Directory UMM :Data Elmu:jurnal:S:Soil Biology And Chemistry:Vol32.Issue8-9.Aug2000:
Soil Biology & Biochemistry 32 (2000) 1131±1139
www.elsevier.com/locate/soilbio
Mineralization and microbial assimilation of 14C-labeled straw in
soils of organic and conventional agricultural systems
Andreas Flieûbach*, Paul MaÈder, Urs Niggli
Research Institute of Organic Agriculture (FiBL), Ackerstrasse, Postfasch, CH-5070 Frick, Switzerland
Abstract
An incubation experiment on straw decomposition was carried out with soils from a long-term ®eld trial at Therwil,
Switzerland. Two conventional agricultural systems, one with (CONFYM) and one without manure, an organic system managed
according to bio-dynamic farming practice (BIODYN) and an unfertilized control were compared. CONFYM received stacked
manure and an additional mineral fertilizer. BIODYN received composted farmyard manure and no mineral fertilizers. Both
systems received the same amount of manure based on 1.4 livestock units haÿ1. The aim of the investigation was to explain the
large dierences in soil microbial biomass and activity between the systems, especially between the manured soils. Dierences in
microbial C-utilization eciency were suggested to be the main reason. We followed the decomposition of 14C-labeled plant
material over a period of 177 days under controled incubation conditions. Prior to incubation, microbial biomass was 75%
higher and qCO2 up to 43% lower in the BIODYN soil than in the conventional soils. At the end of the incubation period, 58%
of the applied plant material was mineralized to CO2 in the BIODYN soil compared to 50% in the other soils. This dierence
became signi®cant 2 weeks after application of plant material and is suggested to be due to decomposition of more recalcitrant
compounds. After addition of plant material, the increase of microbial biomass in the unmanured systems was higher than in
the manured systems, but with a higher loss rate thereafter. The amount of 14C incorporated into Cmic as related to 14CO2
evolved was markedly higher in the BIODYN soil. The results support the hypothesis that agricultural measures applied to the
BIODYN system invoke a higher eciency of the soil microbial community with respect to substrate use for growth. 7 2000
Elsevier Science Ltd. All rights reserved.
Keywords: Organic farming; Long-term ®eld trial; Mineralization; Assimilation; Microbial biomass; Energy use eciency
1. Introduction
Almost 0.5% of European agricultural land (80,000
farms) is under organic management, promoted mainly
by direct or indirect governmental subsidies and the
increasing demand for organically grown food.
Between 1990 and 1997, the area managed organically
in Europe increased from 250,000 ha to almost
2,000,000 ha (Lampkin, 1997). In addition to crop rotation, organic fertilization and rejection of chemically
* Corresponding author. Tel.: +41-62-865-7225; fax: +41-62-8657273.
E-mail address: andreas.¯iessbach@®bl.ch (A. Flieûbach).
produced fertilizers and pesticides, organic farming
systems aim to keep the nutrient ¯ow in a closed cycle
on the farm (IFOAM, 1996). The European Community has released a directive on organic farming
((EWG) No. 2092/91) to assure comparable production standards and several organic farming systems
are certi®ed and/or controled by their label organizations. Bio-dynamic farming diers from other organic
farming systems mainly in the speci®c amendments
made to crops, soils and manure (Table 1) based on
anthroposophic philosophy (Koepf et al., 1976).
Soil organic matter responds to changes in land use
according to the quantity and quality of organic material entering the soil (Jenkinson and Ladd, 1981;
SoÈchtig and Sauerbeck, 1982). Manure and plant resi-
0038-0717/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved.
PII: S 0 0 3 8 - 0 7 1 7 ( 0 0 ) 0 0 0 2 8 - 6
1132
A. Flieûbach et al. / Soil Biology & Biochemistry 32 (2000) 1131±1139
due transformation processes are most important for
organic farmers, who do not use mineral fertilizers and
so rely entirely on biological nutrient cycling processes
(KoÈpke, 1997). These are sensitive indicators of soil
quality (Elliott et al., 1996). Organic farming systems
have the potential to minimize some of the negative
impacts of conventional agriculture (e.g. NO3-losses to
the groundwater, soil erosion, eects of pesticides on
non-target organisms, loss of crop genetic diversity)
(Tilman, 1998), and often lead to improvement of soils
in terms of biological and chemical properties and
physical stability (Drinkwater et al., 1998; MaÈder et
al., 1996; Reganold et al., 1987). Soils from biodynamic farms are similar to conventionally farmed
soils with regard to soil structure but have a higher
production potential (Droogers and Bouma, 1996). On
bio-dynamic farms in New Zealand, the total C and N
clearly increased during pasture and decreased during
cropping phases, which was not the case on conventional farms (Murata and Goh, 1997).
Soil microbial biomass and activity are signi®cantly
increased by crop rotation compared to monoculture
as well as by addition of organic manures (Anderson
and Domsch, 1989). The biologically active pool represents only a small fraction of the total soil organic
matter, but it is often increased in organically managed
soils, as revealed by microbial biomass measurements
(Flieûbach and MaÈder, 1997; Franzluebbers et al.,
1996; Oberson et al., 1993; von LuÈtzow and Ottow,
1994; Zelles et al., 1992), and the physical and chemical properties of soil organic matter (Flieûbach and
MaÈder, 2000; Wander and Traina, 1996). Microbial
biomass and microbial activities involved in phosphorus dynamics are also enhanced in biologically
managed systems (Oberson et al., 1996), emphasizing
the key position of soil microbial activity in transformation of nutrients for the crop.
An active soil micro¯ora which rapidly decomposes
plant litter and manure is important in the mineralization of plant nutrients. Lack of synchronicity with
plant demand, with mineralization coinciding with
periods of low plant requirement, however, may be a
serious problem in soils with high biological activity.
On the other hand, a considerable part of the decomposing material will be used to form new microbial
biomass, and labile as well as stabilized organic compounds in the soil (Jenkinson et al., 1987; Parton et
al., 1987). Catabolic and anabolic soil processes may
®nally reach a steady state under continuous management, with the mean annual C input equaling the
amount of C respired.
The microbial respiration to microbial biomass ratio
(qCO2), which is related to soil development, decreases
with succession and increases with environmental stress
and indicates the energy needed for maintenance of
microbial biomass (Anderson and Domsch, 1993;
Insam and Haselwandter, 1989; Wardle and Ghani,
1995). A high qCO2 in agricultural soils indicates that
nutrients are recycled quickly (Insam et al., 1991).
Thus, qCO2 and processes related to the build-up and
turnover of microbial biomass may be useful indicators
of changes due to dierences in soil management and
farming practice.
In the present study, we compared soils from organic and conventional agricultural systems with
respect to C mineralization and immobilization. Soil
biological properties have altered considerably in the
19 years of the experiment. Within an identical crop
rotation, microbial biomass, qCO2, microbial functional diversity, and microbial P dynamics, all indicated the greater importance of microbial processes in
organically managed soils (Flieûbach and MaÈder,
1997; Oberson et al., 1996). We propose that this is
due to C utilization eciency, as indicated by qCO2
Table 1
Main dierences between the treatments of the DOC-farming systems experiment (2nd and 3rd crop rotation period)
Bio-dynamic (BIODYN)
Conventional (CONFYM)
Mineral NPK (CONMIN)
Unfertilized (NOFERT)
Fertilized with composted farmyard-manure (FYM) (é 881 kg C haÿ1 yÿ1; C/N = 7.9), slurry and
amended with mineral and herbaceous preparationsa according to bio-dynamic farming. Mechanical
weed control
Fertilized with stacked, anaerobically rotted FYM (é 990 kg C haÿ1 yÿ1; C/N = 11.4) and additional
mineral fertilization according to ocial norm, integrated plant protectionb
Unfertilized from 1978 until 1985, but then fertilized with mineral fertilizers according to ocial norm
(é 90 kg N haÿ1 to winter wheat), integrated plant protectionb
Unfertilized since 1978, but amended with mineral and herbaceous preparationsa according to biodynamic farming. Mechanical weed control
a
The bio-dynamic preparations (P) consist of the following: P 500: cow-manure fermented in a cow horn; P 501: silica fermented in a cow
horn, which were amended at rates of 250 and 4 g haÿ1, respectively. Composting additives are yarrow ¯owers (P 502, Achillea millefolium, L.),
camomile ¯owers (P 503, Matricaria recutita, L.), stinging nettle (P 504, Urticaria dioica, L.), oak bark (P 505, Quercus robur, L.), dandelion
¯owers (P 506, Taraxacum ocinale, Wiggers) and valerian ¯owers (P 507, Valeriana ocinalis, L.). A decoct of shave-grass (Equisetum arvense,
L.) is applied once during vegetative growth to wheat and potatoes as a protective agent against plant diseases at rates of 1.5 kg haÿ1. For
further details see Reganold and Palmer (1995); or Koepf et al. (1976).
b
Herbicides (1±2 treatments yÿ1) and fungicides (2±3 treatments yÿ1) according to threshold values, plant growth regulators were applied routinely to winter wheat. Pest control was necessary regularly in potatoes and rarely in winter wheat.
A. Flieûbach et al. / Soil Biology & Biochemistry 32 (2000) 1131±1139
and dierences in light fraction organic matter
(Flieûbach and MaÈder, 2000). This hypothesis was
tested by examining microbial mineralization and immobilization of 14C-labeled plant material.
1133
cores/plot, 0±20 cm depth). In the laboratory, soils
were stored at 48C for 6 weeks, before sieving (
www.elsevier.com/locate/soilbio
Mineralization and microbial assimilation of 14C-labeled straw in
soils of organic and conventional agricultural systems
Andreas Flieûbach*, Paul MaÈder, Urs Niggli
Research Institute of Organic Agriculture (FiBL), Ackerstrasse, Postfasch, CH-5070 Frick, Switzerland
Abstract
An incubation experiment on straw decomposition was carried out with soils from a long-term ®eld trial at Therwil,
Switzerland. Two conventional agricultural systems, one with (CONFYM) and one without manure, an organic system managed
according to bio-dynamic farming practice (BIODYN) and an unfertilized control were compared. CONFYM received stacked
manure and an additional mineral fertilizer. BIODYN received composted farmyard manure and no mineral fertilizers. Both
systems received the same amount of manure based on 1.4 livestock units haÿ1. The aim of the investigation was to explain the
large dierences in soil microbial biomass and activity between the systems, especially between the manured soils. Dierences in
microbial C-utilization eciency were suggested to be the main reason. We followed the decomposition of 14C-labeled plant
material over a period of 177 days under controled incubation conditions. Prior to incubation, microbial biomass was 75%
higher and qCO2 up to 43% lower in the BIODYN soil than in the conventional soils. At the end of the incubation period, 58%
of the applied plant material was mineralized to CO2 in the BIODYN soil compared to 50% in the other soils. This dierence
became signi®cant 2 weeks after application of plant material and is suggested to be due to decomposition of more recalcitrant
compounds. After addition of plant material, the increase of microbial biomass in the unmanured systems was higher than in
the manured systems, but with a higher loss rate thereafter. The amount of 14C incorporated into Cmic as related to 14CO2
evolved was markedly higher in the BIODYN soil. The results support the hypothesis that agricultural measures applied to the
BIODYN system invoke a higher eciency of the soil microbial community with respect to substrate use for growth. 7 2000
Elsevier Science Ltd. All rights reserved.
Keywords: Organic farming; Long-term ®eld trial; Mineralization; Assimilation; Microbial biomass; Energy use eciency
1. Introduction
Almost 0.5% of European agricultural land (80,000
farms) is under organic management, promoted mainly
by direct or indirect governmental subsidies and the
increasing demand for organically grown food.
Between 1990 and 1997, the area managed organically
in Europe increased from 250,000 ha to almost
2,000,000 ha (Lampkin, 1997). In addition to crop rotation, organic fertilization and rejection of chemically
* Corresponding author. Tel.: +41-62-865-7225; fax: +41-62-8657273.
E-mail address: andreas.¯iessbach@®bl.ch (A. Flieûbach).
produced fertilizers and pesticides, organic farming
systems aim to keep the nutrient ¯ow in a closed cycle
on the farm (IFOAM, 1996). The European Community has released a directive on organic farming
((EWG) No. 2092/91) to assure comparable production standards and several organic farming systems
are certi®ed and/or controled by their label organizations. Bio-dynamic farming diers from other organic
farming systems mainly in the speci®c amendments
made to crops, soils and manure (Table 1) based on
anthroposophic philosophy (Koepf et al., 1976).
Soil organic matter responds to changes in land use
according to the quantity and quality of organic material entering the soil (Jenkinson and Ladd, 1981;
SoÈchtig and Sauerbeck, 1982). Manure and plant resi-
0038-0717/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved.
PII: S 0 0 3 8 - 0 7 1 7 ( 0 0 ) 0 0 0 2 8 - 6
1132
A. Flieûbach et al. / Soil Biology & Biochemistry 32 (2000) 1131±1139
due transformation processes are most important for
organic farmers, who do not use mineral fertilizers and
so rely entirely on biological nutrient cycling processes
(KoÈpke, 1997). These are sensitive indicators of soil
quality (Elliott et al., 1996). Organic farming systems
have the potential to minimize some of the negative
impacts of conventional agriculture (e.g. NO3-losses to
the groundwater, soil erosion, eects of pesticides on
non-target organisms, loss of crop genetic diversity)
(Tilman, 1998), and often lead to improvement of soils
in terms of biological and chemical properties and
physical stability (Drinkwater et al., 1998; MaÈder et
al., 1996; Reganold et al., 1987). Soils from biodynamic farms are similar to conventionally farmed
soils with regard to soil structure but have a higher
production potential (Droogers and Bouma, 1996). On
bio-dynamic farms in New Zealand, the total C and N
clearly increased during pasture and decreased during
cropping phases, which was not the case on conventional farms (Murata and Goh, 1997).
Soil microbial biomass and activity are signi®cantly
increased by crop rotation compared to monoculture
as well as by addition of organic manures (Anderson
and Domsch, 1989). The biologically active pool represents only a small fraction of the total soil organic
matter, but it is often increased in organically managed
soils, as revealed by microbial biomass measurements
(Flieûbach and MaÈder, 1997; Franzluebbers et al.,
1996; Oberson et al., 1993; von LuÈtzow and Ottow,
1994; Zelles et al., 1992), and the physical and chemical properties of soil organic matter (Flieûbach and
MaÈder, 2000; Wander and Traina, 1996). Microbial
biomass and microbial activities involved in phosphorus dynamics are also enhanced in biologically
managed systems (Oberson et al., 1996), emphasizing
the key position of soil microbial activity in transformation of nutrients for the crop.
An active soil micro¯ora which rapidly decomposes
plant litter and manure is important in the mineralization of plant nutrients. Lack of synchronicity with
plant demand, with mineralization coinciding with
periods of low plant requirement, however, may be a
serious problem in soils with high biological activity.
On the other hand, a considerable part of the decomposing material will be used to form new microbial
biomass, and labile as well as stabilized organic compounds in the soil (Jenkinson et al., 1987; Parton et
al., 1987). Catabolic and anabolic soil processes may
®nally reach a steady state under continuous management, with the mean annual C input equaling the
amount of C respired.
The microbial respiration to microbial biomass ratio
(qCO2), which is related to soil development, decreases
with succession and increases with environmental stress
and indicates the energy needed for maintenance of
microbial biomass (Anderson and Domsch, 1993;
Insam and Haselwandter, 1989; Wardle and Ghani,
1995). A high qCO2 in agricultural soils indicates that
nutrients are recycled quickly (Insam et al., 1991).
Thus, qCO2 and processes related to the build-up and
turnover of microbial biomass may be useful indicators
of changes due to dierences in soil management and
farming practice.
In the present study, we compared soils from organic and conventional agricultural systems with
respect to C mineralization and immobilization. Soil
biological properties have altered considerably in the
19 years of the experiment. Within an identical crop
rotation, microbial biomass, qCO2, microbial functional diversity, and microbial P dynamics, all indicated the greater importance of microbial processes in
organically managed soils (Flieûbach and MaÈder,
1997; Oberson et al., 1996). We propose that this is
due to C utilization eciency, as indicated by qCO2
Table 1
Main dierences between the treatments of the DOC-farming systems experiment (2nd and 3rd crop rotation period)
Bio-dynamic (BIODYN)
Conventional (CONFYM)
Mineral NPK (CONMIN)
Unfertilized (NOFERT)
Fertilized with composted farmyard-manure (FYM) (é 881 kg C haÿ1 yÿ1; C/N = 7.9), slurry and
amended with mineral and herbaceous preparationsa according to bio-dynamic farming. Mechanical
weed control
Fertilized with stacked, anaerobically rotted FYM (é 990 kg C haÿ1 yÿ1; C/N = 11.4) and additional
mineral fertilization according to ocial norm, integrated plant protectionb
Unfertilized from 1978 until 1985, but then fertilized with mineral fertilizers according to ocial norm
(é 90 kg N haÿ1 to winter wheat), integrated plant protectionb
Unfertilized since 1978, but amended with mineral and herbaceous preparationsa according to biodynamic farming. Mechanical weed control
a
The bio-dynamic preparations (P) consist of the following: P 500: cow-manure fermented in a cow horn; P 501: silica fermented in a cow
horn, which were amended at rates of 250 and 4 g haÿ1, respectively. Composting additives are yarrow ¯owers (P 502, Achillea millefolium, L.),
camomile ¯owers (P 503, Matricaria recutita, L.), stinging nettle (P 504, Urticaria dioica, L.), oak bark (P 505, Quercus robur, L.), dandelion
¯owers (P 506, Taraxacum ocinale, Wiggers) and valerian ¯owers (P 507, Valeriana ocinalis, L.). A decoct of shave-grass (Equisetum arvense,
L.) is applied once during vegetative growth to wheat and potatoes as a protective agent against plant diseases at rates of 1.5 kg haÿ1. For
further details see Reganold and Palmer (1995); or Koepf et al. (1976).
b
Herbicides (1±2 treatments yÿ1) and fungicides (2±3 treatments yÿ1) according to threshold values, plant growth regulators were applied routinely to winter wheat. Pest control was necessary regularly in potatoes and rarely in winter wheat.
A. Flieûbach et al. / Soil Biology & Biochemistry 32 (2000) 1131±1139
and dierences in light fraction organic matter
(Flieûbach and MaÈder, 2000). This hypothesis was
tested by examining microbial mineralization and immobilization of 14C-labeled plant material.
1133
cores/plot, 0±20 cm depth). In the laboratory, soils
were stored at 48C for 6 weeks, before sieving (