Browsing by Author "Bynum, Joshua Brian"
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Item Nodes above white flower and heat units as indicators of harvest aid timing(Texas A&M University, 2005-08-29) Bynum, Joshua BrianThe timing of harvest aid application on cotton (Gossypium hirsutum L.) is critical, and poses potential problems when mistimed. The consequences of premature harvest aid application could result in reduced profit to the grower through the need for additional applications, reduced lint yield, poor fiber quality, and/or delayed harvest. A delayed application of harvest aid materials may also reduce lint yield and fiber quality if late season inclement weather patterns are established. Currently, there are many methods utilized for determining application of harvest aid materials. One method utilizes accumulated heat units, or growing degree days (HU or DD60??s), following plant physiological maturity. Physiological maturity (cutout) is identified as nodes above white flower equals 5 (NAWF=5). This method triggers the application of harvest aid chemicals when 850 HU have been accumulated beyond cutout. Due to differing environmental and edaphic characteristics across the Cotton Belt, application of harvest aid chemicals at this time may be premature in terms of optimizing lint yield and fiber quality. A two-year study was established to determine the proper timing of harvest aid application for picker harvested cotton in south central Texas. The design utilized a split-plot with four replications. The main plots consisted of three nodal positions(NAWF=3, 4, and 5), and the subplots were five HU accumulations (650, 750, 850, 950, and 1050) that corresponded to each of the nodal positions. In both years, lint yields increased with an increase in HU accumulation. Greater yields were achieved when HU accumulation was initiated after NAWF = 4. This two-year study indicates that harvest aid applications made at NAWF = 4 plus 1050 HU would optimize yield potential for picker harvested cotton in south central Texas.Item Physiological applications for determining water use efficiency among cotton genotypes(2009-05-15) Bynum, Joshua BrianDrought stress can substantially alter plant metabolism by decreasing plant growth and photosynthesis. The lack of rapid and reliable screening criteria and measurement techniques for determining water use efficiency (WUE) of crop plants has greatly restricted progress in this critical area of crop improvement. In grain sorghum (Sorghum bicolor L.), WUE was associated with the transpiration ratio [CO2 assimilation (A) / transpiration rate (E), A:E] from leaf gas exchange measurements. Research is needed to identify drought effects on plant productivity and to exploit the use of this knowledge in breeding and agronomic efforts. Therefore, the objectives of this study were to determine if differences in A:E and other physiological parameters existed between two selected cotton (Gossypium hirsutum L.) genotypes and to evaluate the response of cotton genotypes experiencing water stress at two different growth stages on biomass production and yield. Two experiments were conducted using two cotton genotypes differing in drought tolerance. Each experiment was repeated three times in a randomized complete block design with six replications. In Experiment I, the water stress treatment was induced by withholding water when the plants reached the 4-node growth stage. The water stress treatment in Experiment II was imposed at early bloom. Gas exchange and chlorophyll fluorescence measurements were collected during dry-down and recovery periods to determine water stress effects on plant physiology. Biomass was partitioned following the recovery period, to examine phenotypic responses of plants exposed to water stress. The results of these experiments indicate that A:E is significantly increased as leaf water potential (?L) decreases with no differences in A:E between the two genotypes. Gas exchange measurements showed significant decreases with declining ?L and significant increases upon re-watering; yet, no differences were observed between the two genotypes. Chlorophyll fluorescence was not different between genotypes in either light- or dark-adapted leaves. In Experiment I TAM 89E-51 had a significantly greater seedcotton yield; however, in Experiment II TAMCOT 22 had the greater yield. These experiments suggest that the effects of water stress on cotton are a function of the intensity of the stress and the growth stage in which the stress is experienced.