SOIL EROSION - IS IT SOIL EROSION - IS IT SUSTAINABLE?SUSTAINABLE?

Bob Palmer

National Soil Resources Institute

The Innovation Centre

inov4@york.ac.uk

PLANPLAN

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?

SOIL MAPSSOIL MAPS Semi-detailed (1:63,360)

10–15 observations km-2

Detailed (1:10,000, 1:25,000) field by field observation following initial reconnaissance (20–60

observations km-2)

free survey and grid survey

Reconnaissance (1:100,000, 1:250,000) air photo interpretation, geological maps, topographical information, etc,

with limited fieldwork (2–3 observations km-2, or transects and clusters)

National Soil Map (1:250,000) 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 (1:50,000) post-1985, includes 5 Landranger sheets and nuclear power stations

SOIL MAPSSOIL MAPSSOIL MAPS at 1:25,000(2½” to 1 mile) scale forEngland and Wales

SOIL MAPSSOIL MAPSMAP SHEETS of the1:250,000 scaleNational Soil Map ofEngland and Wales, available flat and folded

A seamless digital vector version is now available under lease and as bespoke paper maps

SOIL DEFINITIONS – the SOIL DEFINITIONS – the Soil ProfileSoil Profile

SOIL EROSIONSOIL 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?

IMPACT - SOIL EROSION IMPACT - SOIL EROSION BY WATERBY 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

HISTORICAL PERSPECTIVEHISTORICAL 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

DRIVE FOR SELF DRIVE FOR SELF SUFFICIENCYSUFFICIENCY

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

SSLRC /MAFF EROSION SSLRC /MAFF EROSION PROJECTPROJECT

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 1930’s

SSLRC EROSION PROJECT SSLRC EROSION PROJECT RESULTSRESULTS

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

>30 but <70 most at risk

SOIL STRUCTURE – SOIL STRUCTURE – DegradationDegradation 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

granular andsubangular blocky

subangular blockywith massive clodssubangular blockyand prismaticwith massive clods

platy

well developedprismatic breakingto blocky

Depth (cm)

0

30

60

peds coarserwith depthbecoming massive

Source: Modern Farming and the Soil. MAFF 1970

LAND USE & FARMING LAND USE & FARMING PRACTICEPRACTICE

Change to cereals - reduction in grass

dramatic from 1960’s to today

Lack of crop cover November - March

Decrease in organic matter levels

NSI data shows trend from 1980’s 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 >30

MECHANISMS OF WATER MECHANISMS OF WATER EROSIONEROSION

Splash

1st stage - clogs pores and seals surface

Rill

Ephemeral, seasonal, removed by ploughing

Initially short <1m 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

SOIL EROSIONSOIL 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?

ARE MODERN METHODS ARE MODERN METHODS SUSTAINABLE IN LONG SUSTAINABLE IN LONG TERM (1)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

ARE MODERN METHODS ARE MODERN METHODS SUSTAINABLE IN LONG SUSTAINABLE IN LONG TERM (2)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

YORKSHIRE OUSE YORKSHIRE OUSE CATCHMENT STUDYCATCHMENT 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

SOIL EROSIONSOIL 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?

FACTORS TRIGGERING FACTORS TRIGGERING SOIL EROSIONSOIL EROSION

Sandy or silty textures

Low organic matter content (<2%)

Soil compaction / tramlines

Lack of crop cover - November to March

Cultivation on slopes > 30

Cultivation up and down the slope

Removal of field boundaries

WHAT TO DO - WHAT TO DO - PREVENTING EROSIONPREVENTING EROSION

Arable to grass in sensitive areas

No cultivation on slopes >90 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