Belinda Rawnsley

South Australian Research and Development Institute

(SARDI)

Soil biology

Healthy Soils and Carbon farming workshop June 2012

Introduction

• Why soil biology is important

• Tests to measure soil biology

• How and when to sample

• Improving soil biological health

Soil biology

• Break down organic matter and release nutrients into plant available forms

BAM!

Soil biology

• Break down organic matter and release nutrients into plant available forms

• Suppress soil borne diseases

• Improve and maintain soil structure

Soil biology

• Break down organic matter and release nutrients into plant available forms

• Suppress soil borne diseases

• Improve and maintain soil structure

• Degrade chemicals

• Lock up greenhouse gases in soil

A viable microbial population is essential for soil processes to occur

Soil biology

• Soil organisms change in abundance and

activity due to:

– Temperature

– Moisture

– Plant growth

• Not evenly distributed and occurs in 'hot-

spots' associated with soil organic matter

e.g. decomposing residues, the

rhizosphere and macroaggregates

Soil biological indicators

• Tests designed to measure activity or populations of soil organisms

• Routine soil tests do not measure soil biology

• Wide range of biological indicators to measure effect of soil management

Amount (e.g. microbial biomass, plate counts)

Activity (e.g. soil respiration, enzyme activity)

Diversity (e.g. community composition)

Microbial biomass

• Total population of active microbes in

the soil at the time of sampling

• Influenced by soil properties

• Measured by amount of carbon,

nitrogen, phosphorus and sulphur

• Responds quickly to changes in soil

management

• 1 to 5 % of total organic carbon (source DPIVic).

Microbial biomass and soil carbon

Lower than expected microbial biomass may indicate

a constraint to biological fertility

Source:Soilhealthknowledge.com.au

Seasonal variability of microbial

biomass in vineyards (Barossa Valley, 2009/2010)

0

5

10

15

20

25

30

35

40

Cultivated Biodynamic Permanent

sward

Mulch Grazing

land

To

tal m

icro

bia

l b

iom

ass (

ug

C/g

)

2 Nov 2009

1 Feb 2010

25 March 2010

HIGH

MODERATE

Method: Substrate Induced Respiration (SIR)

Fungi and bacteria

• Measured as a proportion of fungi and

bacteria in soil

• Fungi associated with decomposition and

soil structure stability

• High carbon requirement

• Bacteria regulate nutrient supply e.g.

transform nitrogen into a useable form

• High nitrogen requirement

Nematodes and mycorrhiza

• Beneficial role in the soil

• Free-living (saprophytic)

nematodes feed on bacteria

and fungi

– influence decomposition of

organic matter and nutrient

turnover

• Mycorrhiza fungi grow inside

the root and enhance vine

uptake of Phosphorus

Nematodes

No desired range

– ideal to use

nematode

abundance to

monitor change in

soil management

practice

Higher nematode

bacterial feeders

indicates low OM

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

Conventional

cultivation

Biodynamic Permanent sward Undervine mulch

no

. fr

ee

-liv

ing

ne

ma

tod

es

/20

0 g

so

il

Nov 2009

Feb 2010

Mar 2010

Some providers of soil health tests

Provider Cost Details

CSBP, WA $91 - $121 Microbiology tests, respiration

and direct counts

SWEP, Victoria $245 - $275 Microbiology test, cultural

based

Soil Foodweb, NSW $200 - $1500 Microbiology tests, cultural and

direct counts

Creation Innovation

Agriculture & Forestry,

SA

$50 - $250 Microbiology tests, molecular

based

Typical soil health test data

Total microbial

biomass (TMB) shows

population size of

microbes per g soil

Proportion of

fungi and

bacteria. Fungi % Protozoa,

nematodes

etc.

How to use soil biology tests

• There really are no target values for a

healthy soil in regards to soil biology

• Use tests to monitor changes in soil biology

over time at the same time of year

• Measure soil biology in relation to

management and/or problem areas

• Consider soil type, land use, topography

and plant growth - cannot compare regions

How to sample for soil biological

health

• Majority of organisms in top soil

and in the rootzone

• Bulk to give a representative

sample of the block (composite)

• Separate different areas

• Annuals – Sample planting row and

between the rows (on inter-row

spacing)

• Perennials – Sample in vine/tree row

– Under the drip line within 40 cm of

vine trunk or under tree canopy

Microbial activity at depth

0

20

40

60

80

100

120

140

0-5 5-10 10-20 20-30 30-40

Soil depth (cm)

B-g

luco

sid

ase e

nzym

e a

cti

vit

y

(m

g p

-Nit

rop

hen

ol/

kg

so

il/h

)

Rhizosphere soil

(Rawnsley, 2008)

When to sample

• Perennials – coincide soil sampling with

periods of peak root

growth from flowering to

post-harvest

• Annual crops – after crop harvest or

before seeding in autumn,

but before cultivation

– Sample closer to sowing to

reflect nutritional status

• Avoid directly after

application of soil

amendments or fertilisers

Shoot

growth

Root

growth

Monitor at the same

time of the year

Grapevine growth

Chemical use and soil biology

• Soil biology decompose chemicals and

pesticides – use them as a food source

• Impact of a pesticide depends upon the

rate of degradation

• Minimise use of heavy metals, e.g. copper

Soil Organic Carbon (SOC)

• Changes in soil organic carbon are slow

• Microbial populations change more rapidly

and reflect soil management

Barossa Valley (loam over clay)

Incorporated mulch* 1.8 %

Conventional cultivation 1.0 %

Permanent sward 0.8 %

Biodynamic 0.7 %

*Mulch applied in 2005

Soil organic matter is usually calculated as 1.72 x SOC

How to improve soil biology

• Feed the microbes!

• Organic matter must be continually supplied

How to improve soil biology

• No tillage, stubble retention

• Apply compost

• Use of covercrop and mulch

• Soil additives/amendments

• Use rotations

What about microbial

inoculants?

• If current practices have low microbial

populations, additions of new microbes or

organisms are unlikely to thrive and persist

– increase organic matter

• Products stimulate organisms already in soil

• Manage existing soil biology

• Legume inoculants proven

Soil health tests –

Take home message

• Use soil biological tests in conjunction with chemical and physical analysis

• Monitor soil health over time

– will reflect changes in soil management practices

• Monitor changes within a single block

• Low microbial biomass restrains nutrient

availability…build up soil biology

Acknowledgments

• NRM Board

• Barossa Viticulture Technical Group (BVTG)

• Sponsors of the Geoff Knight Viticulture Innovation Award

– Elders

– GrapeBarossa

– Barossa Grapegrowers’ Vine Selection Society

• Participating grape growers

• Dr Greg Walker (SARDI) for nematode assessment

More web information

• Soil health knowledge bank

Soilhealthknowledge.com.au

• Victorian Resources online >soil health

vro.dpi.vic.gov.au

Soil health factsheets

• soilquality.org.au