Soils *

soils sustain ..% of food production

95

soils host more than … planet’s biodiversity

1/4

what is the level of soil degradation globally?

33%

importance of soil

• antibiotics

• sotres 3x more carbon than all plants on earth

• biodiverse

• critical role in water and carbon cycle

in europe, …% soils are unhealthy

60-70%

what is soil

Soil is the thin layer of organic and inorganic material on the Earth's surface that supports plant life, containing minerals, water, air, and living organisms.

factors affecting soil formation

1. relief

2. vegetation

3. cimate

4. humans

5. soil biota

6. parent material

7. drainage

8. time

zonal soils

major soil group often classified as covering a wide geographic region or zone and embracing soils that are well developed and mature, having taken a long time to develop from the parent material. They are in a state of dynamic equilibrium with the climate, vegetation and parent matter. Within the area of a zonal soils there are variations caused by local factors.

soil horizons

Layers of soil that differ in color, texture, and composition, formed through weathering and organic processes.

upper limit of soil

the highest point in the soil profile where soil processes have a significant effect, typically marked by the top of the organic layer.

lower boundary of soil

the interface between soil and underlying bedrock or parent material, where soil characteristics transition to that of unweathered rock.

5 essential functions of soil

1. cycling nutrients

2. regulating water

3. sustaining plant and animal life

4. filtering and buffering potential pollutants

5. physical stability and support

podsol: location

northern coniferous forest

podsol: climate

• long cool/cold winters

• short mild summers

• precipitation can be variable

• considerable snowfall - leading to spring snow melt

• leads to soil biota activity and slow decomposition

podsol: relief and drainage

• on mountain sides or tops

• up to 350m

• precipitation and drianage leads to rapid leaching or iron and aluminium oxides (eluviation) from the A horizon leaving it rich in silica and ash grey in colour

• deposition of iron oxides in the B horizon (illuvation) creates a red-brown colouring and may concentrate to form a thin solid layer called an iron pan

• iron pan impedes drainage and can cause waterlogging

podsol: soil biota

not much activity here because of the cold climate and this means that the soil is not mixed, leading to clear horizons developing

podsol: natural vegetation

coniferous trees (pines, spruces)

produces litter of needles and pines, creating a thin acidic humus (mor)

podsol: human use

• commercial forestry plantations (conifers)

• in the UK podsols are associated with upland sheep farming and heather moorland for the breeding of grouse

• grouse shooting employs 2500 people and generates £150mn annually

• rough grazing and recreational use

• arable farming difficult because acidity and lack of nutrients means few crops can grow, formation of hard pan can prevent water from draining and lead to waterlogging

brown earth forest soils: location

• 35-55 degrees N of Equator

• largest expanses cover western and central Eruope, western Russia, east coast of America and eastern Asia

• brown earth cover 45% of land in England and Wales

brown earth forest soils: climate

• moderate

• humid temperature

• rainfall totals are modeerate

• temperature range from 4-18 degrees

• good conditions for vegetation growth and soil biota

brown earth forest soils: relief and drainage

• common in lowland areas (below 1000ft) on permeable parent material

• the most common vegetation types are deciduous woodland and grassland

brown earth forest soils: soil biota

• warmer temperatures encourage soil biota activity, making horizons less distint

• leaf litter is more rapidly decomposed

brown earth forest soils: natural vegetation

• deciduous forests (ash, beech, oak)

• plentiful supply of lead litter

• resulting humus is deep and slightly acidic

brown earth forest soils: human use

• more fertile and useful than the other main soil types and populations here are greater

• given deep nature of these soils, their free drainage and often high levels of natural fertility, brown earth soils are often cultivated

• usually easy to work through the year, so they are valued for agriculture

soil problems

• relentless tilling - reduces cohesiveness of soil, more exposed to erosion

• wind erosion

• ploughing

• livestock grazing

• urbanisation

• deforestation

• compaction

• pollution

• acidification

• water-logging

• salinisation

• desertification

• climate change

soil management strategies

1. efficient irrigation and drainage

2. moving livestock

3. cover crops

4. multiple cropping

5. changing soil composition

6. windbreaks

efficient irrigation and drainage

waterlogging, water erosion and salinisation can be caused by water surplus

• drip irrigation can be used to avoid overwatering

• underground drainage systems

• contour ploughing - contours across hills so water doesnt run downhill rapidly

• terracing - steps carved into hillside to spread out water levels rather than flow downhill

• diversion channels - redirect away from crops

moving livestock

• ensures ground not trampled extensively

• avoids overgrazing

• maintains structural integrity of soil

cover crops

Plants grown to prevent soil erosion, improve soil health, and enhance nutrient cycling. They help suppress weeds and can increase organic matter when tilled into the soil.

• maintain soil quality

• maintain soil structure

mutiple cropping

• growing different crops in the same space during a growing season to enhance soil fertility and control pests.

• avoids monoculture which depletes certain nutrients from soils leading to poor soil quality and structural deterioration

changing soil composition

• limit wind erosion and structural deterioration - adding certain materials can encourage a well-binded soil with natural pores

• adding mulch - binds soil

• adding sand - can stop soils clumping and structurally deteriorating

windbreaks

bsuhes, trees, or manmade windbreaks, such as netting can obstruct winds. this can limit wind erosion on arable land, yielding higher productivity

soil erosion

The process by which soil is removed from its surface by wind, water, or human activity, leading to loss of soil quality and fertility.

how much topsoil is lost every year?

75 bn tonnes - equivalent to 9mn ha of productive land lost

repeated erosion reduces the fertility of the soil by:

• removal of topsoil that is rich in crop nutrients and organic matter

• reduction fo the depth of soil available for rooting and water storage for crop growth

• reducing infiltration of water into soil, thereby increasing run off and erosion

soil erosion can lead to:

• loss of seeds, fertilisers and pesticides

• young plants being ‘sandblasted’ (wind erosion)

• increased difficulty (therefore fuel consumption and man hours) of field operations

damage to the envirnment from soil erosion can include:

• deposition of sediment onto roads, neighbouring lands and into drains

• damage to the quality fo water courses, lakes and rivers through excess inputs and increased chemical loading

• increased run-off and sedimentation causing a greater flood-hazard downstream

• sediment in rivers damaging the spawning grounds of fish

wind erosion

The process by which strong winds remove soil and sand from the surface, leading to loss of topsoil and reduced soil quality.

• soil becomes less cohesiveand more susceptible to further erosion.

• more prevalent in dry regions

issues of wind erosion

• most fertile topsoil is blown away, leaving crops with less nutrients for growth

• crops can become buried in thin layers of soil after high winds, which can damage crops and restrict sunlight

• Wind erosion lowers a soil’s capacity to store water as the depth of soil is reduced, which causes the soil to become drier. This, in turn, affects crops as there is less water available, and less space in the topsoil for roots (lowering productivity)

wind erosion control is carried out by

• Increasing soil cohesion by applying organic matter (e.g. farmyard manure) to the soil; this improves its structure

• Increasing the roughness of the soil surface or by leaving crop residues or stubble in fields and not ploughing them into the soil. e.g. done in Burkina Faso, traps dust

• Increasing plant cover so that surface wind speed can be cut

• Increasing plant cover to about 50% gives fields adequate protection from wind erosion

• Planting lines of trees or hedgerows cuts wind speed which reduces both evaporation (up to 20%) and wind erosion. A tree line has a wind speed reduction effect for up to 12x the height of that tree line, both before and after the barrier. This means that the cropped area between windbreaks can be as wide as 100m if the trees are over 5m high.

water erosion

• degradation and wearing away of soil due to water

• most serious type of soil erosion

• climatic factors, relief, topography, interception, irrigation, poor countouring

sheet erosion

a form of water erosion where thin layers of soil are removed uniformly from the land surface, often characterized by a shallow, wide flow of water. It's typically less noticeable than rill or gully erosion but can still lead to significant soil loss.

causes of sheet erosion

naturally by rain/wind

exacerbated by uprooting of root systems by agricultural machinery

potential solutions to sheet erosion

• careful monitoring of soil heights over time - early detection

• no-till agriculture (maintains organic matter in upper levels of soil)

rill erosion

a type of water erosion that forms small channels or rills on the surface of the soil, typically occurring on sloped terrain. It is more severe than sheet erosion and can lead to deeper soil loss if not addressed.

causes of rill erosion

occrus when recently cultivated soils are hit by rain, small water channels form and grow larger as more water gains speed and runs through poorly rooted soil

potetial solutions to rill erosion

• increase surface roughness using grassed waterway. 

• Prevent sheet flow from gaining speed by decreasing flow volume. 

• Plugging channels with mulch or diverting with drainage corridors prevents water from building up volume and speed

gully erosion

a more severe form of erosion than rill erosion, characterized by the formation of larger, deeper channels in the landscape. Gully erosion typically occurs when a concentrated flow of water cuts into the soil, leading to significant land degradation.

causes of gully erosion

common in areas of high water runoff concentration, results in deep channels that dig into the surface

potential solutions to gully erosion

• tilling is a temporary solution, but gullies return to the same place. 

• Usually require extensive labour to replace lost soil and fill in the deep channels.

riverbank erosion

 riverbank erosion is the degradation of riverbank sides, causing large sections of the bank to be eroded away. This can be devastating to agriculture, as it destroys agricultural land. Agricultural land surrounding the Brahmaputra river in Asia have been eroded away through this erosion.

water erosion creates several issues for agriculture:

• Soil is washed away, which causes crops to become unstable, and crops may also be washed way

• Nutrients are leached away into lower parts of the soil, or entirely washed away, which can negatively affect plant growth

• Weeds can spread from other areas if carried in water, which can reduce the productivity of a farm

• Rills and gullies can obstruct farming equipment, reducing the amount of agricultural land and causing potential dangers. Undercut riverbanks are also dangerous, and can collapse

soil erosion in Myanmar

removal of trees for more space for crops means that during rainfall events, topsoil is washed away and into the rivers etc. because of lack of tree roots to trap soil. Fish cannot live in muddy water, so this also has knock-on effects on biodiversity and food sources. This is managed through planting fast-growing trees amongst crops and building small dams to trap soil moving in rivers

the key to reducing soil erosion by rainwater is to reduce the amount of surface flow of water. this is done by:

• Installing and maintaining field drains and ditches. Sediment should be removed from ditches and replaced in the fields where it came from

• Reducing the amount of water running off roads and farm tracks onto fields

• The judicious use of farmyard manure to stabilise the topsoil

• Protecting soil in winter by early swing or the use of cover crops

• Work across slopes whenever possible. Contour ploughing reduces overland flow and the formation of rills and gullies

waterlogging

a condition where soil is saturated with water, leading to reduced oxygen availability for plant roots, which can harm crop growth.

waterlogging occurs under 2 conditions:

1. surface fed - when precipitation, irrigation water or river floodwater exceeds the combination of evapotranspiration and percolation so that the water stays in and on the surface of the soil

2. groundwater fed - when the rate of rising groundwater is not matched by the rate of evapotranspiration. This may be a natural rise in groundwater or be caused by see page from irrigation channels

effect of waterlogging on agricultural productivity

• There is limited oxygen supply in the soil, restricting plant respiration and causing them to ‘drown’.

• Roots may also rot in stagnant water, killing the plant or stunting growth

• Waterlogged conditions can leach away minerals for plant growth, or bring unwanted minerals to the topsoil, such as salts

• Water lowers the temperature of soils, which slows photosynthesis

salinisation

the process where water-soluble salts accumulate in the soil, often due to inadequate drainage or excessive irrigation. It can lead to decreased soil fertility and crop yield.

causes of salinisation

• salinisation occurs when saline water (salt water) rises to the surface of the soil, and then water evaporates. This leaves salt concentrated in the topsoil.

• High temperatures may draw saline soil water to upper parts of the soil. Dry climates may also heighten this process as the salts cannot be leached away by precipitation. 

• Irrigation water has a salt content (as does all water) and sometimes saline water may be used for irrigation when there are limited supplies. If there is no proper drainage or leaching in place, the salts will accumulate

• When groundwater levels rise, salts from lower levels of the soils are brought upwards. Groundwater levels can rise for a number of reasons, including increased precipitation in the area or human interference, such as dams. Fertilisers may also cause salinisation

…. % of soil worldwide is affected by salinisation

10-20

e.g. China’s Northern Plain

solutions to salinisation

• reduce irrigation

• flushing soil (expensive and wastes water)

• switch to salt-tolerant crops (e.g. barley)

• not growing crops for 2-5yrs

• installing underground drainage systems (expensive)

negative effects of salinisation

• Salts are toxic to plants, which can reduce the fertility of plants, reduce yields, or kill them

• High salt contents in soils affect how plants can absorb water. Water usually moves from an area of high concentration to an area of low concentration, this process is known as osmosis. In normal soils, water will move from the soil (high concentration) to the roots (low concentration). However, when the salt content is high, this can hinder the process or even dehydrate the plants. Even when there are sufficient water supplies, plants may still suffer from the effects of salinisation.

• Salinisation may also break up natural soil structure, affecting plant growth and productivity

structural deterioration of the soil

the breakdown of soil structure, leading to reduced fertility and impaired water retention. This can negatively impact plant growth and agricultural productivity.

types of soil structures

• granular and crumb structures - good drainage, top of soil

• blocky structures - promote water retention, subsoil layers

• prismatic and columnar structures - tall, vertical shapes, poor drainage and can restrict root growth.

• platy structures - thin, flat plates stacked horizontally, leading to poor drainage and restricted root development.

causes of structural deterioration of soil

• natural processes such as erosion and weathering

• human activities including over-tillage, compaction, and deforestation

• excessive use of chemical fertilizers and pesticides, damaging soil organisms and structure.

problems of structural deterioration for agriculture

• Water cannot infiltrate due to the lack of space in the soil, meaning plants may become dehydrated

• Root cells need air to survive, which they get from the soil environment. Structural deterioration can remove air pockets and essentially suffocate roots

• Root growth may become obstructed as the roots cannot infiltrate compacted soil

• Soil is hard to work with when the structure has deteriorated, e.g. it is harder to plough or till

compaction

The process of increasing soil density by applying pressure, often resulting in reduced porosity, decreased water infiltration, and impaired root growth.

plough pan

A compacted layer of soil just beneath the surface that prevents water infiltration and root growth, commonly created by excessive ploughing.

solutions for structural deterioration

• drive lines for tractors

• low inflation of tyres

• avoid working when soils wet

• rotate crops

• less tilling

• adding compost/manure

• planting trees

desertification

The process by which fertile land becomes increasingly arid, often due to drought, deforestation, or inappropriate agriculture, leading to a decline in land productivity.

… land is at risk of desertification

1/3