Life in Growing Media: the good, the bad and the ugly? Abstract Life is present or will develop in all growing media: some constituents such as composted bark and green composts may be rich in living organisms; others such as peat may have low populations, whereas inorganic materials such as perlite and mineral wool may be sterile at the point of production. Once planted up, media may be colonised by a rich and diverse array of organisms. Living organisms in media may be benign, such as most saprophytic fungi and bacteria, others such as mycorrhizae may offer positive benefits, and some may be unwelcome due to competition, direct attack by feeding, and production of disease. Weeds may be present in peat bogs, insufficiently composted green and other wastes; they may be absent from coir, bark and processed wood fibre, but present in media prepared from insufficiently composted biodegradable wastes. Insect colonists of media can wreak considerable havoc: among these are the vine weevil and sciarid flies. Microorganisms may cause disease in protected crops, such as the depradations of root attacking Phytophthoras in mineral wool and hydroponic systems, attacks on seedlings and indeed some mature plants by species of Pythium, and the widespread occurrence of various forma speciales of Fusarium oxysporum. Microorganisms may also indirectly affect the performance of growing media by immobilising nitrogen. The sometimes ugly appearance of basidiomycotine fungi arising from media in pots may reduce the market quality of plants. In rare cases growing media may even harbour diseases of human health importance, with legionellosis being one area of current concern. However, living organisms can be harnessed to control diseases and pests, as well as enhancing the performance of media. Mycorrhizal preparations are now widely available for use in growing media. Biological control of insect pests such as vine weevil by fungi and nematodes has proved an astounding success. Control of plant diseases in growing media with preparations of antagonistic fungi is now increasing. Finally, a greater understanding of microbial populations, their identification and significance in growing media is emerging through investigations at the molecular level. These fundamental studies will assist in the identification of saprophytic microflora, evaluation of potential biocontrol agents, identification and quantification of pathogens, both plant and human, in media.

Life in Growing Media

The Good, the Bad and the Ugly( with apologies to Sergio Leone)

Bill Carlile: Bord na Mona

(Horticulture), Main Street,

NEWBRIDGE, Co Kildare

Eire

Gerald Schmilewski.,

Klasmann-Deilmann GmbH

Georg-Klasmann-Str. 2-10

49744 Geeste-Groß Hesepe

Germany

Life in Growing Media: Presentation outline

Introduction Weeds and Pests Microorganisms in growing media constituents Development of microorganisms in growing media

during use

Hydroponics Peat-based growing media Peat-free growing media

Microorganisms of human health importance Detection of microorganisms and microbial activity Manipulation of microorganisms in growing medium

Life in Growing Media: weeds

Rush in peat growing media

Testing peat for weed-free certification

Standard

NS

mediumStandard

Medium +

pine

topping

Standard

Medium +

green

compost

topping

Medium

with

10%

green

compost

Medium

with

30%

green

compost

Medium with

50% green

compost

Liverwort control study: Flannery’s nursery Co Kildare

Life in Growing Media: Liverwort problems

Life in Growing Media: pests

Otiorhynchus sulcatus:

Black vine weevil

Copyright: the naturalgardener.co.uk

Bradysia:

Lycoriella

Sciarid fly/

Fungus gnats

Copyright: UK Horticultural Development Company

Microorganisms and microbial activity in constituents of growing media

0

5

10

15

20

25

30

35

40

45

50

peat pine bark &

chipboard

pine bark &

spruce bark

spruce bark &

chipboard

ug

fo

rma

za

n.g

su

bs

tra

te.h

Dehydrogenase activity in peat and

composted materials

destined for use in growing media.

(from Dickinson, 1995

Plant growth, nutrient status and microbial activity in

peat-free media during storage, PhD thesis,

Nottingham Trent University)

Constituent TVC as cfu.mL bacteria

Peat 2.73 x 103

Coir 1.11 x 106

Composted pine bark

2.00 x 106

Composted spruce bark

1.20 x 106

Data from Johnson,A unpublished

1982)

Total viable counts (bacteria) of

Growing media constituents

Microbial activity in non-peat growing media

constituents

Essential for transformation/removal of readily available C sources

Achieved through composting of bark, green compost, coir

Uptake of simple molecules & degradation and assimilation of easily degraded polymers eg hemicelluloses leads to stable end product that does not readily degrade in pot

Microbial activity in growing media constituents

Composting involves rise in temperatures to 60-70oC

kills off plant pathogens

Degradation of phytotoxic materials eg in bark

Kills of potential human pathogens: coliforms, E.coli, Salmonellae

( takes time: needs investment)

Microbial activity in constituents of growing media

35

40

45

50

55

60

1 2 3 4 5 6 7 8 9 10

Time (weeks)

Tem

pera

ture

o C

Pile-August

Pile-January

Pile-April

0

10

20

30

40

50

60

70

80

1 1 1 1 2 2 3 3 4 5 5 6 8 9 9 10 11 12

Windrow age (week)

Te

mp

(oC

)

16% dairy sludge 8% dairy sludge Inorganic fertiliser

Temperature profiles of windrows

of composted bark (left) and

green compost (below)

Development of microorganisms and microbial activity in growing media: inorganic media

Disease problems in hydroponics/mineral wool: zoosporic pathogens/ Fusarium wilts

Peronosporales: Pythium: Phytophthora spp eg P. cryptogea: P.capsici - rapid spread due to motile spores

Fusarium oxysporum

Control

Irradiation Ozonation Slow sand filtration Antagonists: antimicrobial compounds

Development of microorganisms and microbial activity in growing media: peat substrates

Peat: low microbial count & activity may be seen to be beneficial BUT

After liming & fertilisation of media

little competition if pathogen invades

Pathogens may spread rapidly and devastate crops

Development of microorganisms and microbial activity in growing media: peat substrates

Pythium spp attacking

melons

Development of microorganisms and microbial activity in growing media: saprophytes in peat substrates

Leucocoprinus birnbaumii

Peziza ostracoderma Lepista flaccida

Microbial activity in growing media: peat substrates: shrinkage

0

5

10

15

20

25

30

H6 (Irish) H5 (Irish) H3

(Lithuania)

H2 (Finland)

Sh

rin

kag

e (

mm

)

Data from Aendekerk,T (2001). Decomposition of peat substrates in relation to

physical properties and growth of Skimmia. Acta Horticulturae, 548, 261-268.

Shrinkage of various peats in pots

without plants over 42 weeks

Values linked by the same letter do not significantly differ (Duncan’s

multiple range test p=0.05)

c

b

aa

Microbial activity in growing media: peat substrates: N transformation (Organic N - NH4 – NO3)

5

5.2

5.4

5.6

5.8

6

6.2

6.4

1 2 3 4 5 6

Time (months)

pH

0

5

10

15

20

25

30

35

40

45

50

Am

mo

nia

ca

l-N

(m

g.l

)

pH

Ammoniacal-N

Changes of pH, and ammoniacal nitrogen concentrations in stored peat media. Data from Turner C.P. (1983) Nutrition, salinity and growth of lettuce in blocking media. PhD thesis Trent Polytechnic

0

50

100

150

200

250

300

350

400

0 1 2 3 4 5 6 7 8 9

Storage period (weeks)

Nit

rate

-N (

mg

.l m

ed

ium

)

0

50

100

150

200

250

300

350

Am

mo

niu

m-N

(m

g.l

med

ium

)

Nitrate-N

Ammonium-N

Release of ammoniacal and nitrate-nitrogen during storage of peat media containing hoof & horn fertiliser. Data of

Bunt and Adams from Bunt,A.C.(1976) Modern Potting Composts

Microbial activity in growing media: peat-reduced and peat-free substrates: N immobilisation

A major problem in substrates with low lignin, high cellulose and high hemicellulose content

Bark, wood fibre….paper

Microorganisms can degrade carbohydrate polymers as C sources

N sources- primarily nitrogen added to growing media

N uptake by microorganisms: immobilisation: little or no N for plant uptake: yellowing/stunting

Microbial activity in growing media: peat-reduced and peat-free substrates: N immobilisation

0

20

40

60

80

100

120

1 2 3 4 5 6

Storage period (months)

Nit

rate

-N m

g.L

0

10

20

30

40

50

60

70

Am

mo

niu

m-N

mg

.L

Nitrate-N

Ammonium-N

Rapid immobilisation of nitrogen in a bark-based growing medium

from Dickinson, 1995 Plant growth, nutrient status and microbial activity in peat-free

media during storage, PhD thesis, Nottingham Trent University

Microbial activity in growing media: peat-reduced and peat-free substrates: N immobilisation: consequences

pH EC

µs.cm2

NH4-N

(mg.L)

NO3-N

(mg.L)

P

(mg.L)

K

(mg.L)

7.4 719 0 4 24 747

N immobilisation: solutions involving microbial activity*?

(Add CRF for professional peat media)

(Add extra N)

*Add a source of organic N: hoof & horn: feather meal: chipboard waste

0

50

100

150

200

250

300

350

400

0 2 4 6

Months of storage

Nit

rate

-N m

g.L

0

10

20

30

40

50

60

70

80

Am

mo

niu

m-N

mg

.L

Nitrate-N

Ammonium-N

N from these organic

sources is released by

microbial action &

then mineralised

Release of nitrogen in a medium containing

composted bark and chipboard waste

Data from Dickinson, K.1995 Plant growth, nutrient status and

microbial activity in peat-free media during storage,

PhD thesis, Nottingham Trent University

Microbial activity in peat reduced /peat-free media: shrinkage

0

10

20

30

40

50

60

H5 0-3 H5 5-10 H4 0-3 H4 5-10 H2 0-3 H2 5-10 Hort Cult

Substrate

Perc

en

tag

e s

hri

nkag

e

Data from Prasad & O’Shea (1997): Relative breakdown of peat and non-peat growing media.

Acta Horticulturae, 481, 121-128.

Shrinkage of peats and wood fibre over 18 months

Microbial activity in growing media: peat-reduced and peat-free substrates: saprophytes

Microorganisms of Human Health Importance in Growing Media

Figure 4. Survival of Escherichia coli and Salmonella

typhimurium in an unsterilised peat-based medium

2

3

4

5

6

7

8

0 7 14 21 28

Incubation period (days)

log

cfu

ml-

1 m

ed

ium E.coli

S. typhimurium

Figure 5. Survival of Escherichia coli and Salmonella

typhimurium in an unsterilised peat-free medium

2

3

4

5

6

7

8

0 7 14 21 28

Incubation period (days)

log

cfu

ml-

1 m

ed

ium

E.coli

S. typhimurium

Figure 6. Survival of Legionella pneumophila in sterilised and

unsterilised samples of peat-free growing medium

3

4

5

6

7

8

9

0 1 2 3 4 5 6

Incubation period (weeks)

log

10

cfu

ml m

ed

ium L.pneumophila

in sterilised

peat-free

medium

L.pneumophila

in un sterilised

peat-free

medium

Survival of potential human pathogens

in deliberately inoculated media

From Carlile,W.R. & Hammonds, S.J. (2008)

Microorganisms of human health importance

In growing media. Acta Horticulturae, 779, 67-73

Detection of microorganisms in growing media

Agar plate

Enrichment of selected organisms

ELISA

Nucleic acid techniques: PCR

Data from Dickinson, K.1995 Plant growth, nutrient status and microbial

activity in peat-free media during storage,

PhD thesis, Nottingham Trent University

Detection of microbial activity in growing media

CO2 evolution

O2 consumption (Oxitop®)

Fumigation-incubation

ATP determination

Enzyme activities: dehydrogenase

Control of black vine weevil

(Otiorhynchus sulcatus) by Metarhizium

anisopliae in cyclamen.

Untreated controlMetarhizium treated cyclamen

Life in Growing Media: Biocontrol: insect control

( with thanks to Tariq Butt and Munoo Prasad)

Efficacy of M. anisopliae and imidacloprid for control of

BVW larvae in polyanthus.

0

10

20

30

40

50

60

70

80

90

100

Control Drench Premixed Chemical

Treatments

% C

on

tro

l o

f la

rv

ae

Each pot inoculated with 15 melanized BVW eggs 2 weeks after seedling

transplantation. Plants destructively assessed for number of live larvae per pot 4

weeks post inoculation.

( with thanks to Tariq Butt and Munoo Prasad)

Life in Growing Media: Biocontrol

Life in Growing Media: Mycorrhizae

Endo/Ectomycorrhizae

Assist in P uptake in soil

In optimally fertilised growing

Media, generally little effect

On plant yield & quality

Beneficial where plants are

Moved to soil

Nursery stock: some vegetable

Transplants

Image courtesy; Claude Samson, Premiertech Biotech

Life in Growing Media: disease suppression

Suppressive activity usually associated with antagonistic microorganisms

Easy to detect in culture: inhibition of growth on agar plates

Less easy to demonstrate in vivo

Extensive research with composted materials

Some antagonistic microorganisms used in disease control: B. subtilis

Death in growing media?