The University of Hohenheim is one of the most important agricultural research institutions in Germany and Europe. Agricultural research in Hohenheim primarily focuses on animal husbandry, agricultural engineering, agricultural economics, soil science and crop production. The University of Hohenheim has eleven different institutes. The Institute of Crop Science is one; it deals with all the basic issues involving cultivated plants and agricultural crops as well as optimal cultivation systems for conventional and organic farming.

Lentil research began in Hohenheim in around 2008. Initially, the scientists studied the problems that might arise from lentil cultivation. “Our research unfolded many other aspects related to lentil cultivation and it quickly became clear that there was still potential in this niche culture," says Prof. Dr. Sabine Gruber, who was instrumental in lentil research from the very beginning. In contrast to many other research projects at the University of Hohenheim, the Institute of Crop Science has always worked closely with farmers on this project.

Lentils belong to the legume family. They can enter into symbiosis with soil bacteria of the Rhizobium leguminosarum species and form root nodules. The bacteria bind atmospheric nitrogen in these nodules and make it available to the lentil plant. In return, the plant provides the bacteria with assimilates. This makes lentil plants self-sufficient in nitrogen and hence they do not depend on artificial nitrogen fertilisers. In some other legume species, the seeds are inoculated with rhizobia strains to achieve better yields and qualities. The seeds are soaked in a medium containing the bacteria. This ensures that sufficient rhizobia are available for symbiosis with the plants.

Lentils are not very demanding in terms of where they grow, as long as the soil is permeable and not exposed to waterlogging. This means that they also grow on poor soils that contain few nutrients. However, when it comes to cultivation and harvesting, lentils are very demanding. Because of the way they grow, lentils cannot compete very well with weeds. They have difficulty growing upright, and they need to be grown with so-called companion crops to support them. However, growing them with other crops increases the risk of fungal diseases. Moreover, the plants grow poorly and particularly unevenly, which makes harvesting more difficult. A companion crop can serve as a climbing aid for the plant and prevent it from lodging.

The Institute of Crop Science has been trying for more than a decade to find the optimal companion crop for lentil plants. Many different crops have already been tested: for example, different types of cereals such as oats, barley and wheat, but also other crops such as mustard, linseed, peas, buckwheat and camelina. According to Gruber, oats or camelina are the most suitable. Peas might also work well but are still in the trial phase. It is important that the companion crop is a summer plant, because lentil plants are not very frost tolerant. A good companion crop should be able to compete with weeds, but not suppress the growth of the lentils. It should also have a horizontal leaf position and sufficient stability so that the lentil plants can climb on it.

Since a lot of research on plant cultivation measures has already been done and much is known, the scientists at the University of Hohenheim have expanded their research to other areas of research. The Institute of Crop Science is currently involved in three lentil research projects - LinSel, TRUE and the EIP-AGRI Rhizo-Linse project. LinSel is focused on lentil breeding and TRUE (TRansition paths to sUstainable legume-based systems in Europe) is aimed at identifying suitable ways to expand legume cultivation and consumption in Europe. Rhizo-Linse focuses on finding answers to questions about the rhizobia vaccination of lentil seeds and the bioeconomic potential of lentils in mixed cultures. The reason why the group is focusing on the latter is because it is not yet known whether different rhizobia strains provide lentil plants with better growth conditions and make the plants more robust, and which strains are best suited for this purpose. That’s why no vaccines are yet available.

In the Rhizo-Linse project, the University of Hohenheim is in charge of the experiments on practical lentil cultivation. Some of the experiments take place in greenhouses and some at the University of Hohenheim’s experimental station, the Ihinger Hof in Renningen. Once complete, further tests will be carried out on research farms to assess the plants' practical suitability. The Institute of Crop Science has already carried out similar vaccination tests with soy, and thus brings this experience into the Rhizo-Linse project.

The researchers are hoping that inoculation with suitable rhizobia strains will contribute to higher yields and better lentil quality, making it even more attractive for farmers to grow lentils. In previous experiments, the scientists at the University of Hohenheim achieved yields of up to 3 t/ha, whereas farmers have so far only been able to achieve yields of 400 to 600 kg/ha. “The yield potential of lentils is around 3 t/ha. It would be desirable if we could at least achieve yields of up to 1 t/ha on actual farms,” said Gruber. One of the lentil researchers’ long-term goals is being able to grow lentils without a companion crop. Perhaps this will one day be achieved through suitable rhizobia strains or increased breeding efforts.

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¹ https://www.uni-hohenheim.de/pressemitteilung?tx_ttnews[tt_news]=32569