LeFaSus - Uncovering Legume Soil Fatigue for Sustainable Expansion of European Grain Legume Cultivation

Rationale
Over the past decades, countless efforts have been made to promote the cultivation of legumes, especially grain legumes, in order to reduce the use of mineral N fertilisers, increase biodiversity, reduce dependence on imported feed proteins and improve soil biological properties and humus content.

However, grain legumes are still not widely grown. One of the main reasons is “legume fatigue”, which limits the expansion of legume cultivation in many European environments.

The exact causes of legume fatigue are not known, although soil-borne diseases interacting with abiotic factors are thought to play a key role. Recent results suggest that the balance between pathogen load and soil suppressiveness, rather than pathogen load alone, is critical.
In several farms and/or regions legume fatigue is not reported to be a problem, while in others it severely limits legume production. The reasons for this variation are not fully understood, but Identification of the causes is urgent, but only possible in a collaborative project covering several different environments and including multiple assessments of biotic and abiotic factors.

 
Aims and expected outputs:
To identify the main causal factors and/or indicators of legume fatigue in a variety of European environments. These may be biodiversity parameters or the presence of specific functional groups of the soil or endophytic microbiome, but also interactions with environmental factors or management practices.

To develop easy to implement indicators to assess the risk of legume fatigue, including soil suppressiveness in addition to pathogen load.

Propose agronomic measures to prevent or reduce legume fatigue ( subject to verification in subsequent research).

To provide a fundament for further targeted research.

Hypotheses
Our research is based on the following hypotheses:

1. Higher frequency of legumes leads to lower yields; when legumes are introduced into agricultural systems for the first time, this leads to significant yield losses (“legume fatigue”).
2. The causes are biotic; soil-borne pathogenic fungi play a key role.
3. Rather than pathogen load, a lack of biological suppressiveness of soils is the main factor causing problems in legume crops.
4. In the case of legumes, a more specific suppressiveness (based on a number of specific fungi) is more important than a general suppressiveness.
5. A set of indicators, including biological and environmental parameters, allows the risk to be assessed and strategies to avoid legume fatigue to be developed.

Approach
The first main pillar is a large network of farms in different environments where environmental factors, climate and weather, management practices, yield development and any problems related to legume cultivation will be documented in the first phase of the project. This will include both farms that are successfully growing legumes and those that are experiencing problems.

The second pillar will be selected, already existing long-term experiments (LTE) in several European countries, where different management practices (crop rotations, tillage, organic fertilisation) will be compared.

Based on these two datasets, a subset of farms and LTE will be selected for more in-depth analysis and observation over two seasons, which will include extensive assessments of the soil and root biome, including bacteria, endophytic and saprophytic fungi, arbuscular mycorrhiza, nematodes and protozoa as well as Bioassays on the disease suppressiveness.

Overall, the project will be an important complement to the many other research and extension activities aimed at increasing the share of legumes in crop rotations, as it will focus on the most important obstacle to their implementation on a larger scale.