Dear ,
You were a collaborator in a study of soil biology on blueberry farms. A major aim of the
study was to describe how blueberry soils under organic management differ from those managed
by conventional practices. We sampled eight pairs of organic and conventional blueberry fields
that were matched by USDA-NRCS soil series, and as closely as possible, by blueberry cultivar
and field age. Samples were collected in late September or early October of 2008, July, August,
and October of 2009, and June of 2010. Prior to organic transition, all organic fields surveyed
were managed conventionally, i.e., with synthetic fertilizer and pesticide inputs. The organic
fields were certified by a Michigan Department of Agriculture-accredited agency and managed
according to USDA organic standards for 4 to 25 years prior to our study.
The following pages are data collected from your blueberry field. Results are grouped
into four categories: soil carbon, soil nitrogen, soil enzymes, and soil microbes. Measurements
from your field are shown alongside the average from twelve blueberry fields on sandy soils
(denoted as “MI Average” in the figures below). Because muck soils had average values 2- to
10-times greater than those in sandy soils, muck soils were excluded from the averages. The
results are shown at two soil depths, 0-2 and 0-12 inches, except mycorrhizal colonization (roots
collected at 0-12 inches) and nematode populations (0-2 inch soil depth and blueberry roots,
assessed separately). The error bars represent the spread of data from approximately two-thirds
of Michigan fields; values from your field falling outside the error bars can be considered as a
deviation from the “typical” blueberry field in Michigan. The report concludes with a brief
discussion of the results.
We hope this report is useful to you. I can be reached by email, sadowsky@msu.edu, to
answer any questions you might have. Thank you kindly for participating in the study.
Sincerely,
Jesse Sadowsky
M.S. Plant Pathology 2010
(Reviewed by Eric Hanson, professor of horticulture, hansone@msu.edu, and Annemiek
Schilder, professor of plant pathology, schilder@msu.edu,)
Soil carbon
SOM (%)
Total soil organic matter – consists of all
non-mineral matter in soil (measured on 9Oct-2009).
1
0 - 12" depth
3
4
20
10
5
0 - 2" depth
1
2
0 - 12" depth
3
4
3
Labile carbon (mg / g soil)
5
15
5
NW of weather station
MI Average
2
1
0
1
0 - 2" depth
2
0 - 12" depth
3
4
5
Slow + recalcitrant carbon
(mg / kg soil / day)
Slow + recalcitrant soil carbon – consists
mainly of organic matter that that is not
broken down easily by microbes and
contributes little to overall microbial
activity. It was assessed as the steady rate of
soil respiration after the labile pool of soil
carbon has been consumed during a 462-day
laboratory incubation (measured on 25-Sept2008).
2
NW of weather station
MI Average
0
Labile soil carbon – this organic matter
pool constitutes readily available carbon that
is a major source of energy for soil
microbes. It was modelled as the
exponential decay of CO2 production over a
462-day laboratory soil incubation
(measured on 25-Sept-2008).
0 - 2" depth
25
LF-SOM (mg / g soil)
Light fraction soil organic matter
(LF-SOM) – consists mainly of partly
decomposed fragments of plant debris and
turns over more rapidly (within a few years)
than total soil organic matter. Its density is
less than 1.7 g/cm3 (measured on 25-Sept2008).
NW of weather station
MI Average
9
8
7
6
5
4
3
2
1
0
5
NW of weather station
MI Average
4
3
2
1
0
0 - 2" depth
1
2
3
0 - 12" depth
4
5
Soil respiration – represents carbon that is
immediately available to soil microbes. It
was assessed as the rate of CO2 release from
soil over the first 30 days of a laboratory
incubation. (measured on three dates in
2009).
CO2-C mg / kg soil / day
Soil carbon, cont’d
40
NW of weather station
MI Average
30
20
10
0
0- 2-inch depth
0- 12-inch depth
Ammonium-N – is a preferred nitrogen
source of blueberries and less prone to
leaching and runoff than nitrate (measured
on three dates in 2009).
NH4+-N (mg / kg soil)
Soil nitrogen
35
30
25
20
15
10
5
0
NW of weather station
MI Average
0- 2-inch depth
40
NO3--N (mg / kg soil)
Nitrate-N – is less desirable than
ammonium because it is not utilized
efficiently by blueberries and more prone to
soil leaching and runoff (measured on three
dates in 2009).
0- 12-inch depth
NW of weather station
MI Average
30
20
10
0
Mineral N (nitrate + ammonium) –
indicates soil nitrogen availablility
(measured on three dates in 2009).
NH4+ + NO3--N (mg / kg soil)
0- 2-inch depth
70
60
50
40
30
20
10
0
NW of weather station
MI Average
0- 2-inch depth
2.0
1.5
1.0
0.5
0.0
-0.5
0- 12-inch depth
NW of weather station
MI Average
NH4+ + NO3--N (mg / kg soiil / day)
Potentially mineralizable nitrogen –
assesses the short-term capacity of soil
microbes to release nitrogen from organic
matter. It was measured as the accumulation
of inorganic nitrogen over a 30-day
laboratory soil incubation (measured on
three dates in 2009).
0- 12-inch depth
0- 2-inch depth
0- 12-inch depth
Soil enzyme activity
500
400
300
200
100
0
NW of weather station
MI Average
BG activity nmol / g soil / hour
Beta-glucosidase (BG) – releases glucose
from cellobiose, the final step in cellulose
decomposition. Microbes secrete BG from
their cells to obtain energy (glucose) from
organic matter (measured on three dates in
2009).
0- 2-inch depth
N-acetyl-glucosaminidase (NAG) –
releases N-acetylglucosamine from cell
walls of dead fungi, bacteria, and other soil
organisms, which may then be taken up by
living microbes or broken down further and
taken up by plant roots as a source of
nitrogen (measured on three dates in 2009).
CBH activity nmol / g soil / hour
150
NW of weather station
MI Average
100
50
0
0- 2-inch depth
200
NAG activity nmol / g soil / hour
Cellobiosidase (CBH) – releases cellobiose
from cellulose polymers, an intermediary
step in the breakdown of cellulose, which
may be further decomposed to glucose to be
used as an energy source by microbes. CBH
activity is related to the turnover of plant
debris in soil, including leaves, fine roots
and mulches (measured on three dates in
2009).
0- 12-inch depth
NW of weather station
MI Average
150
100
50
0
0- 2-inch depth
700
600
500
400
300
200
100
0
PHOS activity nmol / g soil / hour
Acid phosphatase (PHOS) – releases
phosphate from various forms of organic
matter, including plant detritus,
phospholipids in microbial cell walls, and
nucleic acids, that can be taken up as a
source of phosphorus by microbes or plant
roots (measured on three dates in 2009).
0- 12-inch depth
0- 12-inch depth
NW of weather station
MI Average
0- 2-inch depth
0- 12-inch depth
Tyrosine aminopeptidase (TAP) – releases
amino acids from peptides and proteins that
make up about half of the total nitrogen
content of soil. Amino acids released by
TAP are taken up by microbes or degraded
further and taken up by plant roots as a
source of nitrogen (measured on three dates
in 2009).
TAP activity nmol / g soil / hour
Soil enzyme activity, cont’d
5
4
3
2
1
0
NW of weather station
MI Average
Peroxidase (PER) – contributes to
transformation and breakdown of structural
polymers in plant debris, such as lignin, and
complex forms of soil organic matter, such
as humus (measured on three dates in 2009).
PER activity nmol / g soil / hour
0- 2-inch depth
14
12
10
8
6
4
2
0
NW of weather station
MI Average
POX activity nmol / g soil / hour
0- 2-inch depth
Phenol oxidase (POX) – contributes to
transformation and breakdown of structural
polymers in plant debris, such as lignin, and
complex forms of soil organic matter, such
as humus (measured on three dates in 2009).
0- 12-inch depth
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0- 12-inch depth
NW of weather station
MI Average
0- 2-inch depth
0- 12-inch depth
Soil microbes
Soil bacteria – feed on organic matter in
soil. They were assessed by counting the
number of bacteria that grew from soil
added to culture media (assessed 25-Sept2008 and 9-Oct-2009).
Ericoid mycorrhizae
(% hair root cells)
25
20
15
NW of weather
station
10
MI Average
5
0
Fall 2008
30
Bacteria × 106 / g soil
Ericoid mycorrhizae – are fungus-root
associations found in the outside cell layer
of hair roots of blueberries. Ericoid
mycorrhizae aid in plant uptake of nitrate
and organic nitrogen from soil. Mycorrhizal
colonization was assessed on roots collected
at 0- to 30-cm soil depth in fall 2008 and
three dates in 2009.
Jul, Aug, Oct
2009
NW of weather station
MI Average
25
20
15
10
5
0
0 - 2"
depth
0 - 12"
depth
0 - 2"
depth
2008
2009
25
Fungi × 104 / g soil
Soil fungi – feed on organic matter in soil.
They were assessed by counting the number
of fungi that grew from soil added to culture
media (assessed 25-Sept-2008 and 9-Oct2009).
0 - 12"
depth
NW of weather station
MI Average
20
15
10
5
0
0 - 2"
depth
0 - 12"
depth
2008
0 - 2"
depth
0 - 12"
depth
2009
Soil microbes, cont’d
400
300
200
100
0
1
0 - 2" depth
2
NW of weather station
MI Average
120
Plant-parasitic nematodes /
100 cm3 soil
Plant-parasitic nematodes in soil – include
lesion, sheath, ring, and spiral nematodes.
They only feed on living roots of blueberries
and other plants (assessed by Michigan State
University Diagnostic Services on 6-Jun2010 at 0- to 2-inch soil depth).
NW of weather station
MI Average
500
Non-plant parasitic nematodes /
100 cm3 soil
Non-plant-parasitic nematodes in soil –
are “beneficial” because they consume other
microorganisms and in the process release
nitrogen and other nutrients. (assessed by
Michigan State University Diagnostic
Services on 6-Jun-2010 at 0- to 2-inch soil
depth).
100
80
60
40
20
0
0
1
0 - 2" depth
2
Summary/Discussion
Across sampling dates, nitrogen availability at 0-12-inch soil depth in your field was
similar to the average for the fields we sampled. Nitrogen availability was slightly lower than
average in the upper two inches of your soil in July, possibly due to temporary nitrogen
immobilization in wood mulch.
Soil biological activity in your field was in general high and on par with many organic
fields. Potentially mineralizable nitrogen and soil respiration rates were closely related,
suggesting microbial activity is associated with nitrogen release in your soil. Enzymes involved
in cellulose breakdown and nitrogen and phosphorus mobilization were higher than the average
Michigan blueberry soil. The deep layer of wood mulch likely contributes to soil health in your
field.
Microbial populations in your soil include higher than average fungal counts but lower
than average bacterial counts. Fungi have threadlike hyphae which allow for movement of
nutrients between nutrient-rich and nutrient-poor substrates within soil microhabitats, while
unicellular bacteria do not have this ability. Fungi may be better-equipped than bacteria to
degrade coarse, high C:N materials such as wood chips, and wood mulch probably increased the
ratio of fungi to bacteria in your soil relative to the average of the fields we sampled.
Nematodes thrive in very moist soils, and soil moisture near the soil surface was
generally low compared to other blueberry fields we sampled. Subsurface drip irrigation in your
field is may thus explain a lower than average count of beneficial, non-plant-parasitic nematodes
in the upper 2 inches of your soil compared to the average field. No pathogenic nematodes were
found in a sample of blueberry roots we submitted to the MSU diagnostic clinic, meaning there
is low risk posed by root-feeding nematodes in your field.