laing soil health 2012 d
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Amazon Tour Guide
Soil Health -
the Basis of
Sustainable Agriculture –
Searching for System Stability
Prof. Mark Laing
UKZN, Pietermaritzburg
The books get it wrong -
it is not the plants that matter, nor soil chemistry
or physics !
It is the MICROBES in the leaf litter!
500 pages on
Biological
Processes in the
soil – for
sustainable
agricultural
production
1. Fix key mineral problems first (P, micros, pH & acid sat.)
2. No tillage – none at all
3. No naked soil - ALWAYS keep the soil covered ALWAYS
4. Crop rotations, with critical inter-crops such as black oats, legumes, brassicas
My Assumption - CA is Adopted
What Happens in A Healthy Soil (1) ?
1. Soil basics are correct (chemistry and physics) – pH, macro- and micronutrients present & balanced
2. Plants provide root exudates, & roots & shoots for SOM / SOC, and pores as they degrade
3. The mulch / cover crop preserves moisture, buffers soil temperature and provides nutrients to the microbes, saprophytes
4. Microbes (esp. fungi) feed on plant nutrients, collect minerals (N, P, K) and store them; they produce polymers to make the soil friable (aggregate stability).
What Happens in A Healthy Soil 2
5. Earthworms feed on microbes, recycling and aerating soils, increasing infiltration rates. This fixes the AFP = soil oxygen
6. Moles feed on earthworms, aerating soils, etc.
7. Plants grow better because of the enhanced soil oxygen and water, and recycled nutrients (root function is dependant upon soil oxygen, water and temperature)
8. Bigger root systems, release more root exudates, therefore grow more soil microbes
9. The virtuous soil cycle – soil, plants, microbes, earthworms in a syncronized dance
The Basic Food Web:
NB – the fungi store the nutrients because
they are the largest biomass in the soil
Life in the Soil Soil microbes at the heart of soil health
• 90% of microbes are in top 15 mm of soil (½ inch !!!!!)
• In a healthy soil, aerobes dominate, so oxygen is critical
• They live on root exudates (10% of photosynthesis) & plant residues
Fungi • Long strands (hyphae)
• Can be vast – hundreds of km long, millions of tons
• Can store soil nutrients, buffer uptake & release
• Only organisms to degrade lignin
• Mycorrhizae release polymers creating aggregate stability - friability
Bacteria • Fast acting
• No residual action
• No storage of nutrients
All minerals and nutrients are degraded, recycled by microbes,
worms, etc., and finally stored by Nature’s “banker”, the fungi,
before giving the minerals back to the plants
Fungi are the hidden heart of the Amazon jungle and the vast temperate forests
Leaf litter, where the resources
of the jungle are recycled
Leaf cutter ants
Natural mulch
Tree trunk being recycled Permanent cover, zero tillage
Earthworms
• Feed on microbes and organic particles
• Recycle nutrients
• Make holes in the soil = oxygen and water in
• Deposit polymers – slime, adds to aggregate stability
• Happy Earthworms Require
Leaf litter on soil surface
Oxygen
Water
Microbes
Stable soil temperature
Soil microbes are food for
earthworms, etc.
What Makes for Sick Soils ? Ploughing, discing & rotavation • Chops up fungi and earthworms, no moles
• Short-term mineralization so temporary nutrition boost to crops, but not sustainable
• Bacteria dominate -> minerals lost, leached
• No fungi = no polymers = loss of aggregate structure , so soil cakes = crusting and compaction. Dead soil is like concrete – no polymers
• No pores x compaction = no oxygen, little water infiltration = poor root growth = less food for microbes and earthworms = death spiral
• No oxygen so fungi die, anaerobic bacteria dominate, H2S released, metals black ppt
Naked Soils
•Naked soil temperature = 50-700C !!!!
kills microbes & chases away earthworms
Kills surface feeder roots of crop plants
• Feeder roots are key for uptake of small water quantities
• Feeder roots are key for uptake of topdressing and foliar sprays
Bakes the naked soil into sun-dried pottery • Zero infiltration, zero oxygen, no microbes
• These soils are biologically DEAD
• A problem for field and tree crops
• Chelating effect of glyphosate exacerbates the problem, binds minerals, kills microbes
Naked Soils
Good CA Practices for Now:
1. Fix soil chemistry and physics initially - P, Ca, Mg, Zn, Bo, Mo, acidity,
buffering, compaction, plough pan, etc.
2. No tillage at all subsequently
3. No naked soils
4. Rotation of suitable crops
5. Ideally - use inter-crops to recycle nutrients and build SOM
6. Farmer level - monitor surface feeder roots, earthworms, moles, infiltration rate, soil tilth
7. Measure soil health when we know how
Start with Soil Chemistry
Fix P, pH, acid sat
Build up SOM, soil N
Good Practices for Now:
1. Fix soil chemistry and physics initially - P, Ca, Mg, Zn, Bo, Mo, acidity,
buffering, compaction, plough pan, etc.
2. No tillage at all subsequently
3. No naked soils
4. Rotation of suitable crops
5. Ideally - use inter-crops to recycle nutrients and build SOM
6. Farmer level - monitor surface feeder roots, earthworms, moles, infiltration rate, soil tilth
7. Measure soil health when we know how
Soybean on Brachiaria debris in Brazil
Good Practices for Now:
1. Fix soil chemistry and physics initially - P, Ca, Mg, Zn, Bo, Mo, acidity,
buffering, compaction, plough pan, etc.
2. No tillage at all subsequently
3. No naked soils
4. Rotation of suitable crops
5. Ideally - use inter-crops to recycle nutrients and build SOM
6. Farmer level - monitor surface feeder roots, earthworms, moles, infiltration rate, soil tilth
7. Measure soil health when we know how
150 tons pa Real cover !
Good Practices for Now:
1. Fix soil chemistry and physics initially - P, Ca, Mg, Zn, Bo, Mo, acidity,
buffering, compaction, plough pan, etc.
2. No tillage at all subsequently
3. No naked soils
4. Rotation of suitable crops
5. Ideally - use inter-crops to recycle nutrients and build SOM
6. Farmer level - monitor surface feeder roots, earthworms, moles, infiltration rate, soil tilth
7. Measure soil health when we know how
Mulch is locally produced and killed Production in cold periods (Avena nigra and Vicia vilosa in winter)
Madagascar highlands
Good Practices for Now:
1. Fix soil chemistry and physics initially - P, Ca, Mg, Zn, Bo, Mo, acidity,
buffering, compaction, plough pan, etc.
2. No tillage at all subsequently
3. No naked soils
4. Rotation of suitable crops
5. Ideally - use inter-crops to recycle nutrients and build SOM
6. Farmer level - monitor surface feeder roots, earthworms, moles, infiltration rate, soil tilth
7. Measure soil health when we know how
Good Practices for Now:
1. Fix soil chemistry and physics initially - P, Ca, Mg, Zn, Bo, Mo, acidity,
buffering, compaction, plough pan, etc.
2. No tillage at all subsequently
3. No naked soils
4. Rotation of suitable crops
5. Ideally - use inter-crops to recycle nutrients and build SOM
6. Farmer level - monitor surface feeder roots, earthworms, moles, infiltration rate, soil tilth / aggregate structure
7. Measure soil health when we know how
How to Measure a Health Soil ?
Soil Science parameters first (Cedara, etc.)
Respiration of the soil (e.g. Solvita test kit from Madumbi) but needs fresh samples
Microbes in the soil
• Most cannot be cultured
• Diversity & Ratios – fungi to bacteria
• DNA studies ? Expensive, slow, complex
NIR spectroscopy
• Quick, cheap, reliable if calibrated properly
• Measures organic molecules, e.g., the soil polymers from fungi and earthworms
Who is going to do this work ? Soil scientists stick to chemistry and physics
and perhaps SOC
Soil microbiologists do not engage with agriculture
Agronomists do not engage with soil microbes
Meta-disciplinary perspective needed
Research Needs:
• Funding and students;
• NIR; DGGE – already available
• Soil samples with soil health ratings; rapid analysis needed
Source of funds ? (PhD student bursary & expenses= R120,000 x 3-4 years)
The most productive, diverse, yet
stable ecosystem on Earth,
despite poor soils
34
Complex Systems Stability in Intensive Agriculture – the future depends upon it
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