Automated Soil Monolith‐Flux Chamber System for the Study of Trace Gas Fluxes

Abstract

Soils are the major source of atmospheric N2O, and better estimates of fluxes are needed to improve the input to climatic general circulation models. We developed a system in a semicontrolled environment to investigate relationships between fluxes of N2O and controlling variables. It consists of 12 soil monoliths (1‐m diam., ≈ 0.6 m deep) in glass fiber casings, the tops of which have been converted into gas flux chambers. These chambers are connected to a gas chromatograph for measurement of N2O and CO2. Gas sampling and analysis is computer controlled and can be done continuously. Temperatures and soil water potential are also recorded continuously. The system has performed reliably since continuous operation began in September 1993. We conducted three experiments, examining the effects of soil water potential, organic matter input, and diurnal temperature variation on N2O fluxes, to illustrate the capabilities of the system. In these experiments, the major emissions of N2O (>800 εg N2O‐N m−2 h−1) occurred when the water potential was above −5 kPa. When plant material was incorporated into the soil, a highly significant correlation was found between N2O and CO2 emissions; the N2O emissions showed pronounced diurnal cycles, with the maxima occurring at night, 4 h after the temperature maxima at 0.1‐m depth. Data interpretation was greatly aided by the frequency and continuity of measurement.

Diurnal fluxes of CO₂ and N₂O from cattle-impacted soil and implications for emission estimates

“…Diurnal cycles of N 2 O emissions were also found in soil monoliths transferred to a greenhouse, with maxima occurring at night (Thomson et al 1997), and were associated with diurnal cycles in soil temperature (Smith et al 1998). Other studies, however, did not document diurnal changes in N 2 O fluxes (e.g., Smith and Dobbie 2001).…”

Collecting large soil monoliths

“…Large soil monoliths (> 50 kg) have been collected (Table 3) to study water movement (Messing and Jarvis 1995), solute transport (Buchter et al 1995;Woodbury et al 1996), earthworm behaviour (Munyankusi et al 1994), gas flux (Thomson et al 1997), and for other purposes (Bhogal and Shepherd 1997;Meskat et al 1999;Shepherd and Withers 2001). Problems arise when the structure of these monoliths has to be kept intact.…”

“…The extraction and transportation methods are therefore critical. However, the technique used for the extraction and preparation of large monoliths is rarely described in the literature except for a few studies (Thomson et al 1997;Meshkat et al 1999). The collection method depends upon the goals and constraints (Tables 1, 2, and 3), the available equipment, the cost and the soil texture.…”

“…Klocke et al (1993) Steel pipe 9.5 Steel reservoir Epoxy resin Meshkat et al (1999) Galvanized steel Not specified Not specified Epoxy paint Messing and Jarvis (1995) PVC pipe 10 PVC Not described Morris and Mooney (2004) Plywood Not specified Not specified Polyurethane foam to fill gaps Munyankusi et al (1994) PVC pipe Not specified PVC cap No stick cooking spray (PAM) Obrist et al (2004) Concrete Not specified Non-specified metal None Schneider et al (1988) Steel plate reinforced with 9.5 Steel plate Rustoleum® expoxy I beam primer and paint Schneider et al (1993) Steel plate not reinforced 9.5 Steel plate Commercial grade enamel Shepherd and Withers (2001) Glass-fibre-reinforced Not specified Glass fibre reinforced Epoxy resin polyester polyester Shan et al (2005) PVC pipe 7 PVC plate Parrafin Starr et al (1995) Steel Not specified Not specified Not specified Thomson et al (1997) Glass-fibre-reinforced 7.7 Steel cutting plate Epoxy resin polyester Woodbury et al (1996) PVC For personal use only.…”

“…Unlike Thomson et al (1997), the cutting system may be very simple and quite precise, even with a column attached to an extension. A long wire, a steel plate, or a long saw blade can be slid between the column and its extension.…”