Chronic N Plots - Sample Collection and Analysis
Fertilization: Fertilizer additions of NH4NO3
and Na2SO4 began in 1988 as six equal
applications over the growing season (May - Sept). Fertilizer was
weighed, mixed with 20 liters of water (equivalent to 0.002 cm
rainfall) and applied using a backpack sprayer.
Na2SO4 applications were discontinued after the
1998 growing season.
Soil Mineralization: In-situ buried bags were used to measure net mineralization, net nitrification and extractable NH4 and NO3 concentrations. Samples were extracted in 1 N KCl, filtered and analysed on a Bran+Luebbe Traacs Autoanalyser using the Berthelot Reaction (NH4-N) or hydrazine reduction (NO3-N) chemistry.
Soil CN: Soils were split into organic and mineral horizons, dried, ground and measured for total carbon and nitrogen content using either a Perkin Elmer or Carlo Erba CHN analyzer.
Litterfall: Total litter mass was measured by collecting annual litterfall in baskets, sorting into species, drying and weighing. Samples were then ground and scanned for percent nitrogen, lignin and cellulose using an NIRSystems near infrared spectrometer.
Green Foliage: Samples collected, dried, ground and scanned for percent nitrogen, lignin and cellulose using an NIRSystems near infrared spectrometer. Samples were digested and digestate measured for base cations using either ICP (1999, 2002) or DCP (1997 and earlier).
B horizon lysimeters: Tension of 50psi was drawn for 24 hours. Soil water samples were collected, filtered and frozen prior to analysis. NH4 and NO3 were measured using the Traacs Autoanalyser (see soil mineralization for methods) and for DOC using a Shimadzu TOC-5000 Total Organic Carbon Analyser with a NDIR detector. TDN was measured using the TOC-5000 with an Antek chemiluminecent detector. Base cations were measured using either ICP (1998 and later) or DCP (1997 and earlier).
O horizon lysimeters (Zero-Tension Lysimeters, ZTL): ZTL's are gravity fed gravel and glass bead filled collection units (0.3 to 1.5cm) located beneath the organic horizon with a tube draining approximately 154 cm2 into a 1 liter bottle. Samples were collected within 1 week following a rain event, weighed, filtered through a 0.7um filter and frozen prior to analysis. N and C were measured in the same manner as B horizon lysimeters. Base cations were measured using either ICP (1998 and later) or DCP (1997 and earlier).
Fine Roots: Fine root cores were taken, roots hand picked, washed, dried, weighed and ground for CHN analysis. Separation by size class and core size/depth were not consistent across years.
Tree DBH: All trees above 5cm DBH were numbered and measured in 1988. In 1996, trees previously too small in 1988 were tagged and measured. DBH measurements were converted to aboveground biomass using published allometric equations.