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

Birkhofer, K; Bezemer, TM; Bloem, J; Bonkowski , M; Christensen , S; Dubois , D; Ekelund , F; Fließbach , A; Gunst , L; Hedlund , K; Mäder , P; Mikola , J; Robin , C; Setälä , H; Tatin-Froux , F; Van der Putten , WH and Scheu, S (2008) Long-term organic farming fosters below- and aboveground biota: Implications for soil quality, biological control and productivity. Soil Biology and Biochemistry, 40, pp. 2297-2308.

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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 soilbased, 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.

EPrint Type:Journal paper
Keywords:DOK trial Ecosystem functioning Farming system Fertilization Generalist predators Microbial community Nutrient cycling Natural enemies Soil fauna Soil quality Sustainability
Subjects: Soil > Soil quality
Soil > Soil quality > Soil biology
Crop husbandry > Production systems > Cereals, pulses and oilseeds
Environmental aspects > Biodiversity and ecosystem services
Research affiliation: Switzerland > FiBL - Research Institute of Organic Agriculture Switzerland > Soil
Deposited By: Birkhofer, Dipl. Biol. Klaus
ID Code:19613
Deposited On:04 Nov 2011 19:06
Last Modified:06 Jan 2021 15:12
Document Language:English
Refereed:Peer-reviewed and accepted

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