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Minimising compaction risk
& optimising N supply
using green manures
Dr Martyn Silgram
ADAS Soils, Crops & Water Group
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National Potato Conference, Dublin,18 Feb 2014
Cultivations prior to planting potatoes
How can cultivations
prior to planting potatoes
minimise compaction
(and the risk of poorer yields)?
Soil structure may be damaged …
• In the previous crop:
o cultivations or harvesting
• In the potato crop:
o ploughing
o cultivations & bed forming
o stone and clod separation
o planting
o crop spraying
o irrigation equipment
o harvesting
Compaction decreases infiltration rate &
increases runoff and diffuse pollution risk
• Soil compaction in the potato crop:
o limits rooting depth and soil water supply
o reduces water and nutrient availability (irrigation frequency)
o increases risks of waterlogging and tuber rot diseases
o reduces the efficiency of irrigation and fertiliser applications
Source: Stalham et al. (1997)
• Resulting in:
o reduced crop yields
o poorer crop quality
o increased risk of runoff and
diffuse pollution of sediment,
P, N, C & surface-applied products
Harvest 2013: Treatments
Treatment Plough Cultivate from
stubble
Deep-ridge/
bed-form
Cultivate from
stubble, de-stone, bed-form
De-stone
(Reekie)
De-stone depth
(25cm or 35cm)
Plant
25/4/13 25/4/13 25/4/13 25/4/13 26/4/13 26/4/13 1/5/13
1 Plough Deep
2 Plough Shallow
3 Simba DTX300 Deep
4 Simba DTX300 Shallow
5 Tillerstar
• 4 replicates of each treatment established on 2 sites (LS)
• Plough: 20cm depth 5 Furrow reversible (150 HP tractor) • Simba DTX: tine (40cm depth) - disc (15cm depth) – roller (175hp tractor) • Tillerstar (two-bed version, 2013 model): 30cm depth (300 HP tractor)
• Seed planting: 10-14 cm depth
Harvest 2013: Basic field data
Loamy sand, Shropshire, England following 4 yrs of cereals
Previous crop: Winter Wheat (straw removed)
Variety: Maris Piper
Cultivated: 25 April 2013
Planted: 1 May 2013 @36cm spacing
Planting depth: 12-14cm (10cm on Tillerstar)
Fertiliser applications P & K on 10 April; N on 11 April
Irrigation: 140mm during June/July (20-25mm)
Harvest date: 1 October 2013
Harvest 2013: Treatments
Simba DTX treatment
(tine - disc – roller unit)
25 April 2013
Harvest 2013: Treatments
Tillerstar treatment
(cultivate – destone - bedform
- all in one operation)
25 April 2013
Harvest 2013: Assessments
Site characterisation (incl. compaction before cultivations)
Soil analysis pre-planting at 0-30, 30-60 and 60-90cm
PCN pre-planting
SMN (0-30, 30-60, 60-90cm depths): 3 weeks post-planting, 1 week post-emergence, at TI, and at canopy closure
Soil compaction: before treatments imposed, after planting, 9 weeks post-emergence and at harvest
Soil pits: one pit per treatment 9 weeks post-emergence (soil structure, bulk density, rooting)
Soil bulk density: prior to bed-forming (before treatments imposed), after planting, 9 weeks after emergence and at harvest
Canopy development: foliar measurements 9 weeks post-emergence
Crop yield and tuber number
Environmental footprint
Soil analysis pre-planting (4/3/13)
Block pH P (mg/l
)
Index K (mg/l
)
Index Mg (mg/l
)
Index SMN
0-90cm
(kg/ha)
1 6.4 27.2 3 85 1 86 2 26.5
2 6.8 24.0 2 73 1 91 2 23.6
3 6.7 19.4 2 90 1 95 2 24.2
4 6.5 18.4 2 75 1 75 2 22.2
Pre-planting compaction data
2013 Tern Farm PCL cultivations project -
Transects across 80m x 80m trial area
(each transect comprises
14-16 replicate sample locations)
0
500
1000
1500
2000
2500
3000
3500
4000
0 2.5 5 7.5 10 12.5 15 17.5 20 22.5 25 27.5 30 32.5 35 37.5 40 42.5 45
Depth (cm)
Pe
ne
tra
tio
n r
es
ista
nc
e (
kP
a)
Transect 1
Transect 2
Transect 3
Transect 4
Wheeling
Transect numbers correspond to Blocks 1-4
Post-planting compaction data
Evidence that Tillerstar works to shallower depth than other
methods
0
500
1000
1500
2000
2500
0 5 10 15 20 25 30
Depth from surface of mid-furrow (cm)
Pe
ne
tro
me
ter
res
ista
nc
e (
kP
a)
Plough Deep
Plough Shallow
Simba Deep
Simba Shallow
Tillerstar
Mean
Depth Depth
Treatment (cm) (cm)
Plough Deep 32.5
Plough Deep 32
Plough Deep 29.75
Plough Deep 39.5 33.4
Plough Shallow 35
Plough Shallow 31.75
Plough Shallow 30
Plough Shallow 35 32.9
Simba Deep 32.5
Simba Deep 32.75
Simba Deep 32.25
Simba Deep 35.5 33.3
Simba Shallow 33.25
Simba Shallow 26.25
Simba Shallow 32.25
Simba Shallow 30 30.4
Tillerstar 23
Tillerstar 27.5
Tillerstar 25
Tillerstar 27 25.6
Compaction: 9 Aug 13
Manual penetrometer
records depth of greatest
compaction
Evidence that Tillerstar
works to shallower depth
than other methods
Uptake Mean Mean (-PCN)
Treatment kg N/ha kg N/ha kg N/ha
Plough Deep 82.57
Plough Deep 62.68
Plough Deep 99.89
Plough Deep 56.74 75.47 81.71
Plough Shallow 63.19
Plough Shallow 115.58
Plough Shallow 68.24
Plough Shallow 51.58 74.65 82.34
Simba Deep 65.09
Simba Deep 100.12
Simba Deep 88.17
Simba Deep 36.82 72.55 82.61
Simba Shallow 118.12
Simba Shallow 87.75
Simba Shallow 83.70
Simba Shallow 60.97 87.64 96.52
Tillerstar 95.30
Tillerstar 67.54
Tillerstar 59.50
Tillerstar 99.24 80.40 80.40
Crop N Uptake: 9 weeks post-emergence
Crop N uptake based
on above ground dry
matter and %N
assessments
Sampled 9 weeks
post-emergence
(30 Jul 2013)
Suggestion of greater N
uptake in Simba
Shallow treatment
Crop rooting: 9 weeks post-emergence
Mean Mean -PCN
Depth Depth Depth
(cm) (cm) (cm)
Plough 53
55
51
50 52.3 53.0
Simba DTX 40
50
50
50 47.5 46.7
Tillerstar 27
25
28
28 27.0 27.0
Maximum rooting depth from soil pit dug across potato bed
Canopy development
No treatment effect on canopy development
13 Jun 13: 5-10% crop cover
24 Jun 13: 45-55% crop cover
17 Jul 13: 75-100% crop cover *
30 Jul 13: 75-100% crop cover *
9 Aug 13: 100% crop cover *
* Except on plots in Block 4 (affected by PCN)
Total Ware Mean Mean
Yield Yield Ware Ware
Treatment Deep/Shallow t/ha t/ha t/ha -PCN plots
Plough Deep 53.97 45.97
Plough Deep 62.67 53.80
Plough Deep 59.08 53.48
Plough Deep 45.56 40.41 48.42 51.08
Plough Shallow 58.36 46.51
Plough Shallow 67.16 59.55
Plough Shallow 57.07 47.36
Plough Shallow 53.87 50.23 50.91 51.14
Simba Deep 59.60 52.66
Simba Deep 64.52 58.16
Simba Deep 52.63 46.81
Simba Deep 28.59 23.17 45.20 55.41
Simba Shallow 63.82 56.11
Simba Shallow 63.45 58.29
Simba Shallow 60.59 52.94
Simba Shallow 33.93 29.59 49.23 55.78
Tillerstar Normal 55.61 49.03
Tillerstar Normal 57.94 50.04
Tillerstar Normal 58.95 53.65
Tillerstar Normal 53.73 50.22 50.74 50.74
Harvest Yield (1 Oct 13)
No treatment effect on rejects
Higher mean yields on
Simba treatments
when PCN-affected
plots omitted
Summary of season results
Some PCN in study field (mostly Block 4)
No significant treatment effect on SMN or canopy development
9 weeks post-emergence:
o apparently greater N uptake in Simba Shallow treatment
o depth to compaction and rooting depths were shallower in Tillerstar treatment – no impact on yield this season, but it could have in a drier year or on unirrigated land
No significant treatment effect of destoning depth, but …
When PCN-affected plots are omitted, there was slightly (10%) greater yield from Simba treatments compared to Tillerstar or Ploughing
Potential fuel/time/cost/carbon savings of single-operation Tillerstar compared to conventional multi-pass operations
Cover crops prior to planting potatoes
What are the benefits
(including N contribution)
from cover crops
to the next potato crop?
The efficiency of fertiliser N uptake is limited
For w. wheat & w. barley:
Light soils - 70%
Medium, clay, silty & organic soils – 60%
Shallow soils over chalk/limestone – 55%
(RB209, 8th Edition, June 2010)
Green manures
Cover crop grown
primarily to add nutrients
and organic matter to soil
Typically grown from aut
- late winter for 4-5
months, and destroyed
while still green
Types of green manure
Cereals (e.g. w. barley,
w. rye)
Legumes (e.g. clover)
Brassicas (e.g. OSR,
mustard, oil radish)
Forage turnips (e.g. in
stubble)
Phacelia
Green manures: N uptake
Species and over-winter weather influence N
retention by green manures
Source: Froment & Cook (1995); Silgram & Harrison (1998)
Green cover: reduced nitrate leaching
NO3 loss is smallest (& N uptake greatest) when cover established early
Cover crops can reduce NO3 loss over-winter by 50 kgN/ha
Green manures also substantially reduce runoff and erosion risk
Source: Lord & Archer (1998)
Green manures: N uptake
Species effect:
o Brassicas > grasses >
legumes
Some cover crop N
available to spring crop
Remaining cover crop N
released slowly; increases
soil organic matter
reserves
Oil radish
Fast growth – weed
suppression, soil
stabilisation
Deep tap root and laterals –
benefit to soil structure and
scavenging SMN
Allelochemical effect
discourages soil-borne
pests
Rapid germination even in
fairly dry seedbed
But susceptible to clubroot
Mustard
Fast growth – weed suppression,
soil stabilisation
Not frost-hardy (easy destruction)
Allelopathic effect on germination
(weeds, ryegrass)
Possible biofumigant effect against
soil-borne pathogens:
o high in glucosinolates
o destruction releases isothiocyanate
o may help control FLN or verticillium
Nutrient value of green manures
N uptake & availability to spring crop depends on
many factors:
species & seed rate
sowing date
over-winter weather
destruction date
chemical composition at destruction
destruction method (flail, spray, cultivate?)
post-destruction weather
Over-winter ground cover helps suppress weed growth
Some species (e.g. mustard) can suppress weed germination
Some species may discourage soil-borne pests/diseases
Some species can fix additional atmospheric N (legumes)
Improved wildlife habitat (including natural pest predators)
Soil structure benefit; improved aeration and water holding (root development); soil AWC and porosity
Reduced risk of runoff, erosion and loss of topsoil and nutrients (N, P) and surface water pollution
Increased N retention & reduced NO3 leaching:
o can increase supply of SMN to next crop
o can contribution to soil organic matter
Potential benefits of green manures
Potential limitations of green manures
rotations limit use to before spring-sown crops
residues - effects on spring cultivations/crop
establishment?
if destroyed late, can delay N supply or moisture
available to next crop
may increase slug risk
persistence (e.g. clover)
best suited to light and medium soils
cost
Green manures: practicalities
Minimise costs (seed rate; methods; no fert/manure)
Exploit available support (policy measures)
Species choice: o N uptake potential
o frost hardiness or lack (e.g. mustard)
o soil conditions (e.g. grasses easier on poorly drained sites)
o ease of destruction
Early establishment critical (mid-Sept)
Destroy after mid-Dec but before end Feb (to discourage seeding and promote rapid N release)
Can be undersown or drilled into stubble
Not practical after late harvest crops
Cover crops prior to planting potatoes
What is the N contribution from cover
crops to the next potato crop?
ADAS site, Telford, UK BL & TR – radish; BR – mustard; TL – w. rye (11 Nov 2011)
Cover Crops: 30 Jan 2012
Cover crop at destruction: 24 Feb 2012
Topsoil SMN going in Potatoes
0
10
20
30
40
50
60
70
24 Feb 19 Mar 10 Apr 8 May
SM
N 0
-30cm
(kg
N/h
a)
Stubble Control
Rye
Mustard
Radish
Potato N Offtake at T.I.
(12 Jun 12)
0
2
4
6
8
10
12
Control Winter Rye White Mustard Hot Radish
Cover crop before potatoes
Nit
rog
en
kg
/ha
Cover crop N uptake at destruction
(16 Feb 2012)
0
10
20
30
40
50
60
70
80
Winter Rye White Mustard Radish
Cover crop
N u
pta
ke k
g/h
a
Potato N offtake at canopy closure
(12 Jul 12)
0
10
20
30
40
50
60
70
80
Stubble Winter Rye White Mustard Radish
Previous over-winter cover crop
Nit
rog
en
Off
tak
e (
kg
N/h
a) Stems
Tubers
Green manures: effect on potato yield
Fert N response results
suggest green manures
released c.50 kg N/ha to
potato crop
No effect on defects
No significant effect on FLN
T/ha T/ha
Yield Yield
Saleable Total
Green manure treatments
Stubble control 29.1 37.0
Winter rye 36.6 44.5
White mustard 34.6 42.6
Oil radish 36.8 44.8
Fert N response (no green manures)
Nil N 30.9 38.4
20 kg N/ha 30.0 39.5
40 kg N/ha 33.8 40.7
60 kg N/ha 37.1 45.6
120 kg N/ha 44.3 51.0
180 kg N/ha 48.9 55.9
240 kg N/ha 56.5 62.2
280 kg N/ha 60.3 64.9
Summary of season results
Mustard and oil radish most effective cover crops at English site, but mustard proved easier to destroy
N response evidence suggests: o <15 kg/ha of cover crop N (Scottish site)
o c.50 kg/ha of cover crop N (English site)
… was made available to the next potato crop
This site difference suggests: o choice of cover crop species strongly influenced
by local climate
o N supply from cover crops is strongly affected by over-winter weather conditions
Green manures:
promoting greater resource efficiency
Green Manures …
take up 30-50 kg N/ha otherwise leached over-winter
conserve water and nutrients otherwise lost
reduce risk of erosion, loss of topsoil and water pollution
can supply available N and benefit soil condition prior to
spring-sown crops
suppress weeds; may discourage pests &/or diseases
species choice, management methods and policy
measures can keep costs down and minimise limitations
establish by mid-Sept; destroy mid-Dec to end Feb
Cultivations and cover crops
3rd season (Harvest 2014):
Currently optimising treatments, combining:
Use of green manures (sown autumn 2013)
Cultivations prior to planting potatoes (autumn
2013 & spring 2014)
TREATMENTS
1. Autumn Stubble then Plough Spring
2. Stubble Clean Autumn DTX then Plough Spring
3. Cover crop into raked stubble; Plough in Spring
4. Autumn DTX plus Cover Crop (one pass)
5. Autumn Stubble then DTX in Spring
Thank you for listening !
