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 = (W_sl x 1.69 x 0.2729)(A_c x T)

Where, S is CO₂ evolution (mg C m^-2 h^-1), W_sl is the soda lime weight gain, 1.69 is the C absorption rate of soda-lime, 0.2729 is C/CO2, A_c 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.