The measurement of nitrous oxide emissions from soil by using chambers

Abstract

Small flux chambers are widely used to measure emissions of nitrous oxide, N 2 O , from soil, the gas being determined by gas chromatography with an electron capture detector. The technique is relatively cheap, and is adaptable to a wide range of site conditions and emission rates: from the order of 1 µg m -2 h -1 to more than 10 mg m -2 h -1 . Increasingly, systems are being automated, to get more information on short-term temporal variability and to collect data over long periods to improve estimates of total annual emissions. Such systems are being used in the field and with soil monoliths installed in a greenhouse. Large chambers 50-60 m 2 in area, with gas analysis by long-path infrared spectrometry, offer a way of overcoming small-scale spatial variability, and are useful in conditions where micrometeorological methods may not be applicable, or when long runs of data are needed from the same site. In studies with small closed chambers, we have measured N 2 0 emissions from grassland ranging from negligible values to about 4 mg N 2 O -N m -2 h -1 (nearly 1 kg N 2 O-N ha -1 d -1 ), with total losses in the range 0.14-5.1% of the nitrogen applied as fertilizer, depending on factors such as soil structure, water potential and temperature, and the chemical form of the fertilizer. Reasonable agreement can be obtained between chamber and micrometeorological flux measurements on homogeneous sites.

N 2 O emissions due to nitrogen fertilizer applications in two regions of sugarcane cultivation in Brazil

“…In Australia Denmead et al (2010) observed emission factors of 2.8% in a sandy loam soil and of 21% in a clay loam soil (acid sulfate soil) both cultivated with sugarcane. It is necessary to consider that the behavior of different fertilizers also depends on soil type and crop (Clayton et al 1997), soil structure, soil water content and temperature (Smith et al 1995), and these variable factors are not considered in the emission factor proposed by IPCC.…”

CO<sub>2</sub>, CH<sub>4</sub> and N<sub>2</sub>O fluxes from soil of a burned grassland in Central Africa

“…In order to measure N 2 O and CH 4 fluxes, we used closed static chambers (Hutchinson and Mosier, 1981;Smith et al, 1995). These were made of PVC collars (7 cm high with a diameter of 15 cm), inserted in the soil to about 5 cm depth in a slot previously dug by a metal cutting ring, and chamber lids (20 cm high with a diameter of 15 cm) provided with a 2-way stopcock sampling port.…”

Nitrous oxide emissions from soil of an African rain forest in Ghana

“…Gas fluxes were measured using closed static chambers (Hutchinson and Mosier, 1981;Smith et al, 1995) made of PVC collars (7 cm high with a diameter of 15 cm), inserted in the soil to about 5 cm depth, and chamber lids (20 cm high with a diameter of 15 cm). To determine gas fluxes, gas (30 ml) was sampled, using gas-tight syringes, from the chamber headspace at 0, 30 and 60 min after closure; it was immediately stored in pre-evacuated gas-tight vials (20 ml), slightly overpressurized, which were sealed with thermal glue and shipped for gas chromatographic analysis (TRACE GC ULTRA, THERMO SCIENTIFIC).…”