ConcernsEcological • feral populations or hybrids with
wild relatives interfere with the habitat
Food purity • outcrossing between nearby fields • feral populations contributing to
yield
The system
• Soil - genesis, resilience • Primary production – crops and weeds• Decomposition – bacteria, fungi,
protozoa, nematodes, collembola, etc. • Element cycling • Herbivory – nematodes, insects,
cattle/sheep + humans
The scales
• Fine soil structure – bacterial, fungal
• Field patch – plant populations• Field – management unit• Farm or group of farms• Landscape
Oilseed rape• Reappeared as a common crop in
1970s• Most Brassica napus, some B. rapa• As a ‘break’ crop in cereals• Oil has a wide range of uses• Outcrossing (contact, wind, insect)• Feral descendents (pod shatter,
inducible dormancy)
It has joined joined the seedbank
In this small plot of 200 m-2
• 10,000 original OSR crop plants
• >100,000 seed shed at harvest
• 100 feral plants one year later
• >1000 feral seeds still in the seedbank
Other arable plants
• Seedbank – 1000 to >10,000 individuals in a square metre
• 10 target weeds • 30 common, 150 less common
species• Non-target species highly valuable
to arable food web• From glacial and more recent
0
10
20
30
40
50
0 200 400 6000
10
20
30
40
50
0 200 400 600
Will OSR affect rest of seedbank ?
Community-scale properties
Ecological impact - conclusions
Ferals and hybrids -• Negligible effect on integrity of soil • Negligible effect on main habitat processes• Mainly fill vacant space – ferals typically 100
m-2
• But might alter seedbank species abundance or species composition
• And some transmission of effect to food web
2. Impurities in yield
• Distance and frequency• Persistence over time• Food quality• Perception and
preference
Impurities in OSR decay slowly
0
0.2
0.4
0.6
0.8
1
0 3 6 9 12 15
time (years)
co
nta
min
ati
on
herbicide
no herbicide
Impurity in yield - conclusions
• Not preventable in oilseed rape under present arable cropping – at low frequency over several km, mediated by a range of
insect vectors and wind-borne pollen – regional process depending on the configuration of fields in a
locality – cross pollination between nearby fields is 1 in 1000 or less
(higher to fields of partial male fertility) – In-field ferals can contribute more (i.e. 1 in a 100) to
impurities
• Can be limited < 0.1% not practicable< 1% uncertain and only with the most rigorous
standards