SOIL EROSION - IS IT SUSTAINABLE?

1
SOIL EROSION - IS IT SUSTAINABLE?

• Bob Palmer
• National Soil Resources Institute
• The Innovation Centre
• inov4_at_york.ac.uk

2
PLAN

• 10 mins background
• NSRI, soil maps and data
• 20 mins soil erosion
• mechanics historical perspective
• 10 mins recent trends
• sustainability issues
• 5 mins Questions extra tea break?

3
SOIL MAPS

• Semi-detailed (163,360)
• 1015 observations km-2
• Detailed (110,000, 125,000)
• field by field observation following initial
  reconnaissance (2060 observations km-2)
• free survey and grid survey
• Reconnaissance (1100,000, 1250,000)
• air photo interpretation, geological maps,
  topographical information, etc, with limited
  fieldwork (23 observations km-2, or transects
  and clusters)
• National Soil Map (1250,000)
• constructed from a mixture of both detailed
  mapping (where available) and reconnaissance
  mapping elsewhere
• paper version available as 6 sheets new digital
  version for GIS
• Semi-detailed (150,000)
• post-1985, includes 5 Landranger sheets and
  nuclear power stations

4
SOIL MAPS
SOIL MAPS at 125,000 (2½ to 1 mile) scale
for England and Wales
5
SOIL MAPS
MAP SHEETS of the 1250,000 scale National Soil
Map of England and Wales, available flat and
folded
A seamless digital vector version is now
available under lease and as bespoke paper maps
6
SOIL DEFINITIONS the Soil Profile
7
SOIL EROSION

• Should we be concerned?
• Implications for sustainability of soils and
  landscape
• Mechanics and occurrence
• Do we understand the processes?
• when, why and where
• How can it be limited?
• Does it need limiting?

8
IMPACT - SOIL EROSION BY WATER

• Activities
• Agricultural intensification
• modern arable systems
• overgrazing
• Recreational use
• Moorland fires
• Forestry management
• site preparation
• felling operations
• Landscaping restored land
• Civil engineering

• Primary causative factors
• Loss of groundcover
• Loss of organic matter
• Lowering of soil permeability infiltration
• Topographic and hydrologic modification
• Lowering of soil aggregate stability

9
HISTORICAL PERSPECTIVE

• Natural process - geological erosion
• Accelerated erosion
• 6000 years BP
• Archaeological evidence
• Research on colluvial deposits indicates
  approximately 10 England Wales affected
• Periods of farming expansion
• Agricultural trends over last 30 years or so

10
DRIVE FOR SELF SUFFICIENCY

• More arable - 1/3rd cultivated
• Hedges removed - ITE showed 28K km in 5 years
• Land drained
• Increase in winter cereals
• CAP and Yields doubled
• Improved pesticides
• spread to formerly too wet areas
• 5-6 applications per year - tramlines
• Seedbeds finer
• Heavier machinery
• Grasslands improved - stocking rates increased

11
SSLRC /MAFF EROSION PROJECT

• 17 Localities in England and Wales
• 30 km2 each
• Air photo interpretation
• Specially flown photos at key times of year
• Site visits
• over period of 3 years
• Farmer questionnaires
• how farmers perceive erosion
• Land Utilisation maps of 1930s

12
SSLRC EROSION PROJECT RESULTS

• As topsoil clay content increases the tendency to
  erode decreases
• High silt and fine sand content most susceptible
• Well structured soils at least risk
• Organic matter content and compaction critical
• Slowly permeable layers
• natural or man-made
• Slope
• gt30 but lt70 most at risk

13
SOIL STRUCTURE Degradation

• agricultural soil with poor (platy and massive)
  structure resulting in hindrance to DRAINAGE and
  ROOT PENETRATION, and reduced WATER HOLDING
  CAPACITY
• caused by a PLOUGH PAN or SMEARED LAYER, or
  DOWNWARD PRESSURE when too plastic, and the
  neglect to notice and rectify the problem

Structure
Depth (cm)
0
granular and subangular blocky
subangular blocky with massive clods
subangular blocky and prismatic with massive clods
30
platy
well developed prismatic breaking to blocky
60
peds coarser with depth becoming massive
Source Modern Farming and the Soil. MAFF 1970
14
LAND USE FARMING PRACTICE

• Change to cereals - reduction in grass
• dramatic from 1960s to today
• Lack of crop cover November - March
• Decrease in organic matter levels
• NSI data shows trend from 1980s to today
• Increase in field size - removal of field
  boundaries
• Use of tramlines by heavy machinery
• Maybe used 6 or 7 times in a year - compaction
• Cultivation up and down the slope, especially
  where gt30

15
MECHANISMS OF WATER EROSION

• Splash
• 1st stage - clogs pores and seals surface
• Rill
• Ephemeral, seasonal, removed by ploughing
• Initially short lt1m separated by small
  depositional fans
• Gulley
• Large scale - filling has to be engineered
• Sheet wash
• Often felt to be of limited extent in UK
• Turbid waters common during rainfall events

16
SOIL EROSION

• Should we be concerned?
• Implications for sustainability of soils and
  landscape
• Mechanics and occurrence
• Do we understand the processes?
• when, why and where
• How can it be limited?
• Does it need limiting?

17
ARE MODERN METHODS SUSTAINABLE IN LONG TERM (1)

• ON-FARM IMPLICATIONS
• OBVIOUS TO FARMER
• Effects on yields
• Ditch and drain clearance
• LESS OBVIOUS
• Increased droughtiness - decline in water holding
  capacity
• Decline in nutrient storage capacity
• Decline in quality of soil structure
• Decrease in soil depth
• Loss of substrate for soil fauna and microflora

18
ARE MODERN METHODS SUSTAINABLE IN LONG TERM (2)

• OFF-FARM IMPLICATIONS
• Soil removal from roads, houses, sewers
• Loss of wild life habitats
• Turbid rivers
• Pollutant movement -
• nitrates, phospates in suspension and bound to
  clay-organic complexes removed by erosion
• Little or no cost to the farmer

19
YORKSHIRE OUSE CATCHMENT STUDY

• Severe degradation in 20 of land across whole
  catchment
• erosion not confined to wheelings
• 55 of land under late harvested crops maize,
  sugar beet and potatoes affected
• 25 of land under winter cereals affected
• Up to 20 increase in water reaching streams
  within 24hrs

20
SOIL EROSION

• Should we be concerned?
• Implications for sustainability of soils and
  landscape
• Mechanics and occurrence
• Do we understand the processes?
• when, why and where
• How can it be limited?
• Does it need limiting?

21
FACTORS TRIGGERING SOIL EROSION

• Sandy or silty textures
• Low organic matter content (lt2)
• Soil compaction / tramlines
• Lack of crop cover - November to March
• Cultivation on slopes gt 30
• Cultivation up and down the slope
• Removal of field boundaries

22
WHAT TO DO - PREVENTING EROSION

• Arable to grass in sensitive areas
• No cultivation on slopes gt90 plus contour
  ploughing
• Grass or buffer strips at key points to reduce
  downslope lengths
• need to be sufficiently robust
• Improved timeliness of farm operations
• early sowing of autumn crops
• avoid traffic in wet conditions
• Maintain topsoil permeability
• organic matter status, structure, subsoiling
• Use of tie ridges to block water movement