soils 101 - university of maryland extensionall plants depend on the soil food對 web for their...
TRANSCRIPT
Department of Environmental Science and Technology
Soils 101
January 2011
Patricia Steinhilber, Ph.D. Ag Nutrient Management Program
University of Maryland College Park
Department of Environmental Science and Technology
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)
Department of Environmental Science and Technology
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
Department of Environmental Science and Technology
Department of Environmental Science and Technology
Question 1
•
What % of the soil volume would be water-filled after several days of heavy rain?
Department of Environmental Science and Technology
Question 1
•
What % of the soil volume would be water-filled after several days of heavy rain?
•
50%
Department of Environmental Science and Technology
First Things First: Soil Solids
•
mineral or inorganic solids−often classified based on particle size
•
organic solids a.k.a. “organic matter”
Department of Environmental Science and Technology
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
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
Department 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
Department of Environmental Science and Technology
The Other Soil Solid Material: Organic Matter
Humus
Biomass
Residues &By-Products
75%
10%
15%
Department of Environmental Science and Technology
Department of Environmental Science and Technology
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
Department of Environmental Science and Technology
Source: USDA
Department of Environmental Science and Technology
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
Department of Environmental Science and Technology
Question 2
How many bacteria are there in a handful of soil?
C) 300,000,000 – 50 billion
Department of Environmental Science and Technology
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
Department of Environmental Science and Technology
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
Department of Environmental Science and Technology
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
Department of Environmental Science and Technology
Question 3
•
What antibiotic used to treat bacterial infections in humans originates from the by-product of a soil organism?
Department of Environmental Science and Technology
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
Department of Environmental Science and Technology
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
Department of Environmental Science and Technology
•
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
Department of Environmental Science and Technology
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
Department of Environmental Science and Technology
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
Department of Environmental Science and Technology
The Interplay of Air and Water: Soil Aeration
•
The exchange of O2 and CO2 between the soil pores and the ambient atmosphere
Hillel
Department of Environmental Science and Technology
Department of Environmental Science and Technology
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)
Department of Environmental Science and Technology
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
Department of Environmental Science and Technology
Now, a Video Interlude -
•
Dr. Ian Pepper, soil microbiologist, Arizona State University
Department of Environmental Science and Technology
Let’s talk about the hydrologic cycle and soil water…
Department of Environmental Science and Technology
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)
Department of Environmental Science and Technology
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
Department of Environmental Science and TechnologyDepartment of Environmental Science and TechnologyDepartment of Environmental Science and Technology
Department of Environmental Science and TechnologyDepartment of Environmental Science and Technology
Department of Environmental Science and Technology
Soil Solution
•
keep well supplied with nutrients
•
minimize adverse conditions for plant growth−acidity−salinity
Department of Environmental Science and Technology
Soil tests can help identify limiting nutrient factors.
Fertilizers can enrich the soil solution when soil tests indicate an insufficiency.
Department of Environmental Science and Technology
Department of Environmental Science and Technology
Question 4
•
What are the plants nutrients?
Department of Environmental Science and Technology
What Elements do Plants Require?
Non-MineralNutrients
Mineral Nutrients
carbonoxygenhydrogen
macronutrients micronutrients
primary secondary iron chlorinezinc boroncoppercobaltnickelmanganesemolybdenum
nitrogenphosphoruspotassium
calciummagnesiumsulfur
Department of Environmental Science and Technology
Forms in Which Nutrients Exist
•
cation – positively charged ion
•
anion – negatively charged ion
•
neutral - uncharged
Department of Environmental Science and Technology
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
Department of Environmental Science and TechnologyDepartment of Environmental Science and Technology
soil acidity:the adverse condition on
humid regions
Department of Environmental Science and Technology
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)
Department of Environmental Science and TechnologyDepartment of Environmental Science and Technology
Department of Environmental Science and Technology
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
Department of Environmental Science and Technology
pore space
Soil Model
biomass
residues &by-products
sandsoil
solution
soilair
mineralsorganic matter silt
humus clay
Department of Environmental Science and Technology
Department of Environmental Science and Technology
Clays and Humus
•
center of chemical reactivity in soil•
engine driving chemical trans- formations in soil
geoscienceworld.org fullwiki.org
Department of Environmental Science and Technology
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)
Department of Environmental Science and Technology
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
Department of Environmental Science and Technology
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
Department of Environmental Science and Technology
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
Department of Environmental Science and Technology
Soil: The Most Complex
Biomaterial on Earth
Department of Environmental Science and Technology
Soil – We can’t grow without it.
Questions?
Smithsonian – Dig it! The Secrets of Soil
Hillel, 2008front cover
Department of Environmental Science and Technology
Department of Environmental Science and Technology
•
•
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