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________________________________________________________________________________ Plant Soil Interaction Discussion Group - April 20, 2016 Topic: Soil Quality Indicators Lecturer: Prof. dr. Oene Oenema __________________________________________________________________________________ Notes to go along with the power point presentation

• What chemical and soil physical properties should every plant ecologist measure as

background info?

• Depends what sphere you are looking at:
• Water quality/air quality
• Indicated by the lack of pollutants
• There is importance for standardization of methods, uniform

methodologies, as there are transboundary effects

• Soil quality
• Very little harmonization of concepts
• Soil is static, spatial variability
• Determined in terms of
• Functioning
• Characteristics
• Pollutants
• Ideal indicators are
• Easy to measure/reliable/cheap
• Interpretable – What does it mean? How does this translate?
• Correlative with ecosystem processes and functions
• Sensitive to management
• Accessible to many users- chose methods that others can also use
• Components of an existing database (comparability) – More influence; your data can

be used by others

• Which indicators should we use?
• Depends on purpose of project:
• Research/policy
• Soil functioning
• Soil plant interaction
• Regulating/buffering water
• Nutrient cycling
• Soil threats
• Erosion
• Compaction
• SOM decline
• Salinization
• Pollution

• There are a whole range of purposes, so there is such a wide range of soil

properties out there, but it depends on what the purpose of your research is.

• Plant responses are not only influenced by the soil, but also by their genes, environment and

management: Y = f(G, E, M) Y= f(G, C, S, M)

• Y = plant response
• G = genes
• E = environment
• S= soil
• M = management
• And mind the interactions!!
• Note that
• Soil factors affecting plant responses
• Water and nutrient delivering capacity
• Soil born pests/disease
• Seed bed/workability (structure of the soil)
• There are direct (water, nutrients, workability, nematodes, weed seeds, pollutants) and

indirect soil controls (management, soil properties, weather conditions) of plant growth.

• Which indicators are useful (and which are not)?
• E.g. BLGG AGROXPERTUS (company) measures 37 indicators
• Difficult to interpret so much information- what does it all mean?
• There is no consensus of what to measure in terms of soil physical and chemical properties
• There’s a lot to use, but the question is, what are we doing with the results?
• What would Prof. dr. Oenema do? What is the minimum we should measure and report for
• ur studies?
• Site characteristics (minimum!)
• Climate
• Land use -previous and current. Land use very much effects soil properties- pH,

nutrients, SOM

• Morphology/drainage – slope,
• Soil type /soil profile/soil depth (rootable depth- defines water delivering capacity

by the soil).

• Soil physical properties -
• Texture
• Bulk density
• Water content/water holding capacity
• Soil structure- aggregate stability
• Chemical
• pH/exchangeable acidity when the pH is less than 4 or so
• SOM
• Extractable N, P, K

• Mineralization capacity – how many nutrients are provided through the experiment

through mineralization (especially when experiment is longer than a few weeks).

• Soil from salt area  EC
• If you have reason to believe there are nutrient imbalances, then secondary and

micro nutrients

• Sampling strategies
• Field- stratified at random (min 100 samples) – geostats analysis
• Bulked sample from field (min 40 samples)
• Bulked sample from plot (4 samples from each plot)- depends on plot size
• Depth- depends on where you take your samples (arable, grassland, natural areas), look at

different horizons

• Most nutrients are in the top
• But half of the water is from below plough layer
• Core size- >2 cm, 100 g of soil in order to get a homogenous sample
• What should be measured at the end of the experiment?
• Depends on research question
• Measure what could have changed
• pH
• water content
• extractable nutrients- N, P, K

Questions/Discussions about the presentation Question: What is your opinion on soil life? Is this an important soil quality indicator? Answer: Yes- for sure to look at nematodes and fungi because of the effects on plant health/crop

• yield. There is an increasing interest in biological activity, this is related to the fact that soil is under

pressure, especially in agriculture. How can biology contribute to soil structure, remediate soil compaction? How to measure? Look at fauna for example, earthworms, also CO2 evolution to see microbial activity. Question: Is this [soil life/measuring soil biology] invested in commercially? Answer: Yes- companies will measure nematodes (crop specific), and fungi, as this is important to determine if crop rotation is working. Commercial companies are starting to look into DNA profiles. Currently though, ‘soil life’ is commercially measured through near infrared, using a calibration

• method. But this is very crude. We can measure a lot, but we have to question, how does this relate

to functioning? Summary of discussion groups If you could choose one soil quality indicator, what would it be? Answers from the small groups:

• Soil type -has relation to many other soil properties
• Soil organic matter

• pH- a lot of things are related and steered by pH
• What does a plant need? Nutrients  measure extractable nutrients
• It is hard to choose only one indicator, if you look at one thing, you miss the context

What do we think of prof. dr. Oenema’s list?

• It could also be interesting and insightful to look at the quality of SOM
• Aggregate stability maybe more important, so should be given a higher priority on the list
• Concept of quality is quite a tricky one- quality for what? An indicator should be type specific
• It is also important to measure and report different organic fertilization strategies
• It is a good idea to characterize the soil, if you were working with another soil, results could

be completely different If you had to choose one soil quality indicator, what would it be?

• Prof. dr. Oenema: crop yield is an integrative indicator of soil quality (Cassman, 1999 PNAS)
• Quote of the day: “It is better to be roughly right than precisely wrong”