Lecture 11 - Soil Aeration

0.22 to 0.18

Oxidized: Mn4+ reduced: Mn2+ Eh when change occurs?

<20%

below what air-filled porosity do negative effects on plant and microbial growth occur

0.3/0.4 to as high as 10%. above 10% can be toxic to plants

carbon dioxide: how soil air differs from the above-ground atmosphere

it is better to aerate soil during growing season because the soil and grass can heal and fill in any of the areas removed by plugs

during growing season vs. before or after growing season

chart. in each reaction, the oxidized form of the element is on the left side and the reduced form is on the right side with the arrows indicating that the reactions can go either way

effect of pH on the Eh at which several important redox reactions theoretically take place

soil water content, macroporosity, O2 consumption

general factors affecting soil aeration

redox potential (Eh) of approximately 0.3 V

generally, below what redox potential is the O2 content of soil considered to be 0

drainage holes for removal of excess water. taller pots allow more aeration in upper part of the medium. use of coarse-grained media (perlite, vermiculite, pumice)

how are containerized plants managed to promote aeration

soil structure and tillage. large, stable aggregates promote aerations. tillage is used to maintain aeration in poorly drained, heavy-textured soils. tile drainage in poorly drained soils

how can agricultural soils be managed to promote adequate soil aeration

GER DONR LEO IONO

how can an oxidizing reaction be distinguished from a reducing reaction

water-filled pores block the diffusion of oxygen to replace what is used by respiration. oxygen diffuses 10,000x faster through air-filled pores than water-filled pores

how does oxygen movement through open pores compare to movement through water-filled pores.

usually PP of O2 is higher in atmosphere than in soil. PP of CO2 is higher in soil than in atmosphere

how does the PP of O2 and CO2 relate between soil and atmosphere

as oxygen content of soil decreases, redox potential also decreases

how is oxygen content related to redox potential

measured as voltage through a platinum electrode

how is redox potential (Eh) usually measured in soils

[(total porosity-volume of water)/total porosity] x 100

how to calculate air-filled porosity

1-(bulk density/particle density)

how to calculate total porosity

drainage of excess water through macropores

macropores vs. no macropores

78%. same as atmosphere

nitrogen: how soil air differs from the above-ground atmosphere

addition of a soil amendment causes microbial population to increase which leads to more O2 being consumed

organic soil amendments vs. no organic amendments

-0.2 to -0.28

oxidized: CO2 reduced: CH4 Eh when change occurs?

0.11 to 0.08

oxidized: Fe3+ reduced: Fe2+ Eh when change occurs?

0.28 to 0.22

oxidized: N03- reduces: N2 Eh when change occurs?

0.38 to 0.32

oxidized: O2 reduced: H20 Eh when change occurs?

-0.14 to -0.17

oxidized: SO4- reduced: S2- Eh when change occurs?

0-20%. depends on depth, porosity, and water content

oxygen: how soil air differs from the above-ground atmosphere

supply oxygen to plant roots (respiration), allow release of toxic gases (methane, ethylene, CO2)

primary functions of soil aeration

saturated and dry are negative, wet is the best

soil moisture status: saturated vs. wet. vs. dry

oxidizing agents

substances that easily accept electrons are called

reducing agents

substances that easily donate electrons are called

air-filled porosity

the percentage of total pore space occupied by air

redox potential (Eh)

the tendency of a substance to accept or reject electrons is called

content of various gases in the soil atmosphere, air-filled porosity, oxidation-reduction (redox) status

three main ways that soil aeration is described

soil aeration by tillage can increase aeration, but it can also affect the organic matter and living organisms in that soil

tillage vs. no tillage

topsoil is better for aeration because there is more organic materials present there, and the soil is generally looser

topsoil vs. subsoil

Eh decreases pretty much immediately, and then stays steady at that lower Eh as time increases

what impact do saturated conditions at or near the soil surface have on the redox potential of soils

breakdown of organic residues, redox transformation of elements, plant growth

what major ecological processes are largely affected by soil aeration

diffusion: move from areas of high partial pressure to areas of low partial pressure

what physical process governs the movement of gases into and within soils

tree transplanting. when transplanting trees, make large, irregularly shaped hole and backfill with porous materials. protect established trees during grading operations

what practices are used in managing trees and lawns for proper aeration

FeO - Fe(II); NH4+ - N(III)

what types of elements/compounds are found in poorly aerated soils

FeOOH - Fe(III); NO3- - N(V)

what types of elements/compounds are found in well-aerated soils

methane (CH4), hydrogen sulfide (H2S), ethylene (C2H4)

which gases are generally associated with waterlogged or anaerobic soil conditions

unfavorable because O2 deficiency and buildup of toxic gases. exceptions (hydrophytes): mangrove trees, rice, cattails

why are waterlogged soils unfavorable for most plant production and what are some exceptions

nutrient availability, mobility of nutrients/pollutants, toxicity of certain elements, corrosivity of soil (pipes, USTs)

why is knowledge of redox potential important for the use and management of soils