Nutrient cycles become unbalanced through: Harvest of crops or timber - PowerPoint PPT Presentation

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Nutrient cycles become unbalanced through: Harvest of crops or timber

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  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 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

  4. Treed riparian buffer along tributary near Lake Erie, Ontario

  5. Riparian Cottonwood Grove, east of Fort Macleod, AB Cattle ranching here


  6. 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

  7. Conservation tillage • Previously called ‘chemical farming’ • Tillage practices leaving at least 30% of surface covered • by 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 worsened • before macropore development.

  8. 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 • Occasionally 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

  9. Leguminous Cover Crops to Supply Nitrogen Vetch, clover or peas Sown after harvest or by airplane while crop still in field 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

  10. 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

  11. 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 • Liquid sent for treatment before use • in irrigation water (strips out ammonia)

  12. Feedlot and Ethanol Plant Lanigan, SK Starch + alpha-amylase enzyme  sugars Sugars + yeast  ethanol + carbon dioxide

  13. 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

  14. 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)

  15. 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 • 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

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

  17. 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

  18. Potassium From beds of solid salts (mined and then purified) Canada is the world’s 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.

  19. 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

  20. (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

  21. GPS-Assisted Soil Sampling and Variable-Rate Fertilizer Application Goal: Maximize profit by only applying the necessary amount of fertilizer at any given point

  22. Soil Erosion and its Control

  23. Much more erosion if natural vegetation is destroyed by plowing

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

  25. Relatively uniform erosion over entire soil surface

  26. Water concentrates in small channels Tillage can erase rills, but cannot replace the lost soil

  27. Appears catastrophic, but more soil is lost through sheet or rill erosion Deep channels cannot be erased by cultivation

  28. In contour-strip farming, the ridges must be high enough to hold back water from heavy rainfall events

  29. Grassed waterways to prevent gully erosion, Kentucky, USA

  30. Terraced farming, SW China

  31. More terraced farming in SW China Photo Credit: A Letts & Christine Xu

  32. Disk chisel tillage

  33. Disk chisel Moldboard plowing (a) (b) (c) No-till farming

  34. Wind Erosion Finer particles move in suspension, medium-sized particles bounce along soil surface, entrained by saltation.

  35. Shelterbelts

  36. Soil Chemical Contamination and Remediation

  37. 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)

  38. 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

  39. 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