‘Beneficial organisms help to naturally reduce the numbers of pests such as lice.’
Biodiversity is higher
Dr Hans-Martin Krause, Dr Paul Mäder, Dr Andreas Fliessbach, all FiBL
Along with adapting to climate change, regulating nutrient cycles and ensuring food security, the loss of biodiversity is one of the most pressing issues for the agricultural sector. Agriculture is the main driver of biodiversity loss. The main factors are the expansion of agricultural land, the associated loss of natural habitats and the intensification of agricultural production through the use of pesticides and fertilisers.
In the DOK trial, we focussed on species whose mobility radius does not significantly exceed the size of the plot when measuring biodiversity. Accordingly, the informative value is limited to microorganisms and soil animals or insects that spend a period of their lives in or on the soil.
The absence of herbicides means that plant diversity and the seed supply of companion herbs are significantly higher in organic systems than in conventional systems. However, this is accompanied by increased weed pressure in the organic systems. But the flora that grows alongside crops also has valuable functions, and flowering plants in particular make a positive contribution to the biodiversity of fauna in organic systems.
Spiders and insects such as ground beetles and rove beetles are about twice as common in the organic systems as in the conventional systems. In addition to avoiding the use of insecticides, a loose plant population with more light and residual weeds in the organic systems also have a positive effect on these predatory species. These beneficial insects help to naturally reduce the numbers of pests such as lice, for example on wheat.
Completely new habitat* within the soil
But a completely new habitat is also opening up within the soil, in which an extraordinary variety of species can be found. An early study from the DOC trial shows that both the quantity and the species diversity of earthworms are significantly higher in organic systems.
These animals loosen the soil, facilitate the infiltration of rainwater through their burrows, thus preventing erosion, and mix crop residues and manure into the soil through their feeding activity. What remains are the worm castings, which bind together well when it rains and are very rich in nutrients. Earthworms also decimate the spores of harmful fungi and thus contribute to the recovery of the soil. In technical jargon, earthworms are also referred to as ‘ecological engineers’ because of their numerous functions.
Important mycorrhizal fungi
The dynamics of the community structure of soil microorganisms are also very closely linked to those of plants and soil animals; a different microbiome was found for each system in the DOK trial. The interaction of the immense number of organisms ensures the numerous functions they perform in the soil, such as recycling nutrients and buffering the effects of dry and wet conditions.
The microbiome is understood to mean the genetic material (DNA) of all the bacteria and fungi found in the soil. Here the bacteria are more strongly influenced by the fertilisation intensity, the fungi more by the system differences. Some fungi, in particular, can form symbiotic relationships with crops, thereby positively influencing nutrient absorption and plant health. The so-called mycorrhizal fungi were found to be more abundant and diverse in the organic systems. This can be attributed to the reduced use of fungicides and fertilisers. The crops benefit from the mycorrhizal fungi because they can access nutrients that are difficult to obtain, such as phosphorus in the soil, through the fungi's extensive network of hyphae (fungal threads).
The latest studies in the DOK trial show that the microorganisms in the organic systems are better networked. Whereas conventionally managed soils specialise in building up protein, soils with dung and slurry have a greater potential for breaking down complex carbon compounds. In summary, the work in the DOK trial shows that increased soil biodiversity in organic systems supports soil functions and can thus mitigate the negative environmental impacts of agricultural practices.
Organic cropping systems tend to foster above-ground diversity (companion herbs) as well as the diversity of soil animals and microorganisms in the soil.
* In biology, a habitat refers to a biotope defined by specific abiotic and biotic factors that relates to a particular species of animal or plant or group of species.
