Measuring CO2 Evolution at Bousson Environmental Research Reserve
Figure 1 - Students gathering samples at Bousson Environmental Research Reserve.

To view close-up of graph, click on it.

There were three control and three fertilized plots 15 x 15 m. The fertilized plots received 100 kg N ha-1 yr-1 in the form of ammonium nitrate (NH4NO3). Amendments were made using a backpack sprayer covering the sample plot twice to ensure equal distribution. Four stratified sampling locations were selected in each fertilized and control plot for measuring CO2 efflux.

Carbon dioxide efflux measurements were taken using a soda-lime technique similar to Edwards (1982). Measurement chambers were 20 cm tall by 27.5 cm in diameter plastic buckets. Prior to measuring, plastic rings of the same diameter as the measurement chambers were placed over the soil. Surface litter found on the edge of the ring was moved and the ring was pushed ~1 cm into the soil. Carbon dioxide was absorbed by soil tins containing 60 g of 1.68- to 3.36-mm (6-12 mesh) indicator-grade soda-lime. Before use in the field, the tins of soda-lime were oven dried at 105°C for 24 hrs, weighed to the 0.0001 g, and covered with a lid. Field measurements were taken by removing the plastic ring from the soil and placing the uncovered tin in the center of the sample site. The measurement chamber was placed over the tins in the depression created by the ring. A weight was gently placed on the chamber to hold it in place. The soda lime was collected ~24 hours later, to include the diurnal cycle of respiration, oven dried at 105°C and reweighed.

During measurements six blanks were made. This was performed in an identical fashion as the CO2 measurements, with the exception of removing them from the chamber after 10-15 s. Blanks accounted for CO2 absorption during placement and retrieval of the tins, and during drying. Soil respiration was calculated as:

S = (Wsl x 1.69 x 0.2729)(Ac x T)

Where, S is CO2 evolution (mg C m-2 h-1), Wsl is the soda lime weight gain, 1.69 is the C absorption rate of soda-lime, 0.2729 is C/CO2, Ac is the chamber area (cm2), T is the sampling time in hours (Grogan, 1998).

Seventeen measurements of CO2 efflux were taken during 2002, from May until November when snow prohibited sampling. Sampling was done weekly during summer months May to July (at the height of CO2 evolution) and then bi-monthly afterwards. Changes in respiration at the fertilized plots were tested for significance using one-way Repeated Measures ANOVA of treatment means. Temperature and moisture measurements were taken at 2.5 cm below the soil surface, from May to September to correlate climatic variability with CO2 evolution. Moisture content was measured using time domain reflectometry (TDR) in % water filled pore space.

Soil respiration measurements at the control and fertilized plots at BERR from May to November using the Soda-Lime method
DateTreatment CO2 Flux from bucket
(mg C m-2 h-1)
  ABCD Celsius% water filled 
pore space
30-May-02Control 1839096115961725
 Control 215116783871221735
 Control 3n.d.435657521631
 Fertilized 1911401181411231731
 Fertilized 2921018676891726
 Fertilized 359n.d.7077691731
6-Jun-02Control 1861481582001481523
 Control 22352411901702091431
 Control 3196147127n.d.1561529
 Fertilized 11632161831871871528
 Fertilized 22111972021831981527
 Fertilized 31661671641651661526
13-Jun-02Control 11971982202042051721
 Control 22473212232562621729
 Control 32411682261621991727
 Fertilized 11881991782181961724
 Fertilized 21981821741651801722
 Fertilized 31681941581721731725
19-Jun-02Control 11831662081921871619
 Control 2227n.d.2231902131630
 Control 32061661542101841727
 Fertilized 11701971951921891621
 Fertilized 21911691421611661619
 Fertilized 31872051891731881724
27-Jun-02Control 12572102142192251918
 Control 22494182342182791928
 Control 3218169153n.d.1801822
 Fertilized 12332152152062171920
 Fertilized 22211981852012011916
 Fertilized 31792222031641921824
3-Jul-02Control 12032002002192062112
 Control 2224n.d.2172552322122
 Control 3206160153n.d.1732020
 Fertilized 11821861622061842112
 Fertilized 22171831851921942112
 Fertilized 32271881901511892119
10-Jul-02Control 11831812192352051714
 Control 2253n.d.2191982231718
 Control 32111881762111961718
 Fertilized 12252221842032091713
 Fertilized 22312131972012101815
 Fertilized 31961932121701931818
16-Jul-02Control 1193168181202186208
 Control 21651961641721742011
 Control 3187185179n.d.1841913
 Fertilized 1204343177214234209
 Fertilized 2187184n.d.161177208
 Fertilized 31801811701331661911
22-Jul-02Control 1211190190214201219
 Control 21803732022372482110
 Control 31791711671921772111
 Fertilized 11801891792121904613
 Fertilized 2215183182182191218
 Fertilized 31851921981671852110
29-Jul-02Control 11862052252472152317
 Control 22474072072002652322
 Control 31901451261591552126
 Fertilized 11982331932322142322
 Fertilized 2208n.d.2012012042318
 Fertilized 31681962011531792122
29-Aug-02Control 1209120162175166n.d.n.d.
 Control 2184n.d.159189177n.d.n.d.
 Control 3159139169n.d.156n.d.n.d.
 Fertilized 1149147148148148n.d.n.d.
 Fertilized 2186150137146155n.d.n.d.
 Fertilized 3131170151158153n.d.n.d.
14-Sep-02Control 1140116n.d.1491351810
 Control 2189n.d.1051511481814
 Control 3n.d.96120971041817
 Fertilized 1118n.d.1151251191811
 Fertilized 2105142110n.d.119199
 Fertilized 3104140115n.d.1201815
21-Sep-02Control 1225175223283226n.d.n.d.
 Control 2283n.d.223n.d.253n.d.n.d.
 Control 3212166203n.d.194n.d.n.d.
 Fertilized 1214204213n.d.210n.d.n.d.
 Fertilized 2196275219267239n.d.n.d.
 Fertilized 3265268254206248n.d.n.d.
5-Oct-02Control 1196n.d.194187193n.d.n.d.
 Control 2n.d.n.d.112131122n.d.n.d.
 Control 3148110130111125n.d.n.d.
 Fertilized 1135n.d.137227166n.d.n.d.
 Fertilized 2118n.d.109154127n.d.n.d.
 Fertilized 3n.d.95n.d.131113n.d.n.d.
19-Oct-02Control 1199160n.d.200186n.d.n.d.
 Control 2n.d.233178n.d.206n.d.n.d.
 Control 3168154n.d.n.d.161n.d.n.d.
 Fertilized 1202183n.d.187191n.d.n.d.
 Fertilized 2164195174159173n.d.n.d.
 Fertilized 3150188202168177n.d.n.d.
9-Nov-02Control 1146129147166147n.d.n.d.
 Control 2147181n.d.108145n.d.n.d.
 Control 3155126164160151n.d.n.d.
 Fertilized 1155n.d.n.d.121138n.d.n.d.
 Fertilized 2128n.d.127125127n.d.n.d.
 Fertilized 3127151152149145n.d.n.d.
24-Nov-02Control 176n.d.726571n.d.n.d.
 Control 25288645063n.d.n.d.
 Control 36660566060n.d.n.d.
 Fertilized 16763226354n.d.n.d.
 Fertilized 25555605256n.d.n.d.
 Fertilized 35967515458n.d.n.d.
 n.d. = no data