Cover Crops:
Benefits, management & Knowledge gaps
Charlotte White, Helen Holmes, Nathan Morris & Ron Stobart
www.adas.uk
What is a Cover Crop?
• Cover crops are grown for the purpose of
‘protecting or improving’ between
regular (cash) crop production
• Must be established by 1st Oct and
retained until 15th Jan (EFA definition)
• Terms ‘cover crop’, ‘catch crop’ and
‘green manure’ sometimes used
interchangeably
• Catch crops: ‘catch’ nutrients and
reduce risk of leaching/run-off
• Establish by 31st Aug (EFA) until at least 1st
Oct
• Green Manures: improve nutrition of
following crop
EFA: Ecological Focus Area
Cover crop species
• Legumes
• Vetch, clovers, peas, beans, trefoil
• Non-legumes
Clover
• brassicas: mustards, radish
• grasses: rye/oats
• others: phacelia, buckwheat, chicory
Radish
Rye
Brassica mix
Brassicas
Legumes
Grasses and cereals
Examples
Mustards, radishes,
Vetch, clovers, peas
Oat, rye, rye-grass
Benefits
Rapid growth
Biofumigant activity
Deep rooting
Late summer/early autumn sown
Sowing
Considerations
Fix nitrogen (modest overwinter)
Potential for deep rooting
Slower growing and often
need to be sown earlier (late
Jul-Aug)
Good autumn establishment Careful establishment of
is critical
small-seeded legumes.
Potential rotational conflicts, Potential rotational conflicts
e.g. clubroot,
Good early ground cover
Wide range of sow dates
Sowing times vary with
species; Jul - Sept.
Can act as a green bridge
for cereal pests and
diseases.
Mixtures
• At least two cover crops
• At least one cereal & one non-cereal (EFA)
• Multiple benefits - combined properties
of single species
• Additional benefits – Species work
together
• e.g. Grass + legume mix enhances N
fixation
• Risk management
• Additional costs
• More complicated management
EFA: Ecological Focus Area
What have cover crop ever done for us?
Potential benefits
Potential problems
•
•
•
•
• Increased pests and disease
Improve yield & quality of cash crops
Nitrogen fixation, uptake & release
Nutrient uptake
Weed suppression
• allelopathic effects
• competition
• Pest suppression
• bio-fumigation effects
• Reduce soil erosion and runoff
• Improve soil health and fertility
• soil organic matter, soil physical
properties and soil biology
• Livestock forage
• Biodiversity, habitat provision and
natural enemy benefits
•
e.g. green bridge linking cash crops
• Increased weed issues
•
e.g. volunteer cover crop plants
• Rotational conflicts
•
e.g. Brassica covers for rotations
with oilseed rape
• Management issues
•
•
Difficult to destroy cover crop
Establishment of following cash
crop
• Increased costs / workload
Nitrogen Fixation
• Wide range of N fixation (30 – 150 kg/ha)
• N fixation requires a lot of energy
• 25-33% C fixed in photosynthesis
• N fixing nodules develop 3-5 weeks after emergence
• N fixation is positively correlated with biomass production
• Most active temp range between 7°C and 20°C
• Modest amount of N fixed over-winter
N fixation after 2 - 3 months
Min
Max
160
N fixation kg/ha
140
120
100
Muella & Thorup-Kristensen (2001)
Nesmith & McCracken (1994)
Buchi et al. (2015)
80
60
40
20
0
Crimson
Clover
Berseem
Clover
Common Hairy Vetch Vicia faba
Vetch
Nitrogen Uptake
Min
Max
140
120
N Uptake kg/ha
• Wide range of N uptake
(30-130 kg/ha)
• Affected by sowing date &
Temp
N Uptake during winter
100
80
60
40
20
• Earlier sowing – greater
biomass & N uptake
0
Rye
White Mustard
oilseed raddish
Odhiambo and Bomke 2008
Ranels and Wagger 1996
Stivers-Youn 1998
Silgram et al. 2015
Impact of sowing date
on autumn cover crop
green area index (GAI)
eight sites, October
2014 , Kellogg’s Origins
(Stobart et al. 2015)
Nitrogen Release
• 10 – 100 N kg/ha available to 1st following cash crop
• Species
• Biomass
• Timing & method of destruction
• C:N Ratio
• A C:N ratio of less than 20 is needed for release of plant available
N (net mineralisation)
• Potential negative effect where crops such as rye deplete soil N
Pest and weed management
Weeds
• Competition depends on early emergence, canopy closure etc.
• Allelopathy
• stimulatory or inhibitory effect of chemical compounds produced by one
plant on another plant
• evidence from rye, barley, sorghum, sunflower, brassicaceae, and others
• need to confirm effects in field conditions
Pests – Bio-fumigation & Trap cropping
• Biofumigation - brassica species
• glucosinolates / volatile compounds released following incorporation
• target pests include potato / beet cyst nematode
• Trap cropping – Some species can act as a trap crop
• e.g. solanum species stimulate premature egg hatch of PCN
Soil Benefits
Impact of cover crop on soil condition
Reduced Erosion
Rugeley, Staffs (03/02/12)
Bare stubble
• Decrease erosion and run off if sufficient
canopy cover (>30%)
Soil Organic Matter
• Effects are variable & difficult to detect
• Increases of 0 – 42% SOM (some studies)
• No study reported a decline
Soil structure & Physical properties
• Roots can break up compacted layers and
create biopores which can improve root
growth of following crops
• Some evidence for increased aggregate
stability & reduced bulk density
Soil Biology
•
Some evidence for increased earthworm
populations
Oil radish
Yield Responses UK data
• Variable
• Not always seen in first following crop
• ~0.36 t/ha yield response from covers ahead of
spring barley (5 years of data)
• Gave economic benefit of £43/ha
(excluding costs of seed & establishment)
• Establishment cost £15 - >£40/ha
• Seed costs £15 - >£60/ha
New Farming Systems (NFS)
NFS supported by The Morley Agricultural Foundation and the JC Mann Trust
Linkages to the to the AHDB ‘Soils Platforms’ project with James Hutton Institute and the Defra SIP Platform
• cover crop and cultivation experiment
• 4 cultivation systems (plough, deep and shallow non-inversion and managed)
• ± autumn cover crops ahead of spring sown crops in rotation with winter wheat
Rotation
Year 1 Year 2 Year 3 Year 4 Year 5 Year 6 Year 7 Year 8 Year 9
(2008) (2009) (2010) (2011) (2012) (2013) (2014) (2015) (2016)
Spring break based ww
sosr
ww
sbn
ww
sbrly
wosr
ww
Mean yield and margin data from wheat years only
Mean yield
Yield
Margin
Margin
Tillage
(t/ha)
(% of plough) (£/ha) (% of plough)
Plough
10.53
100
921
100
Deep
10.63
101
978
106
Shallow
10.17
96
930
101
LSD
0.16 (P<0.001)
-
• Typical margin responses £50 - £75/ha in winter wheat
using legume & brassica cover crops
so
New Farming Systems (NFS)
NFS supported by The Morley Agricultural Foundation and the JC Mann Trust
Linkages to the to the AHDB ‘Soils Platforms’ project with James Hutton Institute and the Defra SIP Platform
Yield (t/ha)
Winter wheat yields,2012
11.0
10.8
10.5
10.3
10.0
9.8
9.5
9.3
9.0
8.8
8.5
8.3
8.0
Cover Crops and shallow tillage
• Yield response (%) to the use of a brassica cover crop
• Generally positive responses with cover crops and shallow tillage
systems
2
0
-2
2008/09
2013/14
2009/10
2010/11
2011/12
-4
12
-6
10
-8
-10
-12
-14
Plough
% yield response to cover crop
% yield response to cover crop
4
2012/13
2014/15
8
6
4
2
0
-2
2013/14
2009/10
2011/12
2012/13
-4
-6
Shallow
2014/15
2010/11
2008/09
Impact of Brassica cover crops on OSR Yield
Yield t/ha
Mean yield loss ca. 6%
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
NFS 2014
No cover crop
Following cover crop
LSD (all): 0.48 t/ha
LSD (cover crop): 0.24 t/ha
LSD (tillage): 0.34 t/ha
CV: 8.3%
Starter Fertiliser?
•
•
•
•
15 cover crop strip comparisons at two sites 2014/15 season
20-40 kg/ha starter N use.
Mean autumn GAI increases c. 15%
Increases in autumn weed establishment
No N
With N
Autumn assessment
Spring assessment
Cover crop
Weed
Cover crop
Weed
Count
(/m2)
GAI Count (/m2) Count (/m2) GAI Count (/m2)
61
1.6
24
29
1.1
21
60
1.8
51
30
1.2
27
Wensum Demonstration Test Catchment Project
(UEA)
Nitrate leaching: NO3 mg N/L, Oct-Dec 2013
• Cover crop field mean: 2.6
• OSR field mean: 4.9
• Wheat field mean: 15.0
• Fallow / control: 18.3
30 kg/ha N applied
c. 15% increase in
above ground biomass
c. 5% reduction
in root biomass
c. 5 kg/ha N
recovered
Knowledge Gaps
•
•
•
•
•
•
•
Variety characterisation
• E.g. Pest & Disease susceptibility, rotational impacts,
environ suitability, mix compatibility
Management
• Residual herbicide effects, method & timing of
establishment/destruction to maximise benefits
More data to calculate cost benefits
Optimise machinery techniques for UK conditions
N and other nutrient cycling & effects of management on this
• Can N be reduced in the following crop?
Management advice when using covers for forage
Measure effects on SOM in the UK – needs long term studies
Recommend
•
A network of linked experiments with common
treatments and assessments to allow joint analysis
Trying cover crops
1. Be clear about the objective
• e.g. N fixation, soil improvement etc.
2. Test a few options & use a control
• Test field strips, Controls e.g fallow or normal cultivation
• Consider management & rotation
3. Monitor progress
• Photos, simple assessments e.g. soil structure
• Yield maps, yield meter or weigh bridge
• Look at 1 or 2 years after use
4. Evaluate the costs and returns
• Keep records inc. for control.
• Can’t always account for wider benefits
• Environ schemes
5. Modify & develop
• E.g. seed rates, timings etc.
Thank you
[email protected]
@c_a_white
ADAS Gleadthorpe, Nottinghamshire, NG20 9PF