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Investigation:

TG-08 (Melillo / Cerri)

LBA Dataset ID:

TG08_SOIL_GAS_WETTING

Originator(s):

1. GARCIA-MONTIEL, D.C.
2. STEUDLER, P.A.
3. PICCOLO, M.C.
      4. NEILL, C.
5. MELILLO, J.M.
6. CERRI, C.C.

Point(s) of Contact:

ORNL DAAC User Services Office Oak Ridge National Laboratory Oak Ridge, Tennessee 37 (ornldaac@ornl.gov)

Dataset Abstract:

Rains at the end of the dry season can trigger increases in emissions of nitric oxide and nitrous oxide from forest and pasture soils in the Amazon Basin. The relative importance of the rain-stimulated emissions in the seasonal and annual budgets of these nitrogen gases for forests and pastures in the western Amazon is not well established. This dataset includes measurements of nitric oxide, nitrous oxide, and carbon dioxide fluxes, soil moisture, soil temperature and soil pools of ammonium and nitrate in response to a simulated rain event applied to forests and pastures of two ages (11 and 26 yrs old). The study took place during the dry season in August 1998 at Fazenda Nova Vida, Rondonia in the Brazilian Amazon.

Beginning Date:

1998-08-17

Ending Date:

1999-08-23

Metadata Last Updated on:

2012-07-18

Data Status:

Archived

Access Constraints:

PUBLIC

Data Center URL:

http://daac.ornl.gov/

Distribution Contact(s):

ORNL DAAC User Services Office Oak Ridge National Laboratory Oak Ridge, Tennessee 37 (ornldaac@ornl.gov)

Access Instructions:

PUBLIC

Data Access:

IMPORTANT: The LBA-ECO Project website is no longer being supported. Links to external websites may be inactive. Final data products from the LBA project can be found at the ORNL DAAC. Please follow the fair use guidelines found in the dataset documentation when using or citing LBA data.
Datafile(s):

LBA-ECO TG-08 Trace Gas Fluxes from Wetted Forest and Pasture Soils, Rondonia, Brazil:  http://daac.ornl.gov/cgi-bin/dsviewer.pl?ds_id=1101

Documentation/Other Supporting Documents:

LBA-ECO TG-08 Trace Gas Fluxes from Wetted Forest and Pasture Soils, Rondonia, Brazil:  http://daac.ornl.gov/LBA/guides/TG08_Soil_Gas_Wetting.html

Citation Information - Other Details:

Garcia-Montiel, D.C., Steudler, P.A., Piccolo, M., Neill, C., Melillo, J., and C.C. Cerri. 2012. LBA-ECO TG-08 Trace Gas Fluxes from Wetted Forest and Pasture Soils, Rondonia, Brazil. Data set. Available on-line [http://daac.ornl.gov] from Oak Ridge National Laboratory Distributed Active Archive Center, Oak Ridge, Tennessee, U.S.A. http://dx.doi.org/10.3334/ORNLDAAC/1101

Keywords - Theme:

Parameter Topic Term Source Sensor
NITRATE LAND SURFACE SOILS FIELD INVESTIGATION ION CHROMATOGRAPH
NITROGEN LAND SURFACE SOILS FIELD INVESTIGATION CHEMILUMINESCENCE
SOIL GAS/AIR LAND SURFACE SOILS FIELD INVESTIGATION GC (GAS CHROMATOGRAPH)
SOIL MOISTURE/WATER CONTENT LAND SURFACE SOILS FIELD INVESTIGATION WEIGHING BALANCE

Uncontrolled Theme Keyword(s):  DRY SEASONS, SEASONAL EFFECTS, SOIL MOISTURE, TRACE GAS GLUXES

Keywords - Place (with associated coordinates):

Region
(click to view profile)
Site
(click to view profile)
North South East West
Rondonia Fazenda Nova Vida -10.15600 -10.15600 -62.81100 -62.81100

Related Publication(s):

Garcia-Montiel, D.C., Steudler, P.A., Piccolo, M.C., Neill, C., Melillo, J.M., and C.C. Cerri. 2003. Nitrogen oxide emissions following wetting of dry soils in forest and pastures in Rondonia, Brazil. Biogeochemistry 64: 319-336.

Data Characteristics (Entity and Attribute Overview):

Data Characteristics:

Data are available in one comma separated ASCII file titled: TG08_Wetup_fluxes.csv



The file is organized as follows.



File name:,TG08_Wetup_fluxes.csv,,,,,,,,,,,,,,,,,,,,,,,,,,,

File date:,15-Dec-11,,,,,,,,,,,,,,,,,,,,,,,,,,,

Associated LME file:,TG08_Wetup,,,,,,,,,,,,,,,,,,,,,,,,,,,

,,,,,,,,,,,,,,,,,,,,,,,,,,,,

Column,Column_heading,Units/format,Explanation,,,,,,,,,,,,,,,,,,,,,,,,,

----1,State,,State in which study was done,,,,,,,,,,,,,,,,,,,,,,,,,

----2,Location,,Location of the study: all data were collected at Fazenda Nova Vida,,,,,,,,,,

----3,Year,,Year in which measurements were made,,,,,,,,,,,,,,,,,,,,,,,,,

----4,Month,,Month in which measurements were made,,,,,,,,,,,,,,,,,,,,,,,,,

----5,Day,,Day of the month on which measurements were made,,,,,,,,,,,,,,,,,,,,

----6,Time,HH:MM,Start time for flux measurements in local time on a 24 hour clock.Local time is GMT-4,,,,,,,,,,,,,,,,,,,,,,,,,

----7,Chronosequence,,Chronosequence id,,,,,,,, ,,,,,,,,,,,,,,,,,

----8,Landuse,,Landuse type: plots were either in forest or pasture,,,,,,,,,,,,

----9,Yr_formed,YYYY,Year in which the pasture was created for pasture sites,,,,,,,,,,,,,,,,,,,,,,,,,

---10,Time_seq,,A sequential integer assigned to each flux measurement in a given plot showing the order measurements were taken. Negative numbers were measurements made before irrigations were applied to treated plots.,,,,,,,,,,

---11,Time_treatment,hours,Time before (negative) or after (positive) irrigation treatment,,,,,,,,,,,,,,,,,,,,,,,,,

---12,Plot,,Plot number: each plot was 1 by 2 meters.,,,,,,,,,,,,,,,,,,,,,,,,,

---13,Treatment,,Irrigate plots were treated with 60 L (30 mm) of water while control plots had no water additions. Measurements taken prior to irrigation treatments in the three plots per land use that did get irrigated were marked control indicating they had not yet been treated.,,,,,,,,,,,,,,,,,,,,,,,,,

---14,NO_flux,ug NO-N m-2 hr-1,,Flux of nitric oxide measured as micrograms of N in the form of nitric oxide per meter squared of soil per hour. Positive values represent a net flux from the soil to the atmosphere and negative values a net flux from the atmosphere to the soil.,,,,,,,,,,,,,,,,,,,,,,,,

---15,CO2_flux,mg CO2-C m-2 hr-1,,Flux of carbon dioxide measured as milligrams of carbon dioxide per meter squared of soil per hour. Positive values represent a net flux from the soil to the atmosphere and negative values a net flux from the atmosphere to the soil.,,,,,,,,,,,,,,,,,,,,,,,,

---16,N2O_flux,ug NO2-N m-2 hr-1,,Flux of nitrous oxide measured as micrograms of N in the form of nitrous oxide per meter squared of soil per hour. Positive values represent a net flux from the soil to the atmosphere and negative values a net flux from the atmosphere to the soil.,,,,,,,,,,,,,,,,,,,,,,,,

---17,NH4_soil_conc_A,ug NH4-N per gm dry soil,Soil ammonium concentration measured in the 0 to 2 cm depth,,,,,,,,,,,,,,,,,,,,,,,,,

---18,NH4_soil_conc_B,ug NH4-N per gm dry soil,Soil ammonium concentration measured in the 2 to 5 cm depth,,,,,,,,,,,,,,,,,,,,,,,,,

---19,NH4_soil_conc_C,ug NH4-N per gm dry soil,Soil ammonium concentration measured in the 5 to 10 cm depth,,,,,,,,,,,,,,,,,,,,,,,,,

---20,N03_soil_conc_A,ug NO3-N per gm dry soil,Soil nitrate concentration measured in the 0 to 2 cm depth,,,,,,,,,,,,,,,,,,,,,,,,,

---21,NO3_soil_conc_B,ug NO3-N per gm dry soil,Soil nitrate concentration measured in the 2 to 5 cm depth,,,,,,,,,,,,,,,,,,,,,,,,,

---22,NO3_soil_conc_C,ug NO3-N per gm dry soil,Soil nitrate concentration measured in the 5 to 10 cm depth,,,,,,,,,,,,,,,,,,,,,,,,,

---23,Soil_moisture_A,gm water/gm dry soil,Percent soil water measured in the 0-2 cm depth,,,,,,,,,,,,,,,,,,,,,,,,,

---24,Soil_moisture_B,gm water/gm dry soil,Percent soil water measured in the 2-5 cm depth,,,,,,,,,,,,,,,,,,,,,,,,,

---25,Soil_moisture_C,gm water/gm dry soil,Percent soil water measured in the 5-10 cm depth,,,,,,,,,,,,,,,,,,,,,,,,,

---26,Temp_air,degrees C,Ambient air temperature,,,,,,,,,,,,,,,,,,,,,,,,,

---27,Temp_soil_A,degrees C,Soil temperature at 2 cm depth,,,,,,,,,,,,,,,,,,,,,

---28,Temp_soil_B,degrees C,Soil temperature at 5 cm depth,,,,,,,,,,,,,,,,,,,,,,

---29,Temp_soil_C,degrees C,Soil temperature at 10 cm depth,,,,,,,,,,,,,,,,,,,,

,,,,,,,,,,,,,,,,,,,,,,,,,,,,

,Missing data is indicated with -9999,,,,,,,,,,,,,,,,,,,,,,,,,,,

,,,,,,,,,,,,,,,,,,,,,,,,,,,,



Sample data from TG08_Wetup_fluxes.csv



State,Location,Year,Month,Day,Time,Chronosequence,Landuse,Yr_formed,Time_seq,Time_treatment,Plot,Treatment,NO_flux,CO2_flux,N2O_flux,NH4_soil_conc_A,NH4_soil_conc_B,NH4_soil_conc_C,N03_soil_conc_A,NO3_soil_conc_B,NO3_soil_conc_C,Soil_moisture_A,Soil_moisture_B,Soil_moisture_C,Temp_air,Temp_soil_A,Temp_soil_B,Temp_soil_C

RONDONIA,NOVA VIDA,1998,8,19,12:17,PVA1,FOREST,0,-2,-20.32,101,CONTROL,48.36, 56.35,0.37,-9999,-9999,-9999,-9999,-9999,-9999,-9999,-9999,-9999,32.5,25,23,23.25

RONDONIA,NOVA VIDA,1998,8,20,7:09,PVA1,FOREST,0,-1,-1.38,101,CONTROL,36.49, 47.71,1.89,21.46,3.03,2.39,43.21,9.33,5.97,12.5,11.29,14.35,20,22.5,23,23

RONDONIA,NOVAVIDA,1998,8,20,9:32,PVA1,FOREST,0,1,0.42,101,IRRIGATE,122.23,90,-5.89,14.18,0.21,0.17,29.39,8.3,4.15,4.19,17.05,15.75,23.5,23.5,23,23

RONDONIA,NOVAVIDA,1998,8,20,10:38,PVA1,FOREST,0,2,1.6,101,IRRIGATE,28.77,77.33,1.88,63.55,1.61,2.07,46.08,11.75,7.67,7.03,15.12,16.67,25.5,24.5,23.5,23

RONDONIA,NOVAVIDA,1998,8,20,11:53,PVA1,FOREST,0,3,2.77,101,IRRIGATE,171.48,66.98,33.1,19.35,1.42,0,22.73,9.27,4.69,17.21,15.7,18.36,27.5,25,23.5,23.5

RONDONIA,NOVAVIDA,1998,8,20,13:53,PVA1,FOREST,0,4,4.7,101,IRRIGATE,104.93,-9999,5.77,-9999,-9999,-9999,-9999,-9999,-9999,-9999,-9999,-9999,28,25,23.5,23

RONDONIA,NOVAVIDA,1998,8,20,15:05,PVA1,FOREST,0,5,5.92,101,IRRIGATE,71.99,69.06,0.03,22.5,1.25,5.64,54.71,12.79,9.13,11.53,14.07,17.82,27.5,25,23.5,23.5

RONDONIA,NOVAVIDA,1998,8,20,16:04,PVA1,FOREST,0,6,6.92,101,IRRIGATE,40.37,71.54,7.13,-9999,-9999,-9999,-9999,-9999,-9999,-9999,-9999,-9999,26,24.5,23.5,23.5

RONDONIA,NOVAVIDA,1998,8,21,11:51,PVA1,FOREST,0,7,26.72,101,IRRIGATE,56.7,70.1,10.1,13.24,0,0,31.07,11.21,9.78,15.04,10.78,17.42,27.5,24,24,22.5

RONDONIA,NOVA VIDA,1998,8,19,12:44,PVA1,FOREST,0,-2,-20.32,102,CONTROL,19.92, 27.76,4.33,-9999,-9999,-9999,-9999,-9999,-9999,-9999,-9999,-9999,32.5,25,22.5,23.5

RONDONIA,NOVA VIDA,1998,8,20,7:35,PVA1,FOREST,0,-1,-1.38,102,CONTROL,6.9,33.15, 8.94,1.84,0.36,0.25,9.21,3.23,3.2,7.97,11.68,10,20.5,23,23,23

RONDONIA,NOVAVIDA,1998,8,20,9:51,PVA1,FOREST,0,1,0.42,102,IRRIGATE,39.5,117.09,-0.76,7.16,0.53,0.26,21.82,3.65,2.98,11.35,11.79,13.31,24,24,23.5,23

RONDONIA,NOVAVIDA,1998,8,20,11:07,PVA1,FOREST,0,2,1.6,102,IRRIGATE,52.81,85.29,-0.24,4.12,0,0,13.29,1.32,4.73,9.45,12.81,18.72,26.5,24.5,23.5,23

RONDONIA,NOVAVIDA,1998,8,20,12:13,PVA1,FOREST,0,3,2.77,102,IRRIGATE,57.84,76.88,9.02,15.12,2.73,0,34.03,6.25,3.84,14.59,11.02,15.59,27.5,25,23.5,23.5

RONDONIA,NOVAVIDA,1998,8,20,14:23,PVA1,FOREST,0,4,4.7,102,IRRIGATE,44.2,-9999,10.31,-9999,-9999,-9999,-9999,-9999,-9999,-9999,-9999,-9999,27,25,23.5,23.5

RONDONIA,NOVAVIDA,1998,8,20,15:23,PVA1,FOREST,0,5,5.92,102,IRRIGATE,43.68,92.34,18.34,12.48,2.98,0,23.88,5.49,5.05,11.41,16.58,15.8,27,25,24,24

RONDONIA,NOVAVIDA,1998,8,20,16:23,PVA1,FOREST,0,6,6.92,102,IRRIGATE,51.62,97.73,4.84,-9999,-9999,-9999,-9999,-9999,-9999,-9999,-9999,-9999,25.5,24.5,23.5,23.5

RONDONIA,NOVAVIDA,1998,8,21,12:12,PVA1,FOREST,0,7,26.72,102,IRRIGATE,22.33,66.97,0.28,3.6,0,12.75,26.01,5,13.37,10.47,9.11,13.54,28,24,24.5,22.5

RONDONIA,NOVA VIDA,1998,8,19,13:08,PVA1,FOREST,0,-2,-20.32,103,CONTROL,57.01, 48.37,6.02,-9999,-9999,-9999,-9999,-9999,-9999,-9999,-9999,-9999,32,25,23,23.5

RONDONIA,NOVA VIDA,1998,8,20,8:06,PVA1,FOREST,0,-1,-1.38,103,CONTROL,30.61, 58.63,-0.68,32.81,1.29,0.16,47.77,14.29,7.66,12.41,10.1,12.2,21.5,23.5,23,23

RONDONIA,NOVA VIDA,1998,8,20,13:26,PVA1,FOREST,0,1,3.75,103,CONTROL,38.01, 67.08,-8.03,35.97,0.48,0.15,163.27,6.23,4.99,8.98,8.89,11.89,29,27,24,23.5

RONDONIA,NOVA VIDA,1998,8,21,12:51,PVA1,FOREST,0,2,27.62,103,CONTROL,18.34, 12.75,9.58,0,0,10.15,14.99,5.65,15.28,9.18,8.63,11.52,28.5,24,24,24

RONDONIA,NOVA VIDA,1998,8,19,13:59,PVA1,FOREST,0,-2,20.32,104,CONTROL,45.56, 58.88,1.39,-9999,-9999,-9999,-9999,-9999,-9999,-9999,-9999,-9999,32.5,25.5,23,23.5

Data Application and Derivation:

Trace gas fluxes from tropical forests are important components of the global carbon and nitrogen budgets. The relative importance of the rain-stimulated emissions in the seasonal and annual budgets of these gases us poorly understood. These data improve our understanding of the effects of land-use change on the seasonal dynamics of soil-atmosphere gas exchange of NO, N2O and CO2.

Quality Assessment (Data Quality Attribute Accuracy Report):

Quality Assessment:

NO: A 1.032 ppmv NO standard in O2 free N2 (Scott-Marrin, Riverside, CA) was diluted with NO/NO2 free air to produce a 49.2 ppbv NO standard. Ambient air was passed sequentially through scrubbers containing drierite and ascarite to produce NO/NO2 free air (<0.06ppbv NO). The analyzer was calibrated before and after each daily field sampling and varied by less than +10% between calibrations.



CO2: A certified standard of 826 ppmv CO2 in air from Scott Specialty Gases was used to calibrate the IRGA. The analyzer was calibrated before and after each daily field sampling and varied by less than 1% between calibrations.



N20: A Scott-certified standard of 0.985 ppmv N2O in N2 was used for calibration. Prior calibrations with multiple standards showed that the detector response was linear from 0.310 ppmv (ambient) to at least 1.00 ppmv. Nitrous oxide fluxes were calculated using the linear change in N2O concentration against incubation time.

Process Description:

Data Acquisition Materials and Methods:

Field site description:

This study was conducted at Fazenda Nova Vida, located at km 472 of highway BR-364 in central Rondonia. Climate of the area is characteristic of humid tropical forest, with an annual precipitation of 2270 mm distributed seasonally with a dry season extending from June through September. Mean annual maximum and minimum temperatures are 25.6 and 18.8 degrees C, respectively, with a seasonal variation of approximately 4 degrees C (Bastos and Diniz 1982).

We used a forest and two pastures, one created in 1987 and the other in 1972. At

the time of this study the pasture created in 1987 was 11 years old and the pasture created in 1972 was 26 years old. In these pastures rates of net N mineralization and net nitrification have decreased compared with the forest (Neill et al. 1995). These sites were part of previous studies of the effect of the conversion of forest to pasture on C, N, and P stocks and dynamics (Neill et al. (1995, 1997); Garcia-Montiel et al. 2000) and trace gas fluxes (Feigl et al. 1995; Steudler et al. 1996;Garcia-Montiel et al. 2001; Melillo et al. 2001; Steudler et al. 2002).



Forest vegetation consisted of open moist tropical forest with a large number of palm trees. This forest was altered by selective logging, which removed 1 to 3 trees/ha between 1987 and 1989. The pastures were formed by slash and burning of the original forest with no intermediate cropping phase, soil tilling, chemical fertilization or liming. Both pastures were planted with Brachiaria brizantha (Hochst) Stapf. All sites used in this study were in areas at an elevation of approximately 150 m with minimal relief. Soils contained between 20 to 30% clay and were classified as redyellow podzolic latosol in the Brazilian classification and as Kandiudult in the U.S. classification (Moraes et al. 1995).



Experimental design:

We established five 1 by 2 m plots in the forest and in the two pastures. One half of each plot was used for gas flux measurements; the other half was used for soil sampling for soil water content and inorganic N pools. We randomly selected three of the five established plots for irrigation. The other two non-irrigated plots were used as controls. On August 18,1998, we simulated a 30 mm of rain in the 11-year-old pasture by sprinkling 60 L of stream water in each plot. Using stream water to irrigate the plots did not cause N fertilization of soils because concentrations of NH4+ and NO3- (0.74 and 2.09 microM/L) were very small relative to the concentrations in the soil solution. The simulation of rain in the forest was conducted on August 20th and in the 26-year old pasture on August 22nd of 1998. The amount of the simulated rain approximated the first rain that generally occurs near the end of the dry season. At each site we measured soil gas fluxes between 1500 and 1700 hours the day before the start of the irrigation, and again at about 0600 hours the day of the treatment (immediately before irrigation). Addition of water to the plot usually took 7 to 8 minutes. We waited about 20 minutes to allow water to percolate into the soil, and then made a series of measurements at 1 to 1.5 hour intervals for the next 12 hours to follow the time course of the emissions. Fluxes were measured once more the next day, approximately 30 to 34 hours after irrigation. Control plots were measured four times over the whole experiment: 1) the day before irrigation, 2) the morning immediately before irrigation, 3) at approximately mid-day on the day of irrigation and 4) the next day at the end of the experiment.



Field sampling:

NO, N2O and CO2 were measured using a re-circulating chamber design. We used a modified two-piece chamber design [Bowden et al., 1990] where the lower portion of the PVC chamber (anchor) was inserted 2 cm into the soils at least 2 days before the experiment and left in place for the duration of the experiment. During each flux measurement, the chamber top was placed on the anchor giving 7.0-8.5 L headspace, and the changes in headspace-gas concentrations were measured over a 20 minute incubation time. The chamber top was also equipped with a luer lock sampling port for collecting headspace-gas samples for N2O analysis.



Soil samples were collected from 0-2, 2-5, and 5-10 cm soil depths in each of the 1x1m subplots assigned for soil coring using a 2.5 cm diameter soil corer. Soil collection was synchronized with gas flux measurements. No soil was collected the day before irrigation, but it was collected early in the morning before irrigation started. Roots and stones were removed by hand the day of collection and soil was mixed by hand.



Shaded ambient air temperature about 1 m above the ground was measured during each incubation.Soil temperature at 2, 5, and 10 cm depth were measured during each incubation.Because of large temperature variation in pastures, readings were conducted before and after the incubation and then average values were used for flux calculations.



Gas measurements:

NO:

We used a Unisearch Associates LMA-4 NO2 analyzer to measure NO concentrations. Our design used the LICOR pumping system to circulate air at 1 L/min through 1/4 Teflon lines connected to the chamber top. The internal NO analyzer pump subsampled this airflow at about 400ml/min and returned the air to circulating sample stream. A Campbell data logger was used to record the outputs from the NO Analyzers at 5-second intervals. Incubations were initiated by collecting ambient air concentration data for at least 1 minute prior to placing the chamber top on the anchor to ensure initial conditions were stable and representative. The Unisearch NO2 analyzer determines NO concentrations using a Luminol chemiluminescent technique with a CrO3 converter to oxidize NO to NO2. We modified the analyzer to increase the efficiency of water removal from the analyzer sample air stream by increasing the pressure differential across the stock Nafion dryer and by connecting an inline silica gel drying tube to the outer shell of the drier. This modification resulted in stable converter efficiencies for at least 50 hrs of use under 25-30 degrees C temperature and approximately 90% relative humidity conditions. We also added a 1/4 Teflon line to return the exhaust from the analyzer air pump back to the circulating sample air stream. Fluxes were calculated from the rate of increase or decrease of NO concentrations using the steepest linear portion of the curve, usually within 1 or 2 minutes after placing the chamber top on the anchor. This procedure allowed deposition of ambient NO2 and O3 to the soil surface [Davidson et al., 1991]. A 1.032 ppmv NO standard in O2 free N2 (Scott-Marrin, Riverside, CA) was diluted with NO/NO2 free air to produce a 49.2 ppbv NO standard. Ambient air was passed sequentially through scrubbers containing drierite and ascarite to produce NO/NO2 free air (less than 0.06ppbv NO). The analyzer was calibrated before and after each daily field sampling and varied by less than +10% between calibrations.



CO2:

We used LICOR model 6252 infrared gas analyzer (IRGA) to measure CO2 concentrations. Our design used the LICOR pumping system to circulate air at 1 L/min through 1/4 Teflon lines connected to the chamber top. A Campbell data logger was used to record the outputs from the CO2 analyzer at 5-second intervals. Incubations were initiated by collecting ambient air concentration data for at least 1 minute prior to placing the chamber top on the anchor to ensure initial conditions were stable and representative. A certified standard of 826 ppmv CO2 in air from Scott Specialty Gases was used to calibrate the IRGA. CO2 emissions were calculated using the steepest portion of the concentration data against incubation time from the first 2 to 4 minutes after the chamber was closed. The analyzer was calibrated before and after each daily field sampling and varied by less than +1% between calibrations.



N2O:

Headspace-gas samples were collected using 10-mL Becton Dickinson syringes equipped with stopcocks for determination of [N2O] at the beginning and at 2 or 3 times during the 15-min chamber incubation. Nitrous oxide concentrations were determined using electron capture gas chromatography with a detector temperature of 310 degrees C. Gas samples were analyzed on site within 12 hours of collection. A Scott-certified standard of 0.985 ppmv N2O in N2 was used for calibration. Prior calibrations with multiple standards showed that the detector response was linear from 0.310 ppmv (ambient) to at least 1.00 ppmv. Nitrous oxide fluxes were calculated using the linear change in N2O concentration against incubation time.



Soil N pools:

Extraction of NH4 and NO3 was done with 2 mol/L KCl . After 24 hr, extracts were centrifuged and 20 mL were preserved with phenyl mercuric acetate for later analyses using an automated flow injection system.



Ammonium-nitrogen was measured colorimetrically after Nessler reaction (Piccolo et al. 1994). Nitrate-nitrogen was measured as NO2- following reduction with a Cd catalyst. (Piccolo et al. 1994) Final soil N pools were corrected for moisture content.



Gravimetric moisture content was obtained by drying a soil subsample to constant weight at 105 degrees C.

References:

Bastos T.X. and Diniz T.D.de A.S. 1982. Avaliacao de clima do Estado de Rondonia para desenvolvimento agricola. EMBRAPA-CPATU, Belem, Brazil, Boletim de Pesquisa 44.



Bowden, R.D., P.A. Steudler, J.M. Melillo, and J.D. Aber. 1990. Annual nitrous oxide fluxes from temperate forest soils in the northeastern United States. J. Geophys. Res. 95: 13,997-14,005.



Davidson, E. A. 1991. Fluxes of nitrous oxide and nitric oxide from terrestrial ecosystems, in Microbial Production and Consumption of Greenhouse Gases: Methane, Nitrogen Oxides, and Halomethanes, edited by J.E. Rogers and W.B. Whitman, pp. 219-235. Am. Soc. for Microbiol., Washington D.C.



Feigl B.J., Steudler P.A. and Cerri C.C. 1995. Effects of pasture introduction on soil CO2 emissions during the dry season in the State of Rondonia, Brazil. Biogeochemistry 31: 1�14.



Garcia-Montiel D.C., Neill C., Melillo J., Thomas S., Steudler P.A. and Cerri C.C. 2000. Soil phosphorus transformations following forest clearing for pasture in the Brazilian Amazon. Soil. Sci. Soc. Am. J. 64: 1792�1804.



Garcia-Montiel D.C., Steudler P.A., Piccolo M.C., Melillo J., Neill C. and Cerri C.C. 2001. Controls on soil nitrogen oxide emissions from forest and pastures in the Amazon. Global Biochem. Cycles 15:1021�1030.



Melillo J., Steudler P.A., Feigl B.J., Neill C., Garcia-Montiel D.C., Piccolo M.C. et al. 2001. Nitrous oxide emissions from forest and pastures of various ages in the Brazilian Amazon. J. Geophys. Res. 24: 34,179�34,188.



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