Forage and seed yield of winter turnip rape established as a mixed crop with cereals

Abstract

SUMMARYCultivation of winter turnip rape (Brassica rapa L. ssp. oleifera (DC.) Metzg.) in Finland has been limited because of its reputation as an unreliable crop and its mid-season sowing time of July, when fields are already sown to other crops. An alternative management practice for winter turnip rape is proposed whereby it would be sown as a mixed crop simultaneously with spring cereals. The growth and yield formation of winter turnip rape grown in mixed stands with four different spring cereals was studied in two field experiments conducted in 2009–11. Pure and mixed stands of winter turnip rape and spring cereals were established in May at two different cereal and winter turnip rape stand densities. Subsequent to cereal harvest, one-third of each winter turnip rape plot was harvested for biomass in autumn, before cessation of growth. Three plant stand types, May- and July-sown monocrops and a mixed crop with oat (Avena sativa L.) were sampled for forage analysis. Plant stand densities were monitored from establishment until maturity. Winter turnip rape yield and its quality, including oil content, protein content and thousand seed weight, were determined. Following favourable overwintering conditions, winter turnip rape established with cereals yielded comparably to that of pure stands in terms of both quantity and quality. However, a pure stand of winter turnip rape out-yielded mixed crop stands after unfavourable overwintering conditions. Leaf removal decreased plant survival and seed yield. Establishing winter turnip rape with a cereal in May is an alternative to sowing it as a monocrop in July. A higher seeding rate is needed for under-sown winter turnip rape. Furthermore, autumn-harvested winter turnip rape monocrop forage potentially represents a high-protein supplement for ruminants.