CH: 3 Agriculture and the environment

INTRODUCTION:

• The science that deals with cultivation (growing)of plants and keeping or
breeding and raising of domesticated animals for food is called
agriculture

• Derived from the Latin words ager – soil and cultura – cultivation or
growing

• Agriculture includes cultivation of soil, and breeding and management

of plants and animals

Soil composition:

• Soil is the outer, loose layer that is found just below the surface of the
Earth

• It is important because it is the medium in which most plants grow

Soil is a mixture of four things:

• Inorganic mineral particles from weathering and erosion of rocks that

are slowly broken down into smaller particles of different sizes

• Organic matter of living plants, animals and microorganisms and their

decaying remains called humus

• Water from precipitation such as rain or snow that drains into it

• Air, which tends to be rich in carbon dioxide and poor in oxygen

In general most soils contain

• 40 – 50 percent inorganic matter

• 5 percent organic material

• 25 percent water

• 25 percent air
Silt:

• Silt soils have a particle size of between 0.002 and 0.05 mm, are fairly
well drained compared with clay and tend to hold more moisture than
sandy soil

• They can however become easily compacted when wet

Loam soil:

• The soil is made of 40% sand, 40% silt and 20% clay

• It has a more equal mixture of small and large grains of rock

• This means it can retain water without getting waterlogged

• It also contains more humus than clay or sandy soil

Chalky soil is a light brown soil. Water drains through it quickly.

Peat is different from other soils because it does not contain any rock particles.
It is made from very old decayed plants and is dark, crumbly and rich in
nutrients (chemicals plants need to grow).

Properties of a soil:

Soil texture – how it feels when you touch or rub

• Sandy – feels gritty

• Silt – feels silky

• Clay – feels sticky

Water holding and drainage: permeability, porosity

Water holding capacity of soil

How the water pass through the soil

Air in the soil:

• spaces for the living organisms in soil to respire

pH of soil:

• whether the Acidic or alkaline

Soil for plant growth:

• Plants require a number of minerals or nutritional elements from the

soil for healthy growth and reproduction

• Minerals are absorbed mostly through their root hairs in the form of
ions (electrically charged atoms or group of atoms), which are found in
salts dissolved in soil water

• The most important minerals required by plants are nitrogen,

phosphorus, potassium and magnesium

Mineral ion Mineral element How they are used in plantsand why needed

Nitrates NO3- Nitrogen For proteins, which are needed for cell growth.

Nitrogen is needed t make amino acids for

proteins

Phosphates Phosphorus Required for respiration and growth.

PO4-
Phosphorus is needed to make DNA and cell
membrane.

Potassium K+ Potassium Required for photosynthesis and respiration to

function effectively

Magnesium Magnesium Used for manufacturing chlorophyll for

Mg2+ photosynthesis

• In addition to the mineral ions, organic matter in soil is the other natural
source of plant nutrients

• Organic matter is the remains of a plant or animal that was once alive
and which has returned to the soil and been decomposed into humus by
bacterial microorganisms

• These and other decomposers such as worms and fungi function as an

integral part of the nutrient or carbon cycle

The organic content of soil is very important:

• It function as a reservoir of nutrients, which is constantly being released
into soil and absorbed by plants

• Every 1 percent of organic matter in the soil will release between 9-14 kg
of phosphorus pentaoxide and 1 – 2 kg of sulfur a year

• It greatly improves the water- holding capacity of soil

• It can store up to 90 percent of its weight in water, which releases slowly

and evenly over a course of a year

• This even release helps to prevent plants becoming waterlogged in very

wet periods and also to survive dry spells(dry period)

• It helps to bind or clump soil into aggregates that improve soil structure,
allowing it to take up and hold water better

• Permeability, which is the ease with which water is able to infiltrate or

move through the soil, will also improve with better soil structure

• It plays an important role in preventing soil erosion

• Increasing organic matter in soil by only 1 percent can reduce erosion by

between 20 and 33 percent

• Organic matter helps to stabilise soil and promotes stronger plant root
growth, which also has a binding effect

• It enables increased water infiltration, which prevents the soil drying out
and becoming vulnerable to wind erosion

• Soil pH is a measure on a scale of 1 to 14

• Soils with a pH value of below 7 are considered acidic

• Values above 7 are alkaline (the opposite of acidic) and the readings of
around 7 are considered neutral

• If the soil solution is too acid or alkaline, some nutrients will not dissolve
easily and therefore will not be available for uptake by plant roots

• This can lead to plants suffering from nutrient deficiency

 • A soil solution pH of between 6 and 7.5 is considered optimal for plants
because most nutrients in the soil will dissolve easily in water at these
levels

• When soil is acidic the nutrients of Phosphorous, molybdenum, calcium

and magnesium will not dissolve easily

• As a result, concentrations of metal ions such as aluminium, magnesium

and iron may become disproportionately high and even reach toxic
levels

• Under alkaline conditions, plant growth can be restricted by a lack of

iron, manganese, phosphorus, zinc, copper and boron in the soil water

• In addition, high levels of calcium in alkaline soil water may also

decrease the solubility and uptake of potassium and manganese by
plants

Soil acidity:

• Even without rain, soil acidity naturally increases over time due to the
decomposition of organic matter that naturally adds acid to the soil

• Environments rich in humus, such as forests with thick layers of decaying

organic matter, will naturally tend to have more acidic soils

• than places such as hot deserts with little rainfall, sparse vegetation
cover and decaying matter

• The burning of coal and other fossil fuels releases sulfur and nitrogen
oxides as waste gases into the atmosphere, where they combine with
water to form acids

• When this water condenses and falls as rain, acidic hydrogen is added to
soils

• Soil acidity can also be increased through the use of chemical- based
fertiliserson farms

• Adding limestone or calcium carbonate with magnesium (called liming)

is the most common method used by farmers to raise the pH levels of
acid soil to the more neutral levels in which most plants will grow
 • Adding large quantities of organic matter such as natural manure
compost and sulfur to alkaline soils has a similar effect of lowering pH
levels to more neutral readings

Differences between a sandy and clay soil:

Property Sandy soil Clay soil

Particle size Large and fine (0.05 – 2 mm smallest particle size –
and is called a ‘light’ soil) (under 0.002mm
across)pore spaces are
minute and tends to be
smooth
Clay is known as a
‘heavy’ soil

Air content High (many large air spaces Low (few and small air
between soil particles spaces)
This an advantages to plants It is often very compact
because their roots are able and difficult for plant
to use the large pore spaces roots to spread through
to move easily through the
soil

This is benefit during heavy

rain periods because the soil
will only rarely become
waterlogged

In times of little rainfall,

however, the same soil will
dry out very quickly

Their light texture and loose

open structure – easy to
plough and can be worked
early in the growing season –
because they warm up
quickly

Drainage Tend to drain quickly but Tend to be water logged

 have plenty of air with little air content
Because water drains quickly In times of heavy rain
through sandy soils they tend clay soils can become
to become acidic and infertile water logged and heavily
as many nutrients such as compacted
calcium are leached out

Permeability to High Low

water(allowing
water to pass
through it)
To make sandy soils easier to Together these qualities
cultivate and support crops, create a thicker and
organic matter(compost), heavier soil, more
manure, leaf mould or clay is difficult to cultivate than
often added sandy soils

This not only increases the This means that there

nutrient- holding capacity are few gaps between
and pH levels, but also for water to drain
improves its structure and through
water holding capacity
Therefore clay soil can
become waterlogged in
heavy rain

It contains little air,

especially when wet,
because there is not
much space between its
small particles

Clay soil:

• Advantage – although they tend to be alkaline, they are potentially very

fertile because high concentrations of nutrients get trapped between
their fine particles

• Adding bulky organic matter, which helps to combine the fine clay
particles into large separate clods, is often required to release the
nutrients for uptake by plant roots
Agriculture is the term used to describe the act of growing crops and raising
livestock for human consumptionand use

(Or)

• Agriculture or farming is the cultivation of the soil for the growing of

crops and the rearing of animals

Two main types:

• Subsistence farming

• Commercial farming

Subsistence farming:

• It is self- sufficiency farming in which farmers concentrate on growing or

rearing enough food to feed themselves and their families.

• It is to ensure the survival of individual family

• If there is excess food produced, it is sold locally to other families or

individuals

• This type of agriculture is very labour- intensive because all of the work
is done by humans and animals and only hand tools and simple
machines are used to work the land

• Low levels of technology and household labour are used to produce on

small output

Advantages of subsistence farming:

• It full fills the basic needs of a family, such as food and clothing

• A small area like a backyard garden is enough for cultivation

• It requires low capital requirement

• There is no labour cost involved. The main source of labour are the
family members of the family
Disadvantage of subsistence farming:

• The family labour is unreliable because they are not paid for working on
the farm

• The produce is consumed by the family. It does not involve any profit by
selling the produce

• Crops may get destroyed as no pest or disease control measures are

adopted

• It aimed at producing food for the family of the farmer. Hence it does
not fulfil the nation’s increased demand for food

Two types:

• Intensive subsistence farming

• Primitive subsistence farming

Intensive subsistence farming:

• The farmer cultivates a small plot of land using simple tools and more
labour

• Uses high inputs of money, labour and fertilizer etc

• Climate with large number of days with sunshine and fertile soils permit
growing of more than one crop annually on the same plot

• Rice is the main crop (other crops – wheat maize, pulses and oilseeds

• It is widespread in the thickly populated areas of the monsoon regions of

South, South East and East Asia

Primitive subsistence farming:

Includes

• Shifting cultivation

• Nomadic herding

Shifting cultivation:

• It is a sustainable method of agriculture and traditional method which

has beenpractised in the areas of heavy rainfall(Amazon basin, tropical
 Africa, parts of southeast Asia and northeast Asia) and quick generation
of vegetation

• A small area of land is cleared and the vegetation burned, providing a

source of nutrients from the ash

• The ashes are then mixed with the soil which becomes fertile to grow
crops

• After the soil loses its fertility, the land is abandoned and the cultivator
moves on and clears another small area of a new plot or forest

• The original area is regenerated, as it receives nutrients and seeds from

surrounding vegetation

• As no lasting damage occurs, this method of agriculture is sustainable

• It is sometimes called ‘slash and burn’ agriculture

Disadvantage:

• It is highly a unsustainable form of agriculture and ecologically very

damaging to forest ecosystems

Nomadic herding:

• Nomadic herding – is practiced in the semi- arid and arid region (having
little or no rain) of Sahara, central Asia

• In this type of farming, herdsman move from place to place with their
animals for fodder and water

• This type of movement arises in response to climatic

constraints(limitation) and terrain

• Sheep, camel, yak and goats are the most commonly reared

• They provide milk, meat, wool, hides and other products to the herders
and their families

Extensive farming:

• It is where a relatively small amount of produce is generated from a

large area of farmland
 • Uses small inputs of labour, money and fertiliser

Commercial farming:

• It is farming for a profit – growing crops or rearing animals to sell at

market

• Most of the work is done by modern machines and technologies such as

Geographic information systems

• Almost all farming in MEDCs (more economically developed countries)

around the world is commercial

• Commercial farms may be arable, pastoral or mixed

• Arable (the production food, fodder and industrial crops) cultivate crops
and are not involved in livestock

• An arable farm may concentrate on one crop (monoculture) such as

wheat or may grow a range of different crops

• Crops grown on arable farm may change overtime

• For example: if the market price of tomato increases, more farmer will
be attracted to grow this crop

• Pastoral (rearing animals for meat and animal products such as wool

• Mixed (both arable and livestock)

Main differences between subsistence and commercial farming types farming:

Subsistence Commercial
Mainly for own consumption farmingfor sale of products
orProducing enough for ones need
Small- scale/ small farms Large- scale/ large farms
More reliable on human and animal mechanised
power
Wider variety of crops / mixed farming More specialised/ perhaps one
with animals plantations/ monoculture
Low inputs/ investments High inputs/ large investments
Importance of planting trees to conserve soil:

 Trees generally increase rainfall interception

 Rainfall reaches the ground more slowly
 As trunk flow and canopy drip slow the movement of water
 Trees stop heavy rain hitting or eroding the surface of the soil and it
reduce runoff
 Organic matter from trees improves soil structure
 Trees acts as windbreaks providing shelter from prevailing winds
 Their roots help to hold the soil together

Strategies for conserving soil:

Soil conservation is the preventing of soil loss from erosion or reduced fertility
caused by over usage, acidification, and otherchemical soil contamination

Techniques for improved soil conservation include:

Terrace ploughing, contour ploughing, dry land farming, crop rotation, mixed
farming, mulch, integral rural development programmes, community
participation, land reform