Reintroduction of rare arable plants in extensively managed fields: Effects of crop type, sowing density and soil tillage

Abstract

Vegetation of arable fields has changed significantly over the past decades as indicated by a marked decline in the abundance and diversity of arable plants. Thus, beyond the preservation of remnant populations, introduction of autochthonous seeds is a necessary measure to promote threatened arable plants and to restore agro-ecosystems. However, there is a lack of knowledge on the most suitable agricultural methods for plant establishment. This topic was investigated for three winter annuals (Legousia speculum-veneris, Consolida regalis, Lithospermum arvense) in a three-year field experiment in southern Germany. We established 14 management treatments with five replicates in a completely randomized block design. In year 1, arable plants were sown in a mixture of 850 seeds m−2 either without crop or with cereal crops in different sowing densities (25 %, 100 %). After crop harvest different types of soil tillage were applied (rotary cultivator, mouldboard plough). In year 2, four different crop types (autumn-sown spelt, spring-sown triticale, pea, clover-grass) were sown, and in year 3, rye was cultivated. Establishment was measured yearly as seed production of the rare arable plants, and their overall population growth rates were calculated at the end of the study period. Highest population growth rates were observed in L. speculum-veneris, followed by C. regalis and L. arvense. Population growth of the target plants decreased significantly with crop and weed cover averaged over the study period. Initial crop sowing densities had a significant impact on first-year establishment, with persisting effects in years 2 and 3. Best results were obtained without cover crop compared to cereals sown with 25 or 100 % sowing density. The establishment of target plants was also affected by crop type in year 2 (spelt > pea > spring triticale > clover-grass). However, establishment was overall high in year 3, when all plots were cultivated with rye. Type of soil tillage had no effect within the crop rotation ‘rye–clover-grass–rye’, while rotary cultivation in ‘without crop–rye–rye’ was positive for the establishment of L. speculum-veneris and L. arvense. The results indicate good opportunities for the reintroduction of rare arable plants under different crop rotations with best results for extensively managed fields with low crop competition.