October 13, 2009
Nitrogen Mysteries In Urban Grasslands
A group of scientists uncover the nitrogen dynamics of a common urban landscape.
Areas of turf-forming species created and maintained by humans for aesthetic and recreational (not grazing) purposes, i.e. "urban grasslands" are an extremely common, but poorly studied ecosystem type. There are over 150,000 km2of urban grasslands in the U.S. and many receive high rates of fertilizer, creating concerns about nutrient runoff to streams, lakes, and estuaries and emissions of greenhouse gases such as nitrous oxide (N2O) to the atmosphere. Most turfgrass research has been done on highly controlled research plots which can be very different than actual urban grasslands which have highly variable management regimes and physical, biological, and chemical conditions.
Differences in NO3- leaching and N2O flux between forests and grasslands were not as high as expected given the higher frequency of disturbance and fertilization in the grasslands. Annual NO3- leaching was usually higher in grass than forest plots, but in a very dry year and when a disturbed forest plot was included in the analysis, differences were small and insignificant. There were few differences in N2O between grass and forest plots, and markedly higher fluxes in wet years. In a dry year, N losses from the grasslands were equal to less than 10% of the amount of N applied in fertilizer, and even in a wet year, losses were less than 40%. Lots of N appears to be retained in urban grasslands, likely because they support rapidly growing vegetation and high stocks of soil organic matter.
While surprising, these results do not suggest that we should not be concerned about the environmental impacts of urban grasslands. If leaching losses equal 40% of the amount of N applied in fertilizer, and high rates of fertilizer (e.g., 200 kg N ha-1 yr-1) are applied, lawns will have a strongly negative effect on receiving water quality. However, our results suggest that urban grasslands have considerable capacity for N retention that should be studied and considered in evaluations of land-use change and in the development of management plans for urban and suburban watersheds.
The full article is available for no charge for 30 days following the date of this summary. View the abstract at http://jeq.scijournals.org/cgi/content/abstract/38/5/1848.
The Journal of Environmental Quality, http://jeq.scijournals.org is a peer-reviewed, international journal of environmental quality in natural and agricultural ecosystems published six times a year by the American Society of Agronomy (ASA), Crop Science Society of America (CSSA), and the Soil Science Society of America (SSSA). The Journal of Environmental Quality covers various aspects of anthropogenic impacts on the environment, including terrestrial, atmospheric, and aquatic systems.
The American Society of Agronomy (ASA) www.agronomy.org, is a scientific society helping its 8,000+ members advance the disciplines and practices of agronomy by supporting professional growth and science policy initiatives, and by providing quality, research-based publications and a variety of member services.