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Soil Quality

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Soil Quality Keith R. Baldwin NC A&T State University Soil Quality the capacity of a specific kind of soil to function within natural or ecosystem boundaries, to ... – PowerPoint PPT presentation

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Title: Soil Quality


1
Soil Quality
  • Keith R. Baldwin
  • NC AT State University

2
Soil Quality
  • the capacity of a specific kind of soil to
    function within natural or ecosystem boundaries,
    to sustain plant and animal productivity, to
    maintain or enhance water and air quality, and to
    support human health and habitation (Doran et
    al., 1996).

3
Soil Health
  • This term is preferred by many farmers because it
    provides a direct value judgment of the soil
    resource.

4
Soil Health
  • It also clearly portrays the idea of soil as a
    living, dynamic organism that functions in a
    holistic way depending on its condition or state
    rather than an inanimate object whose value
    depends on its innate characteristics and
    intended use (Romig et al., 1995).

5
Ecosystem Functions
  • Retain and release nutrients and other chemical
    constituents
  • Partition rainfall at the soil surface into
    runoff and infiltration
  • Hold and release soil water to plants, streams,
    and groundwater
  • Resist wind and water erosion
  • Buffer against the concentration of potentially
    toxic materials

6
A High Quality Soil
  • Reflects an optimum environment for root growth,
    thereby enhancing crop health and productivity.
  • Optimum root growth however, will be tempered by
    plant species, the genetic potential of the
    plant, the environmental conditions imposed by
    weather, and cultural practices used in
    production.

7
Interactions
  • Soil physical properties
  • Soil chemical properties
  • Soil microbiological properties

8
Minimum Data Set
  • Measurement of soil quality requires
    identification of specific parameters, or
    indicators that can be quantitatively measured
    over time and compared to reference conditions or
    judged against some common standards.

9
Interpretation
  • How much change is needed for that change to be
    meaningful?
  • Have random or localized changes in field
    conditions at any particular point in time
    influenced indicator values?

10
Trend Changes
  • Improvements to (or degradation of) soil quality
    can perhaps best be visualized as trend changes
    that point in a positive (or negative) general
    direction over the years.

11
Qualitative vs. Quantitative
  • Qualitative or descriptive indicators typically
    represent opinions or short term changes.
  • Qualitative changes can be assessed using the
    NRCS Soil Quality Indicator Table.
  • Quantitative changes can be assessed using the
    USDA Soil Quality Kit.

12
Field Variation
  • It is important to keep in mind that localized
    and/or random changes in field conditions at any
    particular point in time can influence indicator
    values.

13
How Much Change Matters?
  • Soil pH may change fro 5.9 to 6.0, but is this
    meaningful change?
  • A pH change of 0.1 units would not normally be
    enough change to make a difference in crop
    production, whereas, a pH change from 5.0 to 5.8
    over a two-year period certainly would.

14
Trends
  • Improvements to soil quality can be visualized
    as trend changes that point in a general
    direction over the years.
  • The identified changes need to be definitive,
    important, and rapid enough so that management
    can be altered to influence trends.

15
Soil Physical Properties
  • Bulk density
  • Porosity pore-size distribution
  • Aggregate stability
  • Penetration resistance
  • Water holding capacity
  • Soil crusting
  • Infiltration
  • Hydraulic conductivity

16
Soil Structure, Soil Physical Properties, and
Soil Quality
  • Physically speaking, soil quality is determined
    by the structure of the soil.
  • Soil structure is the network in which soil
    particles are arranged.
  • The nature of this network will determine the
    physical properties of soil.

17
Soil Structure, Soil Physical Properties, and
Soil Quality
  • Soil structure is dynamic affected by climate,
    biological activity, soil management, etc.
  • There are no direct methods to measure soil
    structure.
  • Soil structure is measured indirectly through
    measurement of soil physical properties.

18
Benefits of Aggregation
  • Available water holding capacity
  • Improved soil structure and tilth
  • Improved infiltration
  • Improved hydraulic conductivity
  • Improved oxygen diffusion

19
Macroaggregates
  • Macroaggregates are more transient than
    microaggregates because their organic binding
    agents, roots and hyphae, are more rapidly
    degradable than the older humified material
    making up some of the mineralorganic complexes
    binding the microaggregates.

20
Soil Chemical Parameters
  • Nutrient Availability
  • Soil pH
  • N mineralization potential
  • P buffering capacity
  • Trace metals and pollutants

21
You Heard This Before?
  • Plant nutrient availability is strongly tied to
    soil acidity (pH).
  • Generally, N, P, and K can only exert a
    significant influence on crop yields if soil pH
    is correct.

22
Importance of Soil Chemistry
  • Soil chemistry influences the plant availability
    of nutrients.
  • Farmers can influence soil chemistry through
    additions of fertilizers, incorporation of cover
    crops, and use of other organic materials.

23
Soil Biological Parameters
  • Soil organic matter
  • Microbial respiration
  • Microbial biomass
  • Soil organic C
  • Microbial biomass C and N
  • Mineralizable N

24
The Soil Food Web
25
In 1 teaspoon of soil there are
Bacteria 100 million to 1 billion
Fungi 6-9 ft fungal strands put end to end
Protozoa Several thousand flagellates amoeba One to several hundred ciliates
Nematodes 10 to 20 bacterial feeders and a few fungal feeders
Arthropods Up to 100
Earthworms 5 or more
Travis Gugino - PSU
26
Microorganisms
Bacteria
UBC EM facility
Pseudomonas
Arthrobacter
CIMC
Bacillus
Travis Gugino - PSU
27
Microorganisms
Fungi
Aspergillus
Trichoderma
K.J. Kwon-Chung
PSU Em facility
D.C. Straney
Fusarium
Travis Gugino - PSU
28
Nematodes
29
The Microbial Biomass
  • The C contained in microbial biomass ranges from
    1 to 5 of the total organic C in the soil.
  • Being one of the most labile pools of soil
    organic matter, microbial biomass is an important
    reservoir of plant nutrients.
  • Because process rates are strongly dependent on
    the size of microbial populations, quantification
    of total microbial population is important in
    estimating the rates of C turnover.

30
Nutrient Cycling
  • Soil organic carbon, in particular labile organic
    carbon, has an overwhelming effect on soil
    productivity. It is a major soil nutrient
    reservoir. Balance between decay and renewal
    processes (nutrient dynamics) in this pool
    controls nutrient availability.

31
Diversity promotes stability
Abundance alone cannot explain impacts of soil
organisms on soil quality
32
Southern Conditions
  • The need for crop residues-manures and
    conservation tillage practices to sustain SOC and
    consequently effect changes in soil quality is
    greater for warmer more humid climates.
  • In Georgia, 12 Mg ha-1 crop residues left to
    decompose on the soil surface were required to
    sustain soil quality commensurate with the
    inherent soil and climatic resources.

33
Old Rotation 107 years
  • Continuous cotton with 0 N, 134 kg N, and crimson
    clover or vetch 16 without N
  • 2-yr cotton corn rotation with winter legume and
    winter legume with 134 kg N 160 w/ legume and
    188 w/leg. N
  • 3-yr cotton-winter legume-corn-winter
    cereal-soybean 203

34
Old Rotation 107 years
  • SOC was substantially reduced under continuous
    cotton in the absence of legumes or N.
  • A winter legume cover crop greatly increased SOC
    compared to cotton with or without N.
  • Rotations with N increased biomass and C inputs
    and further increased SOC.

35
Old Rotation 107 years
  • In this highly weathered soil, the 3-yr rotation,
    with copious residue addition to soil, resulted
    in the lowest bulk density, penetration
    resistance, and greatest hydraulic conductivity.
  • Importantly, water-stable aggregates also
    increased.

36
Carbon Management Practices
  • Regular applications of compost, manure, and
    other organic materials.
  • Inclusion of cover crops as green manures in
    cropping systems.
  • Rotations that include forage crops.
  • Reductions in tillage.
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