Performance and Mortality of Rumex obtusifolius and R. crispus in Managed Grasslands are Affected by Nutrient Availability

The reasons for the greater incidence of Rumex obtusifolius in grasslands compared with R. crispus have never been investigated. In a small-plot field experiment in which seedlings of R. obtusifolius and R. crispus were transplanted into a sward dominated by Dactylis glomerata, the growth and survival of seedlings were monitored over three years under control and P, N, NP and NPK fertilizer treatments. The highest plants of R. obtusifolius and R. crispus were generally recorded in the N, NP and NPK treatments and the lowest in the control and P treatment. The maximum recorded heights of R. obtusifolius were 100 cm and of R. crispus 80 cm. The number of leaves per plant, weight of individual plants, cover and fertility were generally higher for R. obtusifolius than for R. crispus. 30% to 80% of transplanted R. obtusifolius plants flowered in the first (seeding) year and this contrasted with no flowering of transplanted R. crispus plants. After cutting, substantially better regrowth of R. obtusifolius was recorded compared to that of R. crispus and surviving R. crispus plants tended to show a gradual reduction in leaf number. The mortality of R. obtusifolius over three years ranged from 0% in the NPK treatment to 13% in the control, with an average of 8% over all treatments. The mortality of R. crispus ranged from 19% in the control to 94% in the NPK treatment with an average of 64% over all treatments. We concluded that R. obtusifolius is better adapted to growing in highly productive temperate grasslands than R. crispus because of its perennial character, larger plant size and higher fertility.