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?