Skip to main content
ARS Home » Northeast Area » University Park, Pennsylvania » Pasture Systems & Watershed Management Research » Research » Publications at this Location » Publication #116700
Title: SPATIAL AND SEASONAL VARIATION OF GROSS NITROGEN TRANSFORMATIONS AND MICROBIAL BIOMASS IN A NORTHEASTERN USA GRASSLAND

Author
item CORRRE, MARIFE - SOIL SCIENCE/FOREST NUT.
item SCHNABEL, RONALD - FORMER ARS EMPLOYEE
item Stout, William

Submitted to: Ecosystems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/6/2001
Publication Date: 4/20/2002
Citation: Corrre, M.D., Schnabel, R.R., Stout, W.L. Spatial and seasonal variation of gross nitrogen transformations and microbial biomass in a northeastern usa grassland. Soil Biology & Biochemistry. v. 34(4). p. 445-457.

Interpretive Summary: In order to improve farm profitability many dairy, beef, and sheep producers in the northeast U.S. are intensifying the management of their grasslands. This change in grassland management will cause a change in nitrogen and carbon dynamics that can affect grass production and environmental quality. Understanding how nitrogen cycling processes in unmanaged grassland vary spatially and seasonally would aid in developing management systems that improve nitrogen availability for plant uptake and decrease nitrogen losses to the environment when grassland management is intensified. In this study, our objectives were: 1) to quantify gross rates of internal nitrogen cycling processes (i.e., mineralization, nitrification, and immobilization) from an unmanaged grassland, and 2) to investigate the role of topography and climatic factors on the spatial and seasonal variation of these processes. We delineated our study site into three topographic units based on soil and drainage types: upper slope, lower slope, and drained lower slope. Our results indicated that the dynamics of ammonia nitrogen in the internal nitrogen cycling was controlled by the spatial and seasonal variation of soil microbial biomass. By knowing these patterns of variation, we can begin to develop grazing systems and soil fertility programs that will increase animal production, increase soil organic matter and soil carbon, and minimize nitrogen loss to the environment.

Technical Abstract: Understanding how N-cycling processes in grassland vary spatially and seasonally would aid in developing management systems that improve N availability for plant uptake. Our objectives were: 1) to quantify gross rates of internal N-cycling processes in an unmanaged grassland, and 2) to investigate the role of topography and climatic factors on the spatial and seasonal variation of these processes. We delineated our study site into three topographic units based on soil and drainage types: upper slope, lower slope, and drained lower slope. Our results indicated that the dynamics of NH4+ in the internal N cycling was controlled by the spatial and seasonal variation of soil microbial biomass, where the spatial variation has resulted from long-term topographic influence and the seasonal variation from seasonal flushes of available organic matter. The drained lower slope had the highest microbial biomass (647 mg C kg-1 and 90 0mg N kg-1), gross N mineralization rate (8 mg N kg-1 d-1), NH4+ immobilization rate (6 mg N kg-1 d-1), and fastest NH4+ turnover rate (0.5 d), indicating that drainage favored microbial growth and activity. The seasonal patterns of NH4+ transformations and microbial biomass showed that an increase in microbial N was paralleled by high NH4+ immobilization and a decrease in microbial C:N ratio, and that NH4+ immobilization was dependent on NH4+ availability (gross N mineralization; r2 = 0.59, P