2000 BES Abstracts

Land use and soil nitrogen cycling

Peter Groffman, Candiss O. Williams, Richard V. Pouyat and Ian Yesilonis

Land use patterns are one of the major sources of patchiness in ecosystem function in the Baltimore area, in both time and space. The area was originally heavily forested (1700), was then almost entirely in agriculture (1850) and is now a mix of forest, agriculture and residential land use. The residential land uses have large areas of grass. Land use influences soil nitrogen cycling through its effects on fertilizer input, soil water, organic matter, pH and disturbance. Quantifying these influences is important for understanding patchiness in ecosystem functions related to soil fertility and the delivery of nitrate (a cause of eutrophication in salt water) to streams and estuaries. There is particular interest in nitrification, the microbial processes that leads to the production of nitrate.

In this study, we sampled 14 forest, 10 row crop agriculture (corn) and 10 grass sites though out the Baltimore metropolitan area in summer 2000. Soils were assayed for microbial biomass carbon and nitrogen content, potential net N mineralization and nitrification, denitrification potential and nitrification potential. As expected, forests had low levels of soil nitrate and nitrification potential compared to grass and agriculture, suggesting that land use conversion leads to increases in nitrate delivery to receiving waters. Grass had intermediate levels of soil nitrate and nitrification and agriculture had the highest levels of these variables. Nitrification was strongly related to soil pH within the different land use classes.