Chris Watts - Smart Agri Systems Platform

Soil management for restoration and
profit –
improving soil structure
Chris Watts & Jackie Stroud
Rothamsted Research, Harpenden, Herts., AL5 2JQ
http://www.rothamsted.ac.uk/
1.
2.
3.
4
Introduction. Roth & long-term experiments
Soil structure
Organic matter: Management and benefits
Organic amendments: FYM, Straw, (crop
residues) AD, Compost
5 Soil strength and drying
6 Tillage
7 Yield potential, attainable yields & actual yields
1
Introduction. Roth & long-term
experiments
Earliest Rothamsted
experiment started 1843
Sir John Bennett Lawes
Sir Joseph Henry Gilbert
Rothamsted
Woburn
Soil Textures
Rothamsted: (Batcombe soil series)
A silty clay loam, c.25% clay over clay-with-flints,
overlying chalk.
Classed as a Chromic Luvisol (FAO) or Aquic Paleudalf (USDA)
Woburn (Cottenham soil series) approx 10 m west of
here also on Greensand ridge:
A sandy loam, c.10% clay overlying sand.
Classed as Cambic Arenosol (FAO) or Typic Udipsamment (USDA)
Weather
The climate is cool, temperate
Average, annual rainfall (30 year mean) is:•Rothamsted:
733 mm
•Woburn:
652 mm
Average, annual mean air temperature
is c.9.5oC
Rothamsted LTEs
Broadbalk Winter Wheat
experiment, started 1843
Hoosfield Spring Barley
experiment, started 1852
Woburn LTEs
Organic Manuring
experiment, started 1964
Ley-Arable experiment,
started 1938
– Also Rothamsted ley-arable experiments
Note on previous slide
Note 170 years of experiment
1 Different fertilizer manure regimes
2 Management 1950’s liming; 1960’s herbicide, 1970’s crop rotations,
1980’s fungicides and growth regulators
3 Continuous evolution in wheats but giant leap early 1960s (green
revolution) short straw able to use higher rates of N
4 Note Yield plateau 1990 on except 2014. Why? Address this later.
So far we have been unable to detect a clear benefit of enhanced SOM for
wheat yields on Broadbalk, but with newer higher yielding varieties having
greater demands for water nutrients perhaps this may change in future.
In 2014 we achieved yields of over 13t/ha for a new winter wheat variety
(Crusoe) grown on Broadbalk.
2
Soil structure
Importance of Soil Structure
• Soil structure is the arrangement of soil particles and of the
pore spaces between them. It includes the size shape and
arrangement of aggregates when primary particles are
clustered together into larger separate units. (0.1µm clay
particle to 10 cm clod).
• Hierarchical nature of soil structure
• Several different mechanisms and processes within the soil
are involved in controlling structure: soil type, physical
chemistry, organic matter
• Likewise, the structure influences the processes
Importance of Soil Structure
Soil structure has a significant influence on virtually all
processes the occur within the soil. Some examples:
• Water infiltration – hence the amount of water that is
stored in the soil, available to plants, runoff, erosion.
• Aeration – needed for root growth and other biological
activity – organic matter turnover.
• Strength and stability – strong soils can impede root
growth and are difficult to cultivate.
• Physical pore structure defines habitats for a range of
biota.
Soil stability & resilience
There is little advantage to having a soil with an ideal
geometrical structure if it does not persist
• Soil structural stability: Ability of structure to resist imposed
stresses without change in its structural form.
• Examples of imposed stresses include: rapid wetting, contact
with free water, raindrop impact, wheel traffic
• Cultivations are often designed to modify soil structure.
• Resilience the ability of soil structure to recover once stress
has been removed.
Mobile Rainfall Simulator
• Mobile rainfall simulator
designed to give a
standard storm on 1 m2;
• raindrop size (D50 = 1.7
mm), travelling at the
correct speed 7.5 m/s.
• Adjustable intensity 12
mm/h to 100+ mm/h
• Energy 20 J/m2 at
intensity of 47 mm/h @ 1
year return period for 10
min duration.
• Note colour of runoff.
Suspended sediment
Highfield/Geescroft Change in Porosity with time (2009)
Influence of management and organic matter on soil porosity
0.7
0.6
Porosity
Water uptake by wheat
0.5
Cultivation
Fallow
0.4
Arable
Grassland
0.3
Slumping
3 Organic matter: benefits and management
Ways of maintaining SOM in arable
cropping
1.
2.
3.
4.
Ley-arable farming – i.e. intermittent pasture
Add crop residues
Add manures or other organic “wastes”
Break or cover crops
…………………………………………………..
5.
Minimise tillage
•
•
•
6.
7.
small effect, mainly redistribution
but useful to concentrate SOM near surface
other benefits
Grow plants with larger roots (breeding)
Grow larger crops by using fertilizers (small effect)
Importance of soil organic carbon on aggregate
stability
Aggregates (1.0 > 2.0 mm) collected from the upper 2 cm, air-dried and then
subjected to 50 mm of simulated rain and finally allowed to dry
4 Organic amendments: FYM, Straw, (crop
residues) AD, Compost
Effect of 22 years of straw incorporation on soil
%C
% C in topsoil, 0-23 cm
(Rothamsted, 25% clay – 3 rates of straw)
Very small SOC
increase at “normal”
straw application rate
2.50
2.00
7 years
1.50
11 years
1.00
22 years
0.50
0.00
0
4.5
9
Rate of straw applied t/ha/yr
18
Effect of 22 years of straw incorporation on soil %C
(note C in sandy soil is only 50% of that in silty clay loam)
(Woburn, 9% clay – 3 rates of straw)
% C in topsoi, 0-23 cm
1.40
1.20
1.00
0.80
11 years
0.60
0.40
0.20
0.00
0
4.5
9
Rate of straw applied t/ha/yr
18
22 years
Electron micrographs of Highfield soils
Control
Sample + Grass
Sample + biochar
Fungal hyphae
extracellular polymeric substances (EPS)?
Rothamsted Research
where knowledge grows
Earthworms
200
Earthworm biomass (g m-2)
180
160
Unidentified
Epigeic
140
Anecic
Endogeic
120
100
80
60
40
20
0
Control
Straw
Straw
Compost Compost Comp+St
FYM
FYM
FYM+St
AD
AD
AD+St
0 t C/ha 1.75 t C/ha 3.5 t C/ha 1.75 t C/ha 3.5 t C/ha 3.5 t C/ha 1.75 t C/ha 3.5 t C/ha 3.5 t C/ha 1.75 t C/ha 3.5 t C/ha 3.5 t C/ha
• There is a significant (p<0.05) synergistic
interaction between straw and manures
5. Soil strength & drying
Different irrigation regimes
0
well watered
4
limited
drying
Matric potential (kPa)
-100
-200
-300
no irrigation
-400
Penetrometer pressure (MPa)
no irrigation
3
limited
drying
2
1
well watered
-500
01/04
01/05
01/06
Date
01/07
0
1/3 1/4 1/5 1/6 1/7 1/8
Date
The matric potential and penetrometer strength of soil under different irrigation
regimes in a field of wheat. Note the greatly increased strength of soil after only
limited drying, and the low matric potential of non-irrigated soil. The colours
correspond to the same irrigation treatments.
The influence of soil strength on crop
yield dry matter as controlled by
irrigation, field traffic & soil type
2000
2006 Un-compacted sand
2006 Compacted sand
2006 Un-compacted clay
2006 Compacted clay
2004 No irrigation
2004 Limited drying
2004 Well-watered
Dry Matter Yield, kg/ha
1800
1600
1400
1200
1000
800
600
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
Q Penetrometer Resistance, MPa
Strong correlation between lower strength soil (penetrometer)
and greater dry matter yield. Strength controlled by irrigation or
wheeling in 2 soil types.
In the field: measuring soil drying.
Electrical Resistive Tomography (ERT) (with Lancaster)
A M N B
Electrode
A
M
N
B
1
Survey 3
level 5
7
Distance (m)
Electrical current is injected between electrodes A and B (above)
and voltage measured between electrodes M and N. The
electrode spacing controls the depth and width of sensitivity. By
carrying out measurements at different electrode spacing and
different positions we essentially probe the subsurface.
Dry zone
beneath crop
Resistivity (Wm)
The resistivity image above is from an ERT survey with 96 electrodes positioned at 0.3m spacing along 12
plots of wheat at Woburn. The green rectangles show the crop boundaries. High resistive zones (in red) are
where moisture content is reduced due to crop use. The different wheats show
contrasting drying footprints – some extending to 0.6m and deeper.
Seasonal drying patterns under 11 wheat varieties (+ fallow) measured
using ERT technique
Woburn - Butt Close. Sandy soil. (note drying restricted to top 50 cm)
t0 = 16 May
0
14 June
Depth (m)
21 June
28 June
10 July
2 Aug
5
10
Measurement error <2% RMS
More conductive
15
X (m)
20
25
30
More resistive
41
Seasonal drying patterns under 11 wheat varieties (+ fallow)
measured using ERT technique
Woburn – Warren Field. Silt-clay-loam.
(note soil drying to greater depth than sandy soil)
t0 = 13 May
0
Depth (m)
13 June
20 June
27 June
9 July
1 Aug
Measurement error <5% RMS
5
10
More conductive
15
X (m)
20
25
30
More resistive
42
Ratio inversion ERT
Butt Close
10
July
28
June
20
214
August
June
Warren Field
9August
July
127
June
13
June
More conductive
More resistive
43
Measuring root distributions with the core-break
method
Cores 9 cm in diameter were taken to a depth of 1m following anthesis in 2014. The cores were then broken every 10 cm to
reveal the soil surface. These were then photographed and used to count the number of roots and pre-existing pores.
Examples of two photographs
(35mm wide and 30 mm)
0
P<0.001
Depth cm
20
40
Battalion
Hybrid Hystar
Rht 3
Rht C
Robigus
Pore count
SED for root count data
60
80
100
0
10
20
30
Root or pore count cm-1
Soil below 40 cm may be inherently too strong for wheat roots
because of weight of soil above but have to rely on pre-existing pores
40
50
6
Tillage – an indicator of soil strength
and structure
Draught Force (A MEASURE of SOIL STRENGTH)
Strain gauged frame
(to measure draught forces)
Doppler radar sensor
(forward speed)
Laser proximity sensors
(depth & front furrow width)
Draught Force
Measure force to pull plough (draught)
We know depth and width of work
Force/area = strength
Therefore able to map soil strength.
Broadbalk Wheat Experiment (est 1843).
Soil strength mapped by measuring plough draught
Strip Numbers
PLOUGH DRAUGHT AT BROADBALK,
ROTHAMSTED
Clay %
Specific draught, kPa
20 18 16 14 12 10 08 06 03 2.1
19 17 15 13 11 09 07 05 2.2 01
300 m
Sections
0
Continuous wheat
(straw incorporated)
1
Continuous wheat
Clay, %
2
Rotation (2nd wheat)
250 m
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
3
Rotation (3rd wheat)
200 m
4
Rotation (forage maize)
Strip Numbers
Specific
20 18 16 14 12 10 08 06 03 2.1
19 17 15 13 11 09 07 05 2.2 01
0
Continuous wheat
(straw incorporated)
1
Continuous wheat
300 m
Draught, kPa
140
250 m
2
Rotation (2nd wheat)
135
130
3
Rotation (3rd wheat)
125
120
200 m
115
4
Rotation (forage maize)
110
150 m
100 m
5
Rotation (winter oats)
105
6
Continuous wheat
(restricted fungicides)
95
7
Rotation (1st wheat)
50 m
0m
0m
50 m
100 m
100
150 m
5
Rotation (winter oats)
90
6
Continuous wheat
(restricted fungicides)
85
80
75
100 m
70
8
Continuous wheat
(no herbicides)
65
9
Continuous wheat
50
7
Rotation (1st wheat)
60
55
Sections
8
Continuous wheat
(no herbicides)
50 m
0m
0m
9
Continuous wheat
50 m
100 m
100
90
80
70
60
50
40
30
20
10
0
3.0
Histogram shows addition of
mineral N has small effect on
SOC compared to long-term
additions of FYM
2.5
2.0
1.5
1.0
0.5
0.0
N0
Kg N/ha 0
N1
48
N2 N3 N4 N6 FYM
Treatment
96 144 192 288 (35 t FYM)
SOC, Soil organic Carbon, g/g
S, Specific draught, kPa
Crop management & Plough
Draught (Mineral Fertilizer)
3.0
Much larger
crops + roots
associated
with increased
mineral N &
FYM
2.5
2.0
1.5
1.0
0.5
0.0
N0
Kg N/ha 0
N1
48
N2 N3 N4
Treatment
96
144 192
N6 FYM
288 (35 t FYM)
7
6
5
4
3
2
1
0
Yield, Mg/ha
100
90
80
70
60
50
40
30
20
10
0
SOC, Soil organic Carbon, g/g
S, Specific draught, kPa
Crop management & Plough
Draught (Mineral Fertilizer)
3.0
88
2.5
86
84
2.0
82
1.5
80
78
1.0
76
0.5
74
72
0.0
N0
Kg N/ha 0
N1
48
N2 N3 N4 N6 FYM
Treatment
96 144 192 288 (35 t FYM)
Bigger crops result in lower soil strength; as a result of better soil structure?
Biological tillage so sustainable intensification
7
6
5
4
3
2
1
0
Yield, Mg/ha
S, Specific draught, kPa
90
SOC, Soil organic Carbon, g/g
Crop management & Plough
Draught (Mineral Fertilizer)
7 Yield potential, attainable yields & actual
yields
Concluding comments
• Soil structure has a significant influence on
virtually all processes occurring in the soil.
• Managing soils in ways that maintain or
increase organic matter will have a positive
effect on soil structure.
• Soil management is a key component in
maximising crop yield.
acknowledgements
•
•
•
•
•
•
•
•
Jackie Stroud
Tom Sizmur
Andy MacDonald
David Powlson
Andy Whitmore
Richard Whalley
Pete Shanahan (Lancaster University)
Andy Binley (Lancaster University)