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