Faba beans are legumes, more closely related to vetch than to common beans. Faba beans (Vicia faba) are also called fava or broad beans. The larger beans are often used as a vegetables or dried pulses and small faba beans are used as cover crops. In much of Canada, fabas are winterkilled. This means they make a great fall cover crop — they don’t need to be tilled or incorporated until the spring, or not incorporated at all under no-till conditions where the next crop is planted right into the winterkilled mulch.
In a Massachusetts study, faba bean cover crops accumulated as much as 192 kg of nitrogen per hectare (171 lb N/acre). Much of the nitrogen was made available to the following corn crop but only under certain conditions.
The key to maximizing the nitrogen accumulation of fabas was to plant them around August 1st, which is early for most fall cover crops. When planted in mid-August, the cover crop accumulated much less nitrogen (67 kg/ha compared to 192 kg/ha when planted August 1st).
The other important aspect was the timing of the nitrogen release. The faba beans held the nitrogen in their tissues over the winter. In the spring, as the cover crop decomposed, the nitrogen was released. In conventional tillage systems, half of the nitrogen was released by the end of May—too early to be used by the sweet corn crop. The remaining nitrogen was released later. In no-till systems, half the nitrogen was made available before the end of June; consequently much of the N could be taken up by the corn. Again, the other half was released later.
“Averaged over two years, sweet corn planted into the residues of the earliest sown faba bean produced 19 per cent more marketable ears, 23 per cent higher fresh ear weight, and 39 per cent less unfilled ear tip compared with sweet corn grown in plots lacking a prior faba bean cover crop,” write the authors.
The faba bean-sweet corn relationship is just one example of the use of cover crops. The latest research reveals how timing and tillage affect the success of cover crop systems.
Source: Fatemeh Etemadi, Masoud Hashemi, Omid Zandvakili, et al. 2018. Nitrogen Contribution from Winter-Killed Faba Bean Cover Crop to Spring-Sown Sweet Corn in Conventional and No-Till Systems. Agronomy Journal. Volume 110, Pages 455-462.
- Janet Wallace