Cotton (Gossypium hirsutum) is able to survive relatively large levels of both water and salinity stress. The objective of this study was to evaluate cotton lint production and soil salinization under a conjunctive use strategy using saline water at deficit levels. A three-year experiment applying irrigation at deficit amounts on cotton was conducted in Pecos, Texas on a Hoban silty clay loam. Treatments were four irrigation water qualities, conjunctively applied. Initial irrigation was with water having an electrical conductivity (ECIW) of 4.5 dSm-1, representing about one-third of the total amount of water applied. Thereafter, treatments were applied using water of varying ECIW, e.g., 1.5, 4.5, 9.0, and 15.0 dSm-1 for all subsequent irrigations. Total irrigation plus rain was approximately two-thirds of full water requirements. Lint yields for the three years averaged 1050, 1008, 809, and 794 kg ha-1, respectively, and treatment levels did not decline over time. However, the soil salinity levels of the three more saline treatments increased throughout the test period. Yields declined due to salinity prior to reaching the published threshold value (Maas and Hoffman, 1977) of ECe = 7.7 dSm-1. Under the deficit conditions of two-thirds of the full water requirements, the threshold level was lowered to 4.5 dSm-1. The overall yield loss that resulted from limiting water by one-third was three times > than the yield loss from even the highest salinity treatment. Relative lint yield was reduced 3% for each dSm-1 of ECIW. The pre-dawn and solar-noon leaf water potential values decreased at a rate of 0.026 and 0.042 MPa per dS m-1 of the ECIW, respectively. Study conclusions were that yields within treatments remained stable for three years. However, the increase of salinity in the soil profile indicated that long-term viability of using highly saline water conjunctively is impractical under deficit irrigation conditions. In the short-term, however, saline water of up to 15.0 dS m-1 can be used at mid-season under deficit conditions on Hoban silty clay loam soil to secure 75% of the yield level obtained by using high quality water if a pre-plant irrigation of medium quality water is first applied.

Thesis (Ph. D.)--Washington State University. / Includes bibliographical references.

Thesis (Ph. D.)--Washington State University, December 2006. / Includes bibliographical references.

Master of Science / Department of Agronomy / Kraig L. Roozeboom / Due to decreased availability of irrigation water in central and western Kansas and an increase in water restrictions, producers are looking for more efficient ways to use available irrigation water. Drought-tolerant technologies have become popular in hybrids for stress-prone environments across central and western Kansas and are marketed for their ability to produce greater grain yields with less water. The objective of this research was to understand how DT and non-DT corn hybrids respond in a wide range of environmental conditions in terms of soil water status change, canopy indicators of stress, dry matter partitioning, and grain yield. Soil water status change, yield, and canopy response characteristics of two DT hybrids, and one non-DT hybrid were compared at five locations over two years in rain-fed, semi-irrigated, or fully irrigated regimes making a total of 18 environments. Field experiments were established in 2014 and 2015 near Topeka, Scandia, Hutchinson, Garden City, and Tribune, KS. Two corn hybrids with different approaches drought tolerance (Pioneer 1151 AQUAmax, bred drought tolerance and Croplan 6000 DroughtGard, bred drought tolerance plus transgenic drought tolerance), and one hybrid with no specific drought tolerance characteristics but with proven performance in favorable environments (Croplan 6274) were used in the experiment. Soil moisture content (measured using a neutron moisture meter), canopy temperature, ear leaf temperature, and chlorophyll content were measured at tasseling (VT), milk or dough (R3-R4), and physiological maturity (R6) developmental stages. Grain yield was at all 18 environments, and biomass production was estimated at 14 of the environments. Hybrid plasticity of yield results show the response for Croplan 6000DG and Pioneer 1151AM differed, but Croplan 6274 was the same as both other hybrids at the 0.10 alpha level. Yields of all hybrids remained comparable in most environments, but as environment yields increased beyond 200 bu acˉ¹, Croplan 6000DG lagged behind Pioneer 1151AM. Hybrid harvest index plasticity shoed that all hybrids had the same response to environment in harvest index. Although, not statistically significant, when an environment supported favorable harvest index values greater than 0.40, it’s observed that Croplan 6000DG does have an improvement in harvest index relative to the Pioneer 1151AM and Croplan 6274.

Thesis (Ph.D.)--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 plus two media files. Title from title screen of research.pdf file (viewed on May 1, 2009) Vita. Includes bibliographical references.

Limited water supplies for agriculture in the Texas High Plains will require new irrigation technologies and techniques for agriculture to continue in this area. The potential for using one such technology, site-specific irrigation, was evaluated using the Cotton2k crop simulation model. This model and two other simulation models were evaluated for their ability to track water movement and usage over three growing seasons. The models were tested for sites in Lubbock and Hale County, Texas. Cotton2k performed well compared to the other two models on tests of cumulative evapotranspiration and applied water yield relations and equal to the other models for tracking soil water profiles. A global optimization method, simulated annealing, was tested for its ability to spatially calibrate soil water parameters of Cotton2k. The algorithm found multiple parameter sets for the same objective function results. This result runs contrary to expectations for the simulated annealing algorithm, but is possibly from the relationship between available water capacity and crop yield. The annealing algorithm was applied to each sampling point at the Hale County site and improved yield predictions for 32 of 33 points as compared to simulations made with soil textural information alone. The spatially calibrated model was used with historic weather from five seasons to evaluate a site-specific strategy where water was shifted from lower to higher yielding areas of fields. Two irrigation strategies, one with irrigations weekly and one with irrigations applied when 30% of available water was depleted, were tested. With sitespecific management, the weekly interval strategy produced higher yields for two of three water levels, as compared to uniform management. With the soil moisture depletion strategy, site-specific management produced lower yields than uniform management for all three water levels examined. Yield improvement and water savings were also demonstrated for implementing site-specific irrigation when non-producing portions of fields were previously being watered.

Increased water scarcity due to changing climate, population growth, and economic development is a major threat to the sustainability of irrigated agriculture in the Western United States and other regions around the world. Management practices, such as controlled deficit irrigation, that seek to maximize the productivity of a limited water supply are critical. When using controlled deficit irrigation, remote sensing of crop canopy temperature is a useful tool for assessing crop water status and for more precise irrigation management. However, there is potential that nutrient deficiencies could compound the interpretation of water status from leaf temperature by altering leaf color and radiation balance. One objective of this thesis was to evaluate whether nitrogen fertility status of maize interacts with remotely sensed leaf temperature under full and limited irrigation. Another objective was to evaluate the effect of varying irrigation and nitrogen regimes on three water stress indices: Crop Water Stress Index (CWSI), Degrees Above Non-Stressed (DANS), and Degrees Above Canopy Threshold (DACT). Replicated studies were conducted using maize grown in both the glasshouse and the field. The glasshouse study consisted of combinations of well-watered and drought irrigation and sufficient and deficient nitrogen levels, while the field study consisted of combinations of well-watered, limited or controlled deficit, and drought irrigation and sufficient, sufficient delayed, and deficient nitrogen levels. In the glasshouse, leaf chlorophyll content was reduced moderately by limited irrigation and more so by N deficiency. For most observations in the glasshouse, the remotely sensed leaf temperatures were affected by irrigation, but not by N level. With drought irrigation, leaf temperature averaged 29.0° C, compared to 27.9 °C for the well-watered treatment. Similar results were observed in the field, illustrating the utility of canopy temperature in detecting water stress and that the measurement was not confounded by N status. It was also found that irrigation had a significant effect on all three water stress indices. For example, in the glasshouse, cumulative DANS was 32.2 for the drought treatment and 15.5 for the well-watered treatment. Similar results were found for other stress index measurements both in the glasshouse and the field. DANS underestimated stress on days when the reference crop was stressed and overestimated stress on low temperature days. DACT risks finding no stress when temperatures are below the canopy threshold temperature of 28.0 °C. Thus, CWSI is the most effective index, given that it takes humidity and air temperature into account. Indices were only weakly related to leaf area, biomass or grain yield, or crop water productivity. Linear regression of Nitrogen Sufficiency Index and its effect on crop growth found significant effects on biomass and grain yield, crop water productivity, and final leaf area. Thus, water stress indices are useful tools in evaluating crop water status, but consideration of other factors, such as nutrient status, must be taken for prediction of crop growth and yield.

The evaluation of environmental and genotypic effects on fruit physical and chemical characteristics enables assessment of the feasibility of selecting diploid and/or triploid cultivars for either specific or more diverse locations. Isolation and characterization of genes encoding enzymes in the carotenoid biosynthetic pathway provides fundamental genetic information which can facilitate breeding of watermelon cultivars having desirable flesh colors and enhanced beneficial carotenoids. For the environmental studies, the effects of deficit irrigation on lycopene content, total soluble solids, firmness, and yield of diploid and triploid watermelon were evaluated in different locations and growing seasons. Irrigation regimes were 1.0 evapotranspiration (ET), 0.75 ET, and 0.5 ET. To investigate if there is a consistent response in cultivars across diverse locations, studies were conducted in three distinct Texas regions. Deficit irrigation reduced total marketable yield, and increased the yield of small fruits. Location and irrigation regimes had major influences on yield. Soluble solids content increased with deficit irrigation at 0.5 ET in triploids, but not in diploids. Flesh firmness also increased in triploids compared to diploids. Lycopene content increased with maturity at all irrigation regimes and cultivars. This work confirms that deficit irrigation directly reduces yield, but does not reduce lycopene and fruit quality of the triploids used in this study. From the genetic studies, a total of eight genes encoding enzymes in the carotenoid biosynthetic pathway were isolated and characterized. Two members of the phytoene synthase (PSY) gene family were identified; PSY-A was expressed in all type of tissues, but PSY-B transcript was detected only in ovary, leaf, and root tissues. Gene expression of carotenoid isomerase (CRTISO) was not detected in salmon yellow. A color inheritance study of watermelon flesh indicated that a single gene might determine color difference between canary yellow and red without an inhibitory effect. A cleaved amplified polymorphic sequence (CAPS) marker developed from the SNP marker tagging two different lycopene β-cyclase (LCYB) alleles cosegregated perfectly with color phenotypes. It was concluded that color determination may be due to a reduced activity of LCYB enzyme in red, whereby a phenylalanine is conserved among canary yellow and valine is conserved among red watermelon.

Thesis (M.Sc.(Agric.))--University of Western Australia, 2006.

Thesis (Ph.D.). / Written for the Dept. of Bioresource Engineering. Title from title page of PDF (viewed 2008/02/12). Includes bibliographical references.