Know Your Soils - Bernalillo County Open Space Backyard ... · Know Your Soils By: Shawn Hardeman Backyard Farming Series April 21, 2012. 2 Module Objects •To be able to interpret

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Know Your Soils

By: Shawn Hardeman

Backyard Farming Series

April 21, 2012

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Module Objects

• To be able to interpret a soil survey report

• To convey a basic understanding of soils,

soil properties, their regional distribution,

and the service they provided

• To be able conceptualize and describe at the

basic level how air, water, and nutrients

move through the soil

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What is soil?

“soil is the elegant, complex mixtures of

minerals, organic matter, soil

microorganisms, various burrowing

creatures and insects, and countless other

forms of life that acts as a medium for plant

growth.”

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Soil Properties

• Soil Texture

– Texture is how we describe the mineral

particles in a soil

– The three particle types are sand, silt and clay

– Based in the percentage of these particles we

can describe soils in textural classes

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Soil Properties (texture)

• Soil Texture Triangle

• Soil texture is defined as the relative proportion of the various soil particles in a soil

• Soil texture influences the physical and chemical properties of a soil

Source: http://www.soilsensor.com/soiltypes.aspx

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• 12 Textural Classes

• Textural classes are determined by mechanical analysis.

• Or, textural classes can be inferred in the field by feel.

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• Basic flowchart for

determining textural

class by feel

• Results are not 100%

• It’s free and fun

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Soil Properties (particle size)

• Particle Size (soil separates) from USDA

– Sand, coarse minerals, 2.0 – 0.05mm

– Silt, medium size minerals, 0.05 – 0.002 mm

– Clay, smallest minerals, < 0.002 mm

Coarse Fragments; gravel, cobble, and stones (> 2.0 mm) are excluded from textural classification but are used to describe the soil as a whole.

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Source:

http://plantandsoil.unl.edu/croptechnology2005/soil_sci/?what=topicsD&informationModuleId=1130447039&topicOrder=2&max=10

&min=0&

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• Surface Area of Soil Particles

– Sand; 0.3 m2/100 g of soil

– Silt; 15 m2/100 g of soil

– Clay; 30,000 m2/100 g of soil

• Which particle has the most influence?

• Surface Area based on Textural Class

– Loamy sand; 240 m2/100 g of soil

– Loam; 12,100 m2/100 g of soil

– Clay; 14,800 m2/100 g soil (not 100% clay)

CLAY

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Soil Properties (CEC)

• Cation Exchange Capacity (CEC)

– The quantity of negative charges in soil existing on the

surfaces of clay and organic matter

– The CEC of a soil represents the total amount of

exchangeable cations that the soil can aDsorb.

– The is measured in centimoles (cmol/kg of soil)

– CEC is important because it provides a reservoir of

nutrients to replenish those removed from the soil water

by plant uptake

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– Essential plant nutrients that exist in the soil as

cations; K+, Ca2+, Mg2+, NH4+

– Other cations include; Na+, H+, Al3+

– There is a balance between cations on the soil

particle and in soil solution

– Problems will arise if Na+ exceeds Ca2+ &

Mg2+, soil dispersion and inhibit plant growth

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– The CEC can improve with an increase in

organic matter

– In sandy soils, CEC will be entirely due to

organic matter

– To a lesser extent, anion exchange capacity is

where phosphate and sulfates are adsorbed, but

nitrate is not

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Soil Properties (porosity)

• Pore Space

– Varies based on

textural class

– Varies based on

compaction

– Air, water,

microbes, soil

nutrients, and

roots all exist in

the pore spaces

Source: http://plantandsoil.unl.edu/croptechnology2005/pagesincludes/printModule.jsp?informationModuleId=1130447039

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Soil Properties (porosity)

• Pore Space – aka, Porosity

– Defined as n or φ = Vv/Vt

• Volume of the void space over total volume

• Which textural class has a greater amount of pore space?

• Which textural class has larger pore spaces?

CLAY

SAND

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Soil Properties

“Among the important physical properties of

soils are those which enable the soil to

receive, hold, and transmit water for the use of

crops.”

Soils and Men, USDA Yearbook, 1938

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Soil Properties (water content)

• Saturated and unsaturated flow

– Water flows in between the pore spaces

Source: https://www.soils.org

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• Water is measured in the soil as water content (θ)

– Volumetric (θv) and Gravimetric (θg)

θg measured in the laboratory

• θg = mass of water/mass of soil

• θv = θg*(bulk density of soil/bulk density of water)

Both are interpreted as a percentage

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• Water in the soil can be describe as a height

• Similar to measuring rainfall

• Described as inch/inch or inch/foot of soil

Source: http://www.fao.org/docrep/r4082e/r4082e03.htm

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• Example: From soil samples it was determined that in the first 6 inches of soil the θv = 0.2. How much water is in the soil?

• 6 inch x 0.2 = 1.2 inches of water

• If an acre-foot of water is equal to 325,851 gallons of water then 1.2 inches of water equals 32,585 gallons over the same area.

– (1.2 in/12in)(325,851 gallons) = 32,585 gallons

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• Available Water Holding Capacity

Source: http://bettersoils.soilwater.com.au/module2/2_1.htm#Figure 3

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• Available Water Holding Capacity

– Saturation: 100% of the pore space is filled

with water; free water present

– Field Capacity: water retained in the soil profile

after the free water has drained

– Permanent Wilting Point: the point at which

plants can no longer extract water from the soil.

“Give the soil a good soaking…”

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Available Water in Soil

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

Coarse

Sand

Fine Sand Loamy

Sand

Sandy

Loam

Light Sand

Clay Loam

Loam Sandy Clay

Loam

Clay Loam Clay

Soil Texture

Inch of Water/Inch of Soil

Field Capacity

Wilting Point

Textural class is the limiting factor

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In inch/inch of soil

Texture Field Capacity Wilting point Available Water

Coarse Sand 0.06 0.02 0.04

Fine Sand 0.1 0.04 0.06

Loamy Sand 0.14 0.06 0.08

Sandy Loam 0.2 0.08 0.12

Light Sand Clay

Loam

0.23 0.1 0.13

Loam 0.27 0.12 0.15

Sandy Clay Loam 0.28 0.13 0.18

Clay loam 0.32 0.14 0.15

Clay 0.40 0.25 0.20

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Source: http://www.noble.org/ag/Soils/SoilWaterRelationships/Index.htm

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Soil moisture available for plant growth makes up approximately 0.01 percent of

the world's stored water. Source: NRCS and http://www.noble.org/ag/Soils/SoilWaterRelationships/Index.htm

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Soil Properties (water movement)

• Water balance: Inflows and outflows

– Precipitation (P)

– Infiltration (I)

– Surface Runoff (R)

– Deep Percolation (D)

– Evapotranspiration (ET)

– Water Storage Change (∆W)

P + I – R = ET + D + ∆∆∆∆W

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Source: http://www.fao.org/docrep/x0490e/x0490e0e.htm

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• Wetting Depth Example:

– Water Holding Capacity (AWC)

• Sandy soil – 0.1 in/in of soil

• Clayey soil – 0.4 in/in of soil

– After applying 3 inches of water to both soils,

how deep will the water penetrate in each?

Sandy soil: 3 in/0.1 in/in = 30 inches

Clayey soil: 3 in/0.4 in/in = 7.5 inches

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• Water Movement in Soil

– Total Water Potential is the sum of

– Gravitational Potential• Water will flow from regions of higher potential to regions of

lower potential (water flows down hill)

– Solute or Osmotic Potential• Water will flow from regions of lower concentrations to

regions of higher concentrations (this drive water uptake in plants)

– Tensiometer Pressure Potential– Matric potential (capillary action)

– Air pressure potential

– Hydrostatic pressure potential

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Source: http://turf.lib.msu.edu/1980s/1988/880323.pdf

Why? It is because of pore space, matirc potential, hydrostatic pressure, and

gravitation potential.

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• Hydraulic Head (for saturated flow)

– The change in the total water potential over a distance

drives the gradient (i)

– The sum of the hydrostatic pressure (p) and

gravitational potential (z); (H = p + z)

• Saturated Hydraulic Conductivity (Ks) inch/sec

– A quantitative measure of a saturated soil's ability to

transmit water when subjected to a hydraulic gradient

• Jw = Ks(i) = Ks(H2-H1)/(L2-L1)

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Source: http://soils.usda.gov/technical/technotes/note6.html

LengthHead Ks

Ksi

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Source: http://soils.usda.gov/technical/technotes/note6.html

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• Infiltration Rate (I)

– Refers to the entry of water into a soil and moves

downward from the soil surface (wetting front)

– At the surface matric potential is dominate over

gravitational forces

– Water is filling the pores

• Infiltration rate is highest when water first enters

the soil and decreases with time as the pores fill up

with water

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Source: Element of Physical Hydrology, 1998

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• The most limiting factor is the saturated

hydraulic conductivity (Ks)

• Dry soils have high infiltration capacity that

decreases as pores begin to fill with water

• Runoff occurs when the infiltration capacity

is reduced to the saturated hydraulic

conductivity

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Soil Properties (summary)

Source: http://soils.usda.gov/technical/manual/

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Soil Forming Factors

• There are 5 soil forming factors to consider

– Parent Material

– Climate

– Topography

– Biological Factor (biota)

– Time

• “Each factor are independent variables that define the soil system,” Hans Jenny, 1941

• For a given combination of each factor only one type of soil exists

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Soil Forming Factors (soil taxonomy)

• There are 12 soil orders worldwide

• 64 soil suborders

• 300 soil great groups

• 2,400 subgroups

• 50,000 soil series in the United States

Source: http://soils.usda.gov/education/facts/formation.html

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Soil Forming Factor: p (parent material)

• Soils can derive from material that was deposited

by the following processes

– Alluvial (concentrated by running water in semiarid)

– Colluvial (mass movement - gravitational)

– Fluvial (rivers and flooding)

– Loess (wind deposited material)

• The act of deposition and sedimentation of material are not soil forming factors

Rock → Weathered Rock → Immature Soil → Mature Soil

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Weathered Rock

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Soil Forming Factors: c (climate)

• Climate: the weather of a particular region

over a long period of time

• Includes precipitation, temperature, and

wind that prevail over a particular region

• Climate is the driving force behind the

weathering of rocks and soils

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Soil Forming

Factors (climate)

Source: http://www-psych.nmsu.edu/~linda/weather.htm

•Precipitation drives the

deposition of parent material,

and the chemical and physical

weathering of that material

•The amount of precipitation

heavily influences soil

development through

weathering and leaching

•Desert soils are not highly

weathered soils due to a lack

of precipitation

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Soil Forming Factors (climate)

• Temperature is important because it regulates

biological and chemical reactions

• Temperature influences the water content in the

soil

• Most of the biological activity encouraged by

temperature will be close to the soil surface

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Soil Forming Factors (topography)

Source: http://www.soils.umn.edu/academics/classes/soil2125/doc/s4chp3.htm

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Soil Forming Factors: b (biota)

• Biota includes plants, animals, micro-organisms, microbes, and human activity

• Their affect on soil formation varies and tied to habitable conditions

• The long-term affect is the accumulation of organic matter over time

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Soil Forming Factors (time)

• Soil systems vary with timeRock → Weathered Rock → Immature Soil → Mature Soil

• The Time begins as soon as the rock material is acted upon by water, temperature, and organisms

• The goal is for soil forming factors to outpace erosion factors

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Soil Forming Factors (time)

• Soil Profile

– O horizon: organic layer

(leaf litter)

– A horizon: surface layer

(top soil)

– B horizon: subsurface

layer (zone of

accumulation)

– C horizon: substratum

layer (weathered rock)

Source: http://soils.usda.gov/education/resources/lessons/profile/

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Comparison of

Soil Forming

Factors

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Soil Forming Factors (Entisols)

Source: http://soils.usda.gov/technical/soil_orders/

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Soil Forming Factors (Entisols)

• Relatively young in age

• Horizons are not well

defined (lack a B horizon)

• Found in floodplains and

river channels

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Soil Forming Factors (Aridisols)


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Soil Forming Factors (Aridisols)

• Rocky material present and

not highly weathered

• Distinct A and B horizon

• Low OM content

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Soil Forming Factors (Mollisols)


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Soil Forming Factors (Mollisols)

• Rich on OM content

• Well defined O, A, & B

horizons

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Soil Forming Factors (Histosols)


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Soil Forming Factors (Histosols)

• Predominately organic

material

• High organic matter

content throughout the

profile

• Formed under saturated or

partly saturated conditions

• Source for peat

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Soil Quality (SOM)

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Soil Quality (SOM)

• Soil Organic Matter

– Humus not Organic Material (i.e. leaves, plant parts)

• Mineral soils contain less than 30% organic matter, by weight

• Mineral soils may have an O horizon and the void space in the A horizon contains less than 10% organic matter

• Organic soils may have more than half of its upper profile containing organic matter (Histosols)

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Soil Quality (SOM)

• Improves soil tilth

– Soil structure

– Surface crusting

– Decreases bulk density

– Supports microbial and microorganisms

– Adds rare/secondary minerals to the soil

– Increase water infiltration

– Increases water holding capacity (AWC)???

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Soil Quality (SOM)

Available Water Capacities in Centimeters per Centimeter of Soil ¹ ²

Soil Texture Classes Greater than or equal to 3 percent OM 0.5 to 3 percent OM Less than 0.5 percent OM

Coarse sand and gravel 0.04-0.06 0.03-0.05 0.02-0.04

Sands 0.07-0.09 0.06-0.08 0.05-0.07

Loamy sands 0.10-0.12 0.09-0.11 0.08-0.10

Sandy loams 0.13-0.15 0.12-0.14 0.11-0.13

Fine sandy loams 0.16-0.18 0.15-0.17 0.14-0.16

Loams and very fine sandy loams 0.20-0.22 0.17-0.19 0.17-0.19

Silt loams 0.22-0.24 0.20-0.22 0.20-0.22

Silty clay loams 0.21-0.23 0.18-0.20 0.18-0.20

Sandy clay loams 0.18-0.20 0.16-0.18 0.15-0.17

Clay loams 0.17-0.19 0.15-0.19 0.14-0.16

Silty clays 0.12-0.14 0.11-0.13 0.10-0.12

Clays 0.11-0.13 0.09-0.11 0.08-0.10

Source: http://www.mo10.nrcs.usda.gov/references/guides/properties/awcrange.html

Rule of Thumb – For every 1% of OM added to the soil adds

about 1.5% to the AWC (source: http://soils.usda.gov)

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Soil Quality (SOM)

• Example: An acre of soil at a depth of 6

inches weights ~ 2,000,000 lbs, which

means that 1% of OM weighs ~ 20,000 lbs.

If it takes 10 lbs of organic material to make

1 lb of organic matter than it would take

200,000 lbs of organic material to increase

the organic matter in the soil by 1%. Source: http://www.noble.org/ag/soils/organicmatter/index.htm

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Soil Quality (SOM)

• What influences SOM?

– Management

• Removing organic material - havesting

– Soil Texture

• Fine-textured vs. coarse-textured

– Climate

• High temps vs. high precipitation

– Landscape position

• Slopes vs. basins

– Vegetation

• Annual lifecycle of grasses vs. trees

Source: http://www.extension.umn.edu

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Soil Survey

• Where to find soil data –

Web Soil Survey

http://websoilsurvey.nrcs.usda.gov/

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Web Soil Survey


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Web Soil Survey


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Web Soil Survey


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Soil Survey

• Climate Data

• Landscape

Position

• Soil Properties

– Ksat

– Salinity

– SAR

– AWC (0.17)

• Land Use

• Typical Profile

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Comparison of Soil Types

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Thank You

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Carbon vs Life Zones

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Nitrogen vs Life Zones

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C/N Ratios vs Life Zones

Documents

Know Your Soils - Bernalillo County Open Space Backyard ... · Know Your Soils By: Shawn Hardeman Backyard Farming Series April 21, 2012. 2 Module Objects •To be able to interpret