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

5

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

10

Dorchester County, MD

Fort MottElkton

Siltier

textureSandier

texture11

12

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

17

Othello Series Extent

Another reason to look

at the properties and

not just the name18

UC Davis Soil Web

19

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

20

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

25

Class VIII

Best for forest,

recreation or

environmental

protection

26

27

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

28

Physical Properties

• Color

• Temperature

• Texture

• Structure

• Density

• Water Movement

29

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

32

. ..... .... .

.. . ..

..

... .

.

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

34

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

42

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

46

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

47

H

Mg

CaAl

K

H

Ca

Mg

K

Bases

Acids

Mostly primary and secondary nutrients

Soil Test Report

48

• 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

49

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-

55

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

56

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)

60

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

62

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

63

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

64

Nitrogen Cycle

65

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

66

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

67

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

68

Phosphorus and Micronutrients in the Soil

69

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)

70

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

71

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

78

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

80

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

91

• 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

103

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