape is susceptible to drought and that this may contribute to the poor yield of some commercial crops. A thorough literature review revealed that there is little information on the water relations of oilseed rape crops and in particular on root growth and function and thus no strong evidence to support the above hypothesis. The aim of this thesis was to investigate root function and water relations of oilseed rape to determine whether it is more sensitive to drought than wheat, a crop species grown in rotation with oilseed rape. The water relations of wheat (Triticum aestivum L. cv. Tybalt) and oilseed rape (Brassica napus L. cv. SW Landmark) were compared in a lysimeter experiment conducted in an open sided glass house to test the hypothesis that oilseed rape was more sensitive to drying soil than wheat. Plants were grown with or without irrigation at a population density equivalent to that of commercial field crops. Irrigated oilseed rape crops transpired more water than wheat crops and oilseed rape showed a greater reduction in growth when water was withheld. The onset of drought also occurred slightly earlier in oilseed rape. In a separate experiment the root hydraulic conductance of oilseed rape, measured on a root surface area basis, was about twice that of wheat (113.1 ± 20.0 mlNm-2Nh-1NMPa-1 for oilseed rape and 53. 5 ± 10.6 for wheat). These results suggest that oilseed rape needs a less dense root system for water extraction than wheat. In the above experiment plants were grown in relatively loose soil repacked into the lysimeters. It has been suggested that oilseed rape is particularly sensitive to soil compaction, which may be a common occurrence in commercial fields. Therefore the sensitivity of oilseed rape and wheat growth to compaction was compared in an experiment under well-watered conditions. Plants were grown in a controlled environment chamber in pots packed with soil at four different bulk densities. Although the root length, shoot mass, leaf area and stomatal conductance of oilseed rape were all reduced by soil compaction, oilseed rape was no more sensitive to soil compaction than wheat under these well-watered conditions. When soil dries it also hardens and high soil strength is known to impede root growth and alter plant-water relations. The hypothesis that oilseed rape is more sensitive to increasing soil strength than wheat was tested in an experiment in which soil bulk density and soil water content were varied to create a range of soil strengths. At low soil strength oilseed rape had a greater stomatal conductance than wheat, but as soil strength increased, stomatal conductance decreased to a greater extent in oilseed rape, indicating a more sensitive response. In dense or strong soil, plants often rely on pores created by earthworms or roots of the previous crop to explore the soil volume. The ability of oilseed rape and wheat to exploit soil pores to penetrate hard soil layers was compared in a pot experiment. A hard layer, comparable to a hard–pan in a cultivated field, was created at twelve centimetre depth of each pot by packing the soil to a bulk density of 1.5 g·cm-3 relatively loose soil at a bulk density of 1.1 g·cm-3 was present above and below the layer. In one treatment seven pores were drilled through the hard layer; controls had none. Presence of pores in the hard layer led to a significant increase in number of roots in the deeper soil, of 29% for wheat and 54% for oilseed rape. This project has shown that the physiological response to drought occurred earlier in oilseed rape than in wheat and that stomatal conductance and biomass production of oilseed rape reacted more sensitively to soil drying. However, water use by oilseed rape does not seem to be limited by the ability of its roots to explore the soil and transport water compared to wheat. The growth and distribution of roots under a range of soil conditions was as good as, if not better than, that of wheat. The implications of these findings for the commercial production of oilseed rape in the UK are discussed.