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

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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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Comparison of labs: biological properties

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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