FEATURE
suppression through changing the
competitive pressures experience by
weeds each year. Growing forage crops
that are cut and baled for hay may play
a similar role to grazing by increasing
the diversity of management actions
between years. i.e. mowing and her-
bicides, rather than grazing and her-
bicides. A trial on this is also currently
underway at Langgewens. The authors
of this article imagine that it may also be
possible for livestock and crop farming
neighbours to come to mutually benefi-
cial arrangements where crop farmers
borrow sheep for weed management in
exchange for supplying forage to sheep
farmers.
This study was conducted using weed
seedbank samples collected from the
Langgewens Long-Term Research Trial,
and was a collaboration between the
Western Cape Department of Agricul-
ture, Stellenbosch University, as well as
Coventry University and Rothamsted
Research in the UK.
The research was led by Chloe MacLar-
en, a PhD student at Coventry University,
and supported by Drs. Johann Strauss,
Pieter Swanepoel, Jonathan Storkey
and Katharina Dehnen-Schmutz.
Figure 1: Weed seedbank abundance,
diversity and wheat yield in different
crop rotations of the Langgewens Long
- Term Trial.
Weed abundance and diversity is
plotted on a logarithmic scale so units
are not shown, but average weed
seed density across the twelve years
in system A was 151 germinable seeds
per square metre in the top 5 cm of
soil, and in system G it was less than 5
germinable seeds per square metre.
In terms of diversity, system A was over-
whelming dominated by ryegrass (Lo-
lium spp.) and knotweed (Polygonum
aviculare), whilst in systems E - H, gous-
blom (Arcotheca calendula), gansogie
(Cotula spp.) and turknaal (Erodium
moschatum) were commonly observed
in low numbers. Wheat yield is shown
as proportional to the average yield in
each year. Throughout the twelve years
of this trial, the average yield across all
wheat plots was 3721 kg/ha.
Figure 2: Sheep graze a medic pasture in the Langgewens Long-Term Trial.
The crop rotations in each of the sys-
tems are as follows:
A – Wheat - Wheat - Wheat - Wheat
B – Wheat - Wheat - Wheat - Canola
C – Wheat - Canola - Wheat - Lupins
D – Wheat - Wheat - Lupins - Canola
E – Wheat - Medic(*) - Wheat - Medic(*)
F – Wheat - Medic/clover(*) - Wheat -
Medic/clover(*)
G – Medic(*) - Wheat - Medic(*) - Canola
H – Wheat - Medic/clover(*) - Wheat -
Medic/clover(*)
Crops marked (*) are grazed. Medic/
clover = a mix of medic and clover spe-
cies. System H differs from system F in
that sheep are kept aside in separate
pastures to graze old man saltbush
until the medics are mature.
Grassroots
Vol 18
No 4
December 2018
06