《土壤学》第八章 土壤空气 soil air

第八章土壤空气 soil air Integration at the local and regional scale Far m and watershed Greenhouse gases, Precision far min g Remote sensing, Soil survey, etc. Air Field and experi mental plots Far ming systems and crop management Soil air and water quality Weeds, etc Soil and Fine scale Rhizosphere [laboratory and small plots] N, P, K, heavy metals Soil organic matter and structure Rhizobium and microflora, etc vater

第八章 土壤空气 soil air

G ases en gas zone H 2 Hydrogen gas N, Nitrogen gas or dinitrogen N,o Nitrous oxide Nox= Ny0 t No t no NH3 Ammonia Co Carbon dioxide CHA Methane So Sulfur dioxide

士壤空气的组成特点 Atmospheric air vs Soil air (%o volume) Sample N2 CO? CH Air 78 0.035 trace Soil air 78 20 035 trace (0-20%)(0-5 土壤空气组成有以下分方面的特点 1.土壤空气中CO2>>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)土壤中根糸、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C2释放与固定问题成为当今土壤科学发畏的前沿领域!

一.土壤空气的组成特点 土壤空气组成有以下分方面的特点: 1.土壤空气中CO2>>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！

Gl bal Ne Prmary Pnduettn Atmesphere and Respiration Fossil fuels Vegetation bll 5、000 Sois ). s Ian Use Detritus 1.580 Surface Ocean 1,020 Marine biota vers IMN Surfacc Sediment Souree Schimel 1995 Adapted by: Craig Nicke Fig. 11.2. The Global Carbon Cycle

370 550 4 330 Air Monthly 531 Annual 300 Fig. 11.1. Atmospheric co, concentration trend at Mauna Loa Station(1958-1996 Credit: Emironment c anada

土壤空气的组成特点( soil air composition) 2.土壤空气中O2<<近地层大气中O2( oXygen) 原因:微生物和根糸等土壤中生物呼吸消耗。 3.土壤空气中水汽压高于近地层大气中水汽压。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。 4.土壤空气中有少量的还原性气体(恨量气体)。特别是土壤通气不良肘,含有 CH4、H2S、H2、N2O、C2H、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 a completely dry soil most of the pores are filled with air. As the soil water content increases the amount of air in the soil decreases The composition of air in an well-aerated soil is close to the composition of atmospheric air, as the oxygen consumed in the soil by plants and micro-organisms is readily replaced from the atmosphere. However, in a poorly aerated soil, the composition of air differs from the atmospheric air

一.土壤空气的组成特点（soil air composition) 2.土壤空气中O2<<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。 3.土壤空气中水汽压高于近地层大气中水汽压。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。 4.土壤空气中有少量的还原性气体（恨量气体）。特别是土壤通气不良时，含有 CH4、H2 S、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 a completely dry soil most of the pores are filled with air. As the soil water content increases the amount of air in the soil decreases. The composition of air in an well-aerated soil is close to the composition of atmospheric air, as the oxygen consumed in the soil by plants and micro-organisms is readily replaced from the atmosphere. However, in a poorly aerated soil, the composition of air differs from the atmospheric air

土壤空气的组成特点 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 0. 1 and 5 per cent and can reach nearly 20 per cent Under reducing conditions soil air may contain methane, hydrogen sulphide, and ammonia 问题:土壤空气质量如何满足作物生长需求的? 有资料表明:如果土壤不具备通气性,那么,土壤空气中O2仅能够作物根糸呼 吸消耗12~40个小肘,可见,土壤气体更新是多么重要。土壤是如何通气的呢?

一.土壤空气的组成特点 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 0.1 and 5 per cent and can reach nearly 20 per cent. Under reducing conditions soil air may contain methane, hydrogen sulphide, and ammonia. 问题：土壤空气质量如何满足作物生长需求的？ 有资料表明：如果土壤不具备通气性，那么，土壤空气中O2仅能够作物根系呼 吸消耗12~40个小时，可见，土壤气体更新是多么重要。土壤是如何通气的呢？

土壤的通气机制( soil aeration) (一丿土壤通气性( soil aeration) 又称为土壤空气更新。指的是土壤空气于近体层大气的交换过程。 (二)土壤通气的主要机制:主要有两种方式 1.整齐交换:土壤空气交换( soil air exchange)也有人叫质流、对流。 主要由于近地层环境因子剧烈变迁所引起的土壤中所有空气成分沿同一个方向 的流动。如:风、气压变化、温度梯度变化、降水和灌溉的作用。 这是特定条件下的土壤气体更新过程。 2.气体扩散( soil air diffusion) 土壤中气体分子因浓度梯度或气体分压不同而产生的气体移动。 土壤CO2↑、O2↓ 土壤失出CO2,吸收O2有人叫“土壤呼吸”( soil respiration) 气体扩散规律服从FiK定律

二.土壤的通气机制(soil aeration) （一）土壤通气性（soil aeration) ; 又称为土壤空气更新。指的是土壤空气于近体层大气的交换过程。 （二）土壤通气的主要机制：主要有两种方式 1.整齐交换：土壤空气交换（soil air exchange）也有人叫质流、对流。 主要由于近地层环境因子剧烈变迁所引起的土壤中所有空气成分沿同一个方向 的流动。如：风、气压变化、温度梯度变化、降水和灌溉的作用。 这是特定条件下的土壤气体更新过程。 2.气体扩散（soil air diffusion) 土壤中气体分子因浓度梯度或气体分压不同而产生的气体移动。 土壤CO2↑、O2↓ 土壤失出CO2 ，吸收O2 ,有人叫“土壤呼吸”（soil respiration) 气体扩散规律服从FicK定律

土壤的通气机制( soil aeration) 土壤中气体扩散过程也可用Fick第一定律表示。 dc dx (4.10) 式中:q表示体积扩散通童LT] D表示土壤中气体表观扩散糸数[L2T1 C表示气体容积分数(浓度)[L3L3 X表示扩散距离[L] 若用扩散气体的分压(P)代替浓度,方程为: dp q=-(D。/B)1(4.11) dx 式中β表示浓度与分压的换算常数(比值 注意:气体扩散是土壤气体交换的主要机制!

二.土壤的通气机制(soil aeration) 土壤中气体扩散过程也可用Fick第一定律表示。 （4.10） 式中：q表示体积扩散通量[LT-1 ] Ds表示土壤中气体表观扩散系数[L2T -1 ] C表示气体容积分数(浓度)[L3 L3 ] x表示扩散距离 [L] 若用扩散气体的分压(P)代替浓度，方程为： （4.11） 式中表示浓度与分压的换算常数（比值 ） dx dc q = −Ds dx dP q Ds = −( / ) 注意：气体扩散是土壤气体交换的主要机制！

三.土壤通气性的指标 (一)呼吸糸数:(RQ, respiratory quotient),也叫“呼吸商“ 定肘间内一定面积土壤上所产生的C○2的容积与所消耗的O2的容积比。 RO= 般情况下,RQ≈1;RQ>1,通气不良。 )土壤通气量 air flux):单位肘间在压力梯度作用下通过单位面积的土壤 空气量(CO2+○2),通气量大,通气性强 三丿土壤扩散率(oDR, oxygen diffusion rate):单位时间通过单位面积土壤 氣气的克数(或微克数)。它标志着土壤空气中○2的补给速率。 当○DR<20×108克时,大部分植物根糸停止生长。正常的土壤ODR要维持在 30×103~40×108以上。豆科植物要求比禾本科要高,甜莱要求更高。 用氧电极(叶t电极)可以测定土壤ODR (四)氧化还原电位(Eh)( soil redox potential)

三.土壤通气性的指标 （一）呼吸系数:（RQ，respiratory quotient),也叫“呼吸商“ 一定时间内一定面积土壤上所产生的CO2的容积与所消耗的O2的容积比。 一般情况下，RQ≈1 ;RQ>1 ，通气不良。 （二）土壤通气量（air flux）：单位时间在压力梯度作用下通过单位面积的土壤 空气量（CO2+O2），通气量大，通气性强。 （三）土壤扩散率（ODR，oxygen diffusion rate)：单位时间通过单位面积土壤 氧气的克数（或微克数）。它标志着土壤空气中O2的补给速率。 当ODR<20×10-8克时，大部分植物根系停止生长。正常的土壤ODR要维持在 30×10-8~40×10-8以上。豆科植物要求比禾本科要高，甜菜要求更高。 用氧电极（Pt电极）可以测定土壤ODR。 （四）氧化还原电位（Eh）（soil redox potential) 2 2 O co V V RQ =