Nutrient cycles become unbalanced through:
1. Harvest of crops or timber
2. Leaching and runoff (exacerbated by irrigation)
3. Monoculture (simplification)
4. Increased demands for rapid plant growth
5. 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
Avoiding the pollution of natural waters
1. 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
Riparian Buffer Strips
Establish or permit growth of dense
vegetation along streambanks or
other water bodies
6-60 m
•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
Treed riparian buffer along tributary near Lake Erie, Ontario
Riparian Cottonwood Grove, east of Fort Macleod, AB
Cattle ranching here
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
(i) Increased infiltration (less overland flow)
(ii) Sediment and nutrients in runoff water
removed (as in buffer strip)
Rye cover crop in Maryland, USA
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.
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.
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
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
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
Hairy vetch on an Ontario farm
Wheat after cotton
Wheat after wheat
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
Feedlot in Vegreville, AB
Biogas Facilities
1. Sand/dirt removed in hopper
2. CH4 produced anaerobically in digestor
3. CH4 piped to cogeneration system,
producing heat and electricity
4. Mixture separated into solid and liquid
5. Lime added to liquid to remove
phosphates and nitrogen for fertilizer
Biogas reservoir bag for electric power
Generation, Valle del Cauca, Colombia
(near Cali)
http://www.ias.unu.edu/proceedings/icibs/ic-mfa/chara/paper.htm
Feedlot and Ethanol Plant
Lanigan, SK
Starch + alpha-amylase enzyme  sugars
Sugars + yeast  ethanol + carbon dioxide
http://www.pound-maker.ca/ethanol.htm
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 )
Industrial and Municipal By-products
Organic wastes for land application
(i) 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
(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
Inorganic Commercial Fertilizers
• Dramatic increase in fertilizer use in latter 1900’s
• 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
Potassium
From beds of solid salts (mined and then purified)
Canada is the world’s largest potash producer
Physical Forms of Inorganic Fertilizer
(i) Dry solids (usually in bulk form)
(ii) 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.
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
Nitrogen
Phosphorus
Water Supply
PPFD
Timing of Fertilizer Application
(i) 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
(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
GPS-Assisted Soil Sampling and
Variable-Rate Fertilizer Application
Goal:
Maximize
profit by
only applying
the necessary
amount of
fertilizer at
any given
point
Much more erosion if
natural vegetation is
destroyed by plowing
Soil aggregates destroyed at surface by rainsplashes,
encouraging sheet and interill erosion
Relatively uniform
erosion over entire
soil surface
Water concentrates
in small channels
Tillage can erase rills,
but cannot replace the
lost soil
Appears catastrophic,
but more soil is lost
through sheet or
rill erosion
Deep channels
cannot be erased
by cultivation
In contour-strip farming, the ridges must be high enough
to hold back water from heavy rainfall events
Grassed waterways to
prevent gully erosion,
Kentucky, USA
Terraced farming, SW China
More terraced farming
in SW China
Photo Credit: A Letts & Christine Xu
Disk chisel tillage
Disk chisel
Moldboard plowing
(a)
(b)
(c)
No-till farming
Wind Erosion
Finer particles move in suspension, medium-sized particles
bounce along soil surface, entrained by saltation.
Shelterbelts
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)
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
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
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
Types of pesticides:
•Insecticides
•Fungicides
•Herbicides
(weed killers)
•Rodenticides
•Nematocides
Insecticides
•Chlorinated hydrocarbons (eg. DDT) until 1970’s
(banned due to persistence and toxicity)
•Organophosphates: easily biodegradable but
very toxic to humans
•Carbamates: low mammalian toxicity and
readily biodegradable
Herbicides
•Generally exhibit lower mammalian toxicity
(plants targetted)
•Deleterious effects
on aquatic vegetation
(plants that provide
habitat for fish &
shellfish)
•Variety of options
available
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
Industrial Organics
Contaminate soils by accident or neglect
Gasoline: benzene, polycyclic aromatic hydrocarbons
Solvents: trichloroethylene
Explosives: trinitrotoluene (TNT)
Lubricants, hydraulic fluids transformer insulators and
epoxy paints: PCB’s – causes cancer and hormone effects
in humans and disrupts reproduction in birds
*extremely resistant to decay*
Examples of
industrial
contaminants
Abandoned
wood-preserving
facility in
Michigan, USA
Contaminants
In woodpreservers:
polycyclic
aromatic
hydrocarbons
(PAHs),
chlorophenols,
dioxins,
furans and
arsenic
(inorganic)
Bioremediation of wood-preservative contaminated soil using
white rot fungi in North Carolina. Chemicals of concern include
pentachlorophenol and lindane
PCB and dioxincontaining soils
covered with
tarp at a
superfund clean-up
site, Michigan, USA
Where do inorganic pollutants go?
Several possibilities
1. Vaporize into the atmosphere
2. Absorbed by soils
3. Percolate and leach through soil
4. React chemically within soil
5. Broken down by microorganisms
6. Wash into streams through surface runoff
7. Absorbed by plants & animals, becoming part of food chain
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)
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
2. 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
Phytoremediation
Plant roots take up pollutants from the soil:
(i) 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.
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
Some pollutants become trapped, so that they are virtually
unaffected by microbes (isolated from living cells and their
enzymes)
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
Toxic Inorganic Substances
Mercury
Lead
Nickel
Cadmium
Arsenic
Copper
Molybdenum
Manganese
Selenium
Fluorine
Zinc
Chromium
Boron
Elimination of inorganic chemicals
1.
2.
Reduce application of toxins
Immobilization
Maintain 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)
Landfills
1. Natural attenuation landfill
2.
Containment-type landfill