Grain legumes are an important source of plant protein in both food and animal feed. Despite this, there is not much grain legume cultivation in Europe. Instead, large quantities of soybeans are imported.  

"Most of the soybeans we import to Europe come from South America. Soybean cultivation in South America is often associated with deforestation and negative impacts on natural ecosystems," explains Chiara De Notaris, now at the Euro-Mediterranean Center on Climate Change. 

To address the high import of grain legumes to Europe, the European Union, as part of its "Farm to Fork" strategy, has a specific focus on increasing the production of grain legumes within European borders. 

The most cultivated grain legume in Europe 

Therefore, researchers from the Department of Agroecology at Aarhus University have studied faba bean productivity, yield stability, and nitrogen fixation in a long-term organic and conventional crop rotation experiment. 

"We have examined how different agricultural practices affect faba bean cultivation," says senior researcher Jim Rasmussen from the Department of Agroecology at Aarhus University. He continues, "Faba bean is one of the most cultivated grain legumes in Europe and grows well in the cool climate in the Northern part of the continent. " 

Faba bean is a valuable crop due to their high protein content and ability to enrich soil fertility. Typically, when comparing faba bean yields with winter cereal crops, the yield can be up to 50% lower. However, when compared to spring cereals, the researcher found the differences in productivity to be less pronounced, and yield stability being comparable. 

Therefore, the researchers assessed various parameters to determine the overall productivity of faba bean, including yield levels and stability, as well as nitrogen fixation. 

Organic farming has lower yields due to disease pressure 

The study revealed significant differences between organic and conventional farming systems regarding faba bean productivity. 

"Our results show that conventional crop rotations contribute to higher yields and higher yield variability in faba bean production compared to organic methods. The lower yields in organic rotations are mainly due to disease pressure during the grain filling period," explains Chiara De Notaris. 

Faba beans are known for their ability to form a symbiotic relationship with nitrogen-fixing bacteria, which enables them to access atmospheric nitrogen and convert it into a usable form. This study shows that both organic and conventionally managed faba beans have high nitrogen-fixing abilities, with more than 80% of plant nitrogen obtained from fixation. This high nitrogen input ultimately leads to improved plant growth and, importantly, higher yields. 

"When we prioritise soil health, biodiversity, and the reduction of chemical inputs, as an organic system, we need to create a favourable environment for faba beans to thrive. We can clearly see a difference in the results between organic and conventional experiments, and shall in coming years focus on reducing disease pressure in organic faba beans to close the yield gap to conventional systems" says Jim Rasmussen, adding, "We need to gain more knowledge about the factors that affect the productivity and sustainability of faba beans because it is crucial for optimising their cultivation. Grain legumes like faba beans play a significant role building a sustainable food security in the future." 

Long-term experiments are indispensable 

The study is based on data from 2015-2018 in a long-term crop rotation experiment established in 1997 in Foulum, Denmark. Since then, researchers have been investigating how different crop systems' impact and management affects long-term productivity and environmental impacts. 

"We wouldn't be able to conduct this kind of research or obtain similarly insights without long-term experiments like the one in Foulum. They are simply necessary when evaluating the performance of different crops under various agricultural practices. Long-term experiments like these contribute to the development of sustainable and robust farming systems," says Jim Rasmussen.  

"Without these long-term experiments, this study would not have been possible. Now, we have a result that clearly tells us that to obtain a sustainable organic faba bean production in Denmark with good yields and high nitrogen fixation, we need to improve the management of diseases during the grain filling period," concludes Chiara De Notaris.