Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/6/2008
Publication Date: 8/12/2008
Citation: Guza, A.E., Renner, K.A., Laboski, C., Davis, A.S. 2008. Effect of early spring fertilizer nitrogen on weed emergence and growth. Weed Science. 56(5):714-721. Interpretive Summary: An unintended consequence of N fertilizer use on crops is that weeds may also benefit from higher N levels, with effects on germination, emergence, competitiveness, and subsequent management of weeds. We examined the emergence and growth of five weed species in the lab and in the field under multiple rates of N fertilizer applied either in early April, late April, or May. Emergence of some species and dry weight of all species increased with increasing N application rate in 2003 and 2004. Reducing N availability near the soil surface, where most weed seeds accumulate, may decrease weed emergence and growth, and lengthen the window for timely herbicide applications.
Technical Abstract: The timing of N fertilizer application in sugar beet and other early season crops may influence the germination, emergence, competitiveness, and subsequent management of weeds. The objective of this research was to determine the influence of total inorganic soil N (Nit) on the germination, emergence, and growth of five weed species. Germination in petri dishes and emergence and growth of five weed species in the field under multiple rates of urea ammonium nitrate (UAN 28%) fertilizer applied in either early April, late April, or May was evaluated each year. Germination of all species in petri dishes decreased at 190 and 290 ppm Nit compared with the untreated control (20 ppm). In the field, Nit increased as N application rate increased; however, usually less than 50% of the applied N was present as Nit in the 0- to 8-cm soil depth three to five weeks after application. The duration of the available N pulse in the upper 8 cm of the soil was dependent on the N application rate and calendar date. Ten to 20 kg ha-1 of additional Nit compared with the untreated control was available in the 8- to 16-cm soil depth five weeks after applying 112 and 168 kg ha-1 of N in 2004. Applying UAN 28% increased the emergence of some seeded weed species at each planting date each year. Emergence of common lambsquarters and giant foxtail from the natural seed bank did not increase with N fertilizer application. Total weed biomass increased with increasing N application rate at all seeding dates in 2003, and in two of three seeding dates in 2004. Reducing N availability in the 0- to 8-cm soil depth may decrease weed emergence and growth, enhancing the opportunity to make timely herbicide applications for weed control.