Assessing heterogeneity in soil nitrogen cycling: a plot-scale approach

Abstract

The high level of spatial and temporal heterogeneity in soil N cycling processes hinders our ability to develop an ecosystem-wide understanding of this cycle. This study examined how incorporating an intensive assessment of spatial variability for soil moisture, C, nutrients, and soil texture can better explain ecosystem N cycling at the plot scale. Five sites distributed across a regionally representative vegetation and elevation gradient at the Coweeta Hydrologic Laboratory in the southern Appalachian Mountains were sampled five times between November 2010 and March 2012. We used electromagnetic induction (EMI) to survey for soil moisture, soil texture, and near-infrared reflectance spectroscopy (NIRS) to estimate extractable NH4+, total C, and total N concentrations. Laboratory assays of nitrification and denitrification potential rates were used as an index for N cycling dynamics. Multivariate regression analysis indicated that the NIRS and EMI survey data explained 30 to 90% of the variability in potential nitrification rates (p < 0.01) and 16 to 70% of variability in potential denitrification rates (p < 0.01). Two extrapolation approaches were used to calculate the mean and the variability of potential rates: (i) stratified selection of collected samples based on EMI and NIRS predictors; and (ii) random selection of collected samples. The mean for potential nitrification rates based on EMI and NIRS stratification yielded similar (oak–pine and mixed oak) and greater (northern hardwood and cove hardwood) rates, whereas potential denitrification rates were greater in all sites for the stratified-based estimates. This study demonstrated that the application of geophysical tools may enhance our ecosystem-level understanding of the N cycle.

  • Citation: Baas, Peter; Mohan, Jacqueline E.; Markewitz, David; Knoepp, Jennifer D. 2014. Assessing heterogeneity in soil nitrogen cycling: a plot-scale approach. In: 12th North American Forest Soils Conference. Whitefish, MT, 16-20 June 2013. Soil Science Society of America Journal. 78(S1): S237-S247. Doi:10.2136/sssaj2013.09.0380nafsc
  • Keywords: CH, cove hardwood; EMI, electromagnetic induction; MO-high; high-elevation mixed oak; MO-low, low-elevation mixed oak; NIRS, near-infrared reflectance spectroscopy; NH, northern hardwood; OP, oak-pine; pDNF, potential denitrification, pNTR, potential nitrification; WS, Watershed
  • Posted Date: August 21, 2014
  • Modified Date: September 29, 2014
  • Print Publications Are No Longer Available

    In an ongoing effort to be fiscally responsible, the Southern Research Station (SRS) will no longer produce and distribute hard copies of our publications. Many SRS publications are available at cost via the Government Printing Office (GPO). Electronic versions of publications may be downloaded, printed, and distributed.

    Publication Notes

    • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.
    • Our online publications are scanned and captured using Adobe Acrobat. During the capture process some typographical errors may occur. Please contact the SRS webmaster if you notice any errors which make this publication unusable.
    • To view this article, download the latest version of Adobe Acrobat Reader.