Chapter 6 Soil Air and Heat Regime
Chapter 6 Soil Air and Heat Regime
Section 1 Soil air 一、 Composition of soil air Compare soil air with atmosphere( Volume % Atmosphere O cO2 2 Other g ases Atmosphere 20.94 0.03 78050.95 near soil surface Soil air18.0-0.15-78.8 20.030.6580.24
Section 1 Soil air 一 、Composition of soil air Atmosphere O2 CO2 N2 Other gases Atmosphere near soil surface 20.94 0.03 78.05 0.95 Soil air 18.0- 20.03 0.15- 0.65 78.8- 80.24 － Compare soil air with atmosphere（Volume %）
Characteristics of soill air 1. The level of CO2 in soil is about eight times higher than the normal atmospheric level 2. The O2 level in soil air is slightly lower than it is in atmospheric air 3. Soil air usually is much higher in water vapor than is the atmosphere Also, under waterlogged conditions, the concentrations of gases such as methane(CH4) and ydrogen sulf ide(h2s)are notably higher in soil air
Characteristics of soil air 1．The level of CO2 in soil is about eight times higher than the normal atmospheric level. 2．The O2 level in soil air is slightly lower than it is in atmospheric air. 3．Soil air usually is much higher in water vapor than is the atmosphere. 4 ． Also, under waterlogged conditions, the concentrations of gases such as methane（CH4）and hydrogen sulfide (H2S) are notably higher in soil air
The soil air contents of the mulches and bare cotton farmland in different growth stages(%) Plastic mulches Bare soil Depth /cm 05-01 07-29 05-01 07-29 CO O CO CO2 O2 CO 0 0.915 0.0560.056 50.158204971.0062043907020.6490.21120653 10042020.3971.06020.2750.10420.5130.27920668 150250204860.86519.953013420857038520506 200483204781348200600.15020.1210.40620.634 300.573198651.15920503132018115720.362 500.922199291.52019698040220.198128119.873 Average0615201241.26819.953|026920.3290.8472022
Depth /cm Plastic mulches Bare soil 05-01 07-29 05-01 07-29 CO2 O2 CO2 O2 CO2 O2 CO2 O2 0 － － 0.915 － － 0.056 0.056 － 5 0.158 20.497 1.006 20.439 0.70 20.649 0.211 20.653 10 0.420 20.397 1.060 20.275 0.104 20.513 0.279 20.668 15 0.250 20.486 0.865 19.953 0.134 20.857 0.385 20.506 20 0.483 20.478 1.348 20.060 0.150 20.121 0.406 20.634 30 0.573 19.865 1.159 20.005 0.313 20.181 1.157 20.362 50 0.922 19.929 1.520 19.698 0.402 20.198 1.281 19.873 Average 0.615 20.124 1.268 19.953 0.269 20.329 0.847 20.022 The soil air contents of the mulches and bare cotton farmland in different growth stages (%)
CO合土,变不O2,内土暗 空其(主 0.5 10千%19520225 21.0 20 : E0.40 .0一2 图61土壤剖面上OO2和O2体积含量分布示意图 (引自 J.R. Chter,1986)空土(
三、 The movement of soil air (一)、 Convection( Mass flow) Convection -The soil air is transferred from higher pressure area to lower pressure area. D q -(k nVp Where gv is the volume convective flux of air; k is the permeability of the air-filled pore space; n is the viscosity of soil air; vis the pressure gradient in soil air
二、 The movement of soil air （一）、Convection (Mass Flow) Convection –The soil air is transferred from higher pressure area to lower pressure area. Where qv is the volume convective flux of air; k is the permeability of the air-filled pore space; is the viscosity of soil air; is the pressure gradient in soil air. qv = −(k /)p
(二)、 Soil air diffusion .a difference in the concentration of a particular gas in one zone compared with any other zone in the soil can result in the movement of that gas by a process called diffusion The process of diffusion can be represented by a flow equation in which the driving force is the gas concentration gradient (Fick’sLaw) gd==D x .where qd is the diffusive flux(mass diffusing across a unit area per unit time), d is the gas diffusion coefficient, and dc/dx is the concentration gradient of the gas Soil respiration
（二）、Soil air diffusion • The process of diffusion can be represented by a flow equation in which the driving force is the gas concentration gradient (Fick’s Law). dx dc qd = −D •where qd is the diffusive flux (mass diffusing across a unit area per unit time), D is the gas diffusion coefficient, and dc/dx is the concentration gradient of the gas. •A difference in the concentration of a particular gas in one zone compared with any other zone in the soil can result in the movement of that gas by a process called diffusion. Soil respiration:
Section Soil hea
Section 2 Soil heat
一、 The source of soil heat 太阳人 云层散射 大气散射 大气吸收 (-- Solar radiation Solar radiation is the 太 primary source of energy to heat soils But clouds ad dust particles intercept the sun's 达辐射 rays and absorb, scatter, or reflect most of the energy. E 图62地面辐射平衡示意图
一、The source of soil heat （一）Solar radiation Solar radiation is the primary source of energy to heat soils. But clouds ad dust particles intercept the sun’s rays and absorb, scatter, or reflect most of the energy. H I E a
(二) Biologicalheat Organic matter is decomposed y microorganism. (-) Heat inside the earth
（二）Biological heat Organic matter is decomposed by microorganism. （三）Heat inside the earth
