A planning tool for integrating crop choices with weed management in the Northern Great Plains
Abstract Crop production in the Northern Great Plains is rapidly changing because of no-till practices; producers now grow a diversity of crops with winter wheat to increase production as well as to manage weeds. With the multitude of crops available, producers are asking for guidelines to sequence crops in rotations that help weed management. We developed a planning tool that lists various choices with crops when designing a rotation; the choices are arranged by impact on weed dynamics as quantified by research in the region. The tool includes choices among crops, such as varying crops with different life cycles, planting dates, or row spacing, and choices within an individual crop, such as varying cultivar or planting date. Choices among crops impact weeds the most, whereas choices within an individual crop are less effective and usually lead to lower crop yield. For example, rotations comprised of two cool-season crops followed by two warm-season crops can reduce weed populations six- to 12-fold. In contrast, replacing a standard-height cultivar with a taller cultivar that is more competitive with weeds, is often inconsistent for weed management, whereas crop yield may be less. Producers associated with the Northern Plains Sustainable Agricultural Society felt that the planning tool would encourage long-range planning as well as help integrate weed management with the design of cropping systems. The purpose of the tool is to encourage ecologically based weed management, which can reduce herbicide inputs by 50% for Northern Great Plains producers.
Characterizing traits that enhance the competitiveness of winter wheat (Triticum aestivum) against jointed goatgrass (Aegilops cylindrica)
Our objective was to identify traits in winter wheat important to competitiveness against jointed goatgrass, measured as increased wheat yields and reduced jointed goatgrass seed production. Jointed goatgrass is an important winter annual grass weed that cannot be controlled selectively in winter wheat. Seven cultivars of soft white winter wheat were grown with and without competition from jointed goatgrass over two growing seasons. Measurements of numerous traits of winter wheat and jointed goatgrass were recorded throughout each growing season. The data were analyzed using path analysis with latent variables to determine which traits most enhanced competitiveness. In a drier year, increased rate of height development was important in maintaining wheat yields when wheat was growing in competition with jointed goatgrass. Increased rate of height development also was an important trait in reducing jointed goatgrass seed production. In a wet year compared to a dry year, the number of wheat heads per plant, the rate of water use, and weight gain were positively correlated to maintaining winter wheat yields. Jointed goatgrass seed production in the wet year was reduced overall compared to the dry year, but from the cultivars tested, there were no traits identified that were critical in enhancing this loss of seed production. This study suggests that cultivars with greater height development rates will be more competitive when growing in fields infested with jointed goatgrass.
Thermal incompatibility analysis of metal-ceramic systems based on flexural displacement data.
The feasibility of simple tests or analytical methods for prediction of residual stress states in metal-ceramic (MC) prostheses has not been demonstrated. Biomaterial metal-ceramic strips have been proposed to provide sensitive measures of transient and residual stress states through the measurement of midpoint deflection after cooling from the ceramic sintering temperature. The objective of this study was to apply the elastic-viscoelastic analogy to calculate transient and residual midpoint deflections in MC biomaterial strips and to compare these values with deflections measured with a beam-bending viscometer (BBV). Calculations and measurements were made for five MC systems that were found from a clinical study to be "thermally compatible" systems. Metal strips, 64 mm in length, 3 mm wide, and either 0.5 mm, 1.0 mm, or 2.0 mm in thickness, were veneered with four 0.25-mm thick layers of opaque porcelain. Midpoint deflection of the MC strips (ceramic oriented in the posterior position) was measured during cooling from an initial temperature of 700 degrees C. In general, the directions of the measured residual deflections did not agree with the "textbook" convention that negative deflections are associated with positive thermal contraction mismatch (alpha(M) - alpha(c) > 0) regardless of metal thickness. For a metal thickness of 0.5 mm, the residual midpoint deflection for all thermal contraction mismatch cases, except one, was positive (upward deflection) whereas the residual midpoint deflections were all negative when the metal thickness was increased to 1 or 2 mm, independent of the thermal contraction mismatch. The best agreement between calculated and measured values of residual midpoint deflection (+16 microns vs. +14 +/- 2.3 microns, respectively was obtained for MC biomaterial strips with a Ni-Cr alloy (0.5 mm thick) while the largest difference (+346 microns vs. +61 +/- 43.8 microns) was obtained for MC bimaterial strips with a Au-Pd allow (0.5 mm thick). In all but one case, changes in deflection direction as a function of metal thickness were correctly predicted by the viscoelastic analysis. The results of this study indicate that a viscoelastic model is useful for estimating thermal compatibility conditions of MC systems.