Sheep grazing vs. cutting: regeneration and soil nutrient exploitation of the grassland weed Rumex obtusifolius

Summary

Broad-leaved dock (Rumex obtusifolius L., Polygonaceae) is an agronomically
important perennial weed causing decreases in pasture yields and fodder quality.
Non-chemical control measures for dock are often limited to frequent pulling and
cutting, additionally it is usually avoided by grazing animals. Here, the regeneration of
R. obtusifolius in a Rumex-infested grassland grazed by a sheep breed that explicitly
feeds on dock (Ovis aries L. cv. East Prussian Skudden) was compared to cutting.
Therefore, regeneration of 90 R. obtusifolius plants of three different size classes was
monitored in three plots during three grazing and cutting cycles. Plant height and
number of fruit-stands of regrown R. obtusifolius was significantly lower, number of
leaves significantly higher after grazing than after cutting, while plant diameter was
unaffected. Initially medium and large-sized plants (>40 cm diameter) were significantly
more sensitive to grazing or cutting than initially smaller sized plants. Soil
nitrate and ammonium concentrations in the vicinity of R. obtusifolius correlated with
some regrowth parameters but were not affected by grazing or cutting. Sheep-grazed
grassland communities comprised fewer legumes (p=0.002), more grasses (p=0.010)
and fewer sward gaps (p=0.025) than cut grassland. At the end of the experiment,
abundance of R. obtusifolius in sheep grazed plots was lower than in cut plots
(p=0.089) suggesting that regrowth potential of this weed was depleted by continuous
grazing and higher sward density. In conclusion, these data suggest that sheep could
be considered in grassland management schemes to both directly and indirectly control
Rumex infestations.