Soil Properties & Functions Related to Irrigation - Natural Resources Conservation Service
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Natural Resources Conservation Service
Soil Properties & Functions
Related to Irrigation
Kelly Attebury January 21, 2015
Resource Soil Scientist Lubbock, TX
Today’s topics
• Water related soil features
Inherent and Dynamic properties
• Soil Survey Information
Where to find current maps
What is soil?
Naturally occurring mixture of mineral and organic
ingredients with a definite form, structure, and
composition.
Mineral
constituents:
Sand
Silt
Clay
The way a soil “feels” is called the texture. Sand – gritty Silt – silky Clay – sticky
Inherent Properties
(Things we can’t easily change)
• Depth
• Restrictions
• Texture
• Clay type
Texture Soil Depth
Cation
Clay
Exchange
type
Capacity
Stable clays:
(Illitite/Kaolinite: 1 - 40 meq/100g)
Ability of a soil to hold and release
positively charged elements and
compounds (plant nutrients).
Examples:
Calcium
Potassium
Magnesium
Expansive clays:
(Smectite: 80 - 120 meq/100g) Adapted from: Soil Fertility and Fertilizers, 5th Edition, Samuel L.
Tisdale, Macmillan Publishing Company.
Dynamic Properties
(Things we can change)
• Organic matter • Compaction
• Structure • Available water
• Infiltration rate capacity
• Bulk density • Biologic activity
Organic Material vs Organic Matter
(Well, it’s all the same…right?)
• Dead plant material; organic material; detritus; surface residue: Plant, animal, or other
organic substances recently added to the soil and only begun to show signs of decay.
• Active fraction organic matter: Organic compounds used as food by microorganisms.
• Labile organic matter: Organic matter that is easily decomposed.
• Lignin: A hard-to-degrade compound that is part of the fibers of older plants. Fungi use the
carbon ring structures as food.
• Recalcitrant organic matter: Organic matter such as humus or lignin-containing material that
few soil organisms can decompose.
• Humus or humified organic matter: Complex organic compounds that remain after many
organisms have used and transformed the original material. Humus is important in binding tiny
soil aggregates, and improves water and nutrient holding capacity.
Ready to do some math? • An acre of soil 6 inches deep weighs about 2,000,000 pounds, so 1% organic matter in the soil weighs about 20,000 pounds per acre. • It takes at least 10 pounds of organic material to decompose to 1 pound of organic matter, …so 200,000 pounds (100 tons) of organic material applied/returned to the soil will add 1% of stable organic matter under favorable conditions. That 1 % OM can hold an additional 27,000 gallons of water per acre - about 1 ac. in.!
Amarillo soil
Big Spring, Texas
Native grassland
In crop production
never cropped
about 100 years In CRP about 20
years
11Structure
is the
arrangement
of soil
aggregates.
Diagram from the University of Hawaii at ManoaInfiltration rates through different soil structure types
Diagram from Colorado State UniversityTillage and equipment traffic compacted soil below
Bulk Density the plow layer of a Norfolk, inhibiting root
penetration and water movement through the soil
&
Compaction profile.
General relationship of soil bulk density to root
growth based on soil texture.
Adapted from: The Nature and Properties of Soils, 10th
Edition, Nyle C. Brady, Macmillan Publishing Company.Available Water Capacity (AWC)
Amount of water the soil can store in each layer. Given in
cm of water/cm of soil or inches/foot. Also defined as the
difference between field capacity and wilting point.
• organic matter
• texture
• bulk density
• structure
• salinity
• rock fragments
Relationship between available water and texture
Ohio Agronomy Guide, 14th Ed. Bull. 472-05Biotic soil components Typical number or length
(per handful of soil)
Typical biomass
(pounds/acre)
Plant roots - Residues (exudates)
60-150 in. 3,000
are a source of most carbon for soil
(annual crops) (annual crops)
organisms.
Many times more microorganisms near
1,500-3,000 in. 15,000
plant roots than farther away.
(grasses) (grasses)
Bacteria - Important in OM
decomposition.
Extracellular compounds help bind 300 million-50 billion 400-4,000
soil into aggregates.
Involved in nitrogen cycling.
Fungi – Important in
decomposing lignin.
500,000-100 million 500-5,000
Hyphae grow through soils and help
aggregate soil.
Increase nutrient/water upatakeBiotic soil components Typical number or length
(per handful of soil)
Typical biomass
(pounds/acre)
Actinomycetes – bacteria similar
to fungi with functions similar to
100 million - 2
both. 400 - 4,000
billion
Produce compounds with
distinctive aroma.
Nematodes – are the most
numerous animals in the soil.
1,000 - 10,000 5 - 50
Accelerate decomposition
when they graze on bacteria,
fungi, and plant residues.
Protozoa - Accelerate
decomposition when they
100,000 - 50 million 5 - 100
graze on bacteria, fungi, and
plant residuesBiotic soil components Typical number or length
(per handful of soil)
Typical biomass
(pounds/acre)
Anthropods – help
decomposition when they
(mites, collembola, other
insects) graze on bacteria,
100 - 1,000 1 - 10
fungi, and plant residues.
Collembola (shown) are
important in residue
decomposition.
Earthworms – mixes soils
and creates macroportes
that increase water
infiltration and flow and
0-2 10 - 40
aerate soil.
Soil passage through guts
increase aggregation and
nutrient cycling.
Adapted from: Soil Biology Primer. Ankeny, IA: Soil and Water Conservation Society.Keep the soil
Disturb the soil as
covered as much
little as possible
as possible
Healthy,
Productive
Soils
checklist for
Keep plants
growers
Diversify as much
growing
as possible using
throughout the
crop rotation and
year to feed the
cover crops
soilhttp://soils.usda.gov/sqi/assessment/assessment.html
Soil Surveys
1922
1978Today
References Soil Fertility and Fertilizers, 5th Edition, Samuel L. Tisdale, Macmillan Publishing Company. The Twenty Ten Theme. Blog at WordPress.com, Colby Digs Soil, Sizing Up Soil Structure, posted on July 9, 2012. http://colbydigssoil.com/2012/07/09/sizing-up-soil-structure/ The Nature and Properties of Soils, 10th Edition, Nyle C. Brady, Macmillan Publishing Company. Ohio Agronomy Guide, 14th Edition Bulletin 472-05, Relationship between available water and texture. Tugel, A.J., A.M. Lewandowski, and D. Happe-vonArb, eds. 2000. Soil Biology Primer. Ankeny, IA: Soil and Water Conservation Society. Unlock the Secrets in the Soil, healthy, productive soils checklist for growers. www.nrcs.usda.gov USDA Natural Resources Conservation Service, Soil Quality Indicators, 2008.
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