Soil biochemical indicators as a tool to (2)
ecological indicators 9 (2009) 518–527
available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/ecolind
Soil biochemical indicators as a tool to assess the short-term
impact of agricultural management on changes in organic C
in a Mediterranean environment
A. Lagomarsino a,*, M.C. Moscatelli a, A. Di Tizio a, R. Mancinelli b, S. Grego a, S. Marinari a
a
b
Department of Agrobiology and Agrochemistry, University of Tuscia, Via S.Camillo de Lellis s.n.c., 01100 Viterbo, Italy
Department of Crop Production, Via S.Camillo de Lellis s.n.c., 01100 Viterbo, Italy
article info
abstract
Article history:
Two management systems (conventional vs. organic) in a 3-years crop rotation (pea–durum
Received 23 April 2008
wheat–tomato) were compared after 4 years in order to assess soil carbon (C) changes in a
Received in revised form
short-term period. Biochemical properties of soil, such as microbial biomass C and N (MBC
2 July 2008
and MBN), microbial respiration, N mineralization, dehydrogenase, chitinase, acid–phos-
Accepted 4 July 2008
phatase, arylsulfatase and b-glucosidase activities, were chosen as indicators of soil organic
matter biochemical alteration. The main questions addressed in this study were (1) do soil
biochemical properties discriminate between organic and conventional management sys-
Keywords:
tems in a short-term period? (2) Which biochemical indicator is more effective in predicting
Organic management
soil organic C accumulation in organically managed agricultural soils?
Soil indicators
A general increase of hydrolytic enzymes activities has been observed in soil under
Hydrolytic enzymes
organic management. MBC, MBN and the MBC/TOC ratio (qmic) increased in organic soil
Dehydrogenase
under pea (100%, 50% and 100%, respectively) and durum wheat (55%, 28% and 42%,
C accumulation
respectively), while the basal respiration per unit of microbial biomass (qCO2 ) decreased
Microbial biomass
(48% and 40% under pea and durum wheat, respectively). Moreover, the specific activity of bglucosidase was significantly lower under organic management of pea and durum wheat
and was positively correlated with qCO2 , suggesting a lower maintenance energy requirement of the microbial community.
Soil microbial biomass and enzymatic activities were successfully used to detect shortterm changes in soil and, taking into account its role in soil functioning, b-glucosidase
resulted the most suitable indicator to predict organic C accumulation in soil under organic
management in a Mediterranean environment.
# 2008 Elsevier Ltd. All rights reserved.
1.
Introduction
Total organic carbon (TOC) in soil is usually considered as one
of the most important properties of soils because of its impact
on ecosystem sustainability, affecting other physical, chemical and biological characteristics of soil (Reeves, 1997).
Nevertheless, only drastic changes can modify this parameter
in the short-term. Differently, when comparing soils with
similar physico-chemical properties subjected to different
managements, biochemical properties can be used as indicators because of their great sensitivity to even slight modifications in the short-term (Gil-Sotres et al., 2005). In this study we
selected some biochemical indicators (microbial biomass,
enzyme activities and microbial indices) on the basis of their
* Corresponding author. Tel.: +39 0761 357248; fax: +39 0761 357242.
E-mail address: lagomarsino@unitus.it (A. Lagomarsino).
1470-160X/$ – see front matter # 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.ecolind.2008.07.003
ecological indicators 9 (2009) 518–527
role in soil C and N cycling, which represent the key elements
to evaluate agricultural management sustainability.
In particular, microbial biomass has been suggested as an
integrative signal of the microbial significance in soils because
it is one of the few fractions of soil organic matter (SOM) that is
biologically meaningful, easily measurable, and sensitive to
management or pollution (Powlson, 1994). It is both a source
and sink for nutrients, it participates in the main biogeochemical transformation of C, N, P, S and it contributes to soil
structure and stabilization. For these reasons, microbial
biomass is widely used as indicator in many soil-monitoring
programs (Winding et al., 2005). At the same time, microbially
mediated nitrogen (N) mineralization in soil is important in
order to sustain plant productivity without massive use of
mineral fertilizers.
Moreover enzyme activities can provide indication for
quantitative changes in SOM. It is known that the activities of
most enzymes increase as native SOM content increases,
reflecting larger microbial communities and stabilization of
enzymes on humic materials (Burns, 1982; Bending et al.,
2002). Enzymes allow microbes to access energy and nutrients
present in complex substrates and catalyze decomposition
and nutrient mineralization as well as humification processes
(Sinsabaugh et al., 1993; Asmar et al., 1994; Masciandaro and
Ceccanti, 1999; Allison and Vitousek, 2005). Among hydrolytic
enzymes, acid phosphatase and b-glucosidase activities have
been frequently used as indicators of changes in quantity and
quality of SOM (Gil-Sotres et al., 2005). N-Acetyl-glucosaminidase activity is considered to be important in C and N cycling
because it participates in the processes whereby chitin is
converted to amino sugars, which is one of the major sources
of mineralizable N in soils (Ekenler and Tabatabai, 2002). NAcetyl-glucosaminidase and arylsulphatase activities are also
considered as indirect indicators of the presence of fungal
biomass because sulphate esters (substrates of arylsulphatase) are only present in fungal cells (Bandick and Dick, 1999)
and chitin is the main constituent of fungal cell wall tissue
(Miller et al., 1998). Dehydrogenase activity typically occurs in
all intact, viable microbial cells. Thus, its measurement is
usually related to the presence of viable microorganisms and
their oxidative capability (Trevors, 1984).
Representing single biochemical properties as an index can
be a valid approach to evaluate the significance of microbial
populations and microbial activity in the cycling of elements
in soils under different management (Nannipieri, 1994;
Anderson, 2003). The use of quotients avoids the problems
of comparing trends in soils with different organic matter or
microbial biomass content (Sparling, 1997) and appears to
provide more sensitive indications of soil changes than either
activity or population measurements alone (Brookes, 1995;
Dilly and Munch, 1998). The metabolic quotient (basal
respiration per unit of microbial biomass, qCO2 ) reflects the
maintenance energy requirement of soil microbes (Anderson,
2003) and can be a relative measure of how efficiently the soil
microbial biomass is utilizing C resources, as well as the
degree of substrate limitation for soil microbes (Wardle and
Ghani, 1995; Dilly and Munch, 1998). Anderson (2003) indicated
above 2 g C–CO2 h 1 kg MBC 1 as a critical threshold for the
‘‘baseline performance’’ of microbial communities. The
percentage of MBC to TOC (qmic) could be used as a stability
519
indicator for quick recognition of an environmental change
(Anderson, 2003), it reflects the contribution of microbial
biomass to soil organic carbon (Anderson and Domsch, 1989)
and it indicates the substrate availability to the soil microbes,
being values below 2% a signal of SOM depletion (Anderson,
2003). The enzyme activities can also be expressed per unit of
MBC (specific activities), which represent a measure of
microbial physiological capacity, and have been found to be
more closely related to community composition than total
enzyme activity (Waldrop et al., 2000).
It has been shown that in the long-term organic management of agricultural soils positively influences soil properties
(Schjonning et al., 2002; Tu et al., 2006a) since the addition of
organic amendments can improve TOC accumulation in soil
by increasing C pools with a slow turnover time (Lal and
Kimble, 1997). Moreover, green manuring is considered a good
agricultural practice because of its positive effect on soil
fertility, quality and biodiversity (Stark et al., 2007). In the
short-term, several studies supported the evidence of an
increase of microbial biomass and activity under organic
management, leading to high nutrients availability for plants
(Zaman et al., 1999; Tu et al., 2003; Wang et al., 2004; Marinari
et al., 2006). Tu et al. (2003) showed that enhanced soil
microbial biomass and activity were associated with high net
N mineralization rates, which resulted in larger N availability.
In separate studies, Monokrousos et al. (2006) and Melero et al.
(2006) found the activities of enzymes involved in the cycles of
N and phosphorus (P) enhanced through the organic management, with beneficial effects for soil nutrients supply.
Stating that (i) the management systems react differently
in diverse climatic regimes with respect to TOC accumulation
in soil and (ii) short-term TOC changes are usually not
detectable due to the high background of soil C level, the
main questions addressed in this study were: (1) do soil
biochemical properties discriminate the management systems in a short-term period? (2) Which biochemical indicator
is more effective in predicting TOC changes in soil under
Mediterranean environment?
2.
Materials and methods
2.1.
Site description
At the University of Tuscia experimental farm (Viterbo) a longterm field study was established in 2001, in order to compare
organically (ORG) and conventionally (CONV) managed soil in
a randomized block design with three replicated plots of
108 m2. The soil is clay loam and classified as Typic Xerofluvent
(Soil Taxonomy, Biondi, personal communication). For further
details see Mancinelli et al. (2007). In the conventional system
the traditional agricultural practices (e.g. chemical fertilizers
and pesticides, etc.) are adopted, whereas the organic system
is managed following the Regulation 2092/91/EEC. Both
systems have a 3 years crop rotation (pea, Pisum sativum L.;
durum wheat, Triticum durum Desf.; tomato, Licopersicum
esculentum Mill.). Tomato was irrigated during the vegetative
period, providing 3500–4000 m3 ha 1 following potential
evapo-transpiration. In the organic management, the rotation
is implemented with common vetch (Vicia sativa L.) and
520
ecological indicators 9 (2009) 518–527
sorghum (Sorgum vulgare L.) cover crops used as green manure
before tomato transplanting and pea planting, respectively.
Organic fertilizers (Guanito, DIX10; green manure), and
mineral nitrogen fertilizer (NH4NO3) were applied to organic
and conventional fields, respectively, using the equivalent
dose of 120 and 200 kg N ha 1 for durum wheat and tomato,
respectively. Moreover, the crops in both management
systems were sown after minimum tillage (harrowing 15 cm
depth). The three crops are simultaneously cropped in the
experimental field that includes thus 18 plots: 2 systems 3
crops 3 replicates.
2.2.
Soil sampling
Soil sampling was performed in February 2006 and at the end
of the vegetative cycle for each crop (June for durum wheat
and pea, August for tomato), in order to take into account
seasonal fluctuations of biochemical properties (Wick et al.,
2002). After removal of litter layer two soil cores were taken
inside each plot at 20 cm depth and then pooled together. Soil
samples were sieved (
available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/ecolind
Soil biochemical indicators as a tool to assess the short-term
impact of agricultural management on changes in organic C
in a Mediterranean environment
A. Lagomarsino a,*, M.C. Moscatelli a, A. Di Tizio a, R. Mancinelli b, S. Grego a, S. Marinari a
a
b
Department of Agrobiology and Agrochemistry, University of Tuscia, Via S.Camillo de Lellis s.n.c., 01100 Viterbo, Italy
Department of Crop Production, Via S.Camillo de Lellis s.n.c., 01100 Viterbo, Italy
article info
abstract
Article history:
Two management systems (conventional vs. organic) in a 3-years crop rotation (pea–durum
Received 23 April 2008
wheat–tomato) were compared after 4 years in order to assess soil carbon (C) changes in a
Received in revised form
short-term period. Biochemical properties of soil, such as microbial biomass C and N (MBC
2 July 2008
and MBN), microbial respiration, N mineralization, dehydrogenase, chitinase, acid–phos-
Accepted 4 July 2008
phatase, arylsulfatase and b-glucosidase activities, were chosen as indicators of soil organic
matter biochemical alteration. The main questions addressed in this study were (1) do soil
biochemical properties discriminate between organic and conventional management sys-
Keywords:
tems in a short-term period? (2) Which biochemical indicator is more effective in predicting
Organic management
soil organic C accumulation in organically managed agricultural soils?
Soil indicators
A general increase of hydrolytic enzymes activities has been observed in soil under
Hydrolytic enzymes
organic management. MBC, MBN and the MBC/TOC ratio (qmic) increased in organic soil
Dehydrogenase
under pea (100%, 50% and 100%, respectively) and durum wheat (55%, 28% and 42%,
C accumulation
respectively), while the basal respiration per unit of microbial biomass (qCO2 ) decreased
Microbial biomass
(48% and 40% under pea and durum wheat, respectively). Moreover, the specific activity of bglucosidase was significantly lower under organic management of pea and durum wheat
and was positively correlated with qCO2 , suggesting a lower maintenance energy requirement of the microbial community.
Soil microbial biomass and enzymatic activities were successfully used to detect shortterm changes in soil and, taking into account its role in soil functioning, b-glucosidase
resulted the most suitable indicator to predict organic C accumulation in soil under organic
management in a Mediterranean environment.
# 2008 Elsevier Ltd. All rights reserved.
1.
Introduction
Total organic carbon (TOC) in soil is usually considered as one
of the most important properties of soils because of its impact
on ecosystem sustainability, affecting other physical, chemical and biological characteristics of soil (Reeves, 1997).
Nevertheless, only drastic changes can modify this parameter
in the short-term. Differently, when comparing soils with
similar physico-chemical properties subjected to different
managements, biochemical properties can be used as indicators because of their great sensitivity to even slight modifications in the short-term (Gil-Sotres et al., 2005). In this study we
selected some biochemical indicators (microbial biomass,
enzyme activities and microbial indices) on the basis of their
* Corresponding author. Tel.: +39 0761 357248; fax: +39 0761 357242.
E-mail address: lagomarsino@unitus.it (A. Lagomarsino).
1470-160X/$ – see front matter # 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.ecolind.2008.07.003
ecological indicators 9 (2009) 518–527
role in soil C and N cycling, which represent the key elements
to evaluate agricultural management sustainability.
In particular, microbial biomass has been suggested as an
integrative signal of the microbial significance in soils because
it is one of the few fractions of soil organic matter (SOM) that is
biologically meaningful, easily measurable, and sensitive to
management or pollution (Powlson, 1994). It is both a source
and sink for nutrients, it participates in the main biogeochemical transformation of C, N, P, S and it contributes to soil
structure and stabilization. For these reasons, microbial
biomass is widely used as indicator in many soil-monitoring
programs (Winding et al., 2005). At the same time, microbially
mediated nitrogen (N) mineralization in soil is important in
order to sustain plant productivity without massive use of
mineral fertilizers.
Moreover enzyme activities can provide indication for
quantitative changes in SOM. It is known that the activities of
most enzymes increase as native SOM content increases,
reflecting larger microbial communities and stabilization of
enzymes on humic materials (Burns, 1982; Bending et al.,
2002). Enzymes allow microbes to access energy and nutrients
present in complex substrates and catalyze decomposition
and nutrient mineralization as well as humification processes
(Sinsabaugh et al., 1993; Asmar et al., 1994; Masciandaro and
Ceccanti, 1999; Allison and Vitousek, 2005). Among hydrolytic
enzymes, acid phosphatase and b-glucosidase activities have
been frequently used as indicators of changes in quantity and
quality of SOM (Gil-Sotres et al., 2005). N-Acetyl-glucosaminidase activity is considered to be important in C and N cycling
because it participates in the processes whereby chitin is
converted to amino sugars, which is one of the major sources
of mineralizable N in soils (Ekenler and Tabatabai, 2002). NAcetyl-glucosaminidase and arylsulphatase activities are also
considered as indirect indicators of the presence of fungal
biomass because sulphate esters (substrates of arylsulphatase) are only present in fungal cells (Bandick and Dick, 1999)
and chitin is the main constituent of fungal cell wall tissue
(Miller et al., 1998). Dehydrogenase activity typically occurs in
all intact, viable microbial cells. Thus, its measurement is
usually related to the presence of viable microorganisms and
their oxidative capability (Trevors, 1984).
Representing single biochemical properties as an index can
be a valid approach to evaluate the significance of microbial
populations and microbial activity in the cycling of elements
in soils under different management (Nannipieri, 1994;
Anderson, 2003). The use of quotients avoids the problems
of comparing trends in soils with different organic matter or
microbial biomass content (Sparling, 1997) and appears to
provide more sensitive indications of soil changes than either
activity or population measurements alone (Brookes, 1995;
Dilly and Munch, 1998). The metabolic quotient (basal
respiration per unit of microbial biomass, qCO2 ) reflects the
maintenance energy requirement of soil microbes (Anderson,
2003) and can be a relative measure of how efficiently the soil
microbial biomass is utilizing C resources, as well as the
degree of substrate limitation for soil microbes (Wardle and
Ghani, 1995; Dilly and Munch, 1998). Anderson (2003) indicated
above 2 g C–CO2 h 1 kg MBC 1 as a critical threshold for the
‘‘baseline performance’’ of microbial communities. The
percentage of MBC to TOC (qmic) could be used as a stability
519
indicator for quick recognition of an environmental change
(Anderson, 2003), it reflects the contribution of microbial
biomass to soil organic carbon (Anderson and Domsch, 1989)
and it indicates the substrate availability to the soil microbes,
being values below 2% a signal of SOM depletion (Anderson,
2003). The enzyme activities can also be expressed per unit of
MBC (specific activities), which represent a measure of
microbial physiological capacity, and have been found to be
more closely related to community composition than total
enzyme activity (Waldrop et al., 2000).
It has been shown that in the long-term organic management of agricultural soils positively influences soil properties
(Schjonning et al., 2002; Tu et al., 2006a) since the addition of
organic amendments can improve TOC accumulation in soil
by increasing C pools with a slow turnover time (Lal and
Kimble, 1997). Moreover, green manuring is considered a good
agricultural practice because of its positive effect on soil
fertility, quality and biodiversity (Stark et al., 2007). In the
short-term, several studies supported the evidence of an
increase of microbial biomass and activity under organic
management, leading to high nutrients availability for plants
(Zaman et al., 1999; Tu et al., 2003; Wang et al., 2004; Marinari
et al., 2006). Tu et al. (2003) showed that enhanced soil
microbial biomass and activity were associated with high net
N mineralization rates, which resulted in larger N availability.
In separate studies, Monokrousos et al. (2006) and Melero et al.
(2006) found the activities of enzymes involved in the cycles of
N and phosphorus (P) enhanced through the organic management, with beneficial effects for soil nutrients supply.
Stating that (i) the management systems react differently
in diverse climatic regimes with respect to TOC accumulation
in soil and (ii) short-term TOC changes are usually not
detectable due to the high background of soil C level, the
main questions addressed in this study were: (1) do soil
biochemical properties discriminate the management systems in a short-term period? (2) Which biochemical indicator
is more effective in predicting TOC changes in soil under
Mediterranean environment?
2.
Materials and methods
2.1.
Site description
At the University of Tuscia experimental farm (Viterbo) a longterm field study was established in 2001, in order to compare
organically (ORG) and conventionally (CONV) managed soil in
a randomized block design with three replicated plots of
108 m2. The soil is clay loam and classified as Typic Xerofluvent
(Soil Taxonomy, Biondi, personal communication). For further
details see Mancinelli et al. (2007). In the conventional system
the traditional agricultural practices (e.g. chemical fertilizers
and pesticides, etc.) are adopted, whereas the organic system
is managed following the Regulation 2092/91/EEC. Both
systems have a 3 years crop rotation (pea, Pisum sativum L.;
durum wheat, Triticum durum Desf.; tomato, Licopersicum
esculentum Mill.). Tomato was irrigated during the vegetative
period, providing 3500–4000 m3 ha 1 following potential
evapo-transpiration. In the organic management, the rotation
is implemented with common vetch (Vicia sativa L.) and
520
ecological indicators 9 (2009) 518–527
sorghum (Sorgum vulgare L.) cover crops used as green manure
before tomato transplanting and pea planting, respectively.
Organic fertilizers (Guanito, DIX10; green manure), and
mineral nitrogen fertilizer (NH4NO3) were applied to organic
and conventional fields, respectively, using the equivalent
dose of 120 and 200 kg N ha 1 for durum wheat and tomato,
respectively. Moreover, the crops in both management
systems were sown after minimum tillage (harrowing 15 cm
depth). The three crops are simultaneously cropped in the
experimental field that includes thus 18 plots: 2 systems 3
crops 3 replicates.
2.2.
Soil sampling
Soil sampling was performed in February 2006 and at the end
of the vegetative cycle for each crop (June for durum wheat
and pea, August for tomato), in order to take into account
seasonal fluctuations of biochemical properties (Wick et al.,
2002). After removal of litter layer two soil cores were taken
inside each plot at 20 cm depth and then pooled together. Soil
samples were sieved (