Browsing by Author "Overstreet, Laura Flint"

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    Boron Deficiency and Chilling Injury Interactions in Tobacco Transplants Grown in the Float System
    (2002-05-23) Overstreet, Laura Flint; James W. Rideout, Committee Chair; C. David Raper, Committee Member; Judith F. Thomas, Committee Member
    Decades of agricultural research have failed to determine the precise mechanisms of infliction caused by the conditions of boron deficiency and chilling injury. Both conditions affect the quality and marketability of tobacco transplants grown in the float system. Interestingly, boron deficiency and chilling injury produce strikingly similar symptoms in young tobacco transplants; so similar, in fact, that they are often confused for one another. This has lead to severe boron toxicity when growers treated chilling injury as boron deficiency by applying boron to non-deficient float beds. The observation of nearly identical symptoms suggests that boron deficiency and chilling injury have interdependent effects on cell physiology and/or metabolism. Because little research has been conducted on tobacco transplants in the float system, two studies were conducted to determine general parameters for the boron deficiency threshold and effect of non-optimal temperatures and large day/night temperature differentials in this system. The boron deficiency study established that the deficiency threshold for transplants growing at 26/22°C is 10-20 μg B g-1 dry matter. These tissue levels occurred with solution concentrations of 0.19-1.9 μM B. The chilling injury study determined that root and shoot growth of flue-cured cultivars is near maximum at a constant 26/26° C temperature regime. Burley cultivars display a wider range of temperature tolerance, but in general constant day/night temperatures seem to provide the greatest shoot tissue accumulation. A reduction in night temperature resulted in decreased shoot growth in all cultivars. The chilling injury study also examined the effect of boron deficient conditions at each temperature treatment. In general, boron uptake declined at sub-optimal temperature regimes when supplied at concentrations sufficient for near-optimal temperatures. Shoot growth of flue-cured varieties at transplant stage was near maximal at a constant optimal day/night temperature regime (26/26° C) and adequate B concentrations. Sub-optimal temperatures may alter the boron deficiency threshold such that it decreases with decreasing temperatures or with stressful temperature differentials. This may be summarized in the following way: Temperature is the immediate limiting factor in tobacco transplant growth in the float system under conditions of sub-optimal temperatures and low B concentration, and B deficiency is an additional potential limiting factor.
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    Relationships Between Soil Biological and Physical Properties in a Long-term Vegetable Management Study
    (2005-11-29) Overstreet, Laura Flint; Shuijin Hu, Committee Member; Greg D. Hoyt, Committee Chair; Michael Wagger, Committee Member; Wei Shi, Committee Member
    Agricultural management decisions that influence biological activity and diversity include tillage, fertilizer and pest-control inputs, and crop rotations. Our research objective was to characterize relationships between biological and physical properties resulting from long-term agricultural management decisions. A nine-year old factorially-designed field experiment was used to examine the effects of tillage (moldboard plow or strip-tillage), input (synthetic fertilizers and pesticides or inputs approved for organic certification programs), and crop rotation (continuous staked tomatoes or 3-year vegetable rotation) on a suite of biological and physical soil parameters. Biological measurements included microbial, nematode, and earthworm community composition, soil respiration and N mineralization potential, enzyme activity, and microbial biomass. Physical property measurements included aggregate stability, bulk density, and pore-size distribution. Biological properties generally responded to all treatment combinations, but tillage provided the strongest treatment effect in most cases. Compared to strip-tillage, tillage consistently yielded significantly lower values for the following biological measurements: total C and N, above-ground biomass, microbial biomass, enzyme activity, soil respiration, N mineralization, some nematode trophic groups, and earthworms. Compared with organic inputs, synthetic inputs consistently induced significantly lower values for the following biological measurements: microbial biomass, enzyme activity, some nematode trophic groups, and soil respiration. An examination of relationships between biological and physical parameters using redundancy analysis revealed that microporosity was the physical property that was most strongly correlated with most biological parameters. Soil organisms responded to our treatments in the following order: tillage > input > rotation.