**5. Conclusions**

Maize row-intercropping with flowering plants represents an alternative to sole maize cropping, due to the fact that cropping partners can mitigate negative environmental impacts. Some cropping partners proved to be unsuitable for row-intercropping in maize crops. Maize–alfalfa, maize–yellow sweet clover, and maize–common vetch cannot be recommended due to the di fficulties in weed control and sowing as a seed mixture. Common vetch and mixtures which contain common vetch also are not recommended due to the assumed allelopathic e ffects of the decomposing biomass. Maize–squash could be an interesting alternative under mechanical weed control, while maize–nasturtium showed to be an alternative to sole maize cropping under conventional and organic farming, also the maize–bean crop could be an option. The yields and qualities of maize–nasturtium and maize–bean biomass are comparable with sole maize cropping, while the flowers provide a pollen source. Nasturtium could also be possible for grain maize production because no plant parts contaminate the grain. Intercropping maize with nasturtium requires additional studies on chemical weed control and the sowing rate of nasturtium. If a combined sowing of maize and IFP in a single step can be done, there will be no additional consumption of fossil fuels and no increased soil compaction compared to sole maize cropping. However, this requires that the seeds be sown as a mixture. This means that the seeds should be similar in their morphology. This can already be achieved by maize–bean. When maize and IFP are sown separately, plants can be used whose seed morphology di ffers from maize. In this case the seeds are also located between the maize rows and no mechanical weed control or inter-row band application of herbicides can take place. A later sowing of the IFP after finishing all weed control measures (chemical or mechanical), would be possible. However, this would delay the flowering time of the IFP, and an additional flower abundance before maize flowering can no longer be enabled. By sowing in one working step as a seed mixture, the share of IFP should be kept as low as possible to

enable a high proportion of maize. The use of IFP must therefore be well planned a priori, in terms of the benefits for biodiversity, shade tolerance of the IFP, the competitive situation for maize (water, nutrients), the sowing technique, the possibility of weed control, and the possible influences on final biomass. It is suggested that maize intercropping, as already practiced by ambitious farmers, should be further explored by research.

**Author Contributions:** Conceptualization, K.S., C.S., M.M.-L. and K.M.; methodology, V.S.S., C.S., M.M.-L. and K.S.; software, V.S.S.; validation, V.S.S., M.M.-L. and C.S.; formal analysis, V.S.S.; investigation, V.S.S., C.S., M.M.-L. and K.S.; data curation, V.S.S. and C.S.; writing—original draft preparation, V.S.S.; writing—review and editing, V.S.S., M.M.-L., C.S., S.W., K.S. and K.M.; visualization, V.S.S.; supervision, V.S.S., M.M.-L. and C.S.; project administration, V.S.S., C.S., M.M.-L., K.S., S.W. and K.M.; funding acquisition, K.S. and K.M. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Ministry of Rural Affairs and Consumer Protection Baden-Württemberg (MLR) within the project "Diversifizierung des Silo- und Energiemaisanbaus im konventionellen und ökologischen Landbau".

**Acknowledgments:** The authors would like to thank Jan E. Neuweiler of the State Plant Breeding Institute, University Hohenheim for statistical support; Conny Hüber for information about pollinators; Marwin Dauth, Khaliun Sukhbaatar, and Sabine Hubert for data collection and the sta ff of the LTZ Augustenberg for making this joint research project possible.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
