soil quality indicators & plant growth · 2016-05-06 · soil quality indicators & plant...
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Soil quality indicators & plant growth
Oene Oenema
Wageningen University
Plant-soil interaction discussion, Wageningen, 20 April 2016
"What chemical and physical soil properties should every
plant ecologist measure as background information for its
experiment, looking at plant growth?”
Before and after the experiment?
Other properties that are basically always important?
What about soil heterogeneity and sample size?
And do we always need to include soil properties in the papers with pot/field experiments?
Defining the quality of soil, water, air
WATER
AIR
SOIL
HUMANS BIOSPHERE
Air and Water Quality
“Water Quality” mainly refers to pollutant concentration;
“Air Quality” mainly refers to pollutant concentration in air
Transboundary effects; hence need for
● Harmonization of standards and critical values
● Harmonization of methods
Soil Quality
Very little harmonization of concepts, methods and standards
Soil is static, and spatial variability
● Horizontally (pedo-climatic zones & small-scale variability),
● Vertically (horizons, influence of bioturbation)
Soil Quality is defined in terms of
● Degree of functioning (over time), qualitatively/quantitatively
● Characteristics (attributes), quantitatively
● Pollutant concentrations, quantitatively
Ideal indicators
Easy measurable, reliable & cheap
Interpretable
correlate well with
● Ecosystem processes and functions
● Soil threats
Sensitive to management
accessible to many users
components of existing databases
Which indictors?
Depends on the purpose of your project
● Research / policy / commercial
● Soil functioning
● Soil threats
Assessing Soil functions
Sustaining plant and animal life (crop productivity)
Regulating / buffering water
Cycling / buffering nutrients
Filtering and buffering potential pollutants
Physical stability and support
http://www.nrcs.usda.gov/wps/portal/nrcs/main/soils/health/
Assessing Soil threats
Soil erosion (water, wind)
Soil compaction (topsoil, subsoil)
Soil organic matter decline
Soil nutrient depletion
Soil salinization
Soil pollution
Landslides
Sealing
Depend on soil type, geography, climate and management
Soil – plant interactions
Plant responses (Y) are a function of species composition (G), environment (E, a combination of Climate and Soil), and Management (M). Hence,
● Y = f(G, E, M), and
● Y = f(G, C, S, M).
Your interest is mainly in Y = f (S) or Y = f(S, M)
(note, there may be interactions)
Yield, kg/ha
Pro
du
ction
situ
atio
n
Actual
Water &
nutrient limited
Potential Defining factors
Crop features
Radiation
Temperature
CO2
Limiting factors
Water
Nutrients
Reducing factors
Weeds
Pest
Diseases
Pollutants
Crop production ecological principles: Y=GxExM
After Van Ittersum and Rabbinge (1997).
Soil factors affecting plant responses
1. Water delivering capacity; limiting yield
2. Nutrient delivering capacity; limiting yield
3. Soil-born pest and diseases; reducing yield
4. Soil-born weeds; reducing yield
5. Seed bed / Workability; reducing (harvestable) yield
6. Pollutants; reducing yield
● Salt-affected soils, aluminium toxicity, nutrient imbalances
● Metals, organic pollutants & pathogens affect food safety
Plant growht controlling soil factors (i)
Significance
+
-
Direct control Indirect control
-Water -Nutrients -Workability -Nematodes -Weed seeds -Pollutants
Soil properties
Management
Weather conditions
Simple set of indicators for plant growth
limiting factors’
Water holding/supplying capacity
● Soil depth/ rooting depth
● Water retention curve
Nutrient delivery capacity
● Soil depth
● Nutrient delivery: Intensity measure
● Nutrient delivery: capacity measure
Simple set of indicators for
‘plant growth reducing factors’
Soil born diseases
● Number and species of nematodes, fungi
Soil born weeds
● Number and species of seeds of weeds
Soil born pollutants
● Extractable salts, metals, pH
Workability
● Slope, Drainage
● Texture / Structure / drainage
Commercial labs offer many tests / indicators
Comparison of labs: physical properties
20
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FAO
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SoilQ
ual
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.org
SoilQ
ual
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.org
.AU
USD
A -
N
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S
Do
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Par
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Kar
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Physical Bulk density x x x x x x
Macro-porosity x x x
Meso-porosity x
Micro-porosity x
Available water capacity, water holding capacity x x x x x
Residual porosity x
Penetration resistance at 10 kPa x
Saturated hydraulic conductivity x
Dry aggregate size (<0.25 mm) x
Dry aggregate size (0.25 - 2 mm) x
Dry aggregate size (2 - 8 mm) x
Wet aggregate stability (0.25 -2 mm) x
Wet aggregate stability (2 - 8 mm) x
Surface hardness with penetrometer x
Subsurface hardness with penetrometer x
Field infiltrability, infiltration x x x x
Soil texture x x x
Soil structure x x x
Soil porosity x
Surface ponding x
Surface crusting and surface cover x x x
Soil erosion (wind/water) x
Aggregate stability x x
Slaking x x
Water logging x
Subsurface compaction x
Erodability, erosion (x)
Drainage (linked with infiltration) (x)
Soil tilth (x)
Sediment deposition (x)
Aggregation x
(Top) Soil depth x x
Comparison of labs: chemical properties
Chemical Phosphorus x x x x
Nitrate nitrogen x x x
Potassium x x x x
pH x x x x x x
Magnesium x
Calcium x
Iron x
Aluminum x
Manganese x
Zinc x
Copper x
Exchangeable acidity x
Soil colour x
Number and colour of soil mottles x
EC x x x x
Nitrogen x x x x
CEC x
Water repellency x
Boron x
Nutrient holding capacity (x)
Salinity (linked with EC) (x)
Hydrophobicity (x)
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SoilQ
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A -
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Do
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Par
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Kar
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Comparison of labs: biological properties
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SoilQ
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Biological Root health assessment x
Beneficial nematode population x
Parasitic nematode population x
Potential mineralizable nitrogen x x x x x
Decomposition rate x
Particulate organic matter x
Active carbon, reactive carbon x x
Weed seed bank x
Microbial respiration rate x x x x
Glomalin x
Organic matter content x x x
Earthworms (number, size) x x x
Potential rooting depth x x
Particulate organic matter x x
Soil enzymes x x
Total organic carbon x x x x
Total organic nitrogen x
Labile carbon x
Microbial biomass (sometimes including C, N) x x x
Root lesion nematode x
Cereal cyst nematode x
Rhizoctonia x
Crop condition (x)
Root mass (x)
Soil smell (x)
Crop residues (x)
Microbiotic crusts (x)
Minimum set of soil indicators (i)?
Site characterization:
• Climate
• Land use (previous and current)
• Morphology & drainage
• Soil type / soil profile / soil depth
Minimum set of soil indicators (ii)?
Soil physical properties (0-25 cm, or 0-10, 10-20, 10-30
• Texture (clay, silt, sand, stones)
• Bulk density
• Water content / water holding capacity
• Soil structure
• Saturated hydraulic conductivity
• Slaking / aggregate stability
Minimum set of soil indicators (iii)?
Soil chemical properties (0-25 cm, or 0-10, 10-20, 10-30
• pH / Exchangeable acidity
• SOM
• Extractable N, P, K
• Mineralization capacity
• EC
• Extractable pollutants
• Extractable secondary and micro nutrients
• CEC / Mineralogy
Sampling strategies
Stratified at random is prefered method for a field
● A minimum of 100 samples per field needed for geostatistical analyses
Bulked sample from a field
● A minimum of 40 samples randomly taken (or in W shape
Bulked sample from a plot in an experiment
● A minimum of 4 samples randomly taken
Which soil depth?
Arable land: ploughing depth (0-25 cm)
Grassland: 0-10 en 10-25 cm
Natural areas: depth stratification depends on soil horizons
Sample size
Some physical properties: undisturbed samples (>100 cm3)
For other properties:
Core size should be > 2 cm
Total sample weight should be > ~100 g
(but for chemical analyses you need very little)
What should be measured at the end of an
experiment?
Depends on your rearch question.
Properties that may have changed during the experiment:
● pH
● Water content
● Extractable nutrients
Questions?
Suggestions?
What is good soil for plant growth?
Good soil tilth
Sufficient depth
Good soil water holding capacity and drainage
Sufficient, but not excessive, nutrient supply
Small population of plant pathogens and insect pests
Large population of beneficial organisms
Low weed pressure
No chemicals, salts or toxins that may harm the crop
Resilience to degradation and unfavorable conditions
Soil quality defined in terms of crop yield & inputs
Cassman 1999 PNAS
Muencheberg Soil Quality Rating
Mueller et al., 2007, 2010
Example of soil quality derived from soil characteristics
Conclusions
Soil quality is elusive concept, probably best defined in terms of crop productivity
Environmental aspects could be captured by crop yield and nutrient use efficiency
Soil indicators must define its purpose;
● Soil quality
● Soil functions
● Soil degradation
● Soil management
Soil indicators should be selected with care, using a Tier approach
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