Soil potassium supply and Rumex obtusifolius and Rumex crispus abundance in silage and grazed grassland swards

Abstract

Three experiments investigating factors influencing the abundance of Rumex spp. (docks) in silage and grazed grassland swards are presented. In Experiment 1, Rumex obtusifolius plants were sown with perennial ryegrass and white clover in pots in March and harvested at either 5‐ or 10‐week intervals between June and October. The 10‐week harvest interval increased root dry‐matter production of R. obtusifolius compared with the 5‐week interval; herbage (above‐ground material) production was not significantly affected. In Experiment 2, R. obtusifolius and Rumex crispus population densities in grassland swards were correlated with soil P, K and Mg concentrations, and soil pH. In general, silage swards contained higher population densities than grazed swards. There were significant positive correlations between soil K concentrations and abundance of Rumex spp. in grazed swards and in silage swards. In Experiment 3, R. obtusifolius was sown with perennial ryegrass in pots in March. Treatments consisted of nine rates of K fertilization ranging between the equivalent of 0 and 600 kg K ha−1 year−1. Herbage was harvested at regular intervals (4–6 weeks except during the winter) until May of the following year. In general, perennial ryegrass dry‐matter yields were not greatly affected by soil K, whereas limited soil K supply tended to reduce dry‐matter production of R. obtusifolius. It is possible that maintenance of moderate soil K concentrations may play a role in limiting abundance of Rumex spp. in grassland.