Soil health, organic matter and crop yield

A compilation based on talks given by: Tom Sizmur, Chris Watts, Simon Jeffery,

Karl Ritz, Matthew Shepherd Presented by Tim Chamen, SWMC

Ritz

Jeffery

Shepherd

Ritz

Ritz

Shepherd

Shepherd

Shepherd

Sizmur

What is the difference between Organic Matter and Soil Organic Matter

• OM is considered to have become SOM when its original form is no longer recognisable

• SOM is considered to have become humus when it is stable and resists further decomposition

Further reading: http://www.extension.umn.edu/agriculture/tillage/soil-management/soil-management-series/organic-matter-management/

Sizmur

Ritz

Sizmur

Sizmur

Organic matter equilibrium

• For every soil in every climatic region there is a dynamic equilibrium soil organic matter content:

SOM = input - oxidation from soil biota

• our activities act positively or negatively to disturb this equilibrium

Further reading: http://www.fao.org/docrep/009/a0100e/a0100e06.htm Further dedicated reading! http://soilandhealth.org/wp-content/uploads/01aglibrary/010120albrecht.usdayrbk/lsom.html

Jeffery

Importance of Soil Structure

• Soil structure is the arrangement of soil particles and aggregates and of the pore spaces between them.

• 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

Watts

Importance of Soil Structure

Soil structure has a significant influence on virtually all processes that 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.

Watts

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 is the ability of soil structure to recover once stress has been removed.

Watts

Jeffery

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

SOM has the equivalent of around 58% SOC

Watts

Effect of SOC on soil stability Watts

Watts

>

Shepherd

Shepherd

Ways of maintaining SOM in arable cropping

1. Ley-arable farming – i.e. intermittent pasture

2. Add crop residues

3. Add manures or other organic “wastes”

4. Break or cover crops …………………………………………………..

5. Minimise tillage • small effect, mainly redistribution

• but useful to concentrate SOM near surface

• other benefits

6. Grow plants with larger roots (breeding)

7. Grow larger crops by using fertilizers (small effect)

Watts

0.00

0.50

1.00

1.50

2.00

2.50

0 4.5 9 18

% C

in

to

ps

oil

, 0

-23

cm

Rate of straw applied t/ha/yr

7 years

11 years

22 years

Effect of 22 years of straw incorporation on soil %C

(Rothamsted, 25% clay – 3 rates of straw)

Very small SOC increase at “normal”

straw application rate

Watts

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

0 4.5 9 18

% C

in

to

ps

oi,

0-2

3 c

m

Rate of straw applied t/ha/yr

11 years 22 years

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)

Watts

Watts

Watts

Sizmur

Sizmur

Sizmur

Sizmur

Sizmur

Sizmur

Shepherd

Shepherd

Shepherd

Sizmur

Shepherd

Arndt and Rose, 1966

• “Excessive traffic necessitates excessive tillage”

– or

• The more you run over it, the more you have to cultivate it

Direct planting potatoes on non-trafficked soil after onions

Shepherd

In traffic lane – practically zero infiltration

In non-trafficked bed – modest infiltration

In non-trafficked bed with surface crust broken – rapid infiltration

Clay dispersed due to heavy rainfall

Crop management & Plough Draught (Mineral Fertilizer)

Treatment

N0 N1 N2 N3 N4 N6 FYM

SO

C, S

oil

org

anic

Carb

on, g/g

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Yie

ld, M

g/h

a

0

1

2

3

4

5

6

7

S, S

pecific

dra

ught, k

Pa

0

10

20

30

40

50

60

70

80

90

100

Kg N/ha 0 48 96 144 192 288 (35 t FYM)

Much larger crops + roots associated with increased mineral N & FYM

Watts

Crop management & Plough Draught (Mineral Fertilizer)

Treatment

N0 N1 N2 N3 N4 N6 FYM

SO

C, S

oil

org

anic

Carb

on, g/g

0.0

0.5

1.0

1.5

2.0

2.5

3.0

S, S

pecific

dra

ught, k

Pa

72

74

76

78

80

82

84

86

88

90

Yie

ld, M

g/h

a

0

1

2

3

4

5

6

7

Bigger crops result in lower soil strength; as a result of better soil structure? Biological tillage so sustainable intensification

Kg N/ha 0 48 96 144 192 288 (35 t FYM)

Watts

Summary

• Adding OM is the key means of improving soil structure.

• Structure is mostly generated by soil life, which relies on OM as a food source. – soil life recycles nutrients and increases crop yield and

quality.

• Structure effects practically all soil processes.

• Rooting from high yielding crops helps generate structure and increase OM content.

• High OM content and earthworm populations reduce soil strength and increase its resilience.

With thanks to:

• Karl Ritz, Nottingham University

• Tom Sizmur, University of Reading

• Matthew Shepherd, Natural England

• Simon Jeffery, Harper Adams University

• Chris Watts, Rothamsted Research