www.adas.co.uk

Minimising compaction risk

& optimising N supply

using green manures

Dr Martyn Silgram

ADAS Soils, Crops & Water Group

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martyn.silgram@adas.co.uk

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 !