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Recent AbstractsDr. Drew LyonDryland Cropping Systems Specialist
Lyon, D. J., G. L. Hammer, G. B. McLean, and J. M. Blumenthal. 2003. Simulation supplements field studies to determine no-till dryland corn population recommendations for semiarid western Nebraska. Agron. J. 95:884-891. In a 2-yr multiple site field study conducted in western Nebraska during 1999 and 2000, optimum dryland corn (Zea mays L.) population varied from less than 1.7 to more than 5.6 plants m-2 depending largely on available water resources. The objective of this study was to use a modeling approach to investigate corn population recommendations for a wide range of seasonal variation. A corn growth simulation model (APSIM-maize) was coupled to long-term sequences of historical climatic data from western Nebraska to provide probabilistic estimates of dryland yield for a range of corn populations. Simulated populations ranged from 2 to 5 plants m-2. Simulations began with one of three levels of available soil water at planting, either 80, 160, or 240 mm in the surface 1.5 m of a loam soil. Gross margins were maximized at 3 plants m-2 when starting available water was 160 or 240 mm, and the expected probability of a financial loss at this population was reduced from about 10% at 160 mm to 0 % at 240 mm. When starting available water was 80 mm, average gross margins were less than US$ 15 ha-1 and risk of financial loss exceeded 40%. Median yields were greatest when starting available soil water was 240 mm. However, perhaps the greater benefit of additional soil water at planting was reduction in the risk of making a financial loss. Dryland corn growers in western Nebraska are advised to use a population of 3 plants m-2 as a base recommendation. Blumenthal, J. M., D. J. Lyon, and W. W. Stroup. 2003. Optimal plant population and nitrogen fertility for dryland corn in western Nebraska. Agron. J. 95:878-883. Dryland corn (Zea mays L.) production increased more than ten-fold from 1995 through 2000 in semiarid western Nebraska. Corn population and N fertilizer management recommendations for this area are needed. The objectives of this study were to determine the influence of plant population and N fertility on corn yields in semiarid western Nebraska. In 1999 and 2000, experiments were conducted each year at four sites. Factorial experimental treatments were five plant populations (17 300, 27 200, 37 100, 46 900, and 56 800 plants ha-1) and five N fertilizer rates (0, 34, 67, 101, and 134 kg N ha-1) arranged in a randomized complete block with five blocks. Corn yields ranged from less than 100 kg ha-1 to more than 5550 kg ha-1. Overall, grain yield increased 353 kg ha-1 with increasing population from 17 300 to 27 200 plants ha-1. Population increases above 27 200 plants ha-1 resulted in inconsistent yield results. Nitrogen fertilization and plant population effects did not interact. Yields were maximized by 202 kg N ha-1 in the form of soil NO3-N and fertilizer N available before crop emergence. Growers are advised to use a plant population of 27 200 plants ha-1. Economic optimal fertilizer rate can be estimated using the equation: Nfert. = (10.6 x Pcorn - Pfert.) / (0.0526 x Pcorn) - Nsoil, where Pcorn and Pfert. are corn and fertilizer price($ kg-1), respectively, Nsoil is soil test NO3-N (kg ha-1) as determined by preplant soil test in a 0 - 120 cm soil sample and Nfert. is economic optimal fertilizer rate (kg ha-1). Lyon, D. J., A. J. Bussan, J. O. Evans, C. A. Mallory-Smith, and T. F. Peeper. 2002. Pest management implications of glyphosate-resistant wheat (Triticum aestivum) in the western United States. Weed Technol. 16:680-690. Glyphosate-resistant crop species have increased in number over the past decade as growers eagerly adopt this simple and effective weed management technology. Glyphosate-resistant wheat cultivars are being developed and may soon be available to growers. The objective of this paper is to discuss the pest management implications of glyphosate-resistant wheat in the western U.S.A., a region stretching from the Great Plains to the Pacific Ocean that produces more than 80% of the nation’s wheat crop. The benefits of glyphosate-resistant wheat include: 1) improved weed control, particularly of difficult-to-control weeds such as winter annual grasses belonging to the Aegilops, Avena, Bromus, Lolium, Poa, Secale, and Setaria genera; 2) an ability to control weeds resistant to currently available wheat herbicides; 3) an extended application window for control of late-emerging weeds; and 4) improved crop safety. While these benefits are not to be minimized, they need to be considered in light of the concerns surrounding this new technology in wheat. Concerns include: 1) the lack of an equally effective and affordable herbicide to control glyphosate-resistant volunteer wheat, which may increase wheat diseases such as wheat streak mosaic and Rhizoctonia root rot; 2) the possibility that over- reliance on glyphosate will lead to species shifts with unknown consequences for weed management in wheat; and 3) the use of multiple glyphosate-resistant crops in rotation with glyphosate-resistant wheat could rapidly increase glyphosate-resistant weeds, thereby limiting the future utility of glyphosate. If, or when, glyphosate-resistant wheat becomes commercially available, it will require careful management to sustain its usefulness. We have proposed several areas of research we feel are critical to help develop sound management guidelines for deployment and use of this new weed management technology in wheat. These include: 1) developing effective “green bridge” management strategies, i.e, using cultural and chemical approaches to control plants that sustain insect vector populations between wheat crop periods; 2) predicting potential weed species shifts resulting from use of glyphosate-resistant wheat; and 3) developing management systems that include herbicide-resistant wheat on a rotational basis and rotating use of glyphosate with other weed management strategies in the fallow period to minimize the potential development of glyphosate-resistant weeds or weed communities. Kappler, B. F., D. J. Lyon, P. W. Stahlman, S. D. Miller, and K. M . Eskridge. 2002. Wheat plant density influences jointed goatgrass (Aegilops cylindrica) competitiveness. Weed Technol. 16:102-108. Jointed goatgrass is a problem weed in winter wheat production areas of the Great Plains. Winter wheat seeding rates are easily adjusted by the growers and influence competition by some weeds. Field experiments were initiated in Kansas, Nebraska, and Wyoming using winter wheat cultivars selected from leading adapted cultivars from each region to determine the effect of wheat plant density in the fall on jointed goatgrass competitiveness. Three winter wheat seeding rates (50, 67 and 84 kg seed/ha) were used at Hays, KS and Sidney, NE and four seeding rates (33, 50, 67, and 101 kg seed/ha) were used at Torrington and Archer, WY. An analysis of covariance model was fit with winter wheat fall plant density as the covariate. In 1996, winter wheat grain contamination (dockage) was reduced at the rate of about 6% for every 10 additional wheat plants/m2 above the threshold density of 70 plants/m2 at Archer, WY and at the rate of about 0.5% for every 10 additional wheat plants/m2 above the threshold density of 110 plants/m2 at Hays, KS. At Hays the reduction occurred only with the semi-dwarf cultivar ‘Vista’. Increased wheat density reduced jointed goatgrass reproductive tillers in four of six location-year combinations and biomass in two of four location-year combinations. Despite the lack of a consistent reduction in jointed goatgrass competitiveness as the result of increased wheat density, increased seeding rates may be a good, low cost, long-term investment as part of an integrated jointed goatgrass control program in winter wheat. Lyon, D.J., D.D. Baltensperger, and M. Siles. 2001. Wheat grain and forage yields are affected by planting and harvest dates in the central Great Plains. Crop Sci. 41:488-492. Although grazing of winter wheat (Triticum aestivum L.) is a common practice in the southern Great Plains, little is known about the efficacy of wheat as a dual-purpose crop in the Nebraska Panhandle. The objective of this study was to evaluate the effects of establishment and harvest times on forage and grain production of wheat cultivars adapted to the region. Six cultivars were planted at four dates (very early, recommended early, recommended late, and very late) in each of 3 yr. Forage samples were taken from a previously nonharvested area late in the fall, at jointing, and at the boot stage. Grain yield at maturity was measured from each forage harvest treatment and from a full-season unharvested control. In 2 of 3 yr, grain yield was reduced an average of 25% compared with the full-season check when plants were harvested for forage at the joint stage. No grain was produced when forage was removed at the boot stage. Forage removal during the fall averaged 1300 kg/ha dry matter and resulted in insignificant losses in grain yield. While most of the fall growth was too low to the ground for clipping, it could provide high-value supplemental grazing on account of the high crude protein ( 310 g/kg) and in vitro organic matter digestibility (800 g/kg) levels. Spring grazing in this region is limited to the time prior to jointing if market conditions favor grain production. Jasieniuk, M., B.D. Maxwell, R. L. Anderson, J.O. Evans, D.J. Lyon, S. D. Miller, D.W. Morishita, A.G. Ogg, Jr., S. Seefeldt, P.W. Stahlman, F.E. Northam, P. Westra, Z. Kebede, and G.A. Wicks. 2001. Evaluation of models predicting winter wheat yield as a function of winter wheat and jointed goatgrass densities. Weed Sci. 49:48-60. Three models that empirically predict crop yield from crop and weed density were evaluated for their fit to 30 data sets from multistate, multiyear winter wheat-jointed goatgrass interference experiments. The purpose of the evaluation was to identify which model would generally perform best for the prediction of yield (damage function) in a bioeconomic model and which model would best fulfill citeria for hypothesis testing with limited amounts of data. Seven criteria were used to assess the fit of the models to the data. Overall, Model 2 provided the best statistical description of the data. Model 2 regressions were most often statistically significant, as indicated by approximate F tests, explained the largest proportion of total variation about the mean , gave the smallest residual sum of squares, and returned residuals with random distribution more often than Models 1 and 3. Model 2 performed less well based on the remaining criteria. Model 3 outperformed Models 1 and 2 in the number of parameters estimated that were statistically significant. Model 1 outperformed Models 2 and 3 in the proportion of regressions that converged on a solution and more readily exhibited an asymptotic relationship between winter wheat yield and both winter wheat and jointed goatgrass density under the constraint of limited data. In contrast, Model 2 exhibited a relatively linear relationship between yield and crop density and little effect of increasing jointed goatgrass density on yield, thus overpredicting yield at high weed densities when data were scarce. Model 2 had statistical properties that made it superior for hypothesis testing; however, Model 1's properties were determined superior for the damage function in the winter wheat-jointed goatgrass bioeconomic model because it was less likely to cause bias in yield prediction based on data sets of minimum size. Pester, T.A., P. Westra, R.L. Anderson, D.J. Lyon, S.D. Miller, P.W. Stahlman, F.E. Northam, and G.A. Wicks. 2000. Secale cereale interference and economic thresholds in winter Triticum aestivum . Weed Sci. 48:720-727.Secale cereale is a serious weed problem in winter Triticum aestivum -producing regions. The interference relationships and economic thresholds of S. cereale in winter T. aestivum in Colorado, Kansas, Nebraska, and Wyoming were determined over 4 yr. Winter T. aestivum density was held constant at recommended planting densities for each site. Target S. cereale densities were 0, 5, 10, 25, 50, or 100 plants m-2. Secale cereale -winter T. aestivum interference relationships across locations and years were determined using a negative hyperbolic yield loss function. Two parameters - I, which represents the percent yield loss as S. cereale density approaches zero, and A, the maximum percent yield loss as S. cereale density increases - were estimated for each data set using nonlinear regression. Parameter I was more stable among years within locations than among locations within years, whereas maximum percentage yield loss was more stable across locations and years. Environmental conditions appeared to have a role in the stability of these relationships. Parameter estimates for I and A were incorporated into a second model to determine economic thresholds. On average, threshold values were between 4 and 5 S. cereale plants m-2, however, the larger variation in these threshold values signifies considerable risk in making economic weed management decisions based upon these values. Kettler, T.A., D.J. Lyon, J.W. Doran, W.L. Powers, and W.W. Stroup. 2000. Soil quality assessment after weed-control tillage in a no-till wheat-fallow cropping system. Soil Sci. Soc. Am. J. 64:339-346. Adoption of reduced-tillage fallow systems in the western USA is limited by winter annual grass weeds such as downy brome (Bromus tectorum L.). Moldboard plowing is an effective means of controlling downy brome in winter wheat (Triticum aestivum L.)-fallow systems. The purpose of this study was to assess the influence of plowing and secondary tillage operations, for the purpose of weed control, on soil quality attributes of a silt loam soil that had been cropped in a sub-till or no-till (NT) winter wheat-fallow system for more than 20 yr. Compared with undisturbed NT, downy brome populations in plowed NT decreased 97 and 41% in the first and third crops following tillage, respectively. Wheat yields in plowed NT treatments were 30 and 9% greater in the first and third crops following tillage, respectively, compared with undisturbed NT. Soil quality indicators assessed were organic C (OC), total N, inorganic N, pH, electrical conductivity, bulk density, water infiltration rate, and pore-size distribution. Five years after tillage, soil OC decline in the 0- to 7.5-cm depth was 20% in plowed compared with undisturbed NT; however, OC increased 15% in the 7.5- to 15-cm depth and was not different in the 0- to 30-cm depth. Total soil N followed similar trends. Soil inorganic N in plowed NT decreased 37%, and soil pH increased 9%, compared with undisturbed NT, at the 0- to 7.5-cm depth. Occasional tillage with the moldboard plow in a reduced- or no-tillage management system will help control winter annual grass weeds, while retaining many of the soil quality benefits of conservation-tillage management. Jasieniuk, M., B.D. Maxwell, R. L. Anderson, J.O. Evans, D.J. Lyon, S. D. Miller, D.W. Morishita, A.G. Ogg, Jr., S. Seefeldt, P.W. Stahlman, F.E. Northam, P. Westra, Z. Kebede, and G.A. Wicks. 1999. Site-to-site and year-to-year variation in Triticum aestivum-Aegilops cylindrica interference relationships. Weed Sci. 47:529-537. Crop yield loss-weed density relationships critically influence calculation of economic thresholds and the resulting management recommendations made by a bioeconomic model. To examine site-to-site variation in winter Triticum aestivum L. (winter wheat)-Aegilops cylindrica Host. (jointed goatgrass) interference relationships, the rectangular hyperbolic yield loss funcation was fit to data sets from multiyear field experiments conducted at Colorado, Idaho, Kansas, Montana, Nebraska, Utah, Washington, and Wyoming. The model was fit to three measures of A. cylindrica density: fall seedling, spring seedling, and reproductive tiller densities. Two parameters: i , the slope of the yield loss curve as A. cylindrica density approaches zero, and a, the maximum percentage yield regression. Fit of the model to the data was better using spring seedling densities than fall seedling densities, but it was similar for spring seedling and reproductive tiller densities based on the residual mean square (RMS) values. Yield loss functions were less variable among years within a site than among sites for all measures weed density. Fore the one site where year-to-year variation was observed (Archer, WY), parameter a varied significantly among sites for 7 of 10 comparisons. Site-to-site statistical differences were generally due to variation in estimates of i. Site-to-site and year-to-year variation in winter T. aestivum-A . cylindrica yield loss parameter estimates indicated that management recommendations made by a bioeconomic model cannot be based on a single yield loss function with the same parameter values for the winter T. aestivum-producing region. The predictive ability of a bioeconomic model is likely to be improved when yield loss functions incorporating time of emergence and crop density are built into the model’s structure. Lyon, D. J., and D. R. Shelton. 1999. Fallow management and nitrogen fertilizer influence winter wheat kernel hardness. Crop Sci. 39:448-452. Kernel hardness is an important grain attribute for wheat (Triticum aestivum L.) quality and marketing in the USA. The objective of this study was to characterize the effects of fallow management – moldboard plow (Plow), sub-tillage (Sub-till) and no-tillage (No-till) – and N fertilizer (0 and 45 kg N ha-1) on winter wheat kernel hardness, as measured by the Single Kernel Characterization System (SKCS). Rainfed field studies were conducted with ‘Siouxland’ hard red winter wheat from 1995-1997 on an Alliance silt loam (fine-silty, mixed, mesic Aridic Argiustoll) near Sidney, NE. In 1995 and 1996, the kernel hardness index was increased from a 2-yr average of 46.0 to 55.2 by the addition of 45 kg N ha-1, but N fertilizer treatment had no effect on kernel hardness in 1997 when the average kernel hardness index was 72.9. The effect of fallow management on kernel hardness varied from year to year. Kernel hardness was positively correlated with grain protein in 1995 (r = 0.93) and 1996 (r = 0.94), but no meaningful relationship was observed in 1997. Half of the grain samples analyzed by the SKCS in 1995 and 1996 were classified as either soft or mixed wheat. This study suggests that kernel hardness is affected by a number of factors beyond genetics including N management, tillage system, pest infestations, environment, and their interaction. Growers may find that meeting proposed new grain standards is more complex than merely selecting the right cultivar. Daugovish, O., D. J. Lyon, and D. D. Baltensperger. 1999. Cropping systems to control winter annual grasses in winter wheat (Triticum aestivum). Weed Technol. 13:120-126. Field studies were conducted from 1990 through 1997 to evaluate the long-term effect of 2- and 3-yr rotations on the control of downy brome, jointed goatgrass and feral rye in winter wheat. At the completion of the study, jointed goatgrass and feral rye densities averaged 8 and < 0.1 plants/m2 for the 2- and 3-yr rotations, respectively. Downy brome densities averaged < 0.5 plants/m2 for both the 2- and 3-yr rotations, with no treatment differences observed. Winter annual grasses were not eradicated after two cycles of the 3-yr rotations, but weed densities were reduced ten-fold compared to densities after one cycle and more than 100-fold compared with the 2-yr rotations. Wheat grain contamination with dockage and foreign material followed a similar trend. The 3-yr rotations were economically competitive with 2-yr rotations and provided superior control of the winter annual grass weeds.
Updated
Jan. 3, 2007 |