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Research is initiated to determine the role of the four Cs in leading to “over-yielding” of intercrops compared to sole crops by using a long-term experiment with maize and fababean grown at different levels of N and P fertilizers in China Agricultural University.

“Overyielding” means that the intercrop has a significant higher yield than expected from the species composition as compared to how the species perform in sole crops. In addition, theoretical work is initiated by INRA on determining the critical N concentration of intercrops.

Field experiments for determining interactions in species mixtures for improved yield and yield stabilisation

New field experiments have been successfully carried out at the Aristotle University of Thessaloniki (AUTH, Greece), including pea-wheat mixtures (several varieties of each tested), and with/without irrigation, to further study how species mixtures interact for improved acquisition of light and water under different managements.

Field experiment in Greece on wheat-pea intercropping  (@Christos Dordas, AUTH)

Field experiments at the Swedish University of Agricultural Sciences (SLU) and University of Hohenheim (UHOH) have been established during the first year to determine how intercrops and sole crops of pea and oats perform in a field with heterogeneous soil conditions. The sole crops and intercrops were sown in strips along transects with known soil variability within the field.

Field experiment at University of Hohenheim 2018 (@ J. Zachmann, UHO)

The growth season in southern Sweden resulted in severe drought stress of the pea and oat crops resulting in no harvestable pea in sole and intercrop, but the oat yield in the intercrop was about 80% of the sole crop yield indicating the compensation principle of intercropping when one of the component crop is failing due to abiotic stress. The field experiment in UHOH was successful and is currently analysis is being carried out as are new a method to use remote sensing to determine the proportions of species in intercrops with drones.

Modelling above- and below-ground plant interactions in species mixtures

A review article by Noemi Gaudi and 20 co-authors on existing models for annual crop mixtures was published in Agronomy for Sustainable Development vol. 39, April 2019: “Current knowledge and future research opportunities for modeling annual crop mixtures. A review”. It highlights that modelling of annual crop mixtures is in its infancy and gives to model users some important keys to choose the model based on the questions they want to answer, with awareness of the strengths and weaknesses of each of the modelling approaches. Future models will have to simulate impacts of annual crop mixtures on various ecosystem services and the field scale should be included in more integrated scales such as the rotation and the agricultural landscape, including long-term effects.

 https://link.springer.com/article/10.1007/s13593-019-0562-6