Field work including data collection
The research was conducted by implementing a unique split-split plot field experiment allowing disentangling the potential synergistic effects of crop diversification and field margin management while considering distance-effects to this margin. The experiment, conducted over two cropping seasons (2020/2021 and 2021/2022), took place at the University of Bonn Teaching and Research Station for Organic Farming Wiesengut (Hennef, Germany). Four different cropping systems were tested, either with or without a wildflower strip at one margin: (i) a flowering crop in sole cropping, (ii) a cereal crop in sole cropping, (iii) the intercropping of both in an intermediate mixture design, (iv) the cereal crop with undersown companion plants. Winter faba bean (Vicia faba) and winter wheat (Triticum aestivum) were cultivated in 2020/2021, and in 2022 spring breadseed poppy (Papaver somniferum) followed faba bean, and spring barley (Hordeum vulgare) followed wheat. The wildflower strips were sown at the start of the experiment and were mown once a year.
Data collection included the evaluation of crop plant infestation by insect pests and colonization by their natural enemies. Predation cards were used to evaluate the level of predation. Pathogen infestation was evaluated by assessing the percentage of leaf with disease symptoms. The abundance and diversity of flowering weeds were monitored as explanatory covariables of aphid infestation, predator colonization and predation. The potential of flowering weeds in attracting and supporting natural enemies was also evaluated by monitoring insect-flower visitations. Grain yield and weed biomass was obtained at the end of each cropping season, and the impact of weed presence on crop yield was evaluated by comparing plots with and without weeds.
Overview of the results
First, as expected, intercropping significantly reduced insect pest, weeds and disease infestation compared to sole cropping. The presence of natural enemies was higher in sole cropping than in intercropping, indicating that they were tracking pests. Associating wildflower strips to intercropping partially enhanced pest predation, and further reduced aphid infestation.
Second, in intercropping, insect pest infestation was negatively correlated with the presence of weeds. A certain flowering weed species could be identified as supporting the presence of key natural enemies, especially in interaction with wildflower strips at margins. The beneficial effect of weeds to enhance insect pest regulation is especially interesting since crop yield was not significantly impacted by the presence of weeds in intercropping.
Third, intercropping enhanced land-use efficiency by increasing overall productivity per unit of land. This result was expected; but here, land-use efficiency was even enhanced by the presence of wildflower strips at margin.
Exploitation and dissemination
The details of these results are currently being compiled in scientific publications. They include at least two original research articles, in addition to a review paper. An article targeting practitioners is also planned.
The research and parts of its results were presented at:
- the Ökofeldtage (Organic Field Days) (27-30 June 2022, Villmar, Germany),
- the Open Day of the experimental research and teaching station Wiesengut (3 July 2022, Hennef, Germany)
- the XVII Congress of the European Society of Agronomy (29 August to 2 September 2022, Potsdam, Germany),
- the seminar on “Ecological Management of Bio-agressors in Agroecosystems” organised by INRAE where the Fellow was invited (14-15 November 2022, Avignon, France),
- the Tag der Nachhaltigkeit (Sustainability Day) at the University of Bonn (11 May 2023, Bonn, Germany),
- the Terrae conference on “Agroecological crop protection” dedicated to farmers and advisers organised by Natagriwal asbl and Greenotec asbl where the Fellow was invited (5 June 2023, Louvain-La-Neuve, Belgium).
