Effect of different manuring and defoliation patterns on broad-leaved dock (Rumex obtusifolius ) in grassland

The effects of cutting frequency and cutting height on broad-leaved dock (Rumex obtusifolius) in Lolium perenne-based agricultural grassland at two levels of fertillser input were investigated at North Wyke, Devon, UK. Two micro-plot field experiments, containing immature dock plants at uniform densities, with a factorial design, were used to compare: (a) 'organic' and 'low-input' fertilisation, i.e. cattle slurry only vs slurry plus mineral fertillser (NPK at 100-0-64 kg ha(-1) yr(-1)), (b) cutting heights of 5-6 cm vs 10-12 cm, and (c) four harvesting frequencies representative of different grassland management practices (regular 4-weekly cutting, a 'hay-stage' cutting, and two treatments with 'silage-stage' cutting). Expt 1 was established in 1995 with 13 dock plants m(-2) (from excised dock-root sections) and Expt 2 established in 1996 with 25 plants m(-2) (as seed-grown plug plants). Treatments were assessed over the 2 subsequent years to determine treatment effects on total herbage dry matter (DM) yield and dock DM yield, and on in-situ measures of dock ramets. In both experiments, total DM yield was increased by 1.0-2.0 t ha(-1) yr(-1) for treatments receiving NK fertiliser; the proportion of dock was also higher than from slurry-only treatments. In Expt 1, the dock ramet density, mean dock ramet height, mean leaf length and numbers of dock leaves per m(2) were also greater on NK fertilised treatments in autumn of yr 1. Height of cut had no consistent effect on dock yield, but dock ramet density and leaf density in autumn were greater on the 5-6 cm than the 10-12 cm cutting treatment, Expt 2 only. In yr 2 of both experiments cutting at 4-weekly intervals resulted in less dock in the herbage than hay-stage cutting and, particularly in Expt 1, there were associated differences in leaf density and ramet height in autumn; silage-stage treatments were intermediate. Results are discussed in relation to requirements for management options where there is a need to avoid or reduce herbicides.