Jennifer Carson Profile Jennifer grew up spending time on her uncle - - PowerPoint PPT Presentation

Institute of

Agriculture

Jennifer Carson

Profile

Jennifer grew up spending time on her uncle and aunt’s market garden in Spearwood but never considered a career in Agriculture. The possibility was first brought to her attention in first year uni when she saw “Soil Science” on the list of majors right above “Wool Science” and wondered who in earth majored in such obscure

• subjects. Four years later she graduated from the

University of Western Australia with a Bachelor of Science majoring in Soil Biology. During university, Jennifer became interested in the challenge of increasing the sustainability of agriculture and in the possibility that

• rganic farming might offer some solutions to this
• challenge. After university, she worked at Rick and Annie

Dunn’s organic market garden in Perth for 18 months before working as a laboratory assistant at UWA and then travelling overseas. On returning to Perth, Jennifer commenced a PhD at UWA with the Soil Biology Group which she has recently completed.

Institute of

Agriculture

Influence of rock fertilisers on soil microorganisms in an organic pasture

Institute of

Agriculture

Jennifer Carson

Prof Lynette Abbott & Dr Deirdre Gleeson

Institute of

Agriculture

• Introduction:
• Soil microorganisms and rock fertilisers in organic farming
• Evidence that rock fertilisers may influence soil bacteria
• Experiments – Rock fertilisers influence bacteria because of their:
• Composition
• Particle size
• Implications:
• Organic farming – Rock fertilisers can

alter structure of bacterial communities

• Soil biology – Influence of soil minerals
• n bacterial communities underestimated

Outline

Institute of

Agriculture

Microorganisms & rock fertilisers in organic farming

• Microbial processes improve soil fertility, but

uncertain response to management

• Particularly important in organic farming
• Field trials in Australia
• Identify practices that improve soil conditions for

microbial processes – Potential of rock fertilisers

• Rock fertilisers
• Rock phosphate, basalt, mica, lime
• Often poorly effective due to slow dissolution
• Exception – sandy soils with pH<5

Introduction

Institute of

Agriculture

Hypothesise rock fertilisers affect microbial communities due to:

• Effect on plant growth & pH
• Composition
• Particle size

Evidence rock fertilisers affect microorganisms

• Increase biomass & activity when increase plant biomass & soil pH
• In other habitats, composition of minerals affects microbes
• Rock fertilisers can alter particle & pore size distribution, but not linked

to effect on microorganisms

Introduction

Institute of

Agriculture

Composition of rock fertilisers

• Soil is spatial heterogeneous:
• Microbes affected by properties of microhabitats
• Microhabitats differ in mineral composition & size
• Mineral composition affects bacteria in other habitats
• Different minerals colonised by distinct microbial

communities

• Preferential colonisation of minerals containing

nutrients “hotspots” of activity

• Role of soil minerals overlooked
• Microbial community on stones different from soil

“stonesphere”

D

c

Composition

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Agriculture

Hypothesis:

• The microhabitats of different rock fertilisers in soil select distinct

bacterial communities. Experimental design:

• 3 rock fertiliser treatments: mica, basalt and rock phosphate.
• 2 fraction treatments:

rock fertilisers (>1 mm) & soil (<1 mm)

• 3 pasture treatments:
• T. subterraneum (clover),
• L. rigidum (ryegrass)

and unplanted.

Composition

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Agriculture

10cm

With organic Organic matter matter removed

% Composition of soil & rock fertilisers (XRF). P2O5 CaO K2O MgO SiO2 Soil 0.1 99.7 Mica 0.5 1.6 3.9 3.2 73.2 Basalt 0.3 9.5 0.5 5.1 53.7 Rock P 34.7 50.0 0.1 0.3 8.5 Picture mica grains here mica basalt rock phosphate

Composition

Composition of soil & rock fertiliser differed

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Agriculture

• 1. 1-2 mm grains

rock fertilisers added to soil. <1 mm: Soil fraction >1 mm: Rock fertiliser fraction

• 2. Incubate in soil 10 w.
• 4. Total DNA extracted

from fractions & region amplified by PCR. Community structure (composition & relative abundance)

• 3. Sieve

1 mm.

Composition

Microcosm experiment

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Agriculture

Statistics

• PCO (ordination):
• Samples plotted in 2-D space.
• Distance between samples shows difference.
• PERMANOVA
• Permutational multivariate analysis of variance.
• Treatment effects and pairwise comparisons.
• DISTLM (multivariate multiple regression):
• Model variation in bacterial communities using soil properties
• Modelled values for samples can plotted in 2-D space (RDA)

Composition

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Agriculture

Fraction treatments

• Bacterial communities in rock

fertiliser and soil fractions

• Formed separate clusters
• All pairwise comparisons were

significant Microhabitats of rock fertilisers selected bacterial communities with different structure to surrounding soil. Unplanted

• L. rigidum

Mica Basalt Rock phosphate

Composition

Institute of

Agriculture

Unplanted

• L. rigidum

Mica Basalt Rock phosphate

Rock fertiliser fraction

• Bacterial communities in

microhabitats of different rock fertilisers

• Formed separate clusters
• All pairwise comparisons

were significant Microhabitats of mica, basalt & rock phosphate selected bacterial community with distinct structure.

Composition

Institute of

Agriculture

Unplanted

• L. rigidum

Mica Basalt Rock phosphate

Soil fraction

• Bacterial communities in soil with

different rock fertilisers applied

• Formed clusters
• Fewer pairwise comparisons

were significant Applying different rock fertilisers to soil also influenced bacterial community in bulk soil.

Composition

Institute of

Agriculture

Element composition

• Composition of rock fertilisers & soil minerals explained variance in

structure of bacterial communities:

• Unplanted: 44% by P, Mg & Na
• L. rigidum: 35% by P, K & Mg

Bacterial community structure partly determined by nutrient content

• f rock fertilisers and soil minerals.

Composition

Institute of

Agriculture

Implications

• Soil microorganisms in organic farming:
• Rock fertilisers create new microhabitats in soil that select

bacterial communities with distinct structure

• Partly due to their elemental content
• Effect of soil minerals on microorganisms:
• Mineral types in microhabitats may

affect bacterial community structure

• Mineral heterogeneity may contribute

to spatial variation in soil bacteria

Composition

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Agriculture

Particle size & spatial isolation

• Rock fertilisers can alter particle & pore size distribution but not linked

to change in bacterial communities

• Theory predicting texture affects diversity of microbial communities
• When not connected by

water, diversity increases Theory predicts:

• Evidence:
• Texture
• Water content

Particle size

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Agriculture

Hypothesis:

• Texture & water content affect structure and diversity of

bacterial community. Experimental design:

• 2 texture treatments:
• 100% sand & 10% silt+clay
• Ground quartz (<10 μm) so altered

particle size not composition

• 6 water potential treatments:
• Between -15 cm and -55 cm
• Potential so knew size saturated pores

Particle size

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Agriculture

Column experiment

• Soil column connected to water reservoir
• Added 5 cm segments, packing to constant

bulk density

• Soil columns saturated & adjusted to water

potential of -10 cm at column base

• Incubated for 1 w at 25°C.
• Analysed structure & diversity bacterial

communities

56 60 55 50 45 40 35 30 25 20 15 10

Potential (cm)

51 61 68 77 88 102 122 153 204 306

Largest water-filled pores (μm)

Particle size

Institute of

Agriculture

Texture treatments

• Bacterial communities from

different textures:

• Plotted in separate

regions of graph

• All pairwise comparisons

significant

• Bacterial diversity was not

affected by texture Texture affected bacterial communities due to changes in physical properties of soil Supports theory

10% silt+clay 100% sand

35 15 25 15 20 25 45 55 55 40 40

Particle size

10% silt+clay 100% sand

Institute of

Agriculture

35 15 25 15 20 25 30 45 55 55 40

Dry Wet

Water content treatments

• Bacterial communities from

‘wet’ and ‘dry’ soil:

• Plotted in separate

regions of graph

• All pairwise comparisons

significant, except at 56% WFPS

• Bacterial diversity was

higher in dry soil. Water content influences diversity of complex bacterial community in field soil.

40

Particle size

10% silt+clay 100% sand

Institute of

Agriculture

Texture

• Difference in physical properties of soil explained 38% variance in

structure of bacterial communities Silt+clay content 13% Water content 15% Water in pores: 122-153 μm 3.2% 88-102 μm 3.8% 68-77 μm 2.6% Variation in bacterial communities statistically related to changes in physical properties of soil.

Particle size

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Agriculture

Implications

• Soil microorganisms in organic farming:
• Applying rock fertilisers with small particle size may alter the

structure of bacterial communities

• Partly due to their effect on physical properties of soil
• Effect of soil minerals on microorganisms:
• Texture influences bacterial community structure (not only by

altering chemical properties) by altering physical properties

• Texture influences spatial isolation of bacterial communities in

soil

Particle size

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Agriculture

Influence of rock fertilisers

• n soil microorganisms

Implications and future research

• Rock fertilisers have potential to influence soil bacterial communities

Future research examine if changes benefit production

• Nutrient content of rock fertilisers may create “hotspots” of microbial

activity Future research examine if also “hotspot” of nutrient availability

• Rock fertilisers may increase microbial activity by improving physical

conditions in soil