Thematic network CONSIDER (EVK2-CT-2002-20012)
Second periodic report (deliverable 33, DoW)
”Environmental friendly agriculture and soil biodiversity”
Forschungsinstitut für Biologische Landwirtschaft (FiBL), Frick, Switzerland, (November 11-13 2004)
Introduction
CONSIDER deals with the most important anthropogenic activities that pose a threat
towards, or are being implemented to mitigate loss in, soil biodiversity. Threats are
habitat fragmentation and destruction and global climate change, whereas mitigation
activities include land abandonment and environmentally-friendly agriculture.
CONSIDER addresses these four topics, initially at each their workshop. To further
strengthen the focus of discussions, CONSIDER will perform, during the course of its
workshops, assessments or experiments at existing field experiments of relevance to
the theme of the workshop.
The impact of environmental friendly agriculture was the topic of workshop 3
of CONSIDER, held in Frick (Switzerland) November 11-13 2004. High input
agricultural practices have led to a severe conflict between the production of
agricultural goods and the conservation of biodiversity. The conflict is expected to
become even more severe in future with the use of genetically modified crop plants,
e.g. plants resistant to herbicides. A more environmentally-friendly agriculture aims
to reduce the input of fertilizers and pesticides by fostering internal nutrient cycles
and by making full use of the natural enemy complex of pest species in agricultural
landscapes. Fostering internal nutrient cycles can only be achieved by conserving the
below-ground food web components and by intensifying the activity of the
decomposer community. Therefore, a more environmentally-friendly agriculture is
intimately linked to the conservation of soil biodiversity. Fostering the natural enemy
complex of pest species is also linked to the biodiversity of agricultural land, which
preferably should include a more varied plant cover than a crop monoculture
The main goal of this workshop is to evaluate the interrelationships between
(1) agricultural practices and soil biodiversity, (2) soil biodiversity and crop
production (internal nutrient cycles) and (3) soil biodiversity and the diversity of
generalist predators as antagonists of pest species.
The topics were arranged into the themes (i) linkages between diversity in
vegetation and diversity in soil (ii) evidence for the relationship between soil organic
matter and soil biodiversity, (iii) interactions between heterogeneous inputs and the
stability versus variability of populations in time and space, and (iv) multitrophic
interactions at the living plant. Most emphasis was placed on theme (ii) and (iii) at
this workshop.
(i) Linkages between diversity in vegetation and diversity in soil.
In arable farming of any type plant diversity ranges at a very low level between one
and a few species. One aspect dealt with, however, is the relation between crop
variability and soil biodiversity. The possibility exists that a mixture of various crop
plants present each year within an area results in larger biversity belowground
compared to monocultures.
(ii) Relationship between soil organic matter and soil biodiversity
Soil organic matter forms the basis of the decomposer food web where most of
the biodiversity belowground reside. Ecosystem services such as decomposition and
mineralisation rely on the functioning of the below-ground community of organisms.
The below-ground food web is compartmentalized and the channel based on root
exudates (the fast bacterial-based lane) separates from that based on particulate litter
(the slow fungal-based lane). Soil microbial and invertebrate groups differentially
respond to an increase in soil organic matter.
At the workshop driving forces for food-web complexity in detrital systems
were identified. The role of root exudates and particulate litter materials for soil
biodiversity was highlighted in order to trace causes for the differential response of
microbial and invertebrate groups to changes in organic matter. Concepts on
regulating forces of biodiversity in the fungal energy channel of decomposer systems
were discussed, and the relative importance of bottom-up vs. top-down forces for
regulating soil biodiversity were evaluated. These issues can be formulated into the
following key questions dealt with: (a) What does an increase or quality change in
organic residues mean to soil biodiversity? (b)What are the effects of organic farming
on soil (functional) biodiversity and its role in organic matter turnover? (c) What
management practice will improve functional role of soil biodiversity in conserving
matter? One question is to unravel the relationship between soil organic matter and
soil functional biodiversity at the landscape scale. This relationship is certainly not
linear, but over a wide range soil organic matter and invertebrate diversity are indeed
correlated. When employing organic farming and thereby increasing soil organic
carbon by increasing organic matter content (3, 7) soil biodiversity increase.
The relationship between soil organic matter and soil biodiversity depends on
scale. Moreover, quality of crop residues and their distribution in the soil are major
driving forces for soil biodiversity at the local scale. At the workshop techniques and
methodology on analysis of the relationship between soil organic matter and soil
biodiversity on a regional and local scale were evaluated. Techniques for
measurement of litter quality and for analysing the spatial structure of litter resources
were discussed. Concepts on driving forces of soil animal diversity at the regional and
local field scale were developed. In contrast to large-scale patterns, soil biodiversity is
affected much stronger by distribution and quality of litter materials, habitat structure
and local disturbance regimes (2, 4). In comparison to the above ground food web the
driving forces for soil biodiversity are surprisingly little understood (1, 6). For a
number of important soil animal groups such as oribatid mites, nematodes and
protozoa which are extraordinary rich in species there even does not exist a key for
species determination. This illustrates the importance of bringing together experts
within the above-mentioned faunal groups.
(iii) Interactions between heterogeneous inputs and stability/variability of populations
in time and space
Even in cultivated soils where distribution of resources and organisms can be
expected to be more uniform than in natural areas, the cryptic nature of soil organisms
makes it difficult to determine interactions between organisms acting on different
scales (5). The major questions dealt with were (a) What is the importance of crop
frequency or distribution pattern across the landscape for soil biodiversity? And (b)
How will temporal variation in input of organic matter affect soil biodiversity?
(iv) multitrophic interactions at the living plant
Under this heading, workshop 3 focused on the question how soil organisms and
herbivores interact as dependent on amount of soil organic matter respectively
diversity of the crop cover.
1 Giller, P. S. (1996) The diversity of soil communities, the poor mans tropical rainforest. Biodiversity and
Conservation, 5:135-168.
2 Hansen, R. A. (2000) Effects of habitat complexity and composition on a diverse litter microarthropod
assemblage. Ecology 81, 1120-1132.
3 Hawksworth, D. L. (1991) The biodiversity of microorganisms and invertebrates: its role in sustainable
agriculture. Wallingford: CAB International.
4 Huhta, V.; Persson, T., and Setälä, H.(1998) Functional implications of soil fauna diversity in boreal
forests. Applied Soil Ecology 10, 277-288.
5 Klironomos JN, Rillig M, Allen MF, (1999) Designing belowground field experiments with the help of
semi-varaiance and power analyses. Applied Soil Ecology 12: 227-238.
6 Scheu S, Setälä H (2001) Multitrophic interactions in decomposer communities. In: Tscharntke T,
Hawkins BA (eds) Multitrophic level interactions. Cambridge University Press, Cambridge, in press
7 Thomas, C. F. G. and Marshall, E. J. P.(1999) Arthropod abundance and diversity in differently vegetated
margins of arable fields. Agriculture Ecosystems and Environment 72, 131-144.
Abstracts of talks at workshop 3.
Introduction
Productivity, soil fertility and biodiversity in organic agriculture
Andreas Fliessbach & Paul Mäder (Forschungsinstitut für Biologischen Landbau FiBL, Frick,
Switzerland)
The land area of organic agriculture in Europe and in many other countries of the world has increased
considerably in the last years and organic agriculture is investigated intensively in many fields of
research. Earlier the organic farming movement was created by pioneers, whose ideas and innovations
formed an alternative to the so-called „green revolution“ that came along with pesticide use and
synthetic fertilizers. For the first time environmental problems caused by agriculture became evident.
In 1978 the DOK long-term field experiment was installed at Therwil close to Basel comparing the
farming systems „bio-Dynamic“, „bio-Organic“ and „(K)conventional“. In the first years of the trial,
crop yield and feasibility of organic farming were investigated. Soils were analysed with respect to
long-term effects on fertility and were rated in the view of farming effects on the environment. Today
the quality of organic products is the main research interest. Long-term trials like the DOK-trial offer
unique opportunities for this kind of research.
The DOK-trial compares the three systems mentioned above on the basis of the same intensity
of organic fertilization (i.e. the same number of animals per area), the same crop rotation and the same
soil tillage. Fertilization and plant protection are different and done according to the farming system. A
minerally fertilized conventional treatment is mimicking stockless farming and unfertilized plots serve
as controls.
Crop yields of the organic systems averaged over 21 experimental years at 80% of the
conventional ones. The fertilizer input, however, was 34 – 51% lower, indicating an efficient
production. The organic farming systems used 20 – 56% less energy to produce a crop unit and per
land area this difference was 36 – 53%. In spite of the considerably lower pesticide input the quality of
organic products was hardly discernible from conventional analytically and even came off better in
food preference trials and picture creating methods.
Maintenance of soil fertility is important for a sustainable land use. In our DOK field plots the
organically treated soils were biologically more active than conventional, whereas chemical and
physical soil parameters differed less significantly.
Winter wheat yield
Fertilizer (NH4NO3-equivalent)
Energy (Diesel-equivalent)
Plant protection (active ingredients)
Soil microbial biomass
corresponding to ca.
Organic
4.7 t/ha
122 kg/ha
340 l/ha
0-200 g/ha
40 t/ha
700 sheep
Conventional
5.6 t/ha
360 kg/ha
570 l/ha
6.0 kg/ha
24 t/ha
400 sheep
The organic farming systems show an efficient utilization of natural resources and a higher floral and
faunal diversity – features typical for mature ecosystems. We therefore conclude that organically
manured land use systems with grass-clover in the crop rotation and using organic fertilizers from the
farm itself are a realistic alternative to conventional agricultural systems.
Key references
Drinkwater L E, Wagoner P and Sarrantonio M 1998 Nature 396, 262-264.
Mäder P, Fließbach A, Dubois D, Gunst L, Fried P and Niggli U 2002 Science 296, 1694-1697.
Reganold J P, Elliot L F and Unger Y L 1987 Nature 330, 370-372.
Macilwain C 2004 Nature 428, 792-793.
Session I: Economics, management and matter fluxes
Land management, soil carbon sink, and nutrient cycling
Rainer Georg Joergensen (Department of Soil Biology and Plant Nutrition, Nordbahnhofstr. 1a,
University of Kassel, 37213 Witzenhausen, Germany)
The improvement and maintenance of soil fertility is the central aim of organic farming. The soil biota
is a key component of soil fertility, which is related to the capability of primary and secondary
production. The two main functions of soil microorganisms are conducting and maintaining the
majority of enzymatic processes in soil and storing a considerable amount of energy and nutrients in
their biomass. The soil microbial biomass is an indicator of soil fertility and it can be non-selectively
estimated by the fumigation-extraction method and ATP. Soil fertility is related to the capability of
primary and secondary production. Consequently, the formation of soil microbial biomass is related to
the C-input by plants into the soil. However, the relationship between soil microbial biomass C and
grass aboveground dry matter at the Mühlberg site at Frankenhausen, the experimental farm of the
University of Kassel showed only weak significance. This relationship is weakened by a variety of
different factors, especially the water regime, texture and management history.
The turnover of the microbial biomass is the driving force of mobilisation and immobilisation
processes of nutrients, especially of N, P, and S mainly bonded in soil organic matter. The turnover of
the microbial biomass is controlled by soil animals in natural environments, but is also strongly
affected by the land use management of arable sites. The turnover time or mean resident time of
microbial biomass C is the average storage period of an element in this compartment. The turnover rate
R is the reciprocal value of the turnover time T (T = 1 / R) and describes the synthesis and loss of
microbial products per time period. Under equilibrated environmental conditions, there are various
ways of estimating the turnover rate R of microbial biomass C. The most suitable approach is based on
the following calculation: R = Y x M (M = maintenance coefficient: substrate C / C in a constant
microbial biomass, Y = yield coefficient: substrate C in microbial products / substrate C).
Under equilibrated conditions in Lower Saxony an average C input of 4 t ha -1 a-1 (which must be
identical to an average C output as CO2 of 4 t ha-1 a-1) maintains an average microbial biomass of 1.5 t
C ha-1. The yield coefficient of glucose and microbial biomass is similar at 0.55. The turnover rate R
and the turnover time T are consequently: R = 0.55 x 4 / 1.5 a-1 = 1.5 a-1 and T = 0.67 a = 243 d
Assuming that the average turnover of the different C fractions is similar to the average turnover of N
and P containing organic components, which is not necessarily true, the nutrient flux through the soil
microbial biomass can be calculated as follows: Stock  turnover rate R. Based on a turnover rate of
1.5, the means annual flux rates of N, P, and S through the microbial biomass at 27 arable sites in
Lower Saxony, Germany, are 340 kg N ha-1 a-1, 225 kg P ha-1 a-1, and 23 kg S ha-1 a-1, i.e. highly
relevant numbers for plant nutrition.
Key references
Höper, H., Kleefisch, B., 2001. Untersuchung bodenbiologischer Parameter im Rahmen der BodenDauerbeobachtung in Niedersachsen – Bodenbiologische Referenzwerte und Zeitreihen. Arbeitshefte
Boden 2001/4, NLfB, Hannover.
Jenkinson, D.S., Ladd, J.N., 1981. Microbial biomass in soil: Measurement and turnover. In Paul E.A.,
Ladd, J.N. (Eds.), Soil Biochemistry, Volume 5. Dekker, New York, pp. 415-471.
Jörgensen, R.G., 1995. Die quantitative Bestimmung der mikrobiellen Biomasse in Böden mit der
Chloroform-Fumigations-Extraktions-Methode. Göttinger Bodenkundliche Berichte 104, 1-229.
Joergensen, R.G., Brookes, P.C., Jenkinson, D.S., 1990. Survival of the soil microbial biomass at
elevated temperatures. Soil Biology and Biochemistry 22, 1129-1136.
Mäder, P., Fließbach, A., Dubois, D., Gunst, L., Fried, P., Niggli, U., 2002. Soil fertility and
biodiversity in organic farming. Science 296: 1694-1697.
Session II: Organic farming and soil microorganisms
Perspectives on the biological engine of the earth
(Karl Ritz1*, James A. Harris2, Iain M. Young3 and John W. Crawford3 , 1National Soil Resources
Institute and 2Institute of Water & Environment, Cranfield University, Silsoe, Bedfordshire MK45
4DT, UK; 3SIMBIOS Centre, University of Abertay Dundee, Bell Street, Dundee DD1 1HG, UK).
The soil biota can be viewed as the “biological engine of the earth”, controlling many of the key
processes that govern effective soil function and sustainability. This engineering metaphor can be
usefully extended when considering ways in which the soil biota can be studied, viz. genotypically
(‘library of blueprints’); phenotypically (‘component parts’); structurally (‘manifestation of the
engine’); and functionally (‘the working engine’). Management of the biota is best achieved by
manipulating the primary factors that govern biotic activity in soils, notably substrate (i.e. fuel) and
living space. We propose that these tenets must be used in devising sympathetic and effective
management strategies for sustainable agriculture. At the microbial level, species richness is of little
consequence since there scant evidence for relationships between taxonomy and function – it is the
functional repertoire of the organisms that are present, and the resultant interaction pathways, that are
more pertinent. The spatial organisation of soils, particularly the pore network, is crucially important
since it defines the habitat in which all soil life resides and functions, and prescribes the physical
framework in and through which all soil processes occur. Application of X-ray computed
microtomography is providing hitherto unattainable insights into the nature of soil pore networks at
scales directly pertinent to microbes. Whilst the architecture of the soil affects biotic function, the biota
in turn strongly influence the genesis and dynamics of soil structure. This leads to the concept of feedforward and feed-back loops and the potential for self-organisation and regulation in the soil:microbe
system. The pertinence of the physical structure of soils is complemented by apparent consistencies in
both the compositional and functional structure of soil communities. Soil is thus a living system,
founded on an appropriate spatial configuration of communities living within an inner space. If such a
‘characteristic configuration’ hypothesis is correct, this has important implications for the management
and monitoring of soils.
Key references
Crawford, J. W., Harris, J. A., Ritz, K. and Young, I. M. (2005) Towards and evolutionary ecology of
life in soil. Trends in Ecology & Evolution in press,
Ritz, K., McHugh, M. and Harris, J. A. (2004) Biological diversity and function in soils: contemporary
perspectives and implications in relation to the formulation of effective indicators. In Agricultural Soil
Erosion and Soil Biodiversity: Developing Indicators for Policy Analyses, ed R. Francaviglia, pp. 563572. OECD, Paris.
Ritz, K. and Young, I. M. (2004) Interactions between soil structure and fungi. Mycologist 18, 52-59
Young, I. M. and Ritz, K. (2000) Tillage, habitat space and function of soil microbes. Soil and Tillage
Research 53, 201-213
Young, I. M. and Crawford, J. W. (2004) Interactions and self-organization in the soil-microbe
complex. Science 304, 1634-1637
Microorganisms, nutrients and sustainable agriculture
Jaap Bloem1, Ton Schouten2, Wim Didden3, Gerard Jagers op Akkerhuis1, Harm Keidel4, Michiel
Rutgers2 , (1Alterra, Wageningen University and Research Centre, the Netherlands; 2Netherlands
Institute of Public Health and the Environment (RIVM), Bilthoven, the Netherlands; 3Sub-department
*
Presenting, and author for correspondence: k.ritz@cranfield.ac.uk
of Soil Quality, Wageningen University and Research Centre, the Netherlands; 4Blgg bv, Oosterbeek,
the Netherlands).
Soil quality influences agricultural sustainability, environmental quality and, consequently, plant,
animal and human health. Microorganisms are useful indicators of soil quality because they have key
functions in the decomposition of organic matter, nutrient cycling and maintenance of soil structure.
We summarize methods used for monitoring biomass, activity and diversity of soil organisms and show
some results of the Dutch Soil Quality network.
In contaminated soils microbial community structure was changed but diversity was not
always reduced. By contrast microbial biomass and activity were reduced markedly. In agricultural
soils there were large differences between different categories of soil type and land use. Organic
management resulted in an increased role of soil organisms as indicated by higher numbers and
activity. Replacement of mineral fertilizers by farmyard manure stimulated the bacterial branch of the
soil food web. Reduced availability of mineral nutrients appeared to increase fungi, presumably
mycorrhizas. Bacterial DNA profiles did not indicate low genetic diversity in agricultural soils,
compared with some acid and contaminated soils. Organic farms did not show higher genetic diversity
than intensive farms. At extensive and organic grassland farms nitrogen mineralization was about 50%
higher than at intensive farms. Also microbial biomass and activity, and different groups of soil
invertebrates tended to be higher.
Soil biodiversity cannot be monitored meaningfully with only a few simple tools. Extensive
and long-term monitoring is probably the most realistic approach to obtain objective information on
differences between, changes within, and human impact on ecosystems. In most countries, microbial
biomass, respiration and potential N mineralization are regarded as part of a minimum data set. Adding
the main functional groups of the soil food web brings us closer to understanding biodiversity and
gives the potential to relate the structure of the soil community to functions.
Key references
Bloem, J. and Breure, A.M. (2003) Microbial indicators. In: Markert, B., Breure, A.M. and
Zechmeister, H. (eds.) Bioindicators/Biomonitors – Principles, Assessment, Concepts. Elsevier,
Amsterdam, pp. 259-282.
Bloem, J. Schouten, A.J., Didden, W., Jagers op Akkerhuis, G., Keidel, H., Rutgers, M., Breure, A.M.
(2004) Measuring soil biodiversity: experiences, impediments and research needs. In: Francaviglia, R.
(ed.) Agricultural impacts on soil erosion and soil biodiversity: developing indicators for policy
analysis, Proceedings of an OECD expert meeting, 25-28 March 2003, Rome, Italy. OECD, Paris, p.
109-129. (http://webdomino1.oecd.org/comnet/agr/soil_ero_bio.nsf )
Biological control in sports turf using arbuscular mycorrhizal fungi
Alan Gange (School of Biological Sciences, Royal Holloway University of London).
The production of high quality sports turf in Europe is an expensive and labour-intensive business. The
main financial cost is in the use of large quantities of water, pesticides and fertilizers. There is an
environmental cost too; the application of large amounts of pesticide, followed by large amounts of
water means that the potential for groundwater pollution is high. Currently, the practice of sports turf
production is an unsustainable one; many chemicals are likely to be withdrawn on a European-wide
basis and water use is becoming an ever more sensitive issue.
Can we make turf grass sustainable? In order to answer this question, we need to understand
the key factors that contribute to the large use of synthetic chemicals. Undoubtedly, the key to
successful turf management is control of the weed grass Poa annua (annual meadow grass). This
species rapidly colonizes new turf and is present in virtually every established putting green and
football pitch throughout the temperate areas of the world. P. annua is intolerant of drought, requires
high nutrient availability and is subject to many diseases. Hence the heavy use of water, fertilizers and
pesticides. Using novel methods of chemical control, such as selective herbicides or plant growth
regulators, is not a sustainable strategy. Furthermore, there are human health and environmental
concerns associated with this approach. In this talk, I describe how we are investigating the use of soil
dwelling arbuscular mycorrhizal fungi to reduce the growth of the weed. Normally, these fungi are
beneficial to plants, but under certain conditions they can become parasitic.
Parasitism usually arises when the carbon demand of the fungus exceeds the nutrient inflow
that the fungus donates to the plant. Often this occurs in soils where nutrient levels are high, and sports
turf is just such a soil. We have discovered that when fungi invade the roots of Poa, they reduce the
growth and survival of the grass, but have no detrimental effects on the desirable grasses. We believe
this is because in Poa the mycorrhizal association is unbalanced, being in favour of the fungus.
However, for desirable grasses, their nutrient need is greater and hence the fungus is more of a
mutualist. I explain these conditions and show how these fungi could be used as part of a sustainable
approach in this form of agriculture.
Mycorrhiza in organic farming
Paul Mäder1 and Andres Wiemken2 ( 1 Research Institute of Organic Agriculture, Ackerstrasse, CH5070 Frick, Switzerland; 2 Department of Botany, University of Basel, Hebelstrasse 1, CH-4056 Basel,
Switzerland).
The mycorrhizal symbiosis plays a major role in plant nutrient acquisition and soil stabilisation in land
use systems with a low input of external resources. Two main approaches are available to manage the
mycorrhizal symbiosis, (i) manipulation of the indigenous mycorrhizal fungi by appropriate agronomic
practices and (ii) inoculation of crops with selected mycorrhizal fungi.
In organic farming, as one possible low-input system, a package of actions is applied such as
the use of crop rotation, inter- and intra-cropping and manuring. For pest control, resistant varieties,
bio-control agents and prediction modeling are used. The question rises, how sustainable these systems
really are. In long term studies in Switzerland, it was found, that soil fertility was enhanced by organic
farming and that healthy crops were produced more efficiently with respect to energy and nutrient use.
The mycorrhizal symbiosis, as an important indicator of soil fertility, was found enhanced in
organically managed plots and also the species diversity of mycorrhizal fungi was increased. It is
suggested that the higher below ground activity and diversity of microbes in the organic systems
rendered these systems less dependent on external inputs and led to a better soil structure. Moreover it
is concluded that organic low-input systems have a high potential to maintain the mycorrhizas, keeping
the soils fertile and productive.
The use of inocula of mycorrhizal fungi for the development of sustainable agricultural
production systems in Europe is still scarce. Since it was found that even in organically managed soils
and substrates mycorrhizas can be limited, a set of recently introduced commercial inocula and 10
strains of mycorrhizal fungi were multiplied and screened under farm conditions. Poinsettia,
Pelargonium, leak and strawberry were used as test plants. There was a strong interaction between
mycorrhizal fungi strains and crop. Mycorrhiza effects were found to be most pronounced in early
seedling stages and, therefore, this phase of development should be investigated more intensively
applying a combination of selected mycorrhizal fungal strains.
Key references
Mäder P., Frey, B., Vierheilig, H., Streitwolf-Engel, R., Boller, T., Christie, P. und Wiemken, A., 2000:
Transport of 15N from a soil compartment separated by a polytetrafluoroethylene membrane to plant
roots via the hyphae of arbuscular mycorrhizal fungi. New Phytologist 146: 155-161.
Mäder, P., Edenhofer, S., Boller, T., Wiemken, A. und Niggli, U., 2000: Arbuscular mycorrhizae in a
long-term field trial comparing low-input (‘organic’, ‘biological’) and high-input (‘conventional’)
farming systems in a crop rotation. Biology and Fertility of Soils 31, 150-156.
Mäder, P., Fließbach, A., Dubois, D., Gunst, L., Fried, P. und Niggli, U., 2002 : Soil fertility and
biodiversity in organic farming. Science 296: 1694-1697.
Oehl, F., Sieverding, E., Mäder, P., Dubois, D., Ineichen, K., Boller, T., Wiemken, A., 2004: Impact of
long-term conventional and organic farming on the diversity of arbuscular mycorrhizal fungi.
Oecologia 138: 574-583
Oehl, F., Sieverding, E., Ineichen, K., Mäder, P., Boller, T. und Wiemken, A., 2003: Impact of land use
intensity on the species diversity of arbuscular mycorrhizal fungi in agroecosystems of central Europe.
Applied and Environmental Microbiology 69: 2816-2824.
Session III: Organic farming and soil fauna
Nutrient Management in Low External Input Agriculture: Where do the Soil
Fauna Come in?
Lijbert Brussaard1, Ron de Goede1, Abdoulaye Mando2, Elisée Ouédraogo3 & Mirjam Pulleman4
(1Dept. of Soil Quality, Wageningen University, The Netherlands; 2IFDC, Lomé, Togo; 3Centre
Ecologique Albert Schweitzer, Ouagadougou, Burkina Faso; 4Cimmyt, Mexico).
One of the biggest problems in agriculture is nitrogen imbalances: too little N in most of the developing
world (leading to nutrient mining), too much in most of the industrialized countries (leading to
environmental problems). Another widespread concern is water deficits during the growing season.
Hence, the challenge is to increase nitrogen and water use efficiencies, which are closely connected.
We investigated cases in The Netherlands where cattle manure slurry with low C:N ratio and high
inorganic:organic N ratio is slit-injected and cases where cattle manure slurry with high C:N ratio and
low inorganic:organic N ratio is broadcast, as well as intermediate cases. The nitrogen use efficiency at
farm level was much higher (27%) in the latter case than in the former (17%), with a relatively much
larger contribution by earthworms to the mineralization of nitrogen (De Goede et al., 2003).
We also investigated the water use efficiency and nitrogen uptake in crusted soils in sub-Sahelian
Africa, after the addition of mulch. Both were very significantly higher in the presence vs. absence of
non-pest termites (Mando, 1998; Mando et al., 1999). We went on to investigate whether the
manipulation of termites may be an alternative to soil tillage. Under the conditions studied (sorghum
with straw + urea or sheep dung + urea), grain yields were generally higher than under organic or
inorganic fertilizer alone. The risk of physical yield reduction and the risk of lower financial returns
were lower under no-tillage than under tillage, which could be attributed to the beneficial effects of
termites on nitrogen and water use efficiency. Some artificial fertilizer has to be added to a low-quality
organic resource (straw) to overcome initial nitrogen immobilization, also in the presence of termites
(Ouédraogo et al., submitted for publication). We conclude that soil fauna can be manipulated by the
quality of organic resources added, to the effect that nitrogen and water use efficiencies can be
increased.
Key references
de Goede, R.G.M., Brussaard, L., Akkermans, A.D.L., 2003. On-farm impact of cattle slurry manure
management on biological soil quality. Netherlands Journal of Agricultural Science 51: 103-133
Mando, A., 1998. Soil-dwelling termites and mulches improve nutrient release and crop performance
on Sahelian crusted soil. Arid Soil Research and Rehabilitation 12: 153-164
Mando, A. Brussaard, L. and Stroosnijder, L., 1999. Termite- and mulch-mediated rehabilitation of
vegetation on crusted soil in West Africa. Restoration Ecology 7: 33-41
Meta-statistics as a tool is soil ecology: tillage and earthworms
Olaf Schmidt (Department of Environmental Resource Management, National University of Ireland,
Dublin, Belfield, Dublin 4, Ireland).
Meta-analysis is a tool for testing hypotheses in quantitative reviews by combining estimates from
independent studies on a common research question in a meta-dataset. There has been an exponential
increase in the use of meta-analysis in mainstream ecology since the early 1990s, with about 30
ecological meta-analyses being published annually in 2002–2004, but very few relate to soils or soil
ecology. Assembling a meta-dataset should follow a protocol that specifies how the search for relevant
literature will be conducted, what the criteria for inclusion of studies are, what the target data properties
are and which meta-information (e.g. soil properties, climatic data, sampling methods, type of
publication) will be sought. Since studies are given different weight depending on replication and
precision, they can only be included if a mean along with an estimate of variation and number of
replicates can be extracted. In the talk, the application of meta-analysis in soil ecology was illustrated
using a case study on the effects of reduced (non-inversion) versus conventional ploughing cultivation
on earthworm populations. In total, 110 suitable studies were identified and included in a global metadataset. Various hypotheses were tested regarding the overall response of earthworm numbers and
biomass, and the effects of soil texture, rainfall, years of cultivation and sampling method on this
response. The case study highlighted that the reporting standards even in refereed journal articles is
inadequate in many cases (e.g. no variation estimate, missing background information, no usable
species data, multiple or split publishing).
It is concluded that, as soil ecology is coming of age, there is potential for quantitative reviews
of published research that has accumulated over the last decades. Examples which have been
mentioned at the workshop include mycorrhizal effects on plant performance, isotopic diet–tissue shifts
in soil animals and effects of GMOs on non-target soil organisms.
Key references
Arnqvist G, Wooster D (1995) Metaanalysis – synthesizing research findings in ecology and evolution.
Trends in Ecology & Evolution 10, 236–240.
Gates S (2002) Review of methodology of quantitative reviews using meta-analysis in ecology. Journal
of Animal Ecology 71, 547–557.
Gurevitch J, Hedges LV (1999) Statistical issues in ecological meta-analyses. Ecology 80, 1142–1149.
Gurevitch J et al. (2001). Meta-analysis in ecology. Advances in Ecological Research 32, 199–247.
Leimu R, Koricheva J (2004) Cumulative meta-analysis: a new tool for detection of temporal trends
and publication bias in ecology. Proceedings of the Royal Society of London Series B-Biological
Sciences 271, 1961–1966.
Moller AP, Jennions MD (2001) Testing and adjusting for publication bias. Trends in Ecology &
Evolution 16, 580–586.
‘MetaWin’ meta-statistical software, see website <http://www.metawinsoft.com/>.
Species diversity of nematodes and earthworms: effects on nitrogen
mineralization and the bacterial community
M.B. Postma-Blaauw1*, F. T. de Vries1, R.G.M. De Goede1, J. Bloem2, J. H. Faber2, L. Brussaard1,
Jan-Willem van Groenigen2 (1 Wageningen University, Department of Soil Quality, The Netherlands; 2
Alterra Green World Research, The Netherlands; * Corresponding author)
The importance of soil fauna and the diversity of soil trophic groups for ecosystem processes have been
determined in many studies. There is hardly any knowledge, however, on the nature of the interactions
between soil organisms within taxonomic and trophic groups and the importance of these interactions
for ecosystem processes. Detailed knowledge on this subject is needed for a mechanistic understanding
of the role of biodiversity in ecosystem functioning.
We conducted a microcosm experiment with three bacterivorous nematode species (Bursilla
monhystera, Acrobeloides nanus and Plectus parvus), with addition of organic substrate of two
different C:N ratios, and a mesocosm experiment with three earthworm species (L. rubellus, A.
caliginosa, L. terrestris). In both experiments, treatments comprised all single species and all twospecies combinations. In the earthworm experiment, also the three-species combination was studied.
We studied the effect of these species interactions on bacterial biomass (direct counting), bacterial
growth rate (thymidine and leucine incorporation), and on mineralized nitrogen.
All the nematode species interacted with each other, but the nature and effects of these interactions
depended on the specific species combination and on the C:N ratio of the organic substrate. The
interaction between B. monhystera and P. parvus increased the bacterial biomass in the high C:N ratio
treatment and increased soil nitrogen mineralization in the low C:N ratio treatment, whereas the
interactions between the other species had no effect. B. monhystera and P. parvus have the most
different life history strategies, whereas A. nanus has a life-history strategy intermediate to B.
monhystera and P. parvus. We suggest that the difference in life-history strategies between species of
the same trophic group is of importance for their communal effect on soil ecosystem processes.
Similar to the effect of the nematodes, the effect of the interactions between the earthworm species
depended on the specific species combination. The interactions between L. rubellus and A. caliginosa,
and L. rubellus and L. terrestris, resulted in reduced net mineralization of the total soil organic matter,
through increased immobilisation in the bacterial biomass. In contrast, the interaction between A.
caliginosa and L. terrestris resulted in increased bacterial activity and reduced total soil C. When all
three species were combined, the interaction effect of A. caliginosa and L. terrestris dominated.
We conclude that faunal diversity in agricultural soil at the low end of the biodiversity spectrum can
effect N mineralization. The effect of species interactions depends on the taxonomic group, on the
ecological traits of the species present and on the quality of the organic substrate.
Impact of different farming systems on carabids and epigeic spiders – paired
farm approach including semi-natural habitats
Lukas Pfiffner (Research Institute of organic Agriculture (FiBL), 5070 Frick, Switzerland).
A short overview of 44 Studies investigating effects of organic and conventional farming on
invertebrates and birds was given. In most cases organic farming enhanced significantly these taxa
compared to conventional farming (Pfiffner et al. 2001). There is evidence that organic farming
benefits many taxa. Recently a review was published in which 76 studies were analysed and they came
to a similar assessment (Hole et al. 2005). But there is still lack of data comparing different low-input
farming systems which are currently subsidised by certain agri-environmental programs; but also data
of mountain regions and pastoral landsape are rare or very limited. Most of these comparing studies
were performed on arable fields without the neighbouring non-crop habitats. For many arthropods
landscape infrastructure, especially refugees for overwintering (Pfiffner & Luka 2000) and additional
offer of food resources are essential to survive.
In this context a study were presented of a 3-year field survey using a paired-farm approach in
six different landscapes units in northwestern Switzerland considering also the nearby semi-natural
habitats (Pfiffner & Luka 2003). Effects of different low-input farming systems on carabids and spiders
were analysed. Considering all cereal sites of this study, in low-input ICM fields (=no insecticides,
fungicides and growth regulators; ICM: Integrated crop management) 36% less carabids and 8% less
spider specimens were found. In several cases, carabid populations of organic fields (OF) were
significantly richer in species and abundance than in the low-input integrated crop management farmed
plots. Endangered, stenoceous carabids (e.g. Poecilus cupreus, Agonum muelleri) and top-predators
were more abundant in the organic fields. Spider communities differed less in mean number of species
and abundance between the two low-input agricultural systems. Multivariate analysis showed that
farming method and weed abundance were significant factors altering the carabid fauna and weed
diversity influence spider fauna. Lycosid species such as Pardosa agrestis, P. palustris and Trochosa
ruricola which have higher habitat requirements than in arable farmland seem to be enhanced by
organic farming, eurytopic Linyphiids (Erigone atra, Oedothorax apicatus) were more abundant in
low-input ICM fields.
The more abundant and rich weed flora (herbicide effect) and lower crop density (fertiliser
effect) of organic fields may be important anthropogenic factors altering species richness, which may
enhance the occurrence of thermo-xerophilous, some top predators and phyto-zoophagous carabid
species, even compared to low-input ICM. Several species of semi-natural habitats (meadows, wild
flower strips) were more abundant in organic fields than in low-input ICM. This may indicate a more
close interaction between organic farming and semi-natural habitats. There is evidence that these two
low-input farming systems affect differently the carabid assemblages and OF may positively influence
some abundant Lycosids. The comparison of these on-farm data with the DOC-trial shows that on the
level of carabid species the study confirms data of DOC-trial (Pfiffner & Niggli 1996). Agricultural
practices (herbicide application and fertilizer input) and their consequences were found as driving
factors, but also more food resources in organic fields (higher abundance of earthworms, enhanced
mesofauna by farm yard manure) were assumed to improve living conditions for these epigeic
arthropods.
Key references
Hole DG, Perkins AJ, Wilson JD, Alexander IH, Grice PV, Evans AD. 2005. Does organic farming
benefit biodiversity? Biological Conservation 122: 113-30
Pfiffner, L., Niggli, U.(1996): Effects of bio-dynamic, organic and conventional farming on ground
beetles (Col. Carabidae) and other epigaeic arhtropods in winter wheat. Biological Agriculture and
Horticulture 12: 353-364.
Pfiffner, L, & Mäder, P. (1997): Effects of biodynamic, organic and conventional production systems
on earthworm populations. Biological Agriculture and Horticulture 15: 3-10.
Pfiffner, L. Häring, A., Dabbert, S. Stolze, M., Piorr, A. (2001). Contributions of organic farming to a
sustainable environment. In: European Conference ‚Organic Food and Farming - Towards Partnership
and Action in Europe‘, 10.-11. May 2001, Proceedings, Copenhagen, Denmark p 115-123. Document
online available at:
http://www.fvm.dk/kundeupload/konferencer/organic_food_farming/proceedings.pdf
Pfiffner, L., Luka, H. (2000). Overwintering of arthropods in soils of arable fields and adjacent
seminatural habitats. Agriculture, Ecosystems and Environment 78: 215-222.
Pfiffner, L., Luka, H. 2003. Effects of low-input farming systems on carabids and epigeal spiders in
cereal crops – a paired farm approach in NW-Switzerland. Basic and Applied Ecology 4: 117-127.
Above or below ground prey? How to detect trophic links with stable isotopes
Katarina Hedlund (University of Lund, Sweden)
The question of how to detect who is feeding on who among conspicuous soil organisms is frequently
asked both in research concerning conservation biology as well as in ecological farming. It is know that
invertebrate predators as spiders and Staphylinids can feed on above ground herbivore insects as well
as soil organisms. In ecological farming these predators can regulate densities of pests and enhance
crop yields. Here we present a method of how it can be possible to detect what these predators feed on.
Ratios of table isotopes 13C or 15N change in abundance in organisms of different trophic levels and
the expression ”you are what you eat” describes the potential of detecting prey choice by analysing
stable isotopes in predators. We analysed ratios of 13C of fatty acids of both predators, their soil
organism prey, microorganisms and plant tissue. The results show that predators caught in pitfall traps
in restored grasslands mainly feed on above ground herbovires during the summer period.
Session IV: Organic farming and generalist predators
The generalist predator dilemma
W.O.C. Symondson (School of Biosciences, Cardiff University, PO Box 915, Cardiff CF10 3TL, UK)
Levels of biodiversity within agroecosystems relate to all organisms, from microorganisms through to
plants, invertebrates and vertebrates. Here I am concerned primarily with invertebrates. Much work has
been done on how diverse predator communities can, through concerted action, effectively limit prey
(pest) numbers1. However, increasing biodiversity also increases prey diversity and this talk focused
primarily on how generalist predators respond to such diversity. Does increased biodiversity suppress
pests? Sometimes, but field results are inconsistent. This is a black box which may be opened using
molecular tools to track trophic links.
Generalist predators are not thought to developed coupled dynamics with any given prey
species, mainly because as one prey declines the predator can switch to feeding on something else.
Predation of pests is buffered by polyphagy. However, work over five years on carabid-slug
interactions demonstrated that loosely coupled dynamics can develop where a single prey forms a
substantial proportion of the total available prey2. This is often the case in agroecosystems, where
single prey species may dominate, and could explain the long-term fluctuation seen in carabid
populations.
Does a diverse diet improve the fitness of generalist predators and hence pest control or,
conversely, does a diversity of alternative prey divert predators away from feeding on pests?
Experiments in the lab showed that, on all parameters measured, generalist predators (carabids and
spiders) were fitter on diverse diets (predator biomass, eggs laid, egg hatching time etc.) than on single
prey diets (in prep.). However, semi-field miniplot experiments showed that alternative prey, and
especially a diversity of alternative prey, diverted carabid beetles away from feeding on slugs.
Although the carabids could significantly reduce the slug population when no other prey were present,
the presence of alternative prey completely negated that effect 3. However, in the same experiment
predators denied access to any prey other than slugs were the least fit in terms of eggs developing in
females and predator biomass. Clearly, predators were being diverted away from feeding on the slugs
by the alternative prey, but their fitness and fecundity were, at the same time, improved.
Molecular methods, either to detect prey proteins in predator gut samples using prey-specific
monoclonal antibodies or prey DNA using PCR primers, can be used to track trophic links in the field
and to test fundamental hypotheses relating to predator responses to prey diversity4. The monoclonal
antibody approach was illustrated with a study looking at spiders feeding on aphids using an anti-aphid
antibody. The study demonstrated that early in the year the spiders were feeding on Collembola, which
disappeared as soils dried out and temperatures rose. At this stage, before the aphids started to increase
logarithmically, there was disproportionate feeding on aphids by the spider 5. In this instance the
alternative prey helped to increase and maintain the spider population, but temporal segregation
prevented the Collembola from diverting the spiders away from feeing on the pest aphids. A PCRbased study confirmed the value to Collembola to spiders and, in the first published study of arthropod
predation using this technology, showed strong prey preferences by the spiders for particular
Collembola species6. Another study used PCR to study slug consumption by carabids7. This work
found approx. 25% of the beetles in the field tested positive for slug DNA, even in months when few if
any slugs could be detected in the field. Clearly the predators are better at finding their prey than we
are, but without this molecular approach that could not have been appreciated.
Currently at Cardiff we have developed PCR primers to detect a range of invertebrates
including Collembola, molluscs, aphids, earthworms, weevils, nematodes, Lepidoptera and Diptera.
We have overcome the problem of having to analyse each individual predator gut sample with maybe
40+ Pars when the mean number of prey in a generalist predator may be a little as one or two. The
system is based upon multiplex PCR8. All the primers for all the prey that could be in the guts of a
predator are placed in a single PCR reaction tube, along with the DNA extracted from the predator’s
gut. We conduct the multiplex PCR and run the products out on a gel that is scanned by an ABI377
sequencer. Fluorescent labels on the primers allow the sequencer to identify all the prey simultaneously
and send the data to a database. For the first time we can rapidly screen predators for the whole of their
dietary range, an essential prerequisite for studying predator responses to prey diversity in the field.
Key references
Simonton, W.O.C., Sunderland, K.D. & Greenstone, M.H. (2002). Can generalist predators be effective
biocontrol agents? Annual Review of Entomology 47, 561-594.
Symondson, W.O.C., Glen, D.M., Ives, A.R., Langdon, C.J. & Wiltshire, C.W. (2002). Dynamics of
the relationship between a generalist predator and slugs over five years. Ecology 83, 137-147.
Symondson, W.O.C., Cesarini, S., Dodd, P., Harper, G.L., Bruford, M.W., Glen, D.M., Wiltshire C.W.
and Harwood, J.D (submitted) Biodiversity vs. biocontrol: negative effects of alternative prey species
diversity on control of pests by predators. Journal of Applied Ecology.
Symondson, W.O.C. (2002). Molecular identification of prey in predator diets. Molecular Ecology 11,
627-641.
Harwood , J.D, Sunderland, K.D. & Symondson, W.O.C. (2004) Prey selection by linyphiid spiders:
molecular tracking of the effects of alternative prey on rates of aphid consumption in the field.
Molecular Ecology 13, 3549-3560.
Agustí, N., Shayler, S., Harwood, J.D., Vaughan, I.P., Sunderland, K.D. & Symondson, W.O.C.
(2003). Collembola as alternative prey sustaining spiders in arable ecosystems: prey detection within
predators using molecular markers. Molecular Ecology 12, 3467-3475.
Dodd, C.S., Bruford, M.W., Symondson, W.O.C. & Glen, D.M. (2003). Detection of slug DNA within
carabid predators using prey-specific PCR primers. In Slug and Snail Pests: Agricultural, Veterinary &
Environmental Perspectives. British Crop Protection Council, Alton, pp. 13-20.
Harper, G.L., King, R.A., Dodd, C.S., Harwood, J.D., Glen, D.M., Bruford M.W. & Symondson,
W.O.C. (in press). Rapid screening of invertebrate predators for multiple prey DNA targets. Molecular
Ecology.
Detrital subsidies, altered feeding preferences, and the effectiveness of carabids
and spiders in biological control
David H. Wise (University of Kentucky, Kentucky, USA)
Field experiments have established that carabid beetles and wolf spiders that immigrate into cucurbit
gardens can substantially enhance crop production. In spring cucumber gardens wolf spiders exerted
the major effect by preying upon striped cucumber beetles, and carabid predators doubled squash
production in summer gardens by depressing densities of squash bugs. Interactions can be quite
complicated, and the entire complex of generalist ground predators did not always control pests. In
spring gardens the entire carabid-spider complex enhanced cucumber production, with the clear
statistically significant effect due to wolf spiders. In contrast, in summer gardens the carabid-spider
complex had no net effect on crop production, because immigrating wolf spiders counteracted the
positive effect of carabids, most likely by causing declines in another generalist predator of squash
bugs. In squash the negative effect of wolf spiders apparently was due to the presence of another
predator. In its absence, the carabid-wolf spider complex may also have increased squash production,
as occurred with the cucumber crop. These strong interactions prompted an attempt to increase
biological control by engineering the detrital food web. It was hypothesized that adding detritus to
cucumber gardens would lead to increased densities of microbi-detritivores, leading to elevated
densities of carabids and spiders and enhanced control of cucumber beetles. In squash gardens the net
effect of adding detritus on squash bugs and squash production was more difficult to predict. Adding
detritus (a shredded, composted mixture of straw from horse stables) to cucurbit gardens produced a 34x increase in densities of Collembola, a major microbi-detritivore in the system; an initial five-fold
increase in carabids; and a 2-3x increase in wolf spider densities. Surprisingly, the increased densities
of generalist predators had no effect on either cucumber or squash production. The investigators
speculated that the unusually high and low densities of pests (those of cucumbers and squash,
respectively) during the experiment may have caused the failure of the enhanced carabid-lycosid
complex to have any impact on cucurbit production. It was also hypothesized that changes in feeding
relationships by predators also could have contributed to the failure of elevated predator densities to
display control of the cucurbit pests. Perhaps the larger instars and species of predators switched their
feeding from herbivores to feed more heavily on the higher numbers of microbi-detritivores and small
spiders in the detritus addition treatment
We addressed the question of whether or not such a switch can occur by comparing ratios of
stable isotopes of carbon (13C) and nitrogen (15N) in generalist ground predators and two types of
prey – crop pests and microbi-detritivores – in replicated 8x8-m cucurbit gardens subjected to one of
two treatments: a detrital subsidy or no addition of detritus (control). Adding detritus to the garden
caused densities of spiders to double, but in contrast to previous research, did not produce a statistically
significant increase in densities of carabid beetles. In both treatments small sheet-web spiders
(Linyphiidae) and small wolf spiders (Lycosidae) had 13C values similar to those of Collembola,
suggesting that these spiders belong primarily to the detrital food web. Adding detritus increased the
15N of the small generalist predators, most likely because the detrital subsidy markedly increased
densities of microbi-detritivores that had higher 15N signatures than those of Collembola. The larger
predators – large wolf spiders and predaceous ground beetles (Carabidae) -- had 13C values that
usually were similar to those of the major insect pests (striped and spotted cucumber beetles, and
squash bugs). These 13C patterns were similar in control and detrital treatments, as were the trophic
positions of the larger predators as indicated by 15N fractionation. These results suggest that
increasing the abundance of alternative detrital prey does not cause the large generalist predators to
substantially decrease feeding on insect pests; this conclusion is particularly strong for the large wolf
spider Hogna. Thus, a detrital subsidy is a potentially viable strategy for enhancing biological control
of crop pests by generalist predators that also prey on microbi-detritivores in the detrital food web.
Key references
Wise, D. H., D. M. McNabb and J. Halaj. Submitted. Enhanced densities of detrital prey and possible
shifts in consumption of crop pests by generalist predators: a stable-isotope analysis. Ecological
Applications.
Halaj, J. and D. H. Wise. 2002. Effects of a detrital subsidy on the strength of a terrestrial trophic
cascade in a grazing food web. Ecology 83:3141-3151.
McNabb, D. M., J. Halaj and D. H. Wise. 2001. Inferring trophic positions of generalist predators and
their linkage to the detrital food web in agroecosystems: a stable isotope analysis. Pedobiologia 45:
289-297.
Snyder, W. E. and D. H. Wise. 2001. Contrasting trophic cascades generated by a community of
generalist predators. Ecology 82: 1571-1583.
Snyder, W. E. and D. H. Wise. 1999. Predator interference and the establishment of generalist predator
populations for biocontrol. Biological Control 15: 283-292.
Landscape versus management effects on farmland spiders and consequences for
conservation biological control
Martin H. Schmidt (Community Ecology, University of Bern, Baltzerstr. 6, CH-3012 Bern).
Landscape-wide movement of small generalist arthropods has escaped quantification for a long time,
despite the early recognition that it might influence local abundance and diversity (Luczak 1979). As
farmland spiders overwinter predominately outside of arable fields, the colonisation of crops and
thereby local abundance should be related to the availability of perennial non-crop habitats in the
surrounding landscape (Schmidt & Tscharntke 2005a). The circumference around a field in which the
landscape is relevant should further depend on the movement capacity of each species, thereby giving
an indirect measure for its effective dispersal range.
The relation of farmland spiders to the landscape context was studied in winter wheat fields
along a gradient of landscape complexity in Germany in the years 2001-2003. Thereby, abundances of
sheetweb spiders rose with the percentage of non-crop habitats in the surrounding landscape, e.g. from
18-130 webs per m2 in late May 2001 (Schmidt & Tscharntke 2005b). Additionally, the densities of 11
out of 21 common ground-dwelling spider species were locally enhanced by landscape non-crop, and
overall species richness increased with landscape non-crop from 17-22 species per field (MHS,
unpublished data). Wolf spiders were influenced by landscape composition at smaller scales (mostly
between 190-530m radius) than the more ballooning Linyphiidae (up to 3000m radius).
In 2002, the effects of landscape were compared to the effects of local organic versus conventional
management in twelve pairs of organic and conventional fields along a landscape gradient (Schmidt et
al. 2005). Thereby, organic management increased overall activity density by 62%. In contrast, species
richness was determined by landscape, only. Overall, densities of Oedothorax apicatus were affected
mostly by management, Pardosa species by both landscape and management, and other species mostly
by landscape.
Field experiments revealed ground dwelling-predators reduce aphid infestation in winter
wheat (Schmidt et al. 2003, 2004a). Aphid densities increased by 45% when ground-dwelling predators
were excluded, most likely due to reduced aphid predation by spiders.
In conclusion, spiders in wheat fields are strongly influenced by the surrounding landscape, which
could lead to a significant increase of aphid control in landscapes with high amounts of perennial noncrop habitats. This suggests that a purely local orientation of biological control is not sufficient
(Schmidt et al. 2004b). The effectiveness of measures to enhance aboveground enemies of agricultural
pests may depend substantially on how they are applied in space.
Key references
Luczak, J. (1979) Spiders in agrocenoses. Polish ecological studies 5:151-200.
Schmidt MH, Lauer A, Purtauf T, Thies C, Schaefer M & Tscharntke T (2003) Relative importance of
predators and parasitoids for cereal aphid control. Proceedings of the Royal Society of London, Series
B: Biological Sciences 270:1905-1909.
Schmidt MH, Thewes U, Thies C & Tscharntke T (2004a) Aphid suppression by natural enemies in
mulched cereals. Entomologia Experimentalis et Applicata 113:87-93.
Schmidt MH, Thies C & Tscharntke T (2004b) The landscape context of arthropod biological control.
Ecological Engineering for Pest Management: Advances in Habitat Manipulation for Arthropods (eds.
GM Gurr, SD Wratten & MA Altieri) pp. 55-63. CSIRO, Collingwood VIC.
Schmidt MH & Tscharntke T (2005a) The role of perennial habitats for Central European farmland
spiders. Agriculture, Ecosystems and Environment, in press.
Schmidt MH & Tscharntke T (2005b) Landscape context of sheetweb spider (Araneae: Linyphiidae)
abundance in cereal fields. Journal of Biogeography, in press.
Schmidt MH, Roschewitz I, Thies C & Tscharntke T (2005) Landscape context influences the
diversity, and local management the density of ground-dwelling farmland spiders. Journal of Applied
Ecology, in press.
Detritivores as alternative prey for generalist predators – feedbacks on pest
control
Karsten von Berg (Technische Universität Darmstadt, Schnittspahnstraße 3, D-64285 Darmstadt).
Generalist predators play a fundamental role for biocontrol in agro-ecosystems. In times when
herbivores are absent they need to feed on non-pest prey. The decomposer subsystem can act as
alternative prey sustaining populations of carabids, staphylinids and spiders.
The role of detritivores as alternative prey for generalist predators and feedbacks on aphid control were
investigated in six winter wheat fields near Göttingen in 2004. To increase populations of detritivores
an additional food resource, maize mulch, was added to the fields in September 2003. Aphid
populations were counted on wheat plants from June to August inside exclosures of flying predators +
parasitoids, ground dwelling predators and a combination of both. Additionally, pots with wheat plants
grown in garden soil were established inside the plots. These pots showed no significant difference
between aphid population growth on wheat plants in mulched and unmulched fields signifying no
effect of mulch due to changes in attractiveness of the wheat plants to herbivores. Aphid numbers
differed between fields. In two out of six fields aphid populations were 15 times higher than in the
other four fields (1108 vs. 74 individuals per 25 shoots). Mulch decreased aphid numbers only in these
two fields whereas it appeared to increase aphid numbers in the other four fields.
In the high aphid density fields flying predators + parasitoids and ground dwelling predators decreased
significantly aphid populations by 33% and 20%, respectively. There was no significant difference
between impacts of flying predators + parasitoids on aphids in mulched and unmulched fields (decrease
by -33% and -35%). Decrease of aphid populations by ground dwelling predators was significantly
higher in mulched fields (-31%) than in unmulched fields (-8%). Results from pitfall catches show that
numbers of carabids and predatory larvae (staphylinids + carabids) were significantly higher in
mulched fields than in unmulched fields.
These findings suggest that higher densities of prey animals out of the decomposer subsystem
result in higher predator densities and lead to a stronger aphid control in winter wheat. Different aphid
numbers in the fields show the variability in population growth of pest insects. The unequal impact of
mulch indicates that top-down control by generalist predators seems to be different at varying prey
densities.
Manipulating generalist predators at the DOC experiment
Klau Birkhofer (Technische Universität Darmstadt, Schnittspahnstraße 3, D-64285 Darmstadt).
Classical biological control and its applicability are among the most controversially discussed topics in
modern agriculture. In predaceous Arthropods intraguild predation might limit the effect of the
predator community on a pest species and generalist predators might not switch to pest species while
alternative prey is available (Scheu 2001). Both considerations were investigated by manipulating wolf
spider (Lycosidae) densities, as this group is an abundant predator at the sites of the DOC trial in
Therwil, Switzerland (Mäder et al. 2002). During a 5 day long removal period an average of 29±7
lycosids was removed from each of 3 fenced 1,8 m² large enclosures, using standardized visual
searching and pitfall trapping inside a grass and clover meadow. A fenced control was established and
treated in a similar way, with collected spiders being released immediately. After this period all traps
were removed and the plots were left undisturbed for 26 days. Following this period a 3 min D-Vac
suction sample was taken in each plot to quantify the above ground Arthropod density. Lycosid
removal had a significant effect on wolf spider densities (Mann-Whitney U: Z=-1.964, N=3, P<0,05),
nevertheless the treatment had no significant effect on any other analysed Arthropod group (including
Araneae, Carabidae, Staphylinidae, Curculionidae, Chrysomelidae, Cicadellidae, Delphacidae and
Aphidina). A principal component analysis showed a tendency for higher aphid, delphacid and sheet
web (Linyphiidae) densities in wolf spider removal plot, indicating a release from predatory pressure.
Biological explanations for the weak effect include the possibility of a generally weak link between
wolf spiders and the herbivore system. Grass and clover meadows are rich in collembolan and dipteran
abundance, so alternative prey from the detritivore system might be of major importance. Spider aerial
dispersal was at its peak and many sheet web and crab spiders (Thomisidae) ballooned during the four
week experimental period. An average of 108±31 web building spiders were collected from each plot,
the high abundance of this group possibly masked effects by any other predator group. Only weavers
(Curculionidae) showed a significant negative correlation with web spider density (Spearman Rank
Correlation: Rs=-0,841, N=6, P<0,05).
Key references
Mäder P, Fliessbach A, Dubois D, Gunst L, Fried P, Niggli U (2002) Soil Fertility and Biodiversity in
Organic Farming. Science 296:1694-1697
Scheu S (2001) Plants and Generalist Predators as Links Between the Below- Ground and AboveGround System. Basic and Applied Ecology 2:3-13
Questions raised by policy makers and end users:
In general, we found that agriculturists, particularly organic farmers, are very interested in
soil biodiversity. Normally, soil biodiversity is not high up on the policy agenda (if it is there
at all), but there was an awareness that soil biodiversity might matter in farmed soils. This is
partly because, even at the low level of biodiversity present in farmed soils, a minute change
(positive or negative) is likely to affect vast areas of land.
Economics, management and matter fluxes
- The end-user perspective-1
Maria Dirke (Swedish Ecological Farmers Association)
Swedish Ecological Farmers Association is an umbrella organisation for organic farming and organic
farmers in Sweden. We have about 3000 members and have been working since 1985. We are a
member of the IFOAM, International Federation of Organic Agriculture Movements, a global
organisation for certification, market, research, policy issues and more considering organic farming.
We are participating in IFOAM EU Regional Group.
Our focus is to advance organic farming’s development, in volume and in quality and moreover to
strengthen the values of organic production and communicate as consumers’ trust in organic products.
Our work is organised into three main areas: (1) Policy issues (agricultural policy1, standards and
certification, research and extension, market coordination) (2) Information (monthly periodica,
www.ekolantbruk.se , electronic newsletter), (3) Organisational development (office and
administration, cooperation, international work).
Sustainability is the primary objective. The farmers perspective is the system perspective. In
organic farming systems a well managed crop rotation is necessary. Recirculation of nutrients with aim
to minimize risks for nutrient losses. Biodiversity is fundamental – the ongoing development is
alarming and trends have to be changed. The development of organic farming is based on principles
about precaution, ethical and justice. Soil biodiversity is a precondition for successful organic farming
and farmers are enthusiastic about learning more concerning technique and methods to improve
conditions for microorganisms and fauna in the soil as well as predators.
A scientist’s and a farmer’s view of below-ground biodiversity in organic farming
- The end-user perspective-2.
Andreas Gattinger1 and Josef Braun2 (1Technical University of Munich, Chair of Soil Ecology, D85764 Neuherberg; 2Biolandhof Braun, D-85354 Freising-Dürneck).
Soil microbial communities are responsible for productivity and stability of agricultural landuse
systems and important functions in global nutrient cycling. Thanks to the advent of molecular methods
during the last decade, the soil microflora (= microbial biomass) is no longer considered as a black box.
It has been shown that a soil is dwelled by complex microbial communities constituted by members of
all three domains of life: bacteria, eukarya, archaea (e.g. Gattinger et al., 2002, Liesack et al., 1997).
Repeated investigations of soils from long-term field trials in Germany and Switzerland showed that
soil tillage as well as the farming system as such has an effect on size and structure of soil microbial
communities.
Minimum tillage practices such as two layer ploughing (LP) and two layer cultivating (LC)
lead to higher contents of total organic carbon (Corg), dissolved organic carbon (DOC) and microbial
biomass carbon (Cmic) than conventional ploughing (CP, 25 cm depth) (Emmerling et al., 2003). A
depth gradient of these soil ecological criteria was observed for two layer ploughing and two layer
cultivating but not for conventional ploughing. Microbial community structure was different among
tillage treatments with the most pronounced similarities between LP and LC. The bacteria-to-fungi
ratio was highest in the treatment LC and showed a clear depth gradient for LC and LP, which reflected
the utilisation pattern of different C sources (BIOLOG).
1
A sustainable agricultural policy for Europe. IFOAM Position paper, 2002
http://www.ifoam.org/pospap/cap_pos.pdf
The influence of the farming system on size and structure of soil microbial communities was
investigated in soil samples from the DOC trial in Switzerland (Rasche et al., 2003; Esperschuetz,
2004). The DOC long-term field trial consists of plots managed bio-dynamically (BIODYN), bioorganically (BIOORG), conventionally (CONFYM) and of those which are managed conventionally
but only receive mineral fertiliser (CONMIN). Analyses of soil samples from 2000 and 2003 (both
under winter wheat) revealed higher microbial biomasses in the organically fertilised plots, among
these bacterial and eukaryotic biomasses followed the order: CONFYM ≤ BIOORG ≤ BIODYN.
Archaeal communities occurred at moderate abundances following the order: CONMIN < BIODYN =
BIOORG = CONFYM. The preceding crop (winter wheat or maize) did not have an effect on total
microbial biomass. Using the phospholipid fatty acid (PLFA) biomarker approach clear differences in
microbial community structure among the four farming systems were observed. Organic fertilization
had the strongest effect followed by organic farming management, the kind of organic farming
management (BIODYN or BIOORG) and the preceding crop. Diversity indices (Shannon-Weaver)
were calculated for the soils based on PLFA number and distribution. The system CONMIN showed
significantly highest number of PLFA (≈ richness) and highest diversity (H), followed by BIODYN
and BIOORG which had similar values for both. No difference in equitability or eveness (EH) among
farming systems were found. However, apart from the suitability and meaningfulness of diversity
indices in soil ecology, no information can be obtained on the functional aspects of soil microbial
communities. Therefore, combined specific isotope analysis of phospholipid biomarker was applied
which links microbial community structure to carbon transformation processes (Boschker et al., 2000).
First results showed that 6 month after maize harvest, mainly Gram-positve bacteria, fungi and
protozoa incorporated maize-derived C in their membrane lipids. Representatives of the domain
archaea did not show maize incorporation, however archaeal lipids showed significantly higher δ13C
values in BIODYN and BIOORG plots. This indicates that archaeal communities in BIODYN and
BIOORG perform different C transformation processes than in CONFYM and CONMIN plots.
Ongoing analysis of other PLFA fractions will contribute to the knowledge on in situ functions of
microbial communities.
The farming practices of Josef Braun were illustrated as a successful example for managing
soil fertility. Josef Braun and his family are running a 40 ha organic farm located in the north of
Munich, Bavaria consisting of animal husbandry and arable farming. Although the farmer stopped
ploughing already in 1984, he grows high quality seeds of cereal and grass crops for sale. Furthermore,
he achieves the production of high quality hay from the grass–clover lay crucial for the nutrition of his
dairy cows. Mr. Braun tries to adapt the functioning of natural forest ecosystems to his land use
practices by enabling a permanent vegetation cover and cultivating a mixture of plant species in space
and time. In practice he is sowing winter cereals in late summer to make use of the N mineralization
flush in early autumn. The seeds are selected also according to its formation of a structured canopy and
rooting system to increase resource capture. Mr. Braun realizes minimum tillage by inverting the soil
only to 6 cm depth. Soil tillage is performed either in mid August or January when biological activity is
rather low and the earthworms have moved to deeper soil horizons. With these practices Mr. Braun
achieves a more pronounced rooting system in the soil as has been shown by estimating root density
and length in some selected plant-soil profiles. Due to the increase of the root biomass, he observes in
the grass-clover lay a total biomass yield (= above + below-ground biomass) comparable to
conventional maize production. On his fields more than 200 earthworms m 2 were counted which is
much higher than the Bavarian average of 16 animals m2. Applying the spade diagnosis Mr. Braun
determined a higher aggregate stability in his soils along with other beneficial properties.
Josef Braun proposes a combination of several techniques and strategies for future research and
development such as techniques for managing mixed and/or intercropping systems. In his opinion all
efforts and research activities in the field of sustainable cropping systems should meet the requirements
of whole-food nutrition for soils.
Key references
Boschker, H.T.S., Nold, S.C., Wellsbury, P., Bos, D., Graaf, W.D., Pel, R. et al. (1998) Direct linking
of microbial populations to specific biogeochemical processes by 13C-labelling of biomarkers. Nature
392: 801-805.
Emmerling, C., A. Gattinger and A. Embacher (2003): Reduzierte Bodenbearbeitung im Ökologischen
Landbau: Einfluß auf Leistung und Struktur der Bodenmikroorganismengemeinschaft. In: B. Freyer: 7.
Wissenschaftstagung zum Ökologischen Landbau - Ökologischer Landbau der Zukunft, pp. 453-454
(http://orgprints.org/00001736).
Esperschütz, J. (2004): Strukturelle und funktionelle Charakterisierung von mikrobiellen
Gemeinschaften in Bodenökosystemen mit der Phospholipid-Methode und stabilen Isotopentechniken.
Diploma Thesis, Technical University of Munich
Gattinger, A., Ruser, R., Schloter, M., and Munch, J.C. (2002) Microbial community structure varies in
different soil zones of a potato field. Journal of Plant Nutrition and Soil Science 165: 421-428.
Liesack, W., Janssen, P.H., Rainey, F.A., Ward-Rainey, N.L., and Stackebrandt, E. (1997) Microbial
Diversity in Soil: The Need for a Combined Approach Using Molecular and Cultivation Techniques. In
Modern Soil Microbioloy. Elsas, J.D.v., Trevors, J.T., and Wellington, E.M.H. (eds). New York:
Marcel Dekker, pp. 375-439.
Rasche, F., F. Widmer, P. Mäder, A. Gattinger and A. Fließbach (2003): Vergleich von Methoden zur
Ermittlung der mikrobiellen Diversität in Böden des DOK-Versuchs. In: B. Freyer: 7.
Wissenschaftstagung zum Ökologischen Landbau - Ökologischer Landbau der Zukunft, Wien, 2003. pp
447-448 (http://orgprints.org/00002571).
Field experiment
Field sampling will occur in May 2005 according to the plan presented in the attached file.
This document also shows how the sampling of soil biodiversity performed by CONSIDER
(marked in yellow) fits into the extensive sampling program carried out by the researchers at
Frick and colleagues elsewhere.
DOK_Projects.xls