Soil - the foundations of sustainable agro-ecosystems

Question 1

How do we perceive soil?

Answer 1

Do we understand our connections to it?

Question 2

The universe:
13.7 ± 0.13 billion years

Our solar system:
4.5 billion years

Answer 2

Virtually all elements heavier than C have originated from supernovae –exploding super-stars from before our sun existed

Question 3

Soil is a major reservoir of microbial biodiversity with which humans have evolved.

Answer 3

The microbial world influences human wellbeing directly, and indirectly via effects on food
quality, climate and the environment.

Question 4

Urban populations are so psychologically distanced from soil and food production that

Answer 4

they don’t recognize themselves as dependent on world’s ecosystems.

Question 5

The average ‘ecological footprint’ of a human in high income countries like ours is 5-10 ha

Answer 5

but there are only 1.9 ha of productive land per person in the world (in 2003)

Question 6

The supply of water and nutrients from soil to crops in a 15.6 million km2 area (approximately 7800 km3 of topsoil to 0.5 m) is what now largely sustains 7.2 billion humans

Answer 6

Soil functions:
food, fibre and fuel
carbon sequestration
water purification
climate regulation
nutrient cycling
habitat for organisms
flood regulation

Question 7

More than 70% of available freshwater is used in agriculture according to UNESCO 2001, It is estimated that it

Answer 7

takes 5 million litres of water to grow a hectare of maize (Pimental et al., 2004).

Question 8

Soil ecosystem services-

Answer 8

Food production: crops and livestock
Fresh water: filtration and storage
Fibre: cotton, linen, wool 
Wood: construction, paper
Fuel: wood, peat, straw, biomass
Carbon and nutrient storage
Climate regulation
Waste detoxification and pollution control 
Host biodiversity and support the biodiversity of above-ground ecosystems.

Question 9

Climate change effects

Answer 9

mean we are losing earth at an increasing rate

Question 10

Food production and consumption and waste accounts for ~25-33% of global greenhouse gas emissions

Answer 10

Soil ecosystems are the critical foundations of human food supplies – but we are destroying this life support system!

Question 11

When we lose soil, we are losing a resource that is, for practical purposes and human timespans, essentially non-renewable.
Most of the organic matter and fertility of soil is concentrated in the upper 20 cm of soil- the topsoil.

Answer 11

A cm of topsoil typically takes >200 years to form, yet it can be swept away in a few seasons.

Question 12

How we sustainably manage agro-ecosystems now, and in the immediate future, will determine the fate of humanity- determining our quality of life and Earth’s carrying capacity for future generations.

Answer 12

“Each year, we lose 15 billion trees and 24 billion tonnes of fertile soil”

Question 13

For every person on the planet two trees are lost and more than 3 tonnes of soil is eroded every year.

Answer 13

At rates of soil formation in agricultural fields it would require at least 2 ha of land per person to balance this loss- there is less than 1.9 ha of land per person in the world (Rees 2003), of which only 0.2 ha is arable land.

Question 14

Estimate 35.9 Pg yr−1 of soil eroded globally in 2012 (> 4.5 tonnes per person per year)

(Compare this to the Global Land Outlook estimate of 24 bn tonnes)

Answer 14

There appears to have been an overall increase in global soil erosion driven by cropland expansion and human caused land use change from 2001-2012.

Question 15

Large areas of global croplands and deforested regions used for grazing livestock

Answer 15

suffer unsustainable rates of soil erosion

Question 16

South America, sub-Saharan Africa and SE Asia are major areas in which soil erosion has been getting much worse.

Answer 16

However, even the UK has showed a worrying increase.

Question 17

Nearly 33% of the worlds arable topsoil lost to erosion or pollution (especially with salt) in the last 40 years.
Erosion rates from ploughed fields average 10-100 times greater than rates of soil formation.

Answer 17

Erosion leads to preferential removal of organic matter and clay - removing nutrients and releasing CO2.

Question 18

Globally soil erosion is increased

Answer 18

60% by human activity. From Yang et al., (2003).

Question 19

Revised Universal Soil Loss Equation

A = R x LS x K x C x P

Answer 19

A = potential annual soil erosion (1000’s of Kg ha-1 y-1)
R = rainfall erosivity
LS = slope length and steepness factors
K = soil erodibility- controlled by soil texture (% sand, silt, clay),
organic matter content, structure and permeability.
C = cropping and management
P = soil conservation practices to reduce erosion losses

Question 20

Main anthropogenic causes of soil erosion

Answer 20

Cultivation: tillage, bare soil, crops with small roots, reduced soil organic matter, compaction, reduced water storage and infiltration. Soil vulnerability to wind and water erosion.

Over-grazing

Deforestation

Salinization- salt pollution from poor irrigation- leading to very poor vegetation.

Question 21

In Europe soil formation rates including dust deposition range from 0.3-1.4 Mg (tonnes) ha-1 yr-1.

This defines the maximum tolerable rates of soil erosion if soil stocks are not to be degraded.

Answer 21

“Actual soil erosion rates for tilled, arable land in Europe are, on average, 3 to 40 times greater than the upper limit of tolerable soil erosion”.

Question 22

The UK is currently about 52% self-sufficient for food- enough to feed us from 1st January to 10 days into July each year.

Answer 22

Nearly half our food now comes from international sources.

Question 23

India: about 45% the total land area is affected by serious soil erosion.

Answer 23

The average rate of soil erosion is estimated here as 16.4 tonnes per hectare causing a loss of 5.334 billion tonnes annually (about 4 km3).

Question 24

In 2010 the average rate of soil erosion in China was 9.4 tonnes per ha per year, giving a total soil loss of 8.9 billion tonnes (about 7 km3).

Answer 24

Croplands are losing soil at an average rate of nearly 28 tonnes per ha per year!

Question 25

Most arable land in the UK is under constant annual cropping- i.e. each year a crop is sown and harvested- there are no years in which the soil is undisturbed.

Answer 25

We don’t know if the rates of erosion presented here are typical of the UK.

Question 26

Living soil formed over 1000’s of years is haemorrhaging into the oceans.

Answer 26

This is Madagascar’s main river. Soil is being washed away due to deforestation that occurred in the last 20 years.

Question 27

Soil erosion rates may slow down over time once the topsoil has been depleted-

Answer 27

as happened in Australia

Question 28

Soil degradation

Answer 28

Loss of soil quality - loss of organic matter, salinization, loss of nutrients, infertility.
Loss of soil quantity - soil erosion and loss of soil volume by oxidation of peat

Loss of quality often increases risks of loss of quantity too.

Question 29

Loss of topsoil causes soil quality decline- Soil erosion preferentially loses clay, and organic matter that store nutrients.
This reduces the capacity of the soil to store nutrients and water.
More nutrient inputs (fertilizer) are needed to support crop growth.
A higher proportion of fertilizer is washed out causing pollution.

Answer 29

Eroded soil silts up rivers, and degraded soil stores less water- increasing flooding risks.

Question 30

Soil degradation affects about 38% of worldwide agricultural land (World Bank 2013).

Approx. £1.2 bn cost per year of soil degradation in England and Wales

Answer 30

Globally soil degradation costs ~ $10 tn p.a., equivalent to
· 160% of the global spend on healthcare or education
· 540% of global spend on Research and Development

Loss of organic content of soils (47%),
Compaction (39%)
Erosion (12%)
Other (2%)

Question 31

Total income from farming in the UK in 2016 was £4 bn, less than 0.5% of GDP,

Answer 31

but UK farmers, who are less than 1% of the population supply 52% of our food.

Question 32

Agricultural products such as food that soils support are undervalued- legitimizing the lack of soil value. Soil is taken for granted and not valued.

Answer 32

“We are estranged from reality and inclined to treat as valueless everything we have not made ourselves. Far larger is the capital provided by nature and not by man- and we do not even recognize it as such.” EF Schumacher (1973)

Question 33

Graves et al., (2015)

Answer 33

“Due to lack of direct measured data at the national scale, the soil erosion rates were derived from a variety of data sources, including actual observations of erosion rates in the field, peer reviewed literature and expert opinion”

Question 34

The current advice and inspection system of the Rural Payments Agency, overseeing single farm payments is under-resourced with only 1200 farm inspections per year out of about 100,000 farm businesses in England, so on average each farm will be inspected once in 83 years!

Answer 34

With the UK farm owners being on average 59 years old the chances now of being inspected in their lifetimes are pretty slim!