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Gregory A. Endress, Anton G. Endress, and Louis R. Iverson

Differential responses of species to environmental stress may interfere with restoration of prairie ecosystems or change community structure. The impact of increasing atmospheric ozone (O3) concentrations and/or low water on the growth of Andropogon gerardii Vitm. (big bluestem) and Sorghastrum nutans (L.) Nash (indian grass), two common warm-season native grasses, and Setaria faberi Herrm. (giant foxtail), a vigorous annual weed species, were studied in replacement series. Giant foxtail grew better than either big bluestem or indian grass under all tested conditions. The leaf areas of all three species were primarily controlled by water availability. Big bluestem and indian grass accumulated biomass equally well under high water availability, but with low water, indian grass accumulated more biomass than did bluestem. Three-way analysis of variance showed biomass, leaf area, and leaf number differed among species; low water was significant in all cases except for indian grass leaf area; and the O3 effect was significant only in the case of foxtail biomass. The interaction of O3 concentration and low water was significant only for indian grass biomass and leaf number; the interaction of species combination and low water was significant only for big bluestem leaf area and biomass. Relative yield calculations indicated that under conditions of elevated O3 and low water, big bluestem was the least competitive, while indian grass was most competitive. Intraspecific competition was common, each species apparently utilizing the environment in different ways. The results also suggest that giant foxtail at a low relative density may be used as a nurse species in prairie restorations as growth of big bluestem and indian grass were improved when in mixtures with foxtail.

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Andrew J. Hephner, Tyler Cooper, Leslie L. Beck, and Gerald M. Henry

maintained weed-free by hand-weeding to ensure plant growth in response to mowing height was examined without competition. Lateral plant diameter of each plant was measured at the beginning of the study and every 2 weeks thereafter through September. Two

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Brian A. Kahn

competition and gave an average overall LER of 1.18. If onion was the primary crop and a pepper crop was being added, an onion spacing of 15 × 20 cm with pepper planted at 60 × 45 cm reduced shading by the pepper plants and gave an average overall LER of 1

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Michael W. Smith, William D. Goff, and M. Lenny Wells

). This approach maintains cash flow and reduces competition for remaining established trees, frequently resulting in increased total production, improved nut quality, and less disease pressure from pecan scab [ Cladosporium caryigenum (Ellis and Langl

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Brent L. Black, Martin J. Bukovac, and Matej Stopar

Apple fruit size is influenced by position on the spur, and location and number of competing fruits. King fruit appear to have the greatest potential to size and grow best in the absence of intraspur fruit competition (ISFC). Accel (A) and NAA (N), commercial thinning chemicals, influence fruit size beyond their effects on crop load. A 2-year study was conducted to determine the effect of ISFC and position (king, K, or lateral, L) on fruit growth in response to A and N. Branches from `Redchief Delicious' were thinned, after petal fall, to one K, one L, one K + one L, or two L fruits per spur. Whole-tree treatments of N (15 mg·liter–1), A (50 mg·liter–1, 1993; 25 mg·liter–1), and a combination (N+A) were applied at 10-mm king fruit diameter. A nontreated control was included. In 1993, N and N+A reduced fruit size only with ISFC, while A increased fruit size in the absence of ISFC. In 1994, A had no effect, but N and N+A reduced fruit growth with ISFC. In both seasons, A and N decreased the frequency of spurs bearing multiple fruit, while N+A dramatically increased number of spurs with multiple fruits (branch survey).

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Eric T. Stafne and Kathleen D. Kelsey

institutions with different cultures and identities remains problematic, even when educational institutions have similar clientele, as competition for the target audience may cause feelings of rivalry, or even attempts to undermine each other's programs. A

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R.M. Coolman and G.D. Hoyt

Plant interactions are both competitive and cooperative. Farmers use intercropping to the mutual advantage of both main and secondary crops in a multiple-crop-production system. A vegetable crop has a competitive advantage over a younger secondary cover crop interseeded before vegetable maturity. Non-legume intercropped cover crops can use soil N, while a legume intercrop can increase N in agricultural systems by biological N fixation. Intercropping also may be more efficient than monocropping in exploiting limited resources. Relay-planting main crop and intercrop components so that resource demands (nutrients, water, sunlight, etc.) occur during different periods of the growing season can be an effective means of minimizing interspecific competition. Intercropping systems often exhibit less crop damage associated with insect and plant pathogen attacks, and they provide weed control.

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James P. Syvertsen

influence photosynthetic efficiency and assimilate partitioning that can give rise to management practices that increase production efficiency. P availability regulates root form and function to optimize P acquisition from soil. In addition, root competition

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Yim F. So, Martin M. Williams II, and Jerald K. Pataky

). Weed interference can influence certain growth characteristics such as height ( Cavero et al., 2000 ; Maddonni et al., 2002 ) and leaf azimuth orientation ( Maddonni et al., 2002 ). In addition, the mere presence of weeds, and not direct competition

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Marisa T. Potter, Richard J. Heerema, Jill Schroeder, Jamshid Ashigh, Dawn VanLeeuwen, and Cheryl Fiore

status of immature trees as a result of competition. However, there have been no studies investigating the effects of vegetation management on mature pecan orchard productivity under the arid growing conditions of the southwestern United States, where