UCR ENSC 100 MT2 – Final

Green Crops
a crop grown solely for incorporation into the soil
Tensiometers measure
matric potential
760 μS/cm is equal to _ mS/cm
0.760 mS/cm

specific adsorption makes nitrate unavailable to plants.



Porous gypsum blocks are used to measure…
water content
Go from pressure in pressure bomb to soil matric potential
divide by -2
Immobilization of N is most likely to occur when organic residues are added to soil that have a high
C:N ratio
Redox lader in order from first to last
O2, NO3-, Mn(IV), Fe(III), SO42-

You can not grow plants with ocean water because the solute potential and matric potential are too negative.




Oxidation and reduction reactions in a soil are regulated primarily by the availability of hydrogen ions.



Geotechnical Engineering
the study of soils as a support for engineering works or as a structural material.
The Atterberg Limits

define the water content at which a soil’s mechanical behavior changes.made on the <0.5 mm size fraction of the soil.


shrinkage limit – soils can dry without changing volume

plastic limit – The lowest water content at which the soil first begins to act in this plastic manner

liquid limit – a soil behaves as a viscous liquid.


Liquid Limit: (mass of water/Mass dry soil) * 100

Casagrande soil tester

Measuring the Liquid Limit


The Liquid Limit is the water content when the groove closes with 25 drops of the dish.

Drop-cone penetrometer.

Measuring the Liquid Limit


an 80 g steel cone will penetrate the soil to a depth of 20 mm in 5 seconds.

Plastic Index
is the difference between the liquid limit and the plastic limit. PI = LL – PL
Soil that favors compaction and stability.
well-graded” soil
Soils poor for construction
A “poorly-graded” soil has a narrow range of particle sizes
There are three principle reasons to compact a soil:
• Increases load-bearing capacity (increases the shear strength of the soil)
• Prevents soil settlement and frost damage (frost heaving)
• Reduces permeability, thereby reducing water seepage, swelling and contraction.

Proctor Soil Compaction Test


“lubrication theory”

Weight dropped on soil, new height measured, measures compaction


the “lubrication theory” to explain how water helps soil grains slide together to achieve maximum compaction

Erosion Control Practices



– ridging (contouring across the slope),
– vegetative strips and barriers (buffer strips, strip cropping, fabric fence, gravel bags),
– runoff interceptors (terraces and diversions)
– small impoundments (sediment basins and impoundment terraces).


Erosion is P factor

K Factor


five properties

soil properties that influence a soil’s reaction to rainfall and runoff.

• Five properties are used to determine K:
– silt plus very fine sand
– other sand
– organic matter content
– soil structure
– the permeability of the least permeable horizon.

T Factor

The T factor is an estimate of the maximum average annual soil loss that can occur without affecting crop productivity over a sustained period.

• The rate is in tons per acre per year.

Hydrophobicity of Soils


how to fix

HYdrophobic organics get vaporized in heat and sink lower in the soil and condense, forms water repellant layer ~ 2cm thick.


cultivate the soil to break up the layer, surfactqants dissolves it, hydromulching = green newspaper

What affects the formation of the hydrophobic layer?
• A thick layer of plant litter prior to the fire
• High intensity fire
• Prolonged period of intense heat
• Coarse textured soils.
three forms of wind erosion
– Saltation is the lifting and bouncing of particles, moves the most soil out of them all
– Creep is the rolling movement of coarse and very coarse sand grains.
– Suspension is the lifting of clay- and silt-sized particles (<100 µm) into the air where they can be carried long distances.
reclaimed land
Problem with reclaimed land


-acidic “cat-clays” react with oxygen to forms acids

Acid-sulfate soils
• The low pH and high sulfate concentrations are very corrosive to concrete and steel, making building difficult.
• Acid-sulfate soils are widespread around coastal regions.
• If the soils are kept flooded and planted to rice, oxidation can be slowed.
mine tailings.

plies mining for metals and coal that leak contamination to surface and groundwater.


waste rock and processed rock following metal extraction. Much


Frequently, these waste piles become strongly acidic due to chemical reactions with water and oxygen.


Rhizobia are rod-shaped, motile, heterotrophic bacteria. They normally grow aerobically in soil but require low oxygen levels to fix nitrogen.
• The enzyme nitrogenase is required to fix nitrogen and is destroyed by O2.


-live in nodules with hemoglobin

potting soil.

• Potting soil must have a high water-holding capacity but be well drained.


Most potting mixes are combinations of sand (25%) and sphagnum peat moss (75%), or other organic materials


• The grasses used for turf are very sensitive to inadequate oxygen in the root zone, so good aeration is necessary.
compaction is one of the biggest problems with turf


• Sandy soils are preferred because they are well-drained. However, sandy soils need regular watering.

Tile drainage
Putting pipe underground to control water flow
Benefits of biosolids recycling

Increase the organic matter content of soils

Improve aggregate stability, water infiltration, water-holding capacity.

Increase microbial activity in the soil and there is evidence of plant disease suppression.

Macro- and micro-nutrients are in the sludge.

Seattle Biosolids Reuse
– Seattle has a big program to apply liquid biosolids to frests but heavy trucks full of sludge have difficulty driving up the mountain
Concerns with biosludge use

Food chain transfer of heavy metals.


Sewage sludge contains elevated of Cd, Ni, Zn, Cu, Pb, Mo, and Cr. Two of these metals, Cd and Mo, can accumulate in plant tissues to concentrations that are damaging to animals.

Roots of Higher Plants
• In a typical cereal crop, roots are 30-50% of the total plant biomass.
• Roots influence microbial activities.
• Rhizosphere
• Rhizodeposition
• Mucigel (root exudates)

• Typically 10 to 100 mm (0.4 to 4 inches) or more in length.
• Biophagous macrofauna eat living material
– Carnivores (animal eaters)
– Herbivores (plant eaters)
– Microbivores (microorganism eaters)
– Omnivores (animal/plant eaters)


• Saprophagous macrofauna eat dead or decaying material
– Detritivores (detritus eaters)
– Cadavericoles (dead animal/carrion eaters)
– Coprophages (dung eaters)



The four major roles of macrofauna in soil
• Accelerate organic matter breakdown
• Mix organic matter and soil
• Contribute to soil structure
• Act as predators of soil microorganisms.



Most diverse macrofauna


include spiders, mites, cenitpedes, and millipede


-Predators and carnavors


• Wood lice, sowbugs, and pillbugs.
• Detritivores
• Gastropods or mollusks (snails and slugs) eat living and dead material.


Potworms – eat microorganisms.


200 – 2000 µm (0.2 – 2.0 mm) in length.


Mites: Important in nutrient cycling of carbon, nitrogen, and other elements.


Springtails – the most abundant and widely distributed arthropods. Less than 1 mm long. eat detritus, bacteria, fungi, spores, feces, living plants, animals, and decomposing organic matter.


unsegmented roundworms, threadworms, hairworms, or eel worms.


Parasitic Nematodes – the plant, animal, and human parasites. only spend part of their life cycle may be in soil.have small, narrow stylets, or spears, in their stoma (mouth) which they use to puncture the cell walls of fungal hyphae and withdraw the cell fluid.

Root knot nematodes are common in tomatoes and tobacco.



Single celled organisms
Prey on bacteria
Influence nutrient cycling especially near plant roots

multicellular animals that live in water and the thin films of water around soil particles.


Bdelloid rotifers – high resistance to desiccation and can be identified by their leech-like movements

Autotrophic organisms
do not need organic energy substrates; they derive energy from light or inorganic oxidation reactions.
Heterotrophic organisms
energy form organic substrates like sugars.
Activities of Soil Fungi
• Decompose cellulose, starch and lignin
• Major role in humus formation and aggregate stabilization
• Form a symbiotic relationship with plants: mycorrhizal fungi
Mycorrhizae fungi
• Symbiotic fungi with plant roots
• Fungus obtains sugar directly from the plant
• Fungal hyphae increase the root zone (extension of roots)
• Enhanced P uptake (P is immobile in soil)
• Plants are more resistant to drought

• Lichen is not a single organism; Lichens are a symbiosis of fungi, algae, and blue-green bacteria.

• Lichens colonize rocks, exposed soil surfaces, and tree trunks. The algae and blue-green bacteria photosynthesize and fix N2, and the fungus provides water and mineral nutrients.

– Neutralism
– Commensalism
– Synergism
Mutualism – both partners benefit
– Neutralism – neither benefits
– Commensalism – one benefits, the other is unaffected
– Synergism – combined activity exceeds the sum of individual actions
Opportunism –
Amensalism –

Opportunism – rapid growth, resting stages

Amensalism – one species is inhibited by a toxin from another (antibiotics)

Where do you find earthworms?
• Medium-textured upland soil
• Moderate to high moisture
• High organic matter
• Thrive on manure and plant residues (leaf litter and mulch)
• They move between the O-horizon and A-horizon
Factors that depress earthworm populations
• Predators (moles, mice, and certain mites and millipedes)
• Very sandy soils (abrasive grains)
• Ammonia fertilizers
• Insecticides (especially carbamates)
• Tillage
Controlling Nematodes

Broccoli, cauliflower, grain sorghum or millet can lower root-knot numbers, particularly if they are grown for two consecutive years.


French marigolds have been proven to reduce nematode numbers.Allow the marigolds to grow at least 2 months and then plow them under.


• Actinomycetes are prokaryotes that look like fungi but are really filamentous bacteria.
• They have no nuclear membrane

• Require O2 for growth. Aerobic heterotrophs

colors affect reflection of sunlight of a surface





Turbulent transfer:

• Conduction, or diffusive transfer, is the principle way in which heat moves in soil.
– It requires a temperature gradient.
• Convection
– Mass flow: transfer of heat with fluid flow (Not too important in soils)
– Turbulent transfer: movement of heat by wind-driven mixing (not too important in soils but very important for atmospheric transfer of heat, water vapor, and CO2.
Infiltration rates Ok and low

1.2cm/hr is ok


.1cm/hr is low