文档介绍：第八章土壤空气 soil air
土壤空气组成有以下分方面的特点:
>>近地层大气中CO2 (Carbon dioxide)
原因:(1)土壤有机物质的分解释放CO2
(2) 土壤中根系、微生物、土壤动物的呼吸释放CO2
(3)无机碳酸盐的分解CO2
研究土壤中co2释放与固定问题成为当今土壤科学发展的前沿领域!。
(soil position)
<<近地层大气中O2( oxygen)
原因:微生物和根系等土壤中生物呼吸消耗。
。土壤空气几乎为水气饱和的。
因为土壤湿度均在“最大吸湿量“之上。
(恨量气体)。特别是土壤通气不良时,含有CH4、H2S、H2、N2O、C2H6、PH3、CS2等还原性气体和温室效应气体。大气中这些还原性气体少。
Soil Air the part of ground air that is in the soil and is similar to the air of the atmosphere but depleted in oxygen content and enriched in carbon dioxide. Alternatively, the gaseous phase of soil is called soil air. In pletely dry soil most of the pores are filled with air. As the soil water content increases the amount of air in the soil decreases. position of air in an well-aerated soil is close to position of atmospheric air, as the oxygen consumed in the soil by plants and anisms is readily replaced from the atmosphere. However, in a poorly aerated soil, position of air differs from the atmospheric air.
Two important gases in soil air are carbon dioxide and oxygen. Carbon dioxide is produced as a by-product of plant root respiration and biological activity. Oxygen is consumed in the soil by the same processes, and plant roots require oxygen to function normally. For most plant species, transaction of oxygen from the leaves to the roots is not adequate to supply oxygen at the required rate. Hence, plant roots must supplement oxygen supply from soil air. As a result oxygen is depleted from soil air. Oxygen content in soil air is replenished by oxygen from the atmosphere above the soil surface. This transport occurs primarily by gaseous diffusion. In a surface layer of a well-aerated soil, the oxygen content is between 18 and 21 percent, while at a greater soil depth and specially in soils that are wet for a long period it may be very much lower. The carbon dioxide content of soil air is usually between and 5 per cent and can reach near