Nitrogen Relationships of Ornamental Trees in Urban Settings: A First Look (NA-98-0400)

Studies the effect of Nitrogen input on soil solution concentration, estimated Nitrogen losses, and the potential Nitrogen contribution from tree litter for four common ornamental trees in urban landscapes.

Standards for fertilizer application rates of ornamental trees have historically been based upon tree growth responses. Little data exists on the fate of exogenous N applied to tree/turf complexes in urban landscapes. The objective of this study was to determine the effect of N input on i.) soil solution concentration below the tree rooting zone, ii.) on estimated N losses via soil solution, and iii.) the potential N contribution from tree litter, for four common ornamental trees in urban landscapes. We found that low level rates (< 2 lbs N/1000 ft2) of slow release fertilizer N significantly increased soil solution [N] at or below the effective tree rooting depth (p = .01). Furthermore, we determined that during periods of surplus soil moisture there were significant increases in NO3- leaching, particularly in coarse textured soils. We observed a modest relationship (r2 = 0.49) between total N input and total N output and concluded that fertilization using established standards (>2 lbs N/1000 ft2) will produce even greater system N losses than those we encountered. We also determined that potential N contribution from tree litter was, in most instances, below or slightly above than the lower limit of the fertilization standards (2 lbs N/1000 ft2). Furthermore, we observed a species: treatment interaction, suggesting fertilization aimed at litter N replacement should be species and site specific. Lastly, determination of landscape fertility programs often neglects the N contribution from atmospheric deposition. Atmospheric deposition typically exceeds the potential litter N contribution.

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