Long-term organic farming fosters below and aboveground biota: Implications for soil quality, biological control and productivity

K. Birkhofer^1*, T. M. Bezemer^2,3,4, J. Bloem⁵, M. Bonkowski¹, S. Christensen⁶, D. Dubois⁷, F. Ekelund⁶, A. Fliebbach⁸, L. Gunst⁷, K. Hedlund⁹, P. Mader⁸, J. Mikola¹⁰, C. Robin¹¹, H. Setala¹⁰, F. Tatin-Froux¹¹, W. H. Van der Putten^2,3 and S. Scheu¹

Abstract
Organic farming may contribute substantially to future agricultural production worldwide by improving soil quality and pest control, thereby reducing environmental impacts of conventional farming.

We investigated in a comprehensive way soil chemical, as well as below and aboveground biological parameters of two organic and two conventional wheat farming systems that primarily differed in fertilization and weed management strategies. Contrast analyses identified management related differences between “herbicide-free” bioorganic (BIOORG) and biodynamic (BIODYN) systems and conventional systems with (CONFYM) or without manure (CONMIN) and herbicide application within a long-term agricultural experiment (DOK trial, Switzerland).

Soil carbon content was significantly higher in systems receiving farmyard manure and concomitantly microbial biomass (fungi and bacteria) was increased. Microbial activity parameters, such as microbial basal respiration and nitrogen mineralization, showed an opposite pattern, suggesting that soil carbon in the conventional system (CONFYM) was more easily accessible to microorganisms than in organic systems.

Bacterivorous nematodes and earthworms were most abundant in systems that received farmyard manure, which is in line with the responses of their potential food sources (microbes and organic matter). Mineral fertilizer application detrimentally affected enchytraeids and Diptera larvae, whereas aphids benefited. Spider abundance was favoured by organic management, most likely a response to increased prey availability from the belowground subsystem or increased weed coverage. In contrast to most soil-based, bottom-up controlled interactions, the twofold higher abundance of this generalist predator group in organic systems likely contributed to the significantly lower abundance of aboveground herbivore pests (aphids) in these systems.

Long-term organic farming and the application of farmyard manure promoted soil quality, microbial biomass and fostered natural enemies and ecosystem engineers, suggesting enhanced nutrient cycling and pest control. Mineral fertilizers and herbicide application, in contrast, affected the potential for top-down control of aboveground pests negatively and reduced the organic carbon levels.

Our study indicates that the use of synthetic fertilizers and herbicide application changes interactions within and between below and aboveground components, ultimately promoting negative environmental impacts of agriculture by reducing internal biological cycles and pest control. On the contrary, organic farming fosters microbial and faunal decomposers and this propagates into the aboveground system via generalist predators thereby increasing conservation biological control. However, grain and straw yields were 23% higher in systems receiving mineral fertilizers and herbicides reflecting the trade-off between productivity and environmental responsibility.


Source
Soil Biology and Biochemistry (2008) 40: 2297-2308
DOI: 10.1016/j.soilbio.2008.05.007


Author Locations and Affiliations
(1) University of Technology Darmstadt, Zoological Institute, Schnittspahnstraße 3, 64287 Darmstadt, Germany
(2) Netherlands Institute of Ecology (NIOO-KNAW), Centre for Terrestrial Ecology, PO Box 40, 6666 ZG Heteren, The Netherlands
(3) Laboratory of Nematology, Wageningen University and Research Centre, PO Box 8123, 6700 ES Wageningen, The Netherlands
(4) Laboratory of Entomology, Wageningen University and Research Centre, PO Box 8031, 6700 EH Wageningen, The Netherlands
(5) Alterra, Soil Sciences Centre, P.O. Box 47, 6700 AA Wageningen, The Netherlands
(6) Copenhagen University, Department of Terrestrial Ecology, Farimagsgade 2D, 1353 Copenhagen, Denmark
(7) Agroscope Reckenholz-Tänikon Research Station (ART), Reckenholzstrasse 191, 8046 Zürich, Switzerland
(8) Research Institute of Organic Agriculture (FiBL), Ackerstraße, 5070 Frick, Switzerland
(9) Department of Ecology, Lund University, 22362 Lund, Sweden
(10) Department of Ecological and Environmental Sciences, University of Helsinki, Niemenkatu 73, 15140 Lahti, Finland
(11) UMR 1121 INPL (ENSAIA)-INRA Agronomie et Environnement Nancy-Colmar, BP 172, 54505 Vandoeuvre-les-Nancy, France
* Corresponding author, E-mail birkhofer@bio.uni-giessen.de


Posted December 2011