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Title: TILLAGE-INDUCED GAS FLUXES: COMPARISON OF METEOROLOGICAL AND LARGE CHAMBER TECHNIQUES

Author
item DENMEAD, O - CSIRO, AUSTRALIA
item Reicosky, Donald

Submitted to: International Soil Tillage Research Organization Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 7/18/2003
Publication Date: 7/18/2003
Citation: DENMEAD, O.T., REICOSKY, D.C. TILLAGE-INDUCED GAS FLUXES: COMPARISON OF METEOROLOGICAL AND LARGE CHAMBER TECHNIQUES. PROCEEDINGS OF INTERNATIONAL SOIL TILLAGE RESEARCH ORGANIZATION PROCEEDINGS. 2003. P. 38.

Interpretive Summary:

Technical Abstract: CO2 fluxes from soils following tillage are usually large and decline rapidly with time. Establishing the time-course of the CO2 flux in the early stages of the emission is important, but conventional micrometeorological techniques require large treated areas that take time to create. Hence chambers are often used to measure the flux. "Chamber effects" may occur due to soil variability, chamber size and placement, and the level of turbulence in the chamber. We compared chamber measurements of soil CO2 flux after tillage with those calculated simultaneously by novel, non-disturbing, micrometeorological techniques suitable for small treated areas. The experimental area was a wheat field with some crop residue; 12 or 16 furrows were plowed cross-wind in a strip 50m long and 5.6 or 7.3m wide. The chamber was a large (3.25 m**3), tractor-mounted, dynamic, closed chamber employing rapid mixing for fast response. Increases in both CO2 and water vapor concentrations were measured with a Licor 6262 infrared gas analyzer. Flux measurements required only one min. Three meteorological techniques were employed: one using a line-source solution, one using a solution for a semi-infinite strip, and one using a backward Lagrangian stochastic (bLs) model. Inputs were measurements of wind speed and gas concentrations on upwind and downwind edges of the treated area at 0.2m above the surface. Chamber and micrometeorological measurements were made for 1h before and 2h after plowing. There was good quantitative agreement between all three micrometeorological methods for both CO2 and water vapor fluxes, but the agreement between them and the chamber was variable, depending on the wind speed. All methods agreed at a wind speed (at 0.25m) of 2.27 m s**-1, but the chambers gave higher fluxes when the wind speed was less than that value and higher fluxes above it. Interestingly, the "wind" speed within the chamber is a constant 2.2 m s**-1. The clear inference is that wind speed has a large effect on gas fluxes from the tilled soil, particularly in the early stages of the emission. It is suggested that the micrometeorological techniques employed in this study provide attractive alternatives to chambers or could be used to calibrate "chamber effects."