Soils 101 - University of Maryland ExtensionAll plants depend on the soil food對 web for their nutrition.\爀屮\爀屮File name: A-3 \⠀㐀㔀䬀䈀尩. \⠀䄀氀猀漀昀眀⸀樀瀀最

$Page 1: Soils 101 - University of Maryland ExtensionAll plants depend on the soil food對 web for their nutrition.\爀屮\爀屮File name: A-3 \⠀㐀㔀䬀䈀尩. \⠀䄀氀猀漀昀眀⸀樀瀀最$
Department of Environmental Science and Technology

Soils 101

January 2011

Patricia Steinhilber, Ph.D. Ag Nutrient Management Program

University of Maryland College Park


What is Soil?

•

the outer layer of the Earth’s crust (geologists)•

the ecstatic skin of the Earth (William Logan)

•

the living skin of the Earth (Ian Pepper)•

crucible of terrestrial life (Daniel Hillel, soil physicist)•

the pedosphere−

the interface between the lithosphere, hydrosphere and atmosphere (ecologists)


What are Soils?

•

reactive, dynamic, three-phase ecosystems composed of solids, liquids and gases

MineralsAirWaterOrganic Matter

48%

25%

25%

2%topsoil several days afterrainfall or irrigation



Question 1

•

What % of the soil volume would be water-filled after several days of heavy rain?


Question 1

•

What % of the soil volume would be water-filled after several days of heavy rain?

•

50%


First Things First: Soil Solids

•

mineral or inorganic solids−often classified based on particle size

•

organic solids a.k.a. “organic matter”


Mineral Class

Size of Mineral Particles Feel of Particles

sands 0.05 – 2 millimeters (mm) gritty

silts 0.002 – 0.05 millimeters (mm) smooth (like flour, cornstarch or talcum powder)

clays less than 0.002 millimeters (mm) sticky when wet

Major Mineral Classes in a Soil

Department of Environmental Science and TechnologyDepartment of Environmental Science and TechnologyDepartment of Environmental Science and Technology


60% silt

20% clay

20% sand

Department of Environmental Science and TechnologyDepartment of Environmental Science and Technology


Soil Property Textural Groups

coarse-textured medium-textured fine-textured

sands, loamy sands, sandy loams,

loams, silts loams, silt, sandy clay

loams

clays, sandy clays, silty clays, silty clay loams, clay loams

water-holding capacity

low moderate high

susceptibility to erosion

low high moderate

leaching potential

high moderate low

nutrient retention capacity

low moderate high

Effect of Soil Texture on Soil Properties


The Other Soil Solid Material: Organic Matter

Humus

Biomass

Residues &By-Products

75%

10%

15%



Biomass: What It Is

•

the living component of the soil•

consists of a range of creatures −

as small as microscopic viruses & bacteria

−

as large as roots, worms and other creatures that are visible to the unaided eye

−

and everything between


Source: USDA

Presenter

Presentation Notes

Most people are familiar with the above-ground food web: Plants are eaten by herbivores are eaten by carnivores, and so on. But most plant matter is not eaten by herbivores; it is decomposed by the underground food web. All plants depend on the soil food web for their nutrition. File name: A-3 (145KB). (Also fw.jpg 574K, and fwb.jpg at 422K) Image courtesy of the USDA-NRCS.


Question 2 How many bacteria are there in a

handful of soil?

A) 10,000 – 50,000

B) 1,000,000 – 10,000,000

C) 300,000,000 – 50 billion


Question 2

How many bacteria are there in a handful of soil?

C) 300,000,000 – 50 billion


Biomass: What It Does

•

participates in nutrient cycling−break down plant and animal

materials (residues), using what they need and leaving behind what they don’t

•

mineralization


Biomass: What It Does (cont.)

•

creation of biopores−larger organisms move through soil

creating channels or pores

−channels promote water infiltration and create a healthy balance between large and medium pores


Residues and By-products: What They Are

•

dead stuff - crop residues, dead roots and bodies of soil creatures

•

by-products - materials that plant roots and soil creatures release or exude into the soil


Question 3

•

What antibiotic used to treat bacterial infections in humans originates from the by-product of a soil organism?


Question 3•

What antibiotic used to treat bacterial infections in humans originates from the by-product of a soil organism?

•

Streptomycin−Isolated from Streptomyces by Dr.

Selman Waksman of Rutgers University. Led to a Nobel Prize in Medicine in 1952


Residues and By-products: What They Do

•

fuel and nutrients for soil organisms− energy and nutrient source for most of the

soil creatures

•

formation and maintenance of soil aggregates (structure or architecture)− sticky and gummy by-products of residue

decomposition hold soil particles together in clumps or aggregates


•

relatively stable end product of residue decomposition•

composes the majority of organic matter•

resists further decomposition (1% per year) •

it is not a good nutrient or energy source for soil creatures

Last But Certainly Not Least:Humus


Humus: What It Does

•

very small in particle size & high surface area•

charged sites at many locations on the surface•

effective at holding water and nutrients


The Other Half of Soil: Soil Pores (Void Space)

•

soil water− adequate (but not too much) quantity − adequate supply of nutrients−minimize runoff and leaching

•

soil air− source of oxygen for roots and most soil

organisms− constantly enriched with carbon dioxide

from roots and soil organisms


The Interplay of Air and Water: Soil Aeration

•

The exchange of O2 and CO2 between the soil pores and the ambient atmosphere

Hillel



Gas In the Atmosphere

In Soil Air

nitrogen 79% 79%oxygen 20.9% 20.6%

carbon dioxide 0.035% 0.300%

Comparison of Gasses in the Atmosphere and in Soil Air of

Well-Structured Topsoil (several days after rainfall)


Balance Between Water and Air

•

macropores (large pores)− drain quickly after rain or irrigation− allow rapid infiltration of rainfall and

replenishment of oxygen in the root zone

•

mesopores (medium-sized pores)− “storage pores”− hold water in form most plants can use

•

micropores (very small pores)−water is held too tightly to be use to most

plants


Now, a Video Interlude -

•

Dr. Ian Pepper, soil microbiologist, Arizona State University


Let’s talk about the hydrologic cycle and soil water…


Biological Classification of Soil Water

•

excess or gravitational water−water that drains from soil 1-3 days after a

rainfall or irrigation (in macropores)

•

available−water that is in a form crop plants can use

(in mesopores)

•

unavailable−water that is held to tightly by the soil to be

usable by most crop plants (in micropores)


Water and Textural Groups (% water)Coarse-

TexturedMedium- Textured

Fine- Textured

Total 40 50 60

Excess 25 15 15

Available 12 27 * 20

Unavailable 3 8 25




Soil Solution

•

keep well supplied with nutrients

•

minimize adverse conditions for plant growth−acidity−salinity


Soil tests can help identify limiting nutrient factors.

Fertilizers can enrich the soil solution when soil tests indicate an insufficiency.



Question 4

•

What are the plants nutrients?


What Elements do Plants Require?

Non-MineralNutrients

Mineral Nutrients

carbonoxygenhydrogen

macronutrients micronutrients

primary secondary iron chlorinezinc boroncoppercobaltnickelmanganesemolybdenum

nitrogenphosphoruspotassium

calciummagnesiumsulfur


Forms in Which Nutrients Exist

•

cation – positively charged ion

•

anion – negatively charged ion

•

neutral - uncharged


So Which Nutrients Exist in What Form?

•

ammonium - NH4+

•

potassium - K+

•

calcium - Ca+2

•

magnesium - Mg+2

•

iron - Fe+2, Fe+3

•

zinc - Zn+2

•

manganese - Mn+2, Mn+4

•

copper - Cu+2

•

cobalt - Co+2

•

nickel - Ni+2

•

nitrate - NO3-

•

phosphate - H2 PO4-, HPO4

-2

•

sulfate - SO4-2

•

chlorine - Cl-

•

borate - H3 BO3 , H2 BO3-,

B4 O7-2

•

molybdate - MoO4-2


soil acidity:the adverse condition on

humid regions


Adverse Condition Soil Component Affectedinadequate supply of some nutrients

calcium and magnesium may be present in inadequate amounts in acidic soils

excessive or toxic supply of some nutrients or non- essential elements

aluminum, iron, zinc, manganese and copper can be present in excessive and even toxic amounts in acidic soils

some nutrients bound in unavailable forms

phosphorus and molybdenum are so tightly bound to soil clays that they are not available to plants in acidic soils

inhospitable environment

bacteria, such as those needed for nitrogen fixation, can not thrive in acidic soils

Adverse Conditions Due to Soil Acidity (Low pH)



Soils are Biochemical Reactors

•

the various components (soil air, soil water, minerals and organic matter) interact

•

a wide array of chemical and biochemical processes occur


pore space

Soil Model

biomass

residues &by-products

sandsoil

solution

soilair

mineralsorganic matter silt

humus clay



Clays and Humus

•

center of chemical reactivity in soil•

engine driving chemical trans- formations in soil

geoscienceworld.org fullwiki.org


Solid-Liquid Interface

•

adsorption of water and nutrients occurs at surfaces•

small particles have more surface area than the same weight of large particles•

surfaces are often charged; most charge is negative•

negatively charged surfaces attract positively charged ions (cations)


Cation exchange is a big deal!•

cation exchange capacity (CEC)− a soil’s ability to hold cations on charged

surfaces− a measure of the negative charge on the

particles− correlated to clay and humus content of

soils

•

exchange phase− those cations held on surfaces of charged

particles


Importance of CEC

•

nutrient cations exist on exchange phase−are protected from leaching−can replenish the soil solution when

plant uptake or leaching removes nutrients

−the “storehouse” of cationic nutrients


Textural Group Range of Clay Content (%)

Cation Exchange Capacity (CEC)*

sand and loamy sands

0 - 15 1 - 5

sandy loams 15 - 20 5 - 10loams and silt loams

0 - 25 5 - 15

clay loams, sandy clay loams, silty clay loams

20 - 40 15 - 30

clays, sandy clays, silty clays

>49 >30

*cmol/kg or centimoles per kilogram, or an older mode of expression, milliequivalent per 100 grams.

Relationship of Textural Class to Clay Content and CEC


Soil: The Most Complex

Biomaterial on Earth


Soil – We can’t grow without it.

Questions?

Smithsonian – Dig it! The Secrets of Soil

Hillel, 2008front cover



•

[email protected]

•

www.anmp.umd.edu

What would you like to cover in Soils 102?

http://www.ted.com/talks/bonnie_bassler_on_ how_bacteria_communicate.html

mailto:[email protected]

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Documents

Soils 101 - University of Maryland ExtensionAll plants depend on the soil food對 web for their nutrition.\爀屮\爀屮File name: A-3 \⠀㐀㔀䬀䈀尩. \⠀䄀氀猀漀 昀眀⸀樀瀀最

Soils 101 - University of Maryland ExtensionAll plants depend on the soil food對 web for their nutrition.\爀屮\爀屮File name: A-3 \⠀㐀㔀䬀䈀尩. \⠀䄀氀猀漀昀眀⸀樀瀀最