Nutrient cycles become unbalanced through:

1
Soil Nutrient Management

• Nutrient cycles become unbalanced through
• Harvest of crops or timber
• Leaching and runoff (exacerbated by irrigation)
• Monoculture (simplification)
• Increased demands for rapid plant growth
• Increased animal density

Goal of nutrient management Profitable use of
nutrient resources to produce abundant, high
quality plant products while maintaining soil
quality and downstream environmental health
2

• Avoiding the pollution of natural waters
• Apply only enough N and P to meet the needs of
• developing crops
• 2. Employ best management practices
• (i) riparian buffer strips
• (ii) cover crops
• (iii) conservation tillage
• (iv) forest stand management

3

• Riparian Buffer Strips
• Establish or permit growth of dense
• vegetation along streambanks or
• other water bodies
• Grasses and/or trees increase the tortuosity of
  water pathways
• Sediments settle out of slowly moving water
• Dissolved nutrients are taken up by organic
  mulch, mineral soil
• or the plants themselves
• Microbial action breaks down pesticides in
  slow-flowing water
• Design and management
• Cattle need to be fenced out to avoid trampling
• Minimum 10 m for slopes of less than 8 degrees

6-60 m
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Treed riparian buffer along tributary near Lake
Erie, Ontario
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Riparian Cottonwood Grove, east of Fort Macleod,
AB
Cattle ranching here
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• Cover Crops
• Vegetative cover grown on farmland without
  harvest
• Later tilled into soil (green manure) or left as
  surface mulch
• Leguminous plants increase soil nitrogen content
• Provides habitat for beneficial insects
• Protects soil from erosive forces (wind and rain)
• Fall rye and oats used in southern Alberta
• Prevents leaching
• Increased infiltration (less overland flow)
• Sediment and nutrients in runoff water
• removed (as in buffer strip)
• N.B. Nitrate leaches most when vegetation is
  bare. Under
• wet conditions, leaching is often worse in early
  spring and fall.
• Winter annual cereals (rye, wheat, oats) or
  legumes (vetch, clover)
• often are used for this purpose in moist
  climates.

Rye cover crop in Maryland, USA
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• Conservation tillage
• Previously called chemical farming
• Tillage practices leaving at least 30 of surface
  covered
• by plant residues
• Usually reduced runoff volume when soils are
  moist
• Reduces nutrient and sediment load in runoff
  waters
• (greatly reduces sediment-associated nutrient
  loss)
• However, loss of nutrients from leaching may be
  worsened
• before macropore development.

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• Rangeland Nutrient Cycling
• Grass fires move quickly and burn at low
  temperatures
• Less volatilization of nitrogen than forest fires
• Organic matter lost, but nutrients released
  stimulate new growth.
• Burnt land is often more productive than land
  where fire is
• completely controlled
• Grazing stimulates plant production and quality
  if it is
• relatively infrequent and of low intensity

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Leguminous Cover Crops to Supply Nitrogen Vetch,
clover or peas Sown after harvest or by airplane
while crop still in field Cover growth resumes
in spring, with nitrogen fixation Cover crop
then killed with herbicide, mowing or tillage
Hairy vetch on an Ontario farm

• Crop Rotations
• Interrupts weed, disease and
• insect pest cycles
• Differing rooting structures
• appear to improve soil fertility
• May improve mychorrizal diversity
• Legume rotation with non-legumes

Wheat after cotton Wheat after wheat
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• Nutrient Recycling through Animal Manures
• Supplies organic matter and plant nutrients to
  the soil
• Enhances crop and animal production
• Soil conservation
• 4 kg dry weight manure for each kg of animal
  liveweight
• Much of nitrogen is lost as ammonia or via
  denitrification while
• underfoot or in piles
• Intensive livestock Operations
• A 100,000 head beef feedlot produces 200 million
  kg of manure
• Sufficient to add organic matter to 340 km2 of
  farmland
• Manure would have to be hauled up to 20 km
• To save costs/time, some choose heavier local
  application,
• which may cause N or P loss to surface or
  groundwater, or
• even E. coli contamination

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Feedlot in Vegreville, AB

• Biogas Facilities
• 1. Sand/dirt removed in hopper
• 2. CH4 produced anaerobically in digestor
• CH4 piped to cogeneration system, producing heat
  and electricity
• Mixture separated into solid and liquid
• Lime added to liquid to remove phosphates and
  nitrogen for fertilizer

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Biogas reservoir bag for electric power
Generation, Valle del Cauca, Colombia (near
Cali)
http//www.ias.unu.edu/proceedings/icibs/ic-mfa/ch
ara/paper.htm
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Feedlot and Ethanol Plant Lanigan, SK
Starch alpha-amylase enzyme ? sugars Sugars
yeast ? ethanol carbon dioxide
http//www.pound-maker.ca/ethanol.htm
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Storage, Treatment and Management of Animal
Manures Integrated Animal Production Animals
spread manure while grazing Manure from confined
animals hauled onto field Supplementation from
inorganic fertilizer usually required Large
Confinement Systems Daily spreading may be
impractical, so storage required (i) Open-lot
storage (but much N lost via ammonia
volatilization, or rainfall runoff) (ii) Lagoons
(need clay liner to prevent leakage to
groundwater) (iii) Aerobic digestion with biogas
production (slurry still contains most
nutrients) (iv) Heat-dry and pelletize for
fertilizer production (v) Commercial composting
(reduces leaching and runoff losses, but is
labour-intensive See section 12.10 - optional )
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• Industrial and Municipal By-products
• Organic wastes for land application
• Municipal garbage
• After removal of inorganic materials (glass
  metals) municipal solid
• waste can be mixed with sewage sludge or poultry
  manure and spread
• over agricultural land
• Relatively low nutrient content
• (ii) Sewage effluents and sludges (biosolids)
• Wastewater treatment removes pathogens,
  oxygen-demanding organic
• debris and most organic and inorganic pollutants
• Must dispose of sewage sludge (material removed)
• Agroecosystems receive and use P and N,
  preventing eutrophication
• Monitoring required to prevent heavy metal
  contamination
• Nutrient contents are low compared to inorganic
  fertilizers

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• (iii) Food-processing wastes
• Small-scale pollution mitigation technique (low
  nutrient content)
• (iv) Lumber industry wastes
• High-lignin mulches produced (sawdust, wood
  chips, bark)
• Decay slowly
• Low nutrient content problematic

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• Inorganic Commercial Fertilizers
• Dramatic increase in fertilizer use in latter
  1900s
• Now required to feed larger human population
• More required in humid areas or where farming is
  intensive
• Nitrogen
• Fixed under very high temperatures and pressures
  to produce
• ammonia gas.
• Liquified under moderate pressure to anhydrous
  ammonia
• and added to fertilizers
• Produced in Alberta (eg. Agrium)
• Phosphorus
• From apatite (phosphate rock deposits)
• Extremely insoluble, so must be treated with
  sulphuric,
• phosphoric or nitric acid, to produce available
  forms

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Potassium From beds of solid salts (mined and
then purified) Canada is the worlds largest
potash producer

• Physical Forms of Inorganic Fertilizer
• Dry solids (usually in bulk form)
• Liquid (stored, transported and applied from
  tanks)
• Fertilizer Grade
• Three number code (eg. 10-5-10 or 6-24-24)
• Indicates (i) total N content
• (ii) available phosphoric acid content (P2O5)
• (iii) soluble potash content (K2O)
• Limited utility Plants do not take up P2O5 or
  K2O and
• no fertilizer contains these chemicals (these are
  the oxides
• formed upon heating). Also no indication of N
  form.

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• Limiting factor concept
• Plant production can be no greater than the level
  allowed by
• the growth factor present in the lowest amount
  relative to the
• optimum amount for that factor
• Examples
• Temperature Phosphorus PPFD
• Nitrogen Water Supply
• Timing of Fertilizer Application
• Availability when plants need it
• Small starter application at planting time
• Again 4-6 weeks after planting, when plant
  uptake peaks
• Slow-release fertilizers must be applied
  earlier so that
• mineralization is complete
• (ii) Avoid excess availability outside of plant
  uptake period

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(iii) Physiologically-appropriate timing is
important Examples High late-season N may
reduce sugar content of crop High N and P too
early may lead to lodging High P too early may
encourage fast-growing weeds more than tree
seedlings (iv) Practical Field Limitations It
is not always possible to apply fertilizer at the
appropriate time Plants may be too tall to drive
over without damaging them (Flight is an
alternative) It is important not to compact wet
soils Economic costs can be prohibitive at
certain times of the year Time-demands of other
activities may limit options
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GPS-Assisted Soil Sampling and Variable-Rate
Fertilizer Application
Goal Maximize profit by only applying the
necessary amount of fertilizer at any given
point
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Soil Erosion and its Control
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Much more erosion if natural vegetation
is destroyed by plowing
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Soil aggregates destroyed at surface by
rainsplashes, encouraging sheet and interill
erosion
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Relatively uniform erosion over entire soil
surface
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Water concentrates in small channels
Tillage can erase rills, but cannot replace
the lost soil
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Appears catastrophic, but more soil is
lost through sheet or rill erosion
Deep channels cannot be erased by cultivation
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In contour-strip farming, the ridges must be high
enough to hold back water from heavy rainfall
events
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Grassed waterways to prevent gully
erosion, Kentucky, USA
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Terraced farming, SW China
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More terraced farming in SW China
Photo Credit A Letts Christine Xu
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Disk chisel tillage
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Disk chisel
Moldboard plowing
(b)
(a)
(c)
No-till farming
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Wind Erosion
Finer particles move in suspension, medium-sized
particles bounce along soil surface, entrained by
saltation.
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Shelterbelts
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Soil Chemical Contamination and Remediation
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• Toxic Organic Chemicals
• Released from plastics, plasticizers, lubricants,
• refrigerants, fuels, solvents, pesticides
• and preservatives
• Xenobiotics are often toxic to living organisms
  and
• resistant to biological decay
• Compounds are often very similar to natural
  organic
• compounds
• insertion of halogen atoms (Cl, F Br)
• insertion of multivalent nonmetals (N and S)

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• Soil toxins may
• kill or inhibit soil organisms
• be transported to air, water or vegetation
• Sources of soil toxins
• industrial and municipal organic wastes
• discarded machinery
• fuel and lubricant leaks
• military explosives
• pesticides

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• Pesticides
• Pesticides are chemicals designed to kill pests
• Quantity applied is decreasing
• Potency is increasing
• Herbicides are designed to kill weeds (plant
• pests)
• Benefits
• Pesticides provide mosquito control (malaria)
• Protection of crops and livestock against insects
• (increases agricultural productivity)
• Reduction of food spoilage during transport
• Herbicides facilitate conservation tillage

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• Problems with pesticides and herbicides
• Contamination of surface and groundwater
• Negative effects on microbial faunal
  communities
• May remove natural enemies of pest
  species(rendering its use less effective)
• Some fungicides cure fungal diseases, but also
  kill
• mychorrizal fungi
• Sometimes it takes some time to determine that a
• particular product is harmful to humans or
  wildlife (DDT)
• A small proportion of chemical applied reaches
• target (terminates on plant, in air and in soil)
• Desirable pesticide characteristics
• 1. Low toxicity to humans and wildlife
• 2. Low soil mobility
• 3. Low persistence

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• Types of pesticides
• Insecticides
• Fungicides
• Herbicides
• (weed killers)
• Rodenticides
• Nematocides

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Insecticides

• Chlorinated hydrocarbons (eg. DDT) until 1970s
• (banned due to persistence and toxicity)
• Organophosphates easily biodegradable but
• very toxic to humans
• Carbamates low mammalian toxicity and
• readily biodegradable

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• Herbicides
• Generally exhibit lower mammalian toxicity
• (plants targetted)
• Deleterious effects
• on aquatic vegetation
• (plants that provide
• habitat for fish
• shellfish)
• Variety of options
• available

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• Non-target effects
• Biomagnification up the trophic level chain
• Disruption of human endocrine balance by
• traces of pesticides

• Alternatives to pesticides herbicides
• Organic farming
• Crop diversification (reduces insect/weed
  infestation)
• Provision of habitat for beneficial insects
• Organic soil amendments (reduces weeds)
• Pest-resistant plant cultivars

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Industrial Organics
Contaminate soils by accident or
neglect Gasoline benzene, polycyclic aromatic
hydrocarbonsSolvents trichloroethylene Explosive
s trinitrotoluene (TNT) Lubricants, hydraulic
fluids transformer insulators and epoxy paints
PCBs causes cancer and hormone effects in
humans and disrupts reproduction in birds
extremely resistant to decay
Examples of industrial contaminants
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Abandoned wood-preserving facility in Michigan,
USA Contaminants In wood- preservers polycycl
ic aromatic hydrocarbons (PAHs),
chlorophenols, dioxins, furans and arsenic
(inorganic)
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Bioremediation of wood-preservative contaminated
soil using white rot fungi in North Carolina.
Chemicals of concern include pentachlorophenol
and lindane
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PCB and dioxin- containing soils covered with
tarp at a superfund clean-up site, Michigan, USA
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• Where do inorganic pollutants go?
• Several possibilities
• Vaporize into the atmosphere
• Absorbed by soils
• Percolate and leach through soil
• React chemically within soil
• Broken down by microorganisms
• Wash into streams through surface runoff
• Absorbed by plants animals, becoming part of
  food chain

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• Soil remediation following organic
• chemical contamination
• 1. Physical and chemical methods
• Ex situ treatment
• Remove soil and incinerate (high temperature
  chemical
• decomposition)
• Remove soil and apply vacuum extraction or
  leaching
• The treated soil is destroyed
• In situ treatment
• Removal by injection of surfactant (later pumped
  out)
• Water flushing, leaching, vacuum extraction,
  heating (similar to
• ex situ treatment)

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• Organoclays
• Surfactants such as quaternary ammonium compounds
• Can replace metal cations on soil clays
• Clays then attract instead of repel nonpolar
  organic compounds
• Soil contaminants are immobilized, increasing the
  likelihood
• of decomposition before uptake by a plant or
  animal
• Bioremediation
• Enhanced plant and microbial action degrades
  organic
• contaminants into harmless products
• Natural bacteria or bioaugmentation employed
• In situ or ex situ treatment with bacteria works
  on PAHs,
• pentachlorophenol and trichloroethylene
• Biostimulation
• Enhance naturally-occurring microbial populations
  with
• fertilization (sometimes combined with a
  surfactant)
• Can inoculate soils with more effective microbes

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• Phytoremediation
• Plant roots take up pollutants from the soil
• Hyperaccumulation
• Hyperaccumulating plants tolerate high
  contamination levels
• The toxin is removed through harvesting
• (ii) Enhanced rhizosphere phytoremediation
• Plant roots excrete compounds that stimulate the
  growth
• of rhizosphere bacteria that degrade the organic
  contaminant
• Transpiration by the plant causes
  contaminant-laden
• soil water to move toward the plant roots, where
  rhizosphere
• reactions take place
• Phytoremediation is suitable where large areas of
  soil are only
• moderately-contaminated. It is often
  time-consuming.

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Sorbed or Complexed Chemicals Some organic
chemical pollutants are complexed with
soil organic matter or sorbed by inorganic
materials It is very difficult to bioremediate
soils with high complexation or trapping of
pollutants within internal structural layers of
clays However, such pollutants are rather
immobile and are unlikely to cause significant
environmental harm
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Some pollutants become trapped, so that they are
virtually unaffected by microbes (isolated from
living cells and their enzymes)
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Salts from coal bed methane production Water
used to apply pressure becomes high in
sodium Salts can slowly accumulate in the root
zone Impairs aggregation and reduces
hydraulic conductivity Increases
osmotic Potential Can be washed
from well-drained soils with limited success
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Toxic Inorganic Substances Mercury Cadmium Molybd
enum Fluorine Boron Lead Arsenic Manganese Zinc
Nickel Copper Selenium Chromium
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Elimination of inorganic chemicals 1. Reduce
application of toxins 2. Immobilization Maintai
n pH above 6.5 Drain wet soils (oxidized forms
are usually less soluble) Heavy phosphate
application (reduces availability) 3. Removal by
chemical, physical or biological
remediation Hyperaccumulating
plants Chelating compounds can solubilize lead
(used in combination with hyperaccumulators)
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Landfills
1. Natural attenuation landfill
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2. Containment-type landfill
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Global Soil Quality and Human Activities