The flowering stage is the key yield determinant period of soybean. Short-duration water stress occurring during this stage significantly reduced soybean development and final productivity. Seed treatment with uniconazole powder application plays an important role in alleviating the adverse effects of dry soil on plant development. In order to explore effects of uniconazole on soybean morphological characteristics and yield under drought stress, different rate of uniconazole powder were examined under developing gradually drought stress during flowering stage. The yield of soybean decreased under drought, uniconazole application increased yield. All results suggest that 4 mg/kg is the optimal uniconazole application rate under drought for soybean at the flowering stage.

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In many southeastern Coastal Plain soils, subsoil pans have strengths that restrict root growth. To reduce strengths, soils are deep tilled annually, and perhaps biannually for double cropping. We evaluated the effect of deep tillage in fall, in spring, or at both times on strength of a Goldsboro loamy sand (fine loamy, siliceous, thermic Aquic Kandiudult) and on the yield of wheat (Triticum aestivum L.) and drilled soybean [Glycine max (L.) Merr.] in a double‐cropped system. Treatments consisted of all combinations of surface tillage (disked and not disked) and deep tillage (no deep tillage, paratillage before wheat planting, before soybean planting, and before both) in four replicates. Soil strengths, measured as cone indices, showed that disked, non‐deep‐tilled treatments resulted in a pan at the 20‐ to 30‐cm depth, generally associated with an E horizon. In more recently and more frequently deep‐tilled treatments, mean profile cone indices were 0.31 to 0.36 MPa lower than treatments not deep tilled or deep tilled for the previous growing season. If soil was deep tilled only once a year, it was 0.26 MPa softer when tilled only in spring than when tilled only in fall. Deep tillage at the beginning of either season reduced soil cone indices and improved wheat and soybean yields over other treatments. Deep tillage at the beginning of both seasons maintained the softest soil. For every megapascal decrease in mean profile cone index, wheat yields increased 1.5 to 1.7 Mg ha−1 and soybean yields increased 1.1 to 1.8 Mg ha−1

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Simultaneous, non-invasive measurements were made of the rate of photosynthetic CO2 fixation and the state of activation of the chloroplast CF1CF0-ATP synthase (CF) in field-grown sunflower (Helianthus annuus L.) during the dark-to-light transition at sunrise. CO2 fixation showed a linear response with light intensity from zero to about 500-700 μE m(-2) s(-1). However, at light intensities of only 5-22 μE m(-2) s(-1), the energetic threshold for activation of the CF was found to be significantly lowered (as compared to the pre-dawn state), presumably through reduction of the regulatory sulfhdryl groups of the γ-subunit of the CF. When these studies were extended to chamber-grown plants, it was found that as little as 5 seconds of illumination at 4 μE m(-2) s(-1) caused apparently full CF reduction. It is clear, therefore, that the catalytic activation of CF is not rate limiting to the induction of carbon assimilation under field conditions during a natural dark-to-light transition at sunrise. A model, based on the redox properties of the regulatory sulfhydryls, was developed to examine the significance of sulfhydryl midpoint potential in explaining the differences in light sensitivity and oxidation and reduction kinetics, between the CF and other thioredoxin-modulated chloroplast enzymes. Computer simulations of the light-induced regulation of three representative thioredoxin-modulated enzymes are presented.