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Soil and Environmental Analysis: Physical Methods - Chapter 13

Phong trào khí và hòa không khí tràn đầy độ xốp Sự chuyển động của khí thông qua các lỗ chân lông không gian của đất rất quan trọng trong một số khía cạnh. Nó đóng một vai trò quan trọng trong các quá trình đất sinh học, trong đó việc cung cấp oxy, O2, rễ hô hấp và vi sinh vật từ bầu không khí ở trên đất được cân bằng bởi dòng chảy ra nước ngoài của khí carbon dioxide, CO2. Trở kháng của trao đổi khí này thường xuyên gây tổn hại cho sự phát triển của. | 13 Gas Movement and Air-Filled Porosity Bruce C. Ball Scottish Agricultural College Edinburgh Scotland Keith A. Smith University of Edinburgh Edinburgh Scotland I. INTRODUCTION The movement of gases through the pore space of the soil is important in several respects. It plays a vital role in soil biological processes in which the supply of oxygen O2 to respiring roots and microorganisms from the atmosphere above the soil is balanced by the outward flow of carbon dioxide CO2. Impedance of this gas exchange is frequently damaging to plant growth due to deficiency in O2 supply to the roots. Such conditions also give rise to emissions to the atmosphere of the microbially produced gases methane CH4 and nitrous oxide N2O which like CO2 contribute to the greenhouse effect Houghton et al. 1996 conversely part of the methane in the atmosphere is removed by diffusion into well aerated soils where it is oxidized by microorganisms. Soil fumigation to control diseases of horticultural crops depends on movement of the fumigant in the vapor phase emissions of methyl bromide the most widely used fumigant contribute to stratospheric ozone depletion as does N2O . In a very different context emissions of the radioactive gas radon into buildings following the decay of radium present in underlying soils may be sufficient to constitute a health hazard in some localities. The mechanisms responsible for the transport of all these gases are diffusion resulting in a net movement of gas from a zone of higher concentration to one of lower concentration and mass flow where the whole gas mixture moves in response to a pressure gradient. Most gas movement is by diffusion mass flow is important only when pressure differences develop because of changes in barometric pressure temperature or soil water content. The movement occurs Copyright 2000 Marcel Dekker Inc. overwhelmingly in the air-filled pores because diffusion in the gas phase is about four orders of magnitude greater than through water. .