Browsing by Subject "evapotranspiration"
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Item Environmental and genetic strategies to improve carotenoids and quality in watermelon(Texas A&M University, 2007-04-25) Bang, Hae JeenThe 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 ????-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.Item Relationship of salinity and depth to the water table on Tamarix spp. (Saltcedar) growth and water use.(Texas A&M University, 2004-09-30) Schmidt, Kurtiss MichaelSaltcedar is an invasive shrub that has moved into western United States riparian areas and is continuing to spread. Saltcedar is a phreatophyte that can utilize a saturated water table for moisture once established and is also highly tolerant of saline soil and water conditions. Literature has indicated that depth to the water table and salinity have a significant effect on growth and water use by saltcedar. Several studies were initiated to help develop a simulation model of saltcedar growth and water use based on the EPIC9200 simulation model. A study was initiated at the USDA-ARS Blackland Research Center Temple, Texas in the summer of 2002 to better understand the effects of water table depth and salinity on (1) saltcedar above and below ground biomass, root distribution, leaf area and (2) water use. Five different salinity levels (ranging from 0 ppm to 7500 ppm) and three different water table depths (0.5m, 1.0m, and 1.75m) were studied. Results indicated that increasing depth to the water table decreased saltcedar water use and growth. For the 0.5m water table depth, saltcedar water use during the 2002 growing season averaged 92.7 ml d-1 while the 1.75m depth averaged 56.6 ml d-1. Both root and shoot growth were depressed by increasing water table depth. Salinity had no effect on saltcedar growth or water use except at the 1250 ppm level, which used 110 ml of H2O d-1. This salinity had the highest water use indicating that this may be near the ecological optimum level of salinity for saltcedar. A predictive equation was developed for saltcedar water use using climatic data for that day, the previous day's climatic data, water table depth and salinity that included: previous day total amount of solar radiation, water table depth, previous day average wind speed, salinity, previous day total precipitation, previous day average vapor pressure, minimum relative humidity, previous day average wind direction, and maximum air temperature. Data from the field study and a potential growth study were integrated into the model. The model was parameterized for the Pecos River near Mentone, Texas. Predicted saltcedar water use was slightly lower than results reported by White et al. 2003.Item Responses of Grain Sorghum to Profile and Temporal Dynamics of Soil Water in a Semi-arid Environment(2014-02-24) Bell, Jourdan MDevelopment of efficient irrigation strategies is a priority for producers faced with water shortages. Managed deficit irrigation attempts to optimize water use efficiency (WUE) by synchronizing crop water use with reproductive stages. Soil water use and yield of grain sorghum [Sorghum bicolor (L.) Moench], on a Torrertic Paleustoll in the Texas High Plains, USA, were evaluated during the 2010 to 2012 growing seasons under three sprinkler irrigation strategies: full (FI), deficit (DI), and managed deficit irrigation (MDI). Soil water contents were measured weekly at 0.20-m intervals from 0.10 to 2.30 m depth using a neutron moisture gage. Irrigation for the FI treatment was scheduled when root zone water (0 to 1.6 m) was depleted to 50% of the potential plant available water (PPAW). The DI treatment was irrigated at 50% of FI. The MDI treatment was irrigated at 75% of FI between growing point differentiation and half-bloom, 50% of FI after half-bloom, and less than DI prior to growing point differentiation. Fully irrigated sorghum grain yields averaged 3.7 Mg ha^(-1) greater (p < 0.001) than deficit irrigated sorghum in all years. Seasonal crop water use under MDI averaged 29 mm greater than DI. Concomitant with increased water use principally during the reproductive period, MDI yields averaged 1.6 Mg ha^(-1) greater than DI, which was significant in 2010 and 2012 (p ? 0.006). The WUE of FI sorghum was significantly greater than MDI in 2012 (p = 0.003) and DI in 2010 and 2012 (p ? 0.001). In 2011, crop water uptake was restricted to above 0.6 m when water contents deeper in the profile were less than 42% PPAW. In 2010 and 2012, seasonal crop water uptake in the profile below 1.0 m was small (<14 mm) and did not appreciably increase in response to imposed soil water deficits. The rooting zone for evaluating plant water status and hence irrigation scheduling depended on initial profile water contents and possibly root density deeper in the profile. Results suggest that WUE?s of grain sorghum are not compromised under MDI compared with FI in most cropping seasons.