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Coulter J.A.,University of Minnesota | Sheaffer C.C.,University of Minnesota | Haar M.J.,Badlands National Park | Wyse D.L.,University of Minnesota | Orf J.H.,University of Minnesota
Agronomy Journal | Year: 2011

Delayed planting is a common strategy for enhancing weed control in organic soybean [Glycine max (L.) Merr.] production, but it has the potential to reduce yield. Increasing soybean seeding rate may be a way to enhance weed control wiThearly planting, and to mitigate potential yield losses due to delayed planting. From 2006 to 2008, experiments were conducted in southern and central Minnesota in organically managed systems with tillage for weed control to determine agronomic responses of soybean and weed density to planting date and seeding rate for feed- and food-grade soybean cultivars. Increasing seeding rate from 395,400 to 543,600 seeds ha -1 did not enhance weed control or soybean yield, and this was consistent across planting dates and cultivars. Total weed density at harvest and soybean yield were greatest when planting occurred in mid- or late May, and were reduced by 51 and 21% when planting was delayed until mid-June, respectively. Yield of feed-grade cultivars was 21% higher than food-grade cultivars, which was consistent across planting dates. Total weed density at harvest differed among cultivars, and was lowest with two of the three highest-yielding cultivars. These results demonstrate that in organic cropping systems with tillage for weed control in the Upper Midwest, planting in mid- to late May rather than mid-June is critical for maximizing yield, while high seeding rates are not likely to improve yield or weed control. © 2011 by the American Society of Agronomy. All rights reserved. Source

Coulter J.A.,University of Minnesota | Sheaffer C.C.,University of Minnesota | Wyse D.L.,University of Minnesota | Haar M.J.,Badlands National Park | And 3 more authors.
Agronomy Journal | Year: 2011

Cropping systems with less reliance on external inputs could improve agricultural sustainability if they can produce high and stable crop yields over time. A 16-yr experiment was conducted in southwestern Minnesota to evaluate the effects of zero external input (ZEI), low external input (LEI), high external input (HEI), and organic input (OI) systems on crop yield and yield stability in a 2-yr soybean [Glycine max (L.) Merr.]-corn (Zea mays L.) rotation and a 4-yr oat (Avena sativa L.)/alfalfa (Medicago sativa L.)-alfalfa-corn-soybean rotation. Oat yield was stable and highest with the LEI, HEI, and OI systems. Alfalfa yield was highest with the LEI, HEI, and OI systems in the fi rst 8 yr and the OI system in the last 8 yr. Corn grain yield was 0, 13, 26, and 40% greater with the 4-yr rotation than the 2-yr rotation in the HEI, LEI, OI, and ZEI systems, respectively, and was greatest with the HEI system in the 2-yr rotation and the LEI, HEI, and OI systems in the 4-yr rotation. Soybean yield was 7% greater with the 4-yr rotation than the 2-yr rotation and was among the highest with the LEI and HEI systems. Stable corn and soybean yields occurred with the LEI and OI systems, while above-average yield increases under favorable growing conditions occurred with the LEI and HEI systems in alfalfa and the HEI system in corn. These results demonstrate the value of extended crop rotations for corn and soybean, and that high crop yields can be obtained with reduced-input systems. © 2011 by the American Society of Agronomy. Source

Larson D.L.,U.S. Geological Survey | Droege S.,U.S. Geological Survey | Rabie P.A.,West Inc. | Larson J.L.,Polistes Foundation | And 3 more authors.
Journal of Applied Ecology | Year: 2014

Summary: Analyses of flower-visitor interaction networks allow application of community-level information to conservation problems, but management recommendations that ensue from such analyses are not well characterized. Results of modularity analyses, which detect groups of species (modules) that interact more with each other than with species outside their module, may be particularly applicable to management concerns. We conducted modularity analyses of networks surrounding a rare endemic annual plant, Eriogonum visheri, at Badlands National Park, USA, in 2010 and 2011. Plant species visited were determined by pollen on insect bodies and by flower species upon which insects were captured. Roles within modules (network hub, module hub, connector and peripheral, in decreasing order of network structural importance) were determined for each species. Relationships demonstrated by the modularity analysis, in concert with knowledge of pollen species carried by insects, allowed us to infer effects of two invasive species on E. visheri. Sharing a module increased risk of interspecific pollen transfer to E. visheri. Control of invasive Salsola tragus, which shared a module with E. visheri, is therefore a prudent management objective, but lack of control of invasive Melilotus officinalis, which occupied a different module, is unlikely to negatively affect pollination of E. visheri. Eriogonum pauciflorum may occupy a key position in this network, supporting insects from the E. visheri module when E. visheri is less abundant. Year-to-year variation in species' roles suggests management decisions must be based on observations over several years. Information on pollen deposition on stigmas would greatly strengthen inferences made from the modularity analysis. Synthesis and applications: Assessing the consequences of pollination, whether at the community or individual level, is inherently time-consuming. A trade-off exists: rather than an estimate of fitness effects, the network approach provides a broad understanding of the relationships among insect visitors and other plant species that may affect the focal rare plant. Knowledge of such relationships allows managers to detect, target and prioritize control of only the important subset of invasive species present and identify other species that may augment a rare species' population stability, such as E. pauciflorum in our study. © 2014 British Ecological Society. Source

Boyd C.A.,South Dakota School of Mines and Technology | Weiler M.W.,University of North Dakota | Householder M.L.,Badlands National Park | Schumaker K.K.,University of North Dakota
Acta Palaeontologica Polonica | Year: 2014

The synonymization of the cimolestan taxa Cymaprimadon and Chadronia from the Late Eocene Chadron Formation is consistently upheld, despite a lack of supporting evidence. Here we show that the synonymization is unjustified, owing to distinct differences between these taxa in the mandibular tooth count (1-1-3-3 vs. ?-1-4-3), the identity of the enlarged anterior mandibular tooth (incisor versus canine), and the morphology of the crown of m3 (e.g., paraconid on m3 in Cymaprimadon). We also refer a specimen recently collected from the Early Oligocene Brule Formation within the Badlands National Park (BADL 16917) to Chadronia sp., thus making it the youngest occurrence of a pantolestan from North America. Examination of an additional specimen (FMNH UC 349) revealed the presence of a further cimolestan taxon in the White River Group of South Dakota, although the poor quality of the locality and stratigraphic data associated with this specimen precludes erecting a formal name. In total, this study doubles the number of cimolestans from the Late Chadronian and Orellan (Ch4 to Or1) of North America from two to four, and extends the biostratigraphic range of Pantolesta into the North American Oligocene. © 2014 C.A. Boyd et al. Source

Brainard D.C.,Michigan State University | Curran W.S.,Pennsylvania State University | Bellinder R.R.,Cornell University | Ngouajio M.,Michigan State University | And 4 more authors.
Weed Technology | Year: 2013

Nonsynthetic herbicides offer a potentially useful addition to the suite of weed management tools available to organic growers, but limited information is available to guide the optimal use of these products. The objectives of this research were to (1) evaluate the efficacy of clove oil- and vinegar-based herbicides on weeds across multiple states, and (2) assess the potential role of temperature, relative humidity (RH), and cloud cover in explaining inter-state variations in results. From 2006 to 2008, a total of 20 field trials were conducted in seven states using an identical protocol. Seeds of brown mustard were sown and herbicides applied to both mustard and emerged weeds when mustard reached the three- to four-leaf stage. Treatments included clove oil at 2.5, 5, 7.5, and 10% v/v concentrations at 54 L ha-1, and vinegar at 5, 10, 15, and 20% v/v concentrations at 107 L ha-1. Results varied widely across trials. In general, concentrations of at least 7.5% for clove oil and 15% for vinegar were needed for adequate control of mustard. Both products were more effective at suppressing mustard than Amaranthus spp. or common lambsquarters. Poor control was observed for annual grasses. No significant effects of cloud cover on the efficacy of either product were detected. In contrast, RH was positively correlated with control of brown mustard by both clove oil and vinegar with improved control at higher RH. Temperature had no detectable effect on the efficacy of clove oil, but higher temperatures improved control of brown mustard by vinegar. Nomenclature: Clove oil; vinegar; common lambsquarters, Chenopodium album L.; redroot pigweed, Amaranthus retroflexus L.; brown mustard, Brassica juncea L. Czerniak. Source

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