Download Lesson 1 - Why we need fertilisers

After completing this topic you should be able to :
•
State that the increasing world population has led to a need for more efficient food
production.
•
State that growing plants require nutrients, including compounds of phosphorus,
potassium and nitrogen.
•
State that fertilisers are substances, which restore the essential elements for plant
growth to the soil.
•
Explain the importance of the decomposition of plant and animal protein in the
recycling of nitrogen.
•
Give examples of the effect of artificial fertilisers on lochs and rivers.
•
Explain why fertilisers are a mixture of different chemicals to provide a balance of
nutrients.
The population of the world showed a
gradual increase for thousands of years
until the end of the 19th century.
The world population has increased
dramatically over the last 100 years, and
continues to increase at an increasing
rate.
This increase in the population is due to
improvements in housing, sanitation,
healthcare and food production.
Production of food has become very efficient
resulting in better nutrition for a lot of people.
However, in many parts of the world people
experience famine when their crops fail to grow,
due to drought.
Plants are important to life on the planet as they make food. Plants are eaten for
food or animals are eaten which have eaten plants.
As plants grow they make carbohydrates,
proteins, vitamins and oils.
Plants need
from the soil to
grow. There are three essential elements
required for plant growth. These
elements are:
is the
main
element required
by plants as all
contain
.
The
means the
are taken in through the roots of a plant along with
must be soluble in
.
. This
Effects of Shortages of Nutrients on
Plants
Nutrient
Role in Plant growth
Effect of Shortage
Nitrogen
Needed to make protein
and chlorophyll
Stunted growth, pale leaves,
weak roots
Phosphorus
Needed for strong roots,
stem and seeds and for Slow growth of plants, poor fruit
energy transfer
Potassium
Needed to make protein
and sugars
Plants stunted with poor
resistance to frost, drought and
disease
The Nitrogen Cycle
When plants grow
are removed from the soil. In
autumn when a plant dies, it will rot and the nutrients go back
into the soil.
In farming the crops (plants) are harvested and this means
the nutrients are lost from the soil.
To replace the
in the soil the farmer has to spread
on the soil. This ensures there will be enough
in the soil to give high yields of crops.
A natural way of replacing the
is to spread plant and
animal waste on the soil.
Bacteria in the soil, called nitrifying bacteria,
convert the plant and animal protein into nitrates,
which contain nitrogen, a very important
.
Using waste plant and animal protein is much cheaper than fertilisers but it is not
available in large enough quantities.
Some plants called leguminous plants contain little nodules on
their roots, which contain nitrifying bacteria. These bacteria
can convert nitrogen in the air into nitrates.
Examples of leguminous plants are peas, beans and clover.
Farmers used to rotate which crop was grown in a field each
year. In the rotation they would plant peas, bean or clover.
This would return the nitrogen to the soil and ensure that the
crops grown in the field the following year would have a high
yield.
N N
NN
N N
N
OO
O
Nitrogen in the air is called
.
N
O
N
N
N
N N
N
O
N
O O
ON O
O
N
ON O
O
Converting free nitrogen into compounds
containing nitrogen is called
.
ON
O O
Production of fertilisers requires the conversion
of free nitrogen in to fixed nitrogen.
N O
O O
O
O O
N
(
-)
N
Nitrogen atoms, which are found in
compounds, are called
,
as the nitrogen atoms are fixed in a formula.
ON O
O
compounds are the
of
.
Since all plants take in their nitrogen as
- , the production of nitric acid is
nitrates,
a very important industrial process.
The main compounds found in
and
.
(
are
)
,
,
(
)
essential nutrient elements
need to be soluble in water so they can be taken into the plant through
the roots. Most fertilisers are a mixture of chemicals to provide the correct
amount of nutrients for a particular crop. Farmers normally have their soil tested to
ensure they are adding the correct amount of nutrients.
The
shows how
circulates in nature.
OO
N N
N N
N
N N
OO
O
O
N
O
N N
O
N N
Plants take in their
in the form of nitrates. All
containing
compounds are converted to
nitrates by nitrifying
bacteria in the soil.
N
N
N N
eaten
animal
waste
During lightning storms the energy
of the electrical discharge provides
the energy for nitrogen in the air to
react with oxygen to produce
nitrogen dioxide.
Nitrogen dioxide dissolves in
rainwater to form a very dilute
solution of nitric acid.
growing plants
N O
O O
N O
O O
death & decay
N O ON O ON O
O O
O
O
Simple
compounds in soil
(NITRATES)
Nitrifying
bacteria in
leguminous
plants
The chemicals in fertilisers have to be soluble in water to be of use to plants.
Fertilisers in water run-off from fields.
The fertilisers then cause the water plants to
grow rapidly. This results in these stretches of
water becoming choked with plants and rapid
growing microscopic plants called algae.
When these plants and algae die, their decay
removes dissolved oxygen in the water, which
deprives the fish of oxygen, so many of the fish
get killed off.
Fertilisers are easily washed
out of the soil by rain into
streams, rivers and lochs.