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Fort Collins, CO, United States

Gove J.H.,U.S. Department of Agriculture | Ducey M.J.,University of New Hampshire | Valentine H.T.,U.S. Department of Agriculture | Williams M.S.,2150 Center Ave
Forest Ecology and Management | Year: 2012

A new sampling method for down coarse woody debris is proposed based on limiting the perpendicular distance from individual pieces to a randomly chosen sample point. Two approaches are presented that allow different protocols to be used to determine field measurements; estimators for each protocol are also developed. Both protocols are compared via simulation against existing sampling methods that are closely related in terms of theory and field implementation. The new method performed well in comparison to both fixed-area plot and perpendicular distance sampling, and may provide some simplifications in operational field use. © 2012. Source

Halvorson A.D.,2150 Center Ave | Jantalia C.P.,Embrapa Agrobiology
Agronomy Journal | Year: 2011

Converting to no-till (NT) production can affect N requirements for optimizing corn (Zea mays L.) yields while enhancing soil organic carbon (SOC) and N levels. Nitrogen fertilization impacts on irrigated, NT continuous-corn grain, stalk, cob, and stover yields, stover C and N uptake, and C/N ratios were evaluated for 11 yr on a clay loam soil. Changes in SOC and total soil nitrogen (TSN) were also monitored. Grain, stalk, cob, and stover yields increased with increasing N rate, as did N and C uptake. The C/N ratio of stalk residue declined with increasing N rate, but cob C/N ratio was not affected, with an average stover C/N ratio of 68 at the highest N rate. Nitrogen fertilization increased SOC and TSN levels with average SOC and TSN mass rate gains with N application of 0.388, 0.321, and 0.160 Mg SOC ha -1 yr -1 and 0.063, 0.091, and 0.140 Mg TSN ha -1 yr -1 in the 0- to 7.6-,0- to 15.2-, and 0- to 30.4-cm soil depths, respectively. The SOC and TSN mass rate changes were lower without N application. Increases in TSN appeared to be more rapid than SOC, resulting in a decline in the soil C/N ratio with time. Under irrigated, NT continuous corn production, N fertilization optimized grain and residue yields, with the enhanced benefit of increased SOC and TSN levels in the semiarid central Great Plains. Removal of cobs or partial stover residue as a cellulosic feedstock for ethanol production appears possible without negative effects on soil quality under irrigated, NT corn production. © 2011 by the American Society of Agronomy. Source

Merritt D.M.,2150 Center Ave | Merritt D.M.,Colorado State University | Shafroth P.B.,U.S. Geological Survey
Biological Invasions | Year: 2012

Tamarix spp. are introduced shrubs that have become among the most abundant woody plants growing along western North American rivers. We sought to empirically test the long-held belief that Tamarix actively displaces native species through elevating soil salinity via salt exudation. We measured chemical and physical attributes of soils (e. g., salinity, major cations and anions, texture), litter cover and depth, and stand structure along chronosequences dominated by Tamarix and those dominated by native riparian species (Populus or Salix) along the upper and lower Colorado River in Colorado and Arizona/California, USA. We tested four hypotheses: (1) the rate of salt accumulation in soils is faster in Tamarix-dominated stands than stands dominated by native species, (2) the concentration of salts in the soil is higher in mature stands dominated by Tamarix compared to native stands, (3) soil salinity is a function of Tamarix abundance, and (4) available nutrients are more concentrated in native-dominated stands compared to Tamarix-dominated stands. We found that salt concentration increases at a faster rate in Tamarix-dominated stands along the relatively free-flowing upper Colorado but not along the heavily-regulated lower Colorado. Concentrations of ions that are known to be preferentially exuded by Tamarix (e. g., B, Na, and Cl) were higher in Tamarix stands than in native stands. Soil salt concentrations in older Tamarix stands along the upper Colorado were sufficiently high to inhibit germination, establishment, or growth of some native species. On the lower Colorado, salinity was very high in all stands and is likely due to factors associated with floodplain development and the hydrologic effects of river regulation, such as reduced overbank flooding, evaporation of shallow ground water, higher salt concentrations in surface and ground water due to agricultural practices, and higher salt concentrations in fine-textured sediments derived from naturally saline parent material. © 2012 Springer Science+Business Media B.V.(outside the USA). Source

Williams M.S.,2150 Center Ave | Ebel E.D.,2150 Center Ave
International Journal of Food Microbiology | Year: 2014

Indicator organisms, such as generic Escherichia coli (GEC) and coliforms, can be used to measure changes in microbial contamination during the production of food products. Large and consistent reductions in the concentration of these organisms demonstrates an effective and well-controlled production process. Nevertheless, it is unclear to what degree concentrations of indicator organisms are related to pathogenic organisms such as Campylobacter and Salmonella on a sample-by-sample basis. If a strong correlation exists between the concentrations of different organisms, then the monitoring of indicator organisms would be a cost-effective surrogate for the measurement of pathogenic organisms. Calculating the correlation between the concentrations of an indicator and pathogenic organism is complicated because microbial testing datasets typically contain a large proportion of censored observations (i.e., samples where the true concentration is not observable, with nondetects and samples that are only screen-test positive being examples). This study proposes a maximum likelihood estimator that can be used to estimate the correlation between the concentrations of indicator and pathogenic organisms. An example based on broiler chicken rinse samples demonstrates modest, but significant positive correlations between the concentration of the indicator organism GEC when compared to the concentration of both Campylobacter and Salmonella. A weak positive correlation was also observed between concentrations of Campylobacter and Salmonella, but it was not statistically significant. © 2014. Source

Erdman M.M.,U.S. Department of Agriculture | Creekmore L.H.,2150 Center Ave | Fox P.E.,Eastern Regional Office | Pelzel A.M.,2150 Center Ave | And 5 more authors.
Preventive Veterinary Medicine | Year: 2011

Contagious equine metritis (CEM) is a highly contagious venereal disease of horses caused by Taylorella equigenitalis. During testing for semen export purposes, a stallion in Kentucky was found to be T. equigenitalis culture positive in December of 2008. This finding triggered an extensive regulatory investigation to search for additional positive horses, determine the extent of the outbreak, identify the potential source of the outbreak, and ultimately return the United States to CEM-free status. The investigation included over 1000 horses located in 48 states. Diagnostic testing found a total of 22 stallions, 1 gelding and 5 mares culture positive for T. equigenitalis. Epidemiologic analysis indicated that all of the positive horses were linked to a single common source, most likely a Fjord stallion imported into the United States in 2000. The T. equigenitalis strain subsequently spread to other stallions via undetermined indirect mechanisms at shared breeding facilities, and to mares via artificial insemination and live breeding. This CEM outbreak and investigation represent the largest ever in the United States based on the number of exposed horses tested and their geographic distribution. © 2011 Elsevier B.V. Source

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