Title: Resource efficient control of Elymus repens
Abstract: Elymus repens is a perennial grass weed that causes great yield losses in a variety of
crops in the southern and northern temperate zones. Primary control methods for E.
repens are herbicides or intensive tillage, both of which have a number of negative
side-effects, e.g. herbicides can contaminate groundwater, and tillage can cause
increased nitrogen leaching. The aim of this thesis was to investigate how to make non-
herbicide control of Elymus repens more resource efficient in terms of less energy
demanding soil cultivation and reduced nitrogen leaching. Three field experiments
were used to test cover crop competition, mowing and different types of optimised
tillage techniques and timing, as well as the combination of under-sown cover crops
and mowing or row hoeing. The growth, biomass allocation and morphological
responses of E. repens to competition were studied in a greenhouse experiment.
The effect of competition from under-sown cover crops on E. repens seems to
depend greatly on the cover crop biomass achieved. At high biomass levels, the cover
crop can be highly suppressive (Paper IV) and reduce nitrogen leaching (Paper III),
while at low levels they can still provide benefits such as reduced E. repens shoot
biomass and increased subsequent cereal yield (Paper I). However, a low-yielding red
clover cover crop increased E. repens rhizome production by 20-30%. Under-sown
cover crops were successfully combined with both mowing and row hoeing (Paper I &
III), but while repeated mowing reduced E. repens rhizome production by 35% it could
not be shown to give a competitive advantage to the cover crops over E. repens (Paper
I). However, the low nitrogen leaching and reduced downward transport of nitrogen
when mowing or row hoeing was combined with under-sown cover crops make them
interesting control methods for future research. Delaying tine cultivation by a few days
after harvest did not reduce E. repens control, but a delay by 20 days tended to result in
higher E. repens rhizome biomass and shoot densities, compared to performing it
within a few days of harvest. Repeated tine cultivation did not improve control of E.
repens or increase subsequent cereal yield, compared to a single cultivation directly
after harvest. Repeated cultivation during autumn should therefore not be used
categorically, but only when there is reason to believe the shoots will pass the
compensation point due to the autumn conditions. We conclude that a site specific
approach is necessary to achieve resource efficient control of E. repens.
Publication Year: 2015
Publication Date: 2015-01-01
Language: en
Type: dissertation
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