A New Method to Quantify the Impact of S

TECHNICAL REPORTS: VADOSE ZONE PROCESSES AND CHEMICAL TRANSPORT

A New Method to Quantify the Impact of Soil Carbon Management on Biophysical Soil
Properties: The Example of Two Apple Orchard Systems in New Zealand
Markus Deurer* and Siva Sivakumaran HortResearch Ltd.
Stefanie Ralle University of Hannover
Iris Vogeler, Ian McIvor, Brent Clothier and Steve Green HortResearch Ltd.
Jörg Bachmann University of Hannover
A new method to diagnose the environmental sustainability of
specific orchard management practices was derived and tested. As
a significant factor for soil quality, the soil carbon (C) management
in the topsoil of the tree-row of an integrated and organic apple
orchard was selected and compared. Soil C management was
defined as land management practices that maintain or increase
soil C. We analyzed the impact of the soil C management on
biological (microbial biomass C, basal respiration, dehydrogenase
activity, respiratory quotient) and physical (aggregate stability,
amount of plant-available water, conductive mean pore diameter
near water saturation) soil properties. Soil in the alley acted as
a reference for the managed soil in the tree row. he total and
hot-water–extractable C amounts served as a combined proxy for

the soil C management. he soil C management accounted for
0 to 81% of the degradation or enhancement of biophysical soil
properties in the integrated and organic system. In the integrated
system, soil C management led to a loss of C in the top 0.3 m of
the tree row within 12 yr, causing a decrease in microbial activities.
In the tree row of the organic orchard, C loss occurred in the
top 0.1 m, and the decrease in microbial activities was small or
not significant. Regarding physical soil properties, the C loss in
the integrated system led to a decrease of the aggregate stability,
whereas it increased in the organic system. Generally, the impact
of soil C management was better correlated with soil microbial
than with the physical properties. With respect to environmental
soil functions that are sensitive to the decrease in microbial
activity or aggregate stability, soil C management was sustainable
in the organic system but not in the integrated system.

Copyright © 2008 by the American Society of Agronomy, Crop Science
Society of America, and Soil Science Society of America. All rights
reserved. No part of this periodical may be reproduced or transmitted
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without permission in writing from the publisher.
Published in J. Environ. Qual. 37:915–924 (2008).
doi:10.2134/jeq2007.0508
Received 24 Sept. 2007.
*Corresponding author (mdeurer@hortresearch.co.nz).
© ASA, CSSA, SSSA
677 S. Segoe Rd., Madison, WI 53711 USA

I

n New Zealand, most horticultural systems are managed
according to the guidelines of organic or integrated fruit
production. he overall environmental sustainability of organic and
integrated apple production systems in New Zealand was assessed
with a life-cycle analysis by Mila i Canals et al. (2006). he generic
impact of conservative, integrated, and organic apple production
systems on soil quality has also been compared (Glover et al., 2000).
We sought to diagnose the environmental sustainability of specific
management practices. We focused on two production systems: an
integrated apple orchard and an organic apple orchard.

We focused on soil C management as a specific management
practice. Soil C management is defined as “land management practices that maintain or increase soil C” (Kimble et al., 2007). he soil
C management cannot be identified as one particular management
practice. Several management practices and other variables, such as
soil type and climate, influence a soil’s C status. We used the total
soil organic C (Ct) and the hot-water–extractable soil C (CHWC) as
a combined proxy for the soil’s C status. he Ct describes the size of
the entire soil C pool. he CHWC characterizes the labile C fraction
that is well correlated with microbial activities (Ghani et al., 2003).
Soil C is a key property for many environmental soil functions (e.g., filtering excessive plant nutrients or contaminants
from water) (Pierzynski et al., 2007). Following the soil quality
framework (Karlen et al., 2001, 2003), management practices
would be sustainable if key soil functions did not degrade. he
relationship between soil functions and soil organic C is often
indirect. Soil organic C is correlated with biophysical soil properties, which in turn govern soil functions. For example, higher
soil C might lead to higher microbial biomass (Sparling, 1992),
which accelerates the degradation of organic contaminants.
he performance of the soil functions usually depends on
several soil properties and on the initial and boundary conditions
for the specific site. For example, the degradation of organic contaminants in the root zone with high microbial biomass might be

prevented by an atmospheric boundary condition that leads to
preferential flow. In that case, the contaminants would be rapidly
M. Deurer, S. Sivakumaran, I. Vogeler, I. McIvor, B. Clothier, and S. Green, Sustainable
Land Use Team, HortResearch Ltd., Palmerston North, New Zealand. S. Ralle and J.
Bachmann, Inst. of Soil Science, Univ. of Hannover, Hannover, Germany.
Abbreviations: CHWC, hot-water–extractable soil C; Ct, total soil organic C.

915

Fig. 1. View of the integrated and organic orchards in Hawke’s Bay. (A) Aerial view. (B) A tree row in the organic and (C) in the integrated orchard.

transferred from the soil surface to below the root zone. he
microbes in the root zone would not interact with the organic
contaminants, and, therefore, degradation is low. Under these
conditions, there would be no relation between a variation of
microbial biomass in the bulk soil and contaminant decay.
Biophysical properties in topsoils of organic and conventional production systems have been compared (CarpenterBoggs et al., 2000; Castillo and Joergensen, 2001; Fliessbach
et al., 2007; Goh et al., 2001; Gunapala and Scow, 1998; Monokrousos et al., 2006; Werner, 1997). However, the change
in values of biophysical properties of integrated, conventional,
and organic systems have not been quantitatively attributed

to a specific set of management practices. We quantified the
impact of soil C management on biophysical soil properties
in two apple production systems. Our objectives were (i) the
presentation of a framework to quantify the impact of soil C
management on selected environmentally relevant biophysical
soil properties and (ii) the application of the framework to the
topsoils of an organic and integrated orchard system.
In this study, the microbial biomass, basal respiration, respiratory quotient, and dehydrogenase activity were used as
microbiological soil characteristics. Microbial biomass and
basal respiration were selected as key variables to represent C
and nitrogen (N) dynamics in soils (Grant et al., 1993a,b). he
sequestration of C and N, the emission of CO2 and N2O, and
the degradation of organic contaminants are environmentally
relevant soil functions that result from C and N turnover processes. he respiratory quotient combines basal respiration and
microbial biomass. It quantifies the efficiency of the C turnover
Table 1. General soil characteristics of the topsoil (0–0.3 m) of the
organic and integrated orchard systems.
Texture
Sand (%wt)
Silt (%wt)

Clay (%wt)
Bulk density (g cm−3)
pH (H2O)

916

Organic orchard
Silt loam
2.7
65.2
32.1
1.4
6.4

Integrated orchard
Silt loam
0.4
71.1
28.5
1.1

7.1

by the soil’s microbial biomass. he dehydrogenase activity is a
sensitive measure of the microbiological status of a soil (Taylor
et al., 2002) and is often used to indicate the impact of land use
on the soil’s microbiological properties (Parham et al., 2002;
Quilchano and Marañón, 2002). It is also well correlated with
environmentally relevant soil functions, such as the emission of
CO2 and N2O (Włodarczyk et al., 2002).
For describing the soil physical properties, we chose the aggregate stability, the amount of plant-available water, and the
conductive pore diameter close to water saturation. Aggregate
stability is a key property preventing soil erosion (Le Bissonais
and Arrouays, 1997) and loss of phosphorus to surface waters
(de Jonge et al., 2004). Higher amounts of plant-available water
in the root zone enable a more efficient irrigation management,
avoiding the leaching of excessive nutrients below the root zone.
We measured the conductive pore diameter near water saturation
(Sauer et al., 1989) as an indirect indicator for preferential flow.

Materials and Methods

Study Sites
We conducted the case study on an organic and a neighboring integrated apple production system in the Hawke’s Bay
region on the east coast of New Zealand’s North Island (Fig. 1).
Both orchards have the same general soil characteristics (Table
1). he soils are Fluvisols and have a silt-loam texture. he
organic orchard system had been under organic management
(BioGro) since 1997. he apple trees in the orchard were 13 yr
old. he apple variety was ‘Braeburn’, and the rootstock variety
was ‘MM.106’. he tree spacing was 4.6 m within the rows
and 4.4 m between the rows. Green-waste compost was applied
to the topsoil of the tree rows once a year at a rate of 5 to 10
t ha−1, and lime was added at a rate of 300 kg ha−1 every 4 yr.
Lime-sulfur and copper were used as fungicides if needed.
he apple trees in the adjacent integrated orchard system
were 12 yr old. he apple variety was Pacific Rose, and the
rootstock variety was ‘MM.106’. he tree spacing was 3.4 m
within the rows and 4.5 m between the rows. A 0.5-m wide

Journal of Environmental Quality • Volume 37 • May–June 2008

Fig. 2. Schematic overview of the framework to quantify the impact of soil C management on biophysical soil properties

strip under the trees was kept bare by regular herbicide applications. he apple trees were drip-irrigated during the vegetative
period. he irrigation, nutrient, and pest management followed
the guidelines of integrated fruit production (Wiltshire, 2003).

Framework to Quantify the Impact of Soil Carbon
Management on Biophysical Soil Properties
he observation time (Δt) for performing the following
statistical treatment should be long enough to represent the
interaction of the local climate with the biophysical soil property (f). In our case, we suggest a minimum measurement
period of 1 yr for the biological soil properties.

Formal Setup of Variables
We compared the values of a biophysical soil property f at location xi and xj over a time interval Δt. he location xj served as a
reference and did not receive all management practices but was in
all other respects comparable to xi. his meant, for example, that
xi and xj had the same soil type, texture, and climatic conditions
and the same initial conditions such as recent land use history.

Calculation of the Impact
he impact of the C management on the biophysical soil
property at xi and over the time interval Δt, f(xi;Δt), was calculated in five steps (Fig. 2).
• Step 1. Are the proxies of soil C management, Ct and CHWC,
in the managed treatment and the reference statistically
different (checked by step 1)? When this applies, then step 2.
We selected a measurable proxy for the soil C management
P in the soil at x. For our study, we used Ct and the CHWC
divided by the total C contents (CHWC Ct−1) as a combined
proxy for the soil C management at x. If P(xi;Δt) and P(xj;Δt)
were statistically significantly different, then a potential impact of the soil C management on the biophysical soil prop-

Deurer et al.: New Method to Quantify the Impact of Soil C

erty f(xi;Δt) was probable, and we proceeded to the next step.
• Step 2: Are the selected biophysical parameters between
managed treatment and reference statistically different?
When this applies, then step 3:
We tested if the soil biophysical property of the managed
soil f(xi;Δt) and of the reference f(xj;Δt) were statistically significantly different. Only if this was the case did we assume

there was an impact of any management on f(xi;Δt), and we
proceeded to the next step.
• Step 3: What is the impact of all management on the
biophysical soil property in the managed treatment?
he ratio Φ of the biophysical soil property measured at xi
and xj and averaged over Δt yielded the overall impact of all
management practices on f(xi;Δt):
⎡
f ( xi ; Δt ) ⎤⎥
Φ ⎢⎣⎡ f ( xi , j ; Δt )⎥⎦⎤ = − ⎢⎢1 −
f ( x j ; Δt ) ⎥⎦⎥
⎣⎢

[1]

he value of Φ multiplied by 100 denoted the percentage
difference (larger = positive value and smaller = negative
value) in the biophysical soil property at xi compared with the
reference xj. herefore, Φ is a measure of the impact of the
management practices on the biophysical soil property at xi.
• Step 4: What is the correlation between the proxy for soil
C management and the biophysical soil property?
We performed a regression of the biophysical soil property
f(xi,j;Δt) (dependent variable) versus the respective management proxy values P(xij;Δt) (independent variable). his
yielded the variance fraction (R2) that could be explained by
the proxy. We denoted it by R(f(xi,j;Δt);P). he proxy had to
be a statistically significant variable in the regression.
• Step 5: What is the impact of soil C management on the
biophysical soil property in the managed treatment?

917

he correlation between the biophysical soil property and
the proxy for the soil C management, R(f(xi,j;Δt);P) (step 4),
was multiplied by the impact of all management practices on
the biophysical soil property Φ (step 3). By this we estimated
the partial impact I of the soil C management P on the biophysical soil property at xi:
I ⎣⎡⎢ f ( xi , j ; Δt ); P ⎦⎤⎥ = Φ ⎣⎡⎢ f ( xi , j ; Δt )⎦⎤⎥ R ⎣⎡⎢ f ( xi , j ; Δt ); P ⎦⎤⎥

[2]

he value of Ι multiplied by 100 denoted the percentage
increase in the partial impact of the soil C management P on
the particular biophysical soil property at xi.

Reference for the Managed Tree Rows
We used the soil in the alley of each apple orchard as the reference for the managed soil in the tree row (Fig. 1). We selected
the top 0.3 m. his was the depth of the plow layer of the previous land use (market gardening). For analysis, we separated
the top 0.3 m into three increments (0–0.1, 0.1–0.2, 0.2–0.3
m). his enabled us to estimate the depth of the impact of soil
C management on the biophysical soil properties.

Measurement Methods
Measurements for all properties, with the exception of the
conductive pore diameters near water saturation, were taken
from three depths (0–0.1, 0.1–0.2, and 0.2–0.3 m) at three
randomly selected locations of the tree rows and alleys (between the marks of the wheel-tracks) of both orchards.

Total Carbon
he soil samples were analyzed by the Dumas Method for %C
using a LECO CNS-2000 Analyzer (Laboratory Equipment Corporation Ltd, Castle Hill, NSW, Australia). he C contents were
measured in January and November 2006. he CHWC (Ghani et
al., 2003) was measured monthly from April to December 2006.

Microbiological Measurements
he microbiological functioning of the soil was characterized by taking monthly measurements from January to December 2006. We measured microbial biomass according to
the method of Höper (2006) and basal respiration following
Őhlinger et al. (1996).

Dehydrogenase Activity
We used 5 g of soil to perform a dehydrogenase assay with
2,3,5-triphenyltetra-zolium chloride as a substrate (Chandler
and Brookes, 1991). he resulting triphenylformazan concentrations of the extracted solutions were measured with a
spectrophotometer at 485 nm (DU-640; Beckman, Krefeld,
Germany). Using bulk density measurements, the results were
transformed to represent soil layers of a unit area of 1 m2.

Physical Measurements
he physical functioning of the soil was analyzed by measuring water retention (Dane and Hopmans, 2002) and aggregate
stabilities (Le Bissonais, 1996) in the laboratory and by measuring water infiltration rates with tension disk infiltrometers in
the field (Deurer et al., 2008). From the water retention curves,

918

we estimated the plant-available water content as the amount
of water that is retained in the soil between −0.064 and −15
bar. he aggregate stabilities were expressed as a mean weighted
aggregate diameter (Le Bissonais, 1996). From the infiltration
rates at −80 and −10 mm tension, we derived the equivalent
conductive macropore diameter (CMD) (Sauer et al., 1989).

Statistical Methods
he results of each production system (organic, integrated)
were analyzed with a two-way ANOVA with the Genstat
9.1.0.150 software. We selected the treatment (tree row versus
alley) as the first and the soil depth (0.0–0.1, 0.1–0.2, or 0.2–0.3
m) as the second factor. he monthly measurements of microbial
properties were represented as blocks. here were three randomly
selected replicates for each combination of the two factors within
each block. We interpreted the differences between averages of
properties to be significant if they were larger than their respective least significant differences (P ≤ 0.05).

Results
Proxies for the Soil Carbon Management
In both systems, more C was sequestered in the alley than
in the tree rows (P = 0.05). For the organic system, the difference was significant only in the top 0.1 m (Fig. 3A). For the
integrated orchard, all three depths under the tree row had
significantly less C than under the alley (Fig. 3B).
he soil under the tree row of the organic system had a higher
CHWC fraction (P = 0.05) than under the alley (Fig. 4A). he opposite was the case for the integrated orchard (Fig. 4B). In summary,
we found significant differences between tree row and alley for at
least one of the proxies for C management in 0 to 0.2 m for the
organic orchard and in 0 to 0.3 m for the integrated orchard.

Soil Microbiological Functioning: Comparison of Tree
Row and Alley
he C mineralization potential is indicated by the basal
respiration. It was significantly lower in the first depth of the
tree row in both production systems compared with the alley.
Large differences in the microbial activity are indicated by a
significant difference in the microbial biomass. his could be
found for the first two depths of the integrated orchard and
did not occur in any depth of the organic orchard (Table 2).
he respiratory quotients of the organic and integrated tree
rows were not significantly different from the values of the alleys. herefore, no shift in the efficiency of C turnover by the
microbes had occurred in either system. he dehydrogenase
activity was significantly smaller in the tree row than in the alley of both production systems irrespective of depth (Table 2).

Physical Functioning of the Soil: Comparison of Tree Row
and Alley
he tree row management enhanced the aggregate stability in
the organic system and degraded it in the integrated system (Table
3). he conductive macropore diameter near water saturation was
measured only in the first depth. It increased for both systems in

Journal of Environmental Quality • Volume 37 • May–June 2008

Fig. 3. Average (N = 6) total C contents in the top 0.3 m of the soils under the tree row and the alley of the apple orchards. (A) Organic system. The LSD
between the tree row and the alley is 0.48 kg C m−2. (B) Integrated system. The LSD between the tree row and the alley is 0.25 kg C m−2. The C contents
refer to 0.1-m-thick layers that are centered at 0.05, 0.15, and 0.25 m depth. Values with diferent letters were signiicantly diferent (P = 0.05).

the tree row. he tree row management of both systems tended to
decrease the plant-available water in the topsoil and increased it
in the subsoil. Generally, the differences of physical properties between the tree row and the reference of both systems were largest in
the 0- to 0.1-m and 0.2- to 0.3-m depths (Table 3).

Correlation of Biophysical Soil Properties with Proxies
for Soil Carbon Management
he proxies for soil C management explained different fractions of the variability of the biophysical soil properties in the
two systems. For example, the proxies were not significant for the
conductive pore diameter near water saturation in either system
but explained 81% of the variation of the dehydrogenase activity
in the integrated production system (Fig. 5A). he regressions
differed between the production systems (Fig. 5). he total C,
Ct, and CHWC Ct−1 explained 81% of the variation of the dehydrogenase activity in the integrated system but only 58% in the
organic system (Fig. 5). For the aggregate stability, Ct and CHWC
Ct−1 explained a higher fraction of the variation in the organic
(R2 = 0.68) than in the integrated system (R2 = 0.54) (Fig. 5B).
he Ct was a significant variable for all biophysical soil properties apart from the conductive pore diameter near water saturation (Tables 4 and 5). he CHWC was not a significant variable in
the regression for several biophysical properties, including the microbial biomass in the integrated system and the basal respiration
in the organic system (Table 3) and the amount of plant-available

water and the conductive pore diameter near water saturation in
both systems (Table 5). Generally, the proxies for the soil C management explained more of the variability in the microbial soil
properties than in the physical soil properties.

Total and Partial Impact of the Soil Carbon Management
on the Microbiological Functioning of the Soil
he microbial properties decreased between 0 and 33% in the
soil of the tree row of the organic system compared with the reference (Table 4). We could explain 0 to 81% of the variation in microbial properties by the proxies of soil C management (Table 4).
herefore, the impact of the soil C management on the microbial
properties was always smaller than the impact of all management.
For example, the basal respiration in the tree row of the organic
orchard decreased in total by 15%, but we attributed only a reduction of 6% to the soil C management. he decrease in microbial
properties in the tree row compared with the alley was much
higher in the integrated system than in the organic system, ranging
from 0 to 62% (Table 4). For example, the dehydrogenase activity
in the tree row of the integrated system decreased by more than
30% in all depths as a result of soil C management.

Total and Partial Impact of the Soil Carbon Management
on the Physical Functioning of the Soil
he physical properties showed no clear general trend in
the tree row of the organic system compared with the refer-

Fig. 4. Average (N = 9) hot-water–extractable C fractions (CHWC Ct−1) in the top 0.3 m of the soils under the tree row and the alley of the apple
orchards. (A) Organic system. The LSD between the tree row and the alley is 3.48 g kg−1. (B) Integrated system. The LSD between the tree
row and the alley is 2.98 g kg−1. The CHWC Ct−1 relate CHWC to total soil organic C (Ct). The fractions refer to 0.1-m-thick layers that are centered
at 0.05, 0.15, and 0.25 m depth. Values with diferent letters were signiicantly diferent (P = 0.05).

Deurer et al.: New Method to Quantify the Impact of Soil C

919

Table 2. Yearly averages of microbial soil properties for the tree row
and the alley of the organic and integrated orchard systems and
the respective LSDs.
Row
MB-C‡
BR-C§
DHYD¶
qCO2#

143.5
4.0
10.0
1.2

MB-C
BR-C
DHYD
qCO2

60.7
2.5
4.7
1.9

Organic
Integrated
Alley LSD†
Row
Alley LSD†
0–0.1 m depth
148.5 11.3
73.0
112.3
6.7
4.7
0.5
2.9
3.8
0.4
14.9
1.1
4.2
9.7
1.0
1.4
0.5
1.7
1.4
0.4
0.1–0.2 m depth
62.6 11.3
43.0
53.6
6.7
2.4
0.5
2.0
2.4
0.4
6.4
1.1
2.1
5.4
1.0
1.7
0.5
2.1
2.0
0.4
0.0–0.3 m depth
37.3 11.3
26.3
32.3
6.7
1.4
0.5
1.4
1.5
0.4
2.8
1.1
1.2
2.8
1.0
1.7
0.5
2.3
2.1
0.4

MB-C
38.5
BR-C
1.5
DHYD
1.8
qCO2
2.0
† LSD at the P ≤ 0.05 level.
‡ Microbial biomass C in a layer of soil (g C m−2).
§ Basal respiration in a layer of soil (g C m−2 d−1).
¶ Dehydrogenase activity in a layer of soil (g triphenylformazan m−2 d−1).
# Respiratory quotient in a layer of soil (mg BR-C/g MB-C m−2 d−1).

ence (Table 5). he impact of the soil C management on the
physical properties in both systems was smaller than on the
microbial properties (range, −15 to +17%) (Table 5). he
conductive pore diameter near water saturation increased by
94 and 45% in the top 0.1 m of the tree row of the organic
and integrated systems, respectively. However, we could not
attribute this increase to the soil C management. In the integrated orchard, we observed a considerable degradation of the
soil structure (aggregate stability) in the 0- to 0.1-m and 0.2to 0.3-m depths in the tree row. We estimated that C management explained about half of the loss of aggregate stability.
Table 3. Averages of soil physical soil properties for the tree row and
the alley of the organic and integrated orchard systems and the
respective LSDs.
Integrated
LSD
Row
Alley LSD
0–0.1 m depth
MWD†
1.818 1.753
0.292
1.328 1.823 0.278
PAW‡
17.16 21.22
3.016
22.79 31.62 4.421
CMD§
0.475 0.245
0.052
0.435 0.300 0.121
0.1–0.2 m depth
MWD
1.567 1.257
0.292
0.876 1.044 0.278
PAW
13.62 16
3.016
14.05 16.86 4.421
CMD
NA¶
NA
NA
NA
NA
NA
0.2–0.3 m depth
MWD
1.391 0.910
0.292
0.965 1.289 0.278
PAW
18.78 11.16
3.016
23.95 14.5
4.421
CMD
NA
NA
NA
NA
NA
NA
† Aggregate stability indicated by the mean weighted diameter (MWD) (mm).
‡ Plant available water (PAW) content (mm).
§ Conductive macro-pore diameter (CMD) between −80 and −10 mm
tension (mm).
¶ Not available.
Row

920

Organic
Alley

Fig. 5. Regression of soil biophysical properties versus the proxies
for the soil C management. (A) Dehydrogenase activity
(triphenylformazan [TPF] with N = 216 for each system). The R2 for
the organic orchard is 0.81 (RMSE = 1.97), and for the integrated
orchard the R2 is 0.58 (RMSE = 1.99). Total soil organic C (Ct) and
the hot-water–extractable C fractions (CHWC Ct−1) were signiicant
variables. (B) Mean weighted diameter (MWD) with N = 18 for
each system. The R2 for the organic orchard is 0.68 (RMSE = 0.21),
and for the integrated orchard the R2 is 0.54 (RMSE = 0.25). Both Ct
and the CHWC Ct−1 were signiicant variables.

Discussion
Selection of a Suitable Reference
We measured the impact of soil C management on the biophysical soil properties by comparing their values with a reference.
he definition criteria for a reference to measure a soil’s overall
quality are controversial (Karlen et al., 2003; Letey et al., 2003;
Soijka et al., 2003). However, the alley seemed the obvious choice
for a reference to quantify the impact of soil C management in the
tree row. We could assume that the soil under the alley and the tree
row had the same initial C status (i.e., at the time of the establishment of the orchard). Compared with the tree row, the soil under
the alley received very little management. he alley is a long-term
pasture system, albeit with tree roots. Pasture systems are considered the optimal land use for soil C accumulation in the topsoil
(Davis and Condron, 2002; Ross et al., 2002). Also, the soil under
the alley had the same soil type and climate as in the tree row.

Journal of Environmental Quality • Volume 37 • May–June 2008

We assumed that the tree roots contributed equally to
the C status of the soil of the tree row and of the alley. Consequently, the alley soil reference would not be suited to
quantify the impact of any tree-specific management (e.g.,
pruning) on the soil’s C status. However, our objective was to
quantify the impact of a set of soil C management practices
that applied only to the soil of the tree rows (e.g., compost
application, irrigation, or herbicide application).
Another reason to select the soil in the alley as the reference was to make the application of our method practically
feasible for growers and regulatory agencies. To be meaningful, the reference soil has to meet the following conditions:
Condition 1, same soil type; Condition 2, same climatic
boundary conditions; and Condition 3, same initial soil C
status as the soil of the tree row.
It is improbable to identify a soil neighboring an orchard that
is used as a pasture (i.e., suitable as a reference) and simultaneously fulfils all three conditions. he greatest problem is Condition 3. Condition 3 requires not only that the orchard and the
neighboring pasture have the same initial soil carbon status but
also that it was analyzed and documented at the time.
he soil quality framework offered no guidance as to
which soil depths should be selected (Letey et al., 2003). We
chose the depth of the plow layer (0.3 m) of the previous land
use. For this layer we could assume that the ploughing created the same initial C amounts for the soil under the alley as
under the tree row. Other studies comparing the soil quality
of organic and integrated apple production systems characterized the 0- to 0.15-m depth (Glover et al., 2000) or the 0- to
0.3-m depth (Goh et al., 2001). An investigation of the quality of soils across New Zealand and under various land uses
focused on the top 0.1 m (Sparling and Schipper, 2004).

Soil Carbon Management
In contrast to the unknown contributions of several soilC–related management practices, our proxy for soil C management (Ct and CHWC) can be directly quantified. By relating
our impact analysis to the soil C status, our results can be
generalized and should apply to other land uses and sites.
he soil C amount (Ct, CHWC) under the tree row was significantly smaller than under the alley of the integrated orchard. Soil C conservation was not an objective of integrated
orchard management. he tree row without pasture received
little input of root-biomass C and no input of C via compost.
Additionally, the drip irrigation in the tree row led to continuously favorable moisture conditions for C mineralization
and might promote the leaching of dissolved organic C. he
lack of C conservation, and thus a loss of C over time in the
tree rows of integrated production systems such as apple,
kiwifruit, and grapes, are rarely considered. By contrast, the
use of pasture as understorey vegetation for C conservation
is avoided because it competes with the crops for water and
nutrients (Tworkoski and Glenn, 2001). Economic incentives
such as C credits (Sparling et al., 2006) or market access regulations that reward environmental stewardship similar to the
EurepGAP framework might change this in the future.

Deurer et al.: New Method to Quantify the Impact of Soil C

Table 4. Impact of all management practices (∆) and of the soil organic C
management (I) on soil microbial parameters. No values are given if
the diferences of the parameters and/or the proxies between the tree
row and the alley were not statistically signiicant. The value of R refers
to a linear regression with total organic C (Ct) or (given in brackets) to a
multiple linear regression with Ct and hot-water–extractable C fractions.
Organic
R‡

Ơ

I§
∆
0–0.1 m depth
MBC¶
–
–
–
−0.35
BR#
−0.15 0.40 (NS) −0.06 (−0.06) −0.23
DHYD†† −0.33 0.70 (0.81) −0.23 (−0.27) −0.57
–
–
–
–
qCO2‡‡
0.1–0.2 m depth
MBC
–
–
–
−0.20
BR
–
–
–
−0.17
DHYD
−0.26 0.70 (0.81) −0.18 (−0.21) −0.62
–
–
–
–
qCO2
0.2–0.3 m depth
MBC
–
–
–
–
BR
–
–
–
–
DHYD
–
–
–
−0.57
–
–
–
–
qCO2

Integrated
R

I

0.69 (NS) −0.24 (−0.24)
0.31 (0.41) −0.07 (−0.09)
0.56 (0.58) −0.32 (−0.36)
–
–
0.69 (NS) −0.14 (NS)
0.31 (0.41) −0.05 (−0.07)
0.56 (0.58) −0.34 (−0.36)
–
–
–
–
–
–
0.56 (0.58) −0.32 (−0.33)
–
–

† See Eq. [1].
‡ See Eq. [2].
§ See Eq. [2].
¶ Microbial biomass C (MB-C) in a layer of soil (g MB-C m−2).
# Basal respiration C (BR-C) in a layer of soil (g BR-C m−2 d−1).
†† Dehydrogenase activity in a layer of soil (g triphenylformazan m−2 d−1).
‡‡ Respiratory quotient in a layer of soil (mg BR-C/g MB-C m−2 d−1).

In the organic orchard, the management conserved soil C.
Soil C inputs into the soil are generally higher in organic than
Table 5. Impact of all management practices (Δ) and of the soil
organic C management (I) on soil physical parameters. No
values are given if the diferences of the parameters and/or the
proxies between the tree row and the alley were not statistically
signiicant. The value of R refers to a linear regression with
total organic C (Ct) or (given in brackets) to a multiple linear
regression with Ct and hot-water–extractable C fractions.
Integrated
I§
∆
R
I
0–0.1 m depth
–
–
–
−0.27 0.44 (0.56) −0.12 (−0.15)
−0.19
0.30
−0.06
−0.28
0.20
−0.06
0.94
NS (NS)
NS
0.45 NS (NS)
NS (NS)
0.1–0.2 m depth
0.25 0.40 (0.68) 0.10 (0.17)
–
–
–
–
–
–
–
–
–
NA
NA
NA
NA
NA
NA
0.2–0.3 m depth
–
–
–
−0.25 0.44 (0.56) −0.11 (−0.14)
–
–
–
0.65
0.20
0.13
–
–
–
NA
NA
NA
Ơ

MWD¶
PAW#
CMD††
MWD
PAW
CMD
MWD
PAW
CMD

Organic
R‡

† See Eq. [1].
‡ See Eq. [2].
§ See Eq. [2].
¶ Aggregate stability indicated by the mean weighted diameter (MWD) (mm).
# Plant available water (PAW) content (mm).
†† Conductive macro-pore diameter (CMD) between −80 and −10 mm
tension (mm).

921

in integrated or conventional production systems (Fliessbach
et al., 2007; Gunapala and Scow, 1998).
he pasture and regular compost applications in the tree
row of the organic system not only conserved Ct but also led
to more labile C (as CHWC) in the tree row than in the alley.

Soil Microbial Functioning
he degradation of the soil C status in the tree row of the
integrated orchard translated, in general, to a substantial decrease in microbial activities. Most measures of microbial activity decreased in the tree row to 0.2 m depth. In the organic
orchard, the decrease in microbial activities in the tree row
was small and often not significant. For example, there was
no significant difference between the microbial biomass in the
tree row compared with the alley.
A correlation of microbial activities and the soil C status
is expected (Fliessbach et al., 2007; Ghani et al., 2003; Sparling, 1992). We quantified the correlations between microbial
activities and soil C status separately for the integrated and
the organic system. he correlation of the C status with the
basal respiration was similar and low for both systems. he
soil C status could explain 58% of the variability of the dehydrogenase activities in the integrated system and 81% in the
organic system. Soil C seemed to be of different importance
for the enzyme activities in the two systems. Another explanation could be that the total and CHWC pools in the soil of the
integrated and the organic orchards have not only different
sizes but also different qualities.
he basal respiration decreased in the soils under the tree
row in both systems. We attributed less than half of this
decrease to the change in the soil C status. It is difficult to
interpret the decrease of a soil property with respect to the
environmental sustainability of the soil C management. For
example, the decrease of basal respiration would be positive if
less basal respiration indicated a reduction in CO2 emissions.
Conversely, it would be negative if it indicated a smaller degradation potential for C-rich organic contaminants, such as
herbicides.
A quantification of “positive” and “negative” could be
achieved by numerically modeling those functions based on
the measured basal respiration. In the soil-quality framework,
the sum of positive and negative changes of all environmentally relevant functions would quantify sustainability (Karlen
et al., 2003). Consequently, a zero net change of soil quality
could then indicate the overall environmental sustainability of
C management. he scientific merit of such lumped sums is
controversial (Letey et al., 2003; Soijka et al., 2003).
In the integrated system, the dehydrogenase activities
decreased by about 60% down to 0.3 m depth. he same
order of magnitude was found in another study comparing
conventional arable systems without soil C management with
organic systems (Fliessbach et al., 2007). However, we could
now show that only about half of this decrease was due to the
degradation of the soil C status. herefore, other management
practices combined are equally important. he respiratory
quotient was recommended as a sensitive indicator for the im-

922

pact of land-use–related change in soil C status on the microbial functioning of soil (Anderson and Domsch, 1990, 1993;
Sparling, 1992). However, the considerable change in the soil
C status in the integrated orchard did not have any significant
impact on the respiratory quotient. We concluded that the C
management of the topsoil of the integrated orchard was not
sustainable with respect to environmental soil functions that
are sensitive to the soil’s microbial functioning, whereas that
of the organic orchard was sustainable.

Soil Physical Functioning
he degradation of the soil C status in the tree row of the
integrated orchard led to a decrease in the aggregate stability
in the topsoil. Less C on the same soil usually leads to lower
aggregate stability (Le Bissonais and Arrouays, 1997). However, we could attribute only about half of the decrease in the
aggregate stability in the tree row of the integrated orchard to
the soil C management.
Compared with the alley, the aggregate stability in the tree
row of the organic orchard improved in the 0.1- to 0.2-m
depth. We attributed about 70% of this effect to the soil’s C
status. he amount of CHWC was significantly different between the tree row and the reference at this depth. herefore,
the difference might be an effect of the quality rather than the
total quantity of the soil C. For example, compost was applied
only to the tree row and not to the alley.
he tendency for preferential flow in the top 0.1 m increased in both systems compared with the alley. However,
this was not correlated with soil C status. Another study comparing soils in the tree row and the alley in a New Zealand
orchard reported higher infiltration rates in the tree row (Goh
et al., 2001). he authors attributed the higher infiltration
rates to the compaction by vehicles in the alley. In the apple
orchards of our study, the vehicle traffic was confined and
created clearly visible wheel-tracks. We sampled the alley between the wheel-tracks.
Many studies that evaluated soil quality in organic and
conventional or integrated production systems focused only
on biochemical soil properties (Anderson, 2003; Bending et
al., 2004; Castillo and Joergensen, 2001; Fliessbach et al.,
2007; Gil-Sortres et al., 2005; Monokrousos et al., 2006;
Ruf et al., 2003; Schloter et al., 2003). In some studies it was
argued that the soil’s physical parameters can be neglected in
diagnosing soil quality because they have little sensitivity for
land use change (Filip, 2002; Gil-Sortres et al., 2005).
We argue that the soil’s physical properties play a key role
in most environmentally relevant soil functions. We found in
our study that the soil C status was better correlated with its
biochemical than with its physical properties. As an example,
we attributed the lack of correlation of the conductive pore
diameter near water saturation with C management, for example, to the fact that many other factors also influence this
property, which leads to a spatially high variability. Another
study found a weak correlation of soil organic C with the
tendency for preferential macropore flow (Jarvis et al., 2007).
Currently in New Zealand, the only routine measurement for

Journal of Environmental Quality • Volume 37 • May–June 2008

physical soil quality is macroporosity in the top 0.05 to 0.1
m (Sparling et al., 2004). Other physical properties, such as
the hydraulic conductivity and the plant-available water, were
not considered for reasons of high variability and high cost
(Schipper and Sparling, 2000).
In a forthcoming paper, we plan to use the biophysical soil
properties to parameterize a numerical model and evaluate the
performance of various environmental soil functions. hen,
we will compare the performance of the modeled soil functions in the tree row with its reference (alley) and assess the
sensitivity of the performance to the underlying biophysical
soil properties. From the study presented here, we know how
sensitive the biophysical soil properties are to soil C management. herefore, we will be able to quantify how sustainable
the soil C management is with respect to individual soil environmental functions.

Conclusions
Our proposed statistical framework was successful at discriminating between the impact of two contrasting C management strategies on the soil’s biophysical properties. Important implications of this research are:
• We have found that the impact of C management
extended further down the soil profile in the integrated
orchard than in the organic orchard.
• he degradation of the soil C status in the tree row of the
integrated orchard caused a decrease in microbial activity.
For example, the dehydrogenase activity in the tree row
decreased by about 60% down to 0.3 m depth compared
with the reference. In the tree row of the organic orchard,
the decrease in microbial activity was small. here was no
decrease for microbial biomass.
• he degradation of the soil C status in the tree row of the
integrated orchard led to a decrease in aggregate stability.
he soil C conservation in the organic orchard improved
the aggregate stability.
• With respect to environmental soil functions that are
sensitive either to the decrease in microbial activity or
aggregate stability the soil C management was sustainable
in the organic system but not in the integrated system.
For the integrated production system, we recommend the
introduction of regular compost applications and the growth of
pasture in the tree rows. his could prevent a degradation of the
soil’s biophysical functioning, and soil quality could be enhanced.

Acknowledgments
his research was carried out under the SLURI programme
(FRST contract CO2X0405). We thank the German Academic
Exchange Service (DAAD) for financial support that enabled
Stefanie Ralle to carry out her internship in New Zealand.

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