Arbuscular mycorrhizal fungi are important for healthy soils and crops. A pan-European study shows that plant-protection products adversely affect these fungi, reducing their ability to supply plants with phosphorus via their roots.
Arbuscular mycorrhizal fungi or AMF, which account for around 20 to 30% of the microbial biomass of a soil, form a symbiotic association with plants, supplying them with phosphorus and other elements. This free service provided by nature must be looked after, since it helps keep the soil healthy and can contribute to plant yield. Agroscope, FiBL, INRAe (France) and the universities of Zurich (Switz.), Berlin (Germany), Greenwich (UK), Madrid (Spain) and Uppsala (Sweden) studied arable and grassland soils throughout Europe and conducted experiments in greenhouses. Their aim: to discover from two studies the conditions under which AMF pass on the most phosphorus to plants, and what factors influence the amount and diversity of these beneficials in the field.
Response to fungicides and excessively high nutrient levels
The first study showed clearly that AMF in grassland are more efficient at passing on phosphorus to plants than AMF in arable land: on average, 64% more phosphorus reached the plants in the former than in the latter. What was the reason for this? Tillage, fertilisation and fungicide use reduced the diversity and quantities of AMF as well as their ability to establish a symbiotic relationship with the plant roots. Furthermore, the study showed that in fields where fungicides were used, AMF imparted on average 43% less phosphorus to plants than in arable soils without fungicide use.
Plant-protection product residues also in organic soils
In a second study, plant-protection product residues were examined on 100 arable and vegetable-crop fields in Switzerland. Plant-protection product residues were found in all of the tested soils, their numbers ranging from 3 to 32; however, in vegetable production the concentrations were on average 79% higher than in arable soils.
On average, 85% fewer residues were found in organic soils, whether used for arable or vegetable production. Nevertheless, the value never fell to zero. Even twenty years after conversion to organic production, up to 16 plant-protection products could be detected in the soil. Even some plant-protection products which, according to their half-life, should have disappeared long ago were still present in trace quantities. In addition, these two studies confirmed that plant-protection products had a negative effect on AMF; the more plant-protection product residues in the soil, the less AMF were to be found there.
- Fungicide use, ploughing and fertiliser application reduce the variety and quantity of arbuscular mycorrhizal fungi (AMF) as well as their ability to establish a symbiotic relationship with plant roots.
- By contrast, cultivating a variety of crops in an optimally coordinated rotation can help reduce diseases, and thus reduce fungicide use.
- Various studies also show that surface cover has a positive effect on AMF and on soil quality in general.
- Plant-protection product residues were found in all of the examined soils. Individual substances were detected even twenty years after conversion to organic cultivation.
- In the plant-breeding programmes at the research institutions, the focus should be on crop varieties that are better than existing varieties at establishing a symbiotic relationship with AMF.