Agricultural intensification has caused a strong agro-biodiversity decline in Europe, with high losses in rare arable plants. A better understanding of the relationship between these species, agricultural productivity, and other ecosystem functions can improve conservation management. The study was performed on an experimental field near Munich. To examine the results under field conditions, study plots were additionally established on ten arable fields distributed in the Munich Plain, an area with nutrient poor soils in southern Germany. We sowed a mixture of ten rare arable plant species at varying crop densities and compared them to plots without rare arable plants. To assess the effects on plant diversity and productivity, the cover and species richness of rare and common arable plants and the crop and arable plant biomass were assessed. The organic matter, nitrogen concentration, as well as the biomass and abundance of earthworm (biannually sampled for two years) were analyzed to determine the impact on soil fertility. Our results showed that sowing rare arable plants did not negatively affect crop biomass. Arable plant biomass and cover of rare arable plants were highest when no crops were sown. There was no difference between reduced and regular crop sowing densities on rare arable plant cover. In our field experiment, earthworm occurrence and soil organic matter were probably influenced by pre-crops (two years of clover grass before the experiment) and summer droughts during the study period. However, no significant effects of sowing rare arable plants on soil fertility were detected. These results were partly verified from results of the field study. At least on nutrient-poor soils, rare arable plant sowing may be a suitable tool to promote plant diversity conservation without negatively affecting crop production. That the sowing of rare arable plants did not significantly affect the indicators for soil fertility suggests that biomass production of rare arable plants was too low to have an impact on the crops and a benefit for soil fertility. Insignificant effects on crop biomass also suggest that sowing rare arable plants does not automatically lead to crop losses. As organic matter, nitrogen concentration and earthworm occurrence slowly respond to environmental changes, they should be investigated in further long-term experiments. This study shows that conservation of rare arable plants and food production on nutrient poor fields can be combined. Therefore, land sharing may be a suitable tool for nature conservation and ecosystem functionality on arable land.