Nutrient cycles become unbalanced through:

1. Harvest of crops or timber2. Leaching and runoff (exacerbated by irrigation)3. Monoculture (simplification)4. Increased demands for rapid plant growth5. Increased animal density

Goal of nutrient management Profitable use of nutrient resources to produce abundant,high quality plant products while maintaining soil quality anddownstream 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

•Grasses and/or trees increase the tortuosity of water pathways•Sediments settle out of slowly moving water•Dissolved nutrients are taken up by are taken up by organicmulch, 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 tramplingMinimum 10 m for slopes of less than 8 degrees

6-60 m

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)

N.B.: Nitrate leaches most when vegetation is bare. Underwet 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

Conservation tillagePreviously called ‘chemical farming’

•Tillage practices leaving at least 30% of surface coveredby plant residues

•Usually reduced runoff volume•Reduces nutrient and sediment load in runoff waters(greatly reduces sediment-associated nutrient loss)

•However, loss of nutrients from leaching may be worsenedbefore macropore development.

Rangeland Nutrient Cycling

•Grass fires move quickly and burn at low temperaturesLess volatilization of nitrogen than forest fires

•Organic matter lost, but nutrients released stimulate new growthOccasionally burnt land is often more productive than landwhere fire is completely controlled

•Grazing stimulates plant production and quality if it isrelatively infrequent and of low intensity

Leguminous Cover Crops to Supply Nitrogen

Vetch, clover or peasSown after harvest or by airplane while crop still in fieldGrowth resumes in spring, with nitrogen fixationCover 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

Nutrient Recycling through Animal Manures

Supplies organic matter and plant nutrients to the soilEnhances crop and animal productionSoil conservation4 kg dry weight manure for each kg of animal liveweight

Much of nitrogen is lost as ammonia or via denitrification whileunderfoot 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

Biogas Facilities

1. Sand/dirt removed in hopper2. CH4 produced anaerobically in digestor3. CH4 piped to cogeneration system,

producing heat and electricity4. Mixture separated into solid and liquid5. Lime added to liquid to remove

phosphates and nitrogen for fertilizer6. Liquid sent for treatment before use

in irrigation water (strips out ammonia)

Feedlot in Vegreville, AB

Feedlot and Ethanol PlantLanigan, SK

Starch + alpha-amylase enzyme sugarsSugars + yeast ethanol + carbon dioxide

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

Storage, Treatment and Management of Animal Manures

Integrated Animal ProductionAnimals spread manure while grazingManure from confined animals hauled onto fieldSupplementation from inorganic fertilizer usually required

Large Confinement SystemsDaily 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 containsmost nutrients)(iv) Heat-dry and pelletize for fertilizer production(v) Commercial composting (reduces leaching and runoff losses,but is labour-intensive)

Industrial and Municipal By-products

Organic wastes for land application

(i) Municipal garbage• After removal of inorganic materials (glass & metals) municipal solidwaste can be mixed with sewage sludge or poultry manure and spreadover agricultural land• Relatively low nutrient content

(ii) Sewage effluents and sludges• 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 wastesSmall-scale pollution mitigation technique

(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 produceammonia gas.•Liquified under moderate pressure to anhydrous ammoniaand 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

PotassiumFrom 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 GradeThree 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 andno fertilizer contains these chemicals (these are the oxides formed upon heating). Also no indication of N form.

Limiting factor conceptPlant production can be no greater than the level allowed bythe growth factor present in the lowest amount relative to theoptimum amount for that factor

Examples: Temperature Phosphorus PPFDNitrogen Water Supply

Timing of Fertilizer Application(i) Availability when plants need it

Small starter application at planting timeAgain 4-6 weeks after planting, when plant uptake peaksSlow-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 cropHigh N and P too early may lead to lodgingHigh P too early may encourage fast-growing weeds more than tree seedlings

(iv) Practical Field LimitationsIt is not always possible to apply fertilizer at the appropriate timePlants may be too tall to drive over without damaging them(Flight is an alternative)It is important not to compact wet soilsEconomic costs can be prohibitive at certain times of the yearTime-demands of other activities may limit options

GPS-Assisted Soil Sampling and Variable-Rate Fertilizer Application

Goal:

Maximizeprofit byonly applyingthe necessaryamount of fertilizer atany given point

Much more erosion ifnatural vegetation isdestroyed by plowing

Soil aggregates destroyed at surface by rainsplashes,encouraging sheet and interill erosion

Relatively uniformerosion over entire soil surface

Water concentratesin small channels

Tillage can erase rills,but cannot replace thelost soil

Deep channelscannot be erasedby cultivation

Appears catastrophic,but more soil is lostthrough sheet orrill erosion

In contour-strip farming, the ridges must be high enoughto hold back water from heavy rainfall events

Grassed waterways toprevent gully erosion,Kentucky, USA

Terraced farming, SW China

More terraced farmingin SW China

Photo Credit: A Letts & Christine Xu

Disk chisel tillage

(c)

(b)(a)

Moldboard plowing Disk chisel

No-till farming

Wind Erosion

Finer particles move in suspension, medium-sized particlesbounce along soil surface, entrained by saltation.

Shelterbelts

Toxic Organic Chemicals

Released from plastics, plasticizers, lubricants,refrigerants, fuels, solvents, pesticidesand preservatives

Xenobiotics are often toxic to living organisms andresistant to biological decay

Compounds are often very similar to natural organiccompounds: • 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 and Herbicides

•Pesticides are chemicals designed to kill pests•Quantity applied is decreasing•Potency is increasing•Herbicides are designed to kill weeds

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 killmychorrizal 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 characteristics1. Low toxicity to humans and wildlife2. Low soil mobility3. Low persistence

Types of pesticides:

•Insecticides

•Fungicides

•Herbicides (weed killers)

•Rodenticides

•Nematocides

•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

Insecticides

Herbicides

•Generally exhibit lower mammalian toxicity(plants targetted)

•Deleterious effects on aquatic vegetation(plants that provide habitat for fish & shellfish)

•Variety of optionsavailable

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

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

Industrial OrganicsContaminate soils by accident or neglectGasoline: benzene, polycyclic aromatic hydrocarbonsSolvents: trichloroethyleneExplosives: 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

Abandonedwood-preservingfacility in Michigan, USA

Contaminants In wood-preservers:

polycyclic aromatic hydrocarbons (PAHs), chlorophenols, dioxins, furans and arsenic (inorganic)

Bioremediation of wood-preservative contaminated soil usingwhite rot fungi in North Carolina. Chemicals of concern include pentachlorophenol and lindane

PCB and dioxin-containing soilscovered with tarp at a superfund clean-upsite, 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 organicchemical contamination1. Physical and chemical methods

Ex situ treatment •Remove soil and incinerate (high temperature chemicaldecomposition)•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 toex 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 likelihoodof 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 rhizospherereactions take place

Phytoremediation is suitable where large areas of soil are onlymoderately-contaminated. It is often time-consuming.

Sorbed or Complexed Chemicals

Some organic chemical pollutants are complexed with soilorganic matter or sorbed by inorganic materials

It is very difficult to bioremediate soils with high complexationor 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 virtuallyunaffected by microbes (isolated from living cells and theirenzymes)

Salts from coal bed methane production

Water used to apply pressure becomeshigh in sodium

Salts can slowly accumulate in the root zone

Impairs aggregationand reduces hydraulicconductivity

Increases osmoticPotential

Can be ‘washed’ fromwell-drained soils with limited success

Toxic Inorganic SubstancesMercury Cadmium Molybdenum Fluorine BoronLead Arsenic Manganese ZincNickel Copper Selenium Chromium

Elimination of inorganic chemicals

1. Reduce application of toxins2. Immobilization

Maintain pH above 6.5Drain wet soils (oxidized forms are usually less soluble)Heavy phosphate application (reduces availability)

3. Removal by chemical, physical orbiological remediationHyperaccumulating plantsChelating compounds can solubilize lead (used incombination with hyperaccumulators)

Landfills

1. Natural attenuation landfill

2. Containment-type landfill