Microbial Biomass and Nitrate Immobilization in a Multispecies Riparian Buffer

EPA Grant Number: U915246
Title: Microbial Biomass and Nitrate Immobilization in a Multispecies Riparian Buffer
Investigators: Pickle, Joyce
Institution: Iowa State University
EPA Project Officer: Hahn, Intaek
Project Period: January 1, 1997 through December 31, 2000
Project Amount: $68,000
RFA: STAR Graduate Fellowships (1997) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Ecological Indicators/Assessment/Restoration , Fellowship - Ecology and Ecosystems


The objective of this research project is to compare the effects of crop field, cool season grass, and a multispecies riparian buffer (MRB) consisting of trees, shrubs, and native grasses on soil microbial biomass and nitrate immobilization.


A 9-year-old, 20-m wide MRB consisting of four rows of trees nearest the stream, followed by two rows of shrubs and a strip of switchgrass is located along Bear Creek in central Iowa. An N budget is being developed for the MRB, a cool-season grass filter strip and adjacent crop fields. Permanent transects moving from the cropfield to the stream are located perpendicular to the stream through the MRB and the cool-season grass filter strip. Three soil cores to 1-m depths are extracted from tree and switchgrass communities in the MRB and the adjacent crop field. In the cool-season grass filter strip, six cores are removed along the transect at locations equivalent to those in the MRB as well as three in the crop field. These soil cores are divided into five different depths, 0-15 cm, 15-35 cm, 35-60 cm, 60-85 cm, and 85-100 cm, and samples are analyzed separately for microbial biomass and immobilization rates. Samples are taken in April, June, July, August, October, and December.

To determine immobilization potential, 100 mL of KCl are added to 10 g of root-free soil, and concentrations of NO3- and NH4+ are determined through liquid chromatography. Duplicate samples from each depth are then incubated at field capacity. After 2 weeks of incubation the concentrations of NO3- and NH4+ are determined by the same methods. The changes in concentrations are a measure of the amount of microbial immobilization. To determine the microbial biomass at each site, two 50-g samples are taken from each soil core depth. The control is immediately extracted with 100 mL K2SO4- and the total organic carbon is analyzed through a nondispersive infrared detector. The duplicate sample is fumigated with chloroform, extracted after 24 hours, and analyzed. The difference in carbon content reflects the microbial organic matter that was lyzed into the soil upon fumigation, and provides a comparison of microbial biomass between treatments.

Supplemental Keywords:

fellowship, reparian buffer, soil microbial bromass, nitrate immobilization

Progress and Final Reports:

  • 1997
  • 1998
  • 1999
  • Final