Faba bean and spring barley in sequence with catch crops: Grain yields and nitrate leaching

Context/Problem: Importing protein into Europe is causing sustainability challenges, which has resulted in an increasing European interest in locally growing faba bean as a protein source. There is, however, a concern that this may result in higher nitrate leaching compared with conventional cereal-based systems. Objective/Research question: We investigated the risk of nitrate leaching and its mitigation strategy after growing faba bean with catch crops within a conventional European cropping system that also includes catch crops in spring barley. Methods: We conducted a field experiment with faba bean (Vicia faba L.) and three catch crops (chicory (Cichorium intybus L.), perennial ryegrass (Lolium perenne L.) and winter rye (Secale cereale L.)) grown in sequence with spring barley (Hordeum vulgare L.) and replicated in time over a period of three years. Continuous spring barley with catch crops (perennial ryegrass and fodder radish (Raphanus sativus L.)) were used as a reference. Measurements included grain yield and grain nitrogen (N) of the main crops, aboveground biomass and N yield of the catch crops, and nitrate leaching. Results: Grain yield and grain N of faba bean grown with undersown catch crops were not statistically different than without catch crop and post-harvest sown catch crops. Catch crops with faba bean had lower aboveground biomass and N yield than with spring barley. Faba bean as pre-crop compensated for the reduced amount of fertilizer input and also increased the grain yield and grain N of the subsequent spring barley. In 2020–21, nitrate leaching from both spring barley and faba bean without catch crops was not statistically different, with an average of 64 kg NO-N ha. In contrast, in 2021–22, nitrate leaching after faba bean without catch crops was higher with 104 kg NO-N ha, compared with spring barley with 68 kg NO-N ha. Catch crops significantly reduced nitrate leaching on average by up to 55 kg NO-N ha from faba bean and 62 kg NO-N ha from spring barley fields. Conclusions: The study reveals that growing faba bean can reduce N fertilizer input without compromising the grain yield and grain N of following spring barley. Variable nitrate leaching between years from faba bean requires more research on diverse pedo-climatic and agronomic conditions to better assess nitrate leaching risks and reduction strategies. Implications or significance: These results will aid in designing cropping systems including faba bean and catch crops combinations to reduce N fertilizer input and nitrate leaching risks and improve protein sufficiency.