Transcript AbioticEnvironmentFertilisers

© SSER Ltd.
Green plants manufacture organic compounds such as carbohydrates,
proteins and lipids by the process of photosynthesis
The manufacture of these organic compounds requires a supply of inorganic
mineral elements that agricultural crops obtain from the soil
The most important of these inorganic elements are nitrogen, phosphorus
and potassium (NPK); these are commonly described as macronutrients
as they are needed in relatively large amounts by the plants
Other nutrients, known as micronutrients, are required for the healthy growth
of plants and these include trace elements such as iron and magnesium; these
elements are only required in small amounts
NITROGEN – absorbed by plants principally as nitrate ions. Needed for the
manufacture of amino acids, proteins and nucleic acids
PHOPHORUS – absorbed by plants as phosphate ions. Needed for the
manufacture of nucleic acids and ATP
POTASSIUM IONS – required for the efficient functioning of certain
enzymes involved in photosynthesis and respiration
Under natural conditions, organic compounds are passed to the decomposers
whose activity converts these compounds into inorganic nutrients for
recycling; this process is illustrated below for the recycling of nitrogen
When plants are grown as crops for
use by humans, they are harvested
by the farmer and removed
Harvesting this sugar cane crop at
the end of the growing season means that
nutrients, locked up in the crop,
are NOT returned to the soil
In this field, the grass is harvested for use as winter hay and nutrients
are not returned to the soil for recycling
When crops are grown and harvested
year after year, there is a need to
replace the lost nutrients if soil
fertility is to be maintained
Fertilisers are used to replace the
nutrients that are lost from the soil
Fertilisers may be:
Organic, e.g. farmyard manure
Inorganic, e.g. manufactured fertilisers
such as NPK fertiliser that supplies
nitrogen, phosphorus and potassium
Inorganic fertilisers are
composed of
concentrated sources
of macronutrients that
can be spread evenly
over the crop
Manure is a form of organic fertiliser composed of
the faeces of farm animals mixed with straw
This farm manure is being applied as a slurry and is a useful
method for the farmer for disposing of animal waste
Inorganic fertilisers are very soluble in water
and, when present in excess,
are readily leached from the soil and find their
way into water courses
The enrichment of aquatic environments by
nutrients such nitrates and phosphates is
known as EUTROPHICATION
Levels of eutrophication have significantly
increased as a result intensive farming and
these levels are having a damaging effect on the
environment
Nitrates and Phosphates
from excess fertiliser leach
into waterways
Algae and water plant
populations increase
rapidly
When the algae and plants die, they
are decomposed by aerobic bacteria
whose populations subsequently
increase
Dissolved oxygen in the water becomes
depleted as the increased bacterial
population respires
The capacity of the aquatic
environment to support organisms
such as invertebrates and fish is
dramatically reduced and many die
Bacterial population increases
The use of fertilisers in the agricultural fields beyond the trees in this photograph
has resulted in leaching of nutrients into the river
Excess nutrients have caused
the overgrowth of algae in
this river and formed an
algal bloom