Author
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Reicosky, Donald |
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DENMEAD, O - CSIRO |
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Submitted to: International Soil Tillage Research Organization Proceedings
Publication Type: Proceedings Publication Acceptance Date: 7/18/2003 Publication Date: 7/18/2003 Citation: Reicosky, D.C., Denmead, O.T. 2003. Tillage-induced soil properties and chamber effects on gas exchange. In: Proceedings of the International Soil Tillage Research Organization, July 14-18, 2003, Brisbane, Australia. p. 971-976. Interpretive Summary: The increase in carbon dioxide (CO2) in the atmosphere related to concerns about potential global warming and prospects of using soil as a sink for carbon (C) has attracted interest. The cumulative effect of tillage and many cropping rotations has been a 30-50% decrease in soil C that causes undesirable changes in soil physical, chemical and biological properties. Recent studies involving portable chambers for measuring gas loss after tillage methods indicate major gaseous loss of C immediately after intensive tillage. This work evaluated effects of tillage-induced changes in soil properties on CO2 and H2O loss as measured by a portable dynamic chamber. Information was collected on CO2 loss from the soil by measuring the concentration up and downwind with and without the chamber to characterize the plume of CO2 from a plowed strip perpendicular to the prevailing wind. The results suggest plowing created higher soil air permeability more sensitive to pressure fluctuations resulting in higher gas exchange. The tillage-induced change in soil properties led to short-term CO2 losses that were higher than the undisturbed soil. These results are significant to farmers and policy makers in that intensive tillage results in substantial short-term gaseous losses of CO2. This information will assist scientists and engineers in developing improved tillage methods to minimize the gaseous loss and to improve soil C management. Farmers can develop and utilize new management techniques for enhancing soil C by increasing the quantity and quality of crop residues and by changing the type and intensity of tillage. This information will be of direct benefit to the farmers to enable them to maintain crop production with minimal impact on air quality and the environment. Technical Abstract: Agricultural ecosystems can play a significant role in the production and consumption of greenhouse gases, specifically carbon dioxide (CO2) from tillage. This work evaluated effects of tillage-induced changes in soil properties on CO2 and H2O loss as measured by a portable dynamic chamber. Information was collected on CO2 loss from the soil by measuring the concentration up and downwind without the chamber to characterize the plume of CO2 from a 5.5 m-wide plowed strip perpendicular to the prevailing wind. Downwind and upwind CO2 concentration differences were large immediately after tillage and decreased with time verifying the tillage-induced loss without the chamber. Short-term tillage-induced CO2 losses were measured with a large chamber using different air mixing rates and independently verified turbulent mixing pressure effects on CO2 losses. Fan number affected the CO2 and H2O flux from a freshly tilled surface. With only one fan operating (press. = -0.39 Pa), the fluxes were lower than with four fans (press. = -1.62 Pa) suggesting more negative dynamic pressure enhanced the flux. The results suggest plowing created higher soil air permeability more sensitive to pressure fluctuations resulting in higher gas exchange. The tillage-induced change in soil properties led to short-term CO2 losses that were higher than the undisturbed soil. The large differences in CO2 loss between moldboard plow and not-tilled treatments reflect the need for improved soil management and policies that favor less intensive conservation tillage to enable carbon sequestration in agricultural production systems. |
