Introduction to Soils, Their Management and Health · Introduction to Soils, Their Management and...
Transcript of Introduction to Soils, Their Management and Health · Introduction to Soils, Their Management and...
Introduction to Soils, Their Management and Health
Jarrod O. Miller, Ph.D.
Soils are composed of:1. Minerals – from
weathered rocks
2. Organic matter –decomposition from plants, insects, fungus
3. Air – open pore space
4. Water – within pore space
We see the surface, but don’t think about what is underneath
1
Soils are very diverse
This diversity makes fertility and management different across farms, states and regions
However, if you learn some basic soil properties, you can manage your soil and talk to other farmers
2
Parent Material and Nutrients
Nutrient contents of most soils will be related to the material it formed in
Some soils naturally high in nutrients
4
Coastal Plain- weathered
sediments
Piedmont – Metamorphic
and Igneous Rocks
Blue Ridge – Metamorphic
Rocks
Valley and Ridge –
Sedimentary (Carbonates,
shales , sandstone
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GRANITE
SANDSTONE
QUARTZ
Bedrock Soils: Inherit Properties from the Rock
Its helpful to know the bedrock that formed
your soil, but you have to deal with whatever
you have. 6
Bedrock can vary across a field
• Look for stones
• Maybe you will see a
pattern later in the season.
• Maybe not.
7
Coastal Parent
Materials
Sandy
Organic Matter
Silty/Clay
• Alluvium
• Eolian
• Organic
8
Coastal Sediments can still vary
• Fast moving waters deposit sand– Low in nutrients
• Wind deposits sand and silt
• Slower moving deposits clay– Moderate nutrients
• Marshes form organic soils– High in nutrients
Sand
Peat/Swamp
Mixed Texture
USGS 9
California River Sediments
• Gives an view of what may have happened on your farm
• Can be organic matter and nutrient rich
• May have variable texturesClayeySiltySandyStones
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Dorchester County, MD
Fort MottElkton
Siltier
textureSandier
texture11
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Climate: Temperature and Rainfall
• Higher rainfall is good for plants
• But leaches and weathers soils
• Typically less nutrients with higher rainfall
NRCS
NRCS
Topography
Well drained
Eroded, shallow to bedrock
Poorly drained
• Similar issues
with leaching and
erosion
• The older the
landscape, the
more dissected it
is• That means
more hills,
deeper valleys
13
Coastal Plain Landscapes
Drainage ditch
Soil boundaries here aren’t as obvious, but
they typically follow drainage or parent
material
14
Soil Maps and Crop Yields
• Soils were mapped as important natural resource
• Scientists included yield potential depending on the soil type16
Soil Mapping
• Soils were mapped based on their geneticcharacteristics
– How they were formed
• May not relate to what you can do with them
• Soils with different names may have similar uses for agriculture
Sassafras Othello
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Othello Series Extent
Another reason to look
at the properties and
not just the name18
UC Davis Soil Web
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Basic Soil Horizons
• A horizon – Surface layer w/ organic matter
• E horizon – Leached horizon between the A and B horizons
• B horizon – Zone of accumulation of material transported from the A and E horizons
• C horizon – Parent material
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A horizon –thicker and darker means better management
B horizon – More clay = more water and nutrient holding
C horizon – Not weathered
Soil Horizons for agricultureA
B
C
21
Horizons affect plant growth
A horizon – lower clay
B horizon – higher clay
22
Land Capability Classes – related to plant growth• Class 1 soils have slight limitations that restrict their use.
• Class 2 soils have moderate limitations that restrict the choice of plants or that require moderate conservation practices.
• Class 3 soils have severe limitations that restrict the choice of plants or that require special conservation practices, or both.
• Class 4 soils have very severe limitations that restrict the choice of plants or that require very careful management, or both.
• Class 5 soils are subject to little or no erosion but have other limitations, impractical to remove, that restrict their use mainly to pasture, rangeland, forestland, or wildlife habitat.
• Class 6 soils have severe limitations that make them generally unsuitable for cultivation and that restrict their use mainly to pasture, rangeland, forestland, or wildlife habitat.
• Class 7 soils have very severe limitations that make them unsuitable for cultivation and that restrict their use mainly to grazing, forestland, or wildlife habitat.
• Class 8 soils and miscellaneous areas have limitations that preclude commercial plant production and that restrict their use to recreational purposes, wildlife habitat, watershed, or esthetic purposes. 23
Class I
Typically not
very limited
24
Class II
Limitations noted by
the additional letter
• e - erosion
• w - water
• s - problem with
rooting zone
(stones, low water
holding, low
fertility, saline
• c – poor climatic
conditions
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Class VIII
Best for forest,
recreation or
environmental
protection
26
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Soil Properties and Nutrient Availability
• Soils are an applied science:
– Geology – sedimentary geology, mineralogy, volcanic ash, glacial till
– Physics – water movement, structure, density
– Chemistry – nutrient holding, pH, reactions, acidity, salts
– Biology – plant, tree, fungus, nematode, animal, bacterial interactions
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Physical Properties
• Color
• Temperature
• Texture
• Structure
• Density
• Water Movement
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I’m not sure all of these are necessary.
Maybe later when we talk about
systems? I don’t know.
So I think this lecture should start with
properties that make nutrients available.
Later on you include color, temp, water
holding as they interact with roots in a
systems approach.
Soil Color
Dark = organic matter
Red = iron, clay
Grey = water table
• More organic matter typically means more nutrients
• Grey may indicate saturation, effects N cycling and root growth
• Red means more iron or clay – could be related to chemical soil properties30
Soil Temperature
What effects soil temperature?
• Solar radiation
• Soil color (darker colors absorb more)
• Aspect
• Mulch (insulation)
Effects on nutrients?
• Warmer soil increases nutrient
movement (highly related to P)
• Increase biological nutrient cycling
Cold temperatures preventing P availability in rye
31
Particle Size
• Soil particles are considered to be less than 2mm in size
– We had to make that up, based on how soils act
• Sand 0.05 to 2mm
• Silt 0.002 to 0.05 mm
• Clay < 0.002mm
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. ..... .... .
.. . ..
..
... .
.
Sand
Clay
Silt
This is important as you
associate with nutrient
concentrations and CEC
Texture Triangle and Soil Textures
30% Sand
40% Silt
30% Clay
65% Sand
20% Silt
15% Clay
33
Textural Triangle
• You need 90% sand to be called pure sand
• You need 80% silt to be called pure silt
• You only need 40% clay to call a texture clay
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Soil Structure
35
• Particles are attracted to each other
• Glues are important:
– Clay
– Oxides
– Organic matter
– Polysaccharides
Soil Structure: Basic shapes to watch for
Granular – organic matter Blocky - clay
36
Structure and roots
Adds pore space
for roots to move
and find nutrients
and water
37
Infiltration and Conductivity
Infiltration
• How fast water enters the soil
• More water storage for later
• Can move fertilizer into the soil
Conductivity
• How fast water moves through soil
• Can help prevent denitrification (later)
• Increase leaching
38
Chemical Soil Properties
• Cation Exchange Capacity
• pH – Acidity/Alkalinity
• Oxidation State
• Salt Content
39
There are Seventeen Required Nutrients
• Non-mineral elements (we won’t discuss these much)– Carbon, hydrogen, oxygen
• Primary macronutrients (needed in large amounts)• Nitrogen, phosphorus, potassium
• Secondary macronutrients• Calcium, magnesium, sulfur
• Micronutrients• Iron, zinc, manganese, copper, nickel, molybdenum, boron,
chlorine40
41
Cations vs Anions
– Na+1 and K+1
– Ca+2, Mg+2
– Al+3
– Fe, Cu, Zn, Mn, Ni
– NH4+1
– SO4-2
– Cl-1
– BO3-1
– MoO4-2
– NO3-1
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Cation Exchange Capacity (CEC)
• Cation – positively charged ions (K, Ca, Mg, Na)
• Exchange – exchange on and off the soil surface
• Capacity – how much can the soil hold
H
Mg
CaAl
K
HCa
Mg
K
Measured in charge:
meq+ / 100 g soil
Mineralogy, Texture and CEC
43
SAND
Lowest Capacity Highest Capacity
CLAY
Organic Matter has pH Dependent Charge
COOH + OH COO -
COOH + H COOH2 +No Charge
44
Variation in CEC occurs with pH
Pratt and Bair, 1962Helling et al., 1964
CEC of whole Soil CEC split by organic matter and clay
Coastal Soils
45
Charge in Various Soil Materials
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Material CEC (meq/100g)
Kaolinite (1:1) 3-15
Illite (2:1) 15-40
Montmorillonite (2:1) 80-100
Organic Matter 200-400
Sandy Loam 5-10
Loam 5-15
Clay Loam 15-30
Clay >30
Muck (Swamp) 50-100
• Kaolinite is mostly edge charge
• Organic Matter is greatest
• Adding clay or organic matter to soil increases CEC
Not All Nutrients Are Exchangeable
• K
• Ca
• Mg
• Na
• H
• Al
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H
Mg
CaAl
K
H
Ca
Mg
K
Bases
Acids
Mostly primary and secondary nutrients
Soil Test Report
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• Exchangeable cations are listed as %• Includes bases (Ca, Mg, K, Na)• Acids (H)
• Aluminum is there, but H represents it
• You don’t see micronutrients or P listed
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H
Mg
CaAl
K
NaK
Mg
K
Al3+ > H+ > Ca2+ > Mg2+ > K+ = NH4+ > Na+
Lyotropic Series
Anything in soil solution is
more likely to leach
Includes both valance and hydration radius
Held
strongest
Held
weakest
Farm or Garden Soil Test Report
50
• Ca = Mg > K > Na• You will talk about bases and
fertility.• They add Ca, Mg and K
• Where are P, Zn, Mn, ect
Sorption is Tighter Bonds with Soil Surface
51
AlAl
O
O OH
OH O
O
CuK
ExchangeableBound
Micronutrients and Soil pH
Availability highly related to soil pH and sorption– More available at acidic pH (except Mo)
52
Micronutrient Loss: Sorption
As pH rises, we create more negative edge sites for micronutrients to absorb tightly to
53
• pH = Concentration of Hydrogen
• Any addition of H+ makes the solution acidic
• Any addition of OH- makes the solution alkaline
What is pH?
H2O ↔ H+ + OH-
54
Comparing soil pH
Most of our agricultural
soils: pH 5 to 7
Brady and Weil, 2001
CO2 + H2O
H+ + HCO3-
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What causes soils to be acidic?
• Basic cations leach out of the soil before Al3+
• Al > Ca > Mg > K > Na
Warm Wet
Climate
Cool Climate
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57
Soil type
contributes to
natural pH
• Rainfall made
southeast acidic
Soil Mn levels necessary at different pH
Camberato, 2000 – Clemson Extension
This table is for
Coastal Plain soils
(i.e. sandy, low fertility)
Organic Matter is Hard to Describe
• Has fresh parts: cellulose, lignin, sugars , carbohydrates
• Has processed and broken down parts:
– Fulvic acid – dissolved in acid and bases (mobile)
– Humic acid – dissolves in bases
– Humin - insoluble
59
Organic Matter can chelate metals
• Chelate = claw
• Organic ligands (COO-, NH3-) surround metals
• Reduces availability of micronutrients (Mn, Fe, ect)
• Also reduces toxicity of heavy metals (Al)
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Combine that with Fulvic/Humic Acids
61
Cu
• Soil surfaces make micronutrients less mobile
• Fulvic acids make them more mobile (they stay dissolved)
• Fresh organic matter has more fulvic acids
• therefore organic matter can keep micronutrient mobile
Rhizosphere: Roots Can Force these Reactions
• Can release organic acids to chelate
• Can acidify the soil solution to dissolve micronutrients or exchange them from soil surfaces
• Plant roots only contact about 3-5% of the soil surface though
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There are Seventeen Required Nutrients
• Non-mineral elements (we won’t discuss these much)– Carbon, hydrogen, oxygen
• Primary macronutrients (needed in large amounts)• Nitrogen, phosphorus, potassium
• Secondary macronutrients• Calcium, magnesium, sulfur
• Micronutrients• Iron, zinc, manganese, copper, nickel, molybdenum, boron,
chlorine
Lec2
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Average Concentrations in Plant Dry Matter Sufficient for Growth (Jones, 2012)
Element Concentration (mmol/g) #atoms
Molybdenum 0.001 1
Copper 0.10 100
Zinc 0.30 300
Manganese 1.0 1000
Iron 2.0 2000
Boron 2.0 2000
Chlorine 3.0 3000
Magnesium 80 80000
Phosphorus 60 60000
Calcium 125 125000
Potassium 250 250000
Nitrogen 1000 1000000
You need 1000x
more N than Mn
Lec2
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Nitrogen Cycle
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N2
Fixation Commercial
Fertilizer
Legumes
Soil Organic Matter
Manure
N2O
NO
NO2
Denitrific
atio
n
NO3
NH4
UreaR-NH2
NH4
NO3
Leaching
Plant
Uptake(NO3, NH4)
Immobilization
NH3 (gas)
Plant Available Nitrogen
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Soil Organic Matter
NO3NH4
Leaching
Fertilizer N(Ammonium Nitrate)
Nitrogen will is easily lost,
no matter what you do
Depends on
microbe activity
These nutrients are held by CEC
• K
• Ca
• Mg
• Na
• H
• Al
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H
Mg
CaAl
K
H
Ca
Mg
K
Bases
Acids
Mostly primary and secondary nutrients
H
Mg
CaAl
K
SO4-2
• Inorganic S is mostly in the form of the
sulfate anion (SO4-2)
• Its also the form plant roots take up
• It is not held on the cation exchange
• So it leaches easily out of the root
zone
• Not as easy as NO3-
Bu
h-b
ye
Soil Sulfur
-
--
SO4-2
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Phosphorus and Micronutrients in the Soil
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Fe+3
Fe+3Organic Acid
1. A little Fe is soluble in the soil
2. Gets chelated by Organic acid• Can move with mass flow/diffusion
• Allows a little more to dissolve
3. Rhizosphere removes Fe from acid
4. Process starts over
Micronutrients should be managed by pH
Availability highly related to soil pH and sorption– More available at acidic pH (except Mo)
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Nutrient Management
• Nitrogen best managed by timing, whether you use manure or commercial fertilizer
• Ca, Mg, K can be managed by CEC
• P and Micronutrients can be managed by maintaining pH
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What is soil health?
Management of soils to maximize production with less inputs
– Cycling nutrients
– Retaining residue
– Minimizing disturbance
– Building microbial communities
– Trying to reduce external inputs• But you can’t eliminate them!
What is soil health?
Maintaining soil in a “natural” state
Disturbing soils breaks equilibrium
Converting forests to production ag:
Lose organic matter inputs and cycling
Organic matter is a source of food
• For:
– Insects
– Earthworms
– Bacteria
– Fungi
• If you don’t add more they will eat it all!
Subsidence in the Everglades
R. Reddy
When exposed to
oxygen, organic
matter is quickly
broken down by
microbes
A loss of organic matter equals:
• Lost nutrients (N, P, Zn, ….)
• Lost soil structure/adhesion
• Lost water holding
• Lost cation exchange capacity
• Lost microbial diversity
Managing Organic Matter
1. You add organic matter
1. Residue
2. Manure
3. Compost
2. You manage organic matter
1. No till
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Plowing and tillage destroys aggregates
Breaking aggregates
exposes organic matter
to microbial breakdown
Pore Space• Textural porosity – doesn’t change, based on sand silt and clay
• Structural porosity – macropores from aggregation and biology
– Adds pore space, therefore lowers density
You can only pack
particles so tight. That
pore space is set by
texture
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Infiltration and Conductivity
81
Infiltration
• How fast water enters the soil
• slower infiltration means more
erosion or standing water
Conductivity
• How fast water moves through
soil
Roots
Issues with No-till?
Some farms don’t see yield improvements for 6-8 years!
• The field needs to reach a new equilibrium
• Nitrogen is tied up with residue
• Soil biological community needs to become diverse
again
Adding organic matter
Reduced tillage helps keep organic matter around, but how do we increase it?
• Manures
• Cover crop/Green manure
Manure
• Adds organic matter (structure, CEC, ect)– contains N,P, K and micronutrients
– Manure has a low C:N
• Can add microbes to the soil
• Composted manure may add predators of harmful bacteria
• Can add too much N and P (water quality)
How do microbes cycle nutrients?
NO3-
Mineralization
Immobilization
Organic N
Mineral N
ResidueCompostManure
NO3-
CommerciaFertilizer
Nitrogen Cycle
• Mineralization- Plant tissues (organic N) are broken down by microbes, releasing mineral (NO3
-, NH4) nitrogen.
• Immobilization – Mineral nitrogen is taken up by organisms (plants, microbes)
C/N ratio
C
NSoil N
Wood chips
If the C/N is above 30,
the microbes will have to
steal N from the soil to
eat
C/N ratio
• Carbon / nitrogen – When the ratio is above 25, more nitrogen is immobilized, or taken
up, by microbes.
• Plant tissues with lower C/N ratios release N to the soil– Leaves, soft tissues
• Plant tissues with higher C/N cause microbes to take N from the soil– Wood chips, straw
Soil biological diversityOrganic matter is typically split into three parts
Fresh organic matter has
more fulvic and humic
acids
These have more N, P, K
Older organic matter
has more carbon, less
nutrients for microbes
Better for fungi
Cover Crops
• Prevent erosion between production crops
• Hold nutrients in the soil/system
• Can provide additional macropores thru root channels
• Pull moisture from the subsurface
• Provide additional organic matter
• Maintain microbial communities
• Can dry out the soil
• May be difficult to kill
• Timing of planting may be difficultDavid Lamm
Nitrogen Fixation: Legumes
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• A legume is a group of plants that have the ability to develop a symbiotic relationship with a bacteria species that may or may not be specific to a particular plant species
• The bacteria and plant interact to form nodules on plant roots
• Legumes worldwide contribute about 8-12 lb N/acre [about 72% of annual (non-manmade) contribution of all N deposits to soil]
Nitrogen Fixation• Typical legumes
– Perennial clovers (red, white, alsike),
– annual clovers (crimson, arrowleaf),
– medicago spp. (alfalfa, medics),
– vetches (hairy, annual vetch, crownvetch),
– lespedezas, etc.
• Bacteria
– Host specific
– Bradyrhizobia
Estimated Annual N Fixation by Legumes
93
Rolling and Crimping• Lays residue down, aids in planting
• Crimping pinches stem cuts of flow
• Heavy residue mat helps with weed control
David LammNRCSNational Soil Health & Sustainability Leader
Year Round Cover Crops and Soil Strength
• Not all “glues” are the same
• Glomalin/Polysaccharrides> Fe oxides > organic matter > clay
• Organic matter by itself isn’t enough, you need microbial activity
Soil Properties and Aggregates
96
K KCaCation Bridges
Fe Oxide Coatings Cover Soil Charge
SAND Clay is more likely to bond together
Organic Matter can Bond Aggregates
COOH + OH COO -
COOH + H COOH2 +No Charge
Organic matter bonds better with clay soils
SAND
So its easier to build organic matter in higher clay soils
Organic Matter is a nutrient and energy source
Polysaccharrides
• Microbial gums
• Fungal Hyphae - glomalin
Root Exudates
Earthworm casts
Glomalin – Fungal Hyphae
• Hyphae work with plant roots
• Can form a net around particles
• Glomalin sluffs off and can coat aggregates
Nichols, USDA-ARS
101
Aggregates rely on many soil properties
Ca
Things you can’t control:• Oxide coatings• Particle size
Help with initial micro-aggregation
You have some control over nutrients
Management can improve• Plant roots• Fungal Hypha• Microbial Activity
Management can improveOrganic Matter content
Soil Health/Regenerative Ag
• Been around for years, just being marketed differently
• There are things it can and can’t do.
• Its more about efficiency
102
Nichols, USDA-ARS
A Focus on Soil Biology is New
• We have new tools to focus on how soil organisms cycle nutrients
• We have a greater focus on how different cover crops help soil properties
– We don’t have answers for all soil types
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Soil Biology May Help Cycle Nutrients
• Nutrients still have to be there
• Sandy soils are low in nutrients and weather slowly
• Clay soils may see improved plant growth through structure and organic matter nutrients
104
Legumes Help Fix Nitrogen from the Atmosphere
• They don’t add other nutrients.
• If you harvest and sell your crop off site, you have removed nutrients.
• You will need to add some back
105
Research on Mixes Show Mixed Results
• Adding 6 different cover crops doesn’t necessarily equal more soil health
• Research is starting to show that more than 2-3 doesn’t really have a benefit.
• Pick for what you want
– Biomass? Rye
– Tillage? Radish
– Nitrogen? Whatever legume works best in your system
106
What is soil health?
Management of soils to maximize production with less inputs
• Using organic matter additions to improve
– CEC, drainage, nutrient content, microbial diversity, reduced erosion
• Using management to reduce losses of organic matter
– No till, turbo till, cover crops