A Healthy Soil A Biologically Active Soil

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A Healthy Soil A Biologically Active Soil

• Fran Walley
• Department of Soil Science
• U of S

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What is Soil?

• Highly complex mixture of geological materials,
  dead organic matter, living roots, animals and
  microbes, soil water, and soil atmosphere
• Soil provides the physical and chemical
  conditions necessary for plant life, thus animal
  and microbial life
• Kimmons, 1997

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A dynamic system
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A dynamic system
CO2
CO2
NO3
SO4
Bacteria
P2O4
Microbes
SO4
NO3
Fungi
NH4
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Soil and Sustainability

• Sustainability is the use of resources, human,
  natural and man-made, in ways that allow current
  generations to satisfy their needs without
  jeopardising the capacity of future generations
  to meet theirs (OECD, 2001)

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What is Soil Health?

• Depends on your view of soil function

• Supports plant growth
• Seed germination and root growth
• Nutrient and water supply

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Soil Functions

• Regulates and partitions water flow
• Receives, stores and releases moisture

by permission Saskatchewan Interactive
http//interactive.usask.ca/ski/index.html
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Environmental Buffer Phytoremediation
University of Saskatchewan Phytoremediation Team
(19 Aug 2003)
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Additional Functions?
Sequesters Carbon (CO2)
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Organic Matter is the Key to Soil Health!

• OM is a substrate (C and energy source) for
  microbes
• Reserve of N, S, P
• Retains C from the atmosphere
• Retains nutrients by providing cation- and
  anion-exchange capacities

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• Organic matter an effective soil glue and
  promotes aggregation
• Resists erosion
• Reduces crusting
• Maintains soil in an uncompacted condition with
  lower bulk density
• Improves porosity which facilitates air and
  water movement in soil

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• Reduces negative environmental effects of
  herbicides and other pesticides
• Can tie-up various heavy metals
• Supports microbial degraders

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Effects of Cultivation on SOM

• Loss of organic matter
• Reduced by 15 to 30 since cultivation
• On eroded soils, losses up to 90
• Most loss occurs within 10 years of cultivation

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Effects of Cultivation on SOM
Reduced yields
Increased decomposition
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Soil Structural Damage

• aggregate breakdown
• changes in pore space and size
• affects air and water movement
• affects infiltration rate, runoff, erosion

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Solberg/Cochran et al. 2003 http//www.sidney.ars
.usda.gov/
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Cultivation and Soil Erosion
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Cultivation and Salinization

• Changes in hydrologic cycle (clearing trees,
  summerfallow)
• More water moving through the soils, carrying
  dissolved salts and nutrients into depressions
  and groundwater
• Leaky system

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1991 census data 41 of cultivated land in SK
at risk of increasing salinization
Saskatchewan Interactive http//interactive.usask.
ca/ski/index.html
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Important observation..these soil properties
(i.e., properties sensitive to management) can be
useful indicators of soil quality
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What are some key indicators of soil quality?

• Visual
• Physical
• Chemical
• Biological

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Visual

• Aerial photographs
• subsoil exposure, gully formation, salinization,
  etc.
• provides evidence of changes that might threaten
  soil quality
• Pictures dont lie but an inaccurate
  interpretation might

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Physical Indicators

• Soil texture
• Topsoil depth
• Bulk density, compaction
• Porosity, aggregate stability

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Chemical Indicators

• Organic matter
• pH, salinity
• Cation exchange capacity
• Nutrient levels
• Nutrient supply potential (nutrient cycling)
  e.g., Amino sugar N
• Levels of contaminants

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Biological Indicators

• Micro- and macro-organisms
• Activity (respiration)
• Biomass
• Related by-products (including glomalin,
  ergosterol) and enzymes

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Which Indicators Should Be Used?

• No single property tells the entire tale
• The challenge is to identify a suite of
  indicators that are sensitive enough to detect a
  meaningful change in soil quality
• Time-frame typically 1- to 10-yrs (i.e., changes
  occur and managers can react)
• Depends on land use, goals

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Good Indicators..

• Easy to measure
• Sensitive to changes in management, etc.
• Assessed using inexpensive and user-friendly
  measurements
• Relatively rapid measurements available

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Nutrient Availability Often Equated with Soil
Health

• Common soil tests provide estimates of nutrient
  availability
• Changes in nutrient status may be related to the
  size and activity of the SOM
• Highly dynamic nutrient pools (i.e., soil N) may
  be misleading because soil test is only a
  snapshot

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Dead Org. N
Active
Stabilized
Old
Nitrification
Mineralization
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N mineralization depends on the activity of soil
microbes...
....and the size of the organic N pool
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Conventional Till
No Till
Stabilized
Old
(Liang et al. 2004)
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Summary

• Soil quality is in the eye of the beholder
• Any measure of soil quality should tell us
  something about a desired function (something we
  value)
• Useful soil quality measures are responsive to
  management changes
• Soil quality better described by a suite of
  measures than a single measure

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Thank you