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Effect of Fertilizer Nitrogen on Weed Emergence and Growth
- Amy E. Sweeney, Karen A. Renner, Carrie Laboski, Adam Davis
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- Journal:
- Weed Science / Volume 56 / Issue 5 / October 2008
- Published online by Cambridge University Press:
- 20 January 2017, pp. 714-721
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The timing of nitrogen (N) fertilizer application may influence germination, emergence, and competitiveness of weeds. Research was conducted to determine the influence of total inorganic soil N (Nit) on the germination, emergence, and growth of five weed species. In a greenhouse experiment, seed of five weed species were exposed to four levels of N, and seed germination was measured. In the field, urea ammonium nitrate (UAN 28%) was applied at multiple rates at three spring timings, and Nit, weed emergence, and growth were measured for 21 to 35 d after application (DAA). Germination of the four dicotyledonous and single grass species was not stimulated by 450 ppmw of N compared with the untreated control. In the field, Nit of 112 or 168 kg N ha−1, measured at 7 and 21 DAA, was always greater than Nit in the untreated control. The duration of the available N pulse in the upper 8 cm of soil was dependent on N application rate and timing. At 8 to 16 cm of soil depth, Nit was greater when 168 kg N ha−1 was applied compared with no N at 21 and 35 DAA in 2004. Emergence of common lambsquarters increased as N application rate increased for each application date in 2003, but not in 2004. Emergence of ladysthumb increased with N application rate for the April 15, 2003, date; emergence of giant foxtail increased with N application rate for the April 6, 2004, date. Weed biomass was always greater when 168 kg N ha−1 was applied compared with no N, and at four of six N application dates, when 112 kg N ha−1 was applied. This research shows that spring N fertilizer applications increase Nit and weed growth, but the influence of N on weed emergence is dependent on the weed species, seed source, and environmental conditions.
Effect of Weed Management Strategy and Row Width on Nitrous Oxide Emissions in Soybean
- Rebecca R. Bailey, Thomas R. Butts, Joseph G. Lauer, Carrie A. M. Laboski, Christopher J. Kucharik, Vince M. Davis
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- Journal:
- Weed Science / Volume 63 / Issue 4 / December 2015
- Published online by Cambridge University Press:
- 20 January 2017, pp. 962-971
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Nitrous oxide (N2O) is a potent greenhouse gas with implication for climate change. Agriculture accounts for 10% of all greenhouse gas emissions in the United States, but 75% of the country's N2O emissions. In the absence of PRE herbicides, weeds compete with soybean for available soil moisture and inorganic N, and may reduce N2O emissions relative to a weed-free environment. However, after weeds are killed with a POST herbicide, the dead weed residues may stimulate N2O emissions by increasing soil moisture and supplying carbon and nitrogen to microbial denitrifiers. Wider soybean rows often have more weed biomass, and as a result, row width may further impact how weeds influence N2O emissions. To determine this relationship, field studies were conducted in 2013 and 2014 in Arlington, WI. A two-by-two factorial treatment structure of weed management (PRE + POST vs. POST-only) and row width (38 or 76 cm) was arranged in a randomized complete block design with four replications. N2O fluxes were measured from static gas sampling chambers at least weekly starting 2 wk after planting until mid-September, and were compared for the periods before and after weed termination using a repeated measures analysis. N2O fluxes were not influenced by the weed by width interaction or width before termination, after termination, or for the full duration of the study at P ≤ 0.05. Interestingly, we observed that POST-only treatments had lower fluxes on the sampling day immediately prior to POST application (P = 0.0002), but this was the only incidence where weed influenced N2O fluxes, and overall, average fluxes from PRE + POST and POST-only treatments were not different for any period of the study. Soybean yield was not influenced by width (P = 0.6018) or weed by width (P = 0.5825), but yield was 650 kg ha−1 higher in the PRE + POST than POST-only treatments (P = 0.0007). These results indicate that herbicide management strategy does not influence N2O emissions from soybean, and the use of a PRE herbicide prevents soybean yield loss.