Easy? Try the inorganic and organic fertiliser quiz.

 

Find out more about the use of organic fertilisers from The Soil Association web site

 

Which of the following are possible reasons why adding more fertiliser does not keep on increasing yield.

High concentrations of mineral ions can damage the roots.
True
 False
The fertiliser being used may not contain a certain mineral which is required.
True
 False
Another factor may be limiting (e.g. light, temperature).
True
 False
Do the results from the field trials demonstrate the law of diminishing returns.
yes
 no
Suggest why yields are lower at the higher sowing density.
interspecific competition
 intraspecific competition
 mechanical damage
 pests

 

Fertilisers

Plants need nutrients as well as carbon dioxide and water for photosynthesis. Plants also need to make proteins and nucleic acids. In addition to the products of photosynthesis they need other nutrients to do this. Macronutrients are needed in relatively large quantities e.g. nitrogen to make amino acids

Micronutrients are needed in very small amounts. If plants lack these nutrients when they are growing they show specific deficiency symptoms.

Nutrient
use
deficiency symptoms
nitrogen growth, production of proteins and nucleic acids stunted growth, brown older leaves
phosphorus proteins, nucleic acids, ATP poor root growth, dead yellow spots on leaves
potassium enzyme activator poor growth, dehydration, small purple leaves

 

all nutrientsno nitrogenno phosphorus This picture shows the results of an experiment. The wheat plant on the left has been grown with all the nutrients it needs. The stunted one in the middle has been grown without nitrogen and the plant on the right without phosphorus. It has yellow areas on its leaves.

When plants are harvested the nutrients are removed with them. In a natural ecosystem the plants would eventually die and decay, with the nutrients being returned to the soil. Farmers need to use fertilisers containing these nutrients to maintain productivity. Farmers can use organic fertilisers or inorganic fertilisers.

Inorganic
Organic
manufactured e.g. ammonium nitrate animal manure, sewage sludge
has concentrated amounts of macronutrients may contain important micronutrients
more easily leached from the soil adds organic matter which improves soil structure
can be applied in smaller amounts as it is concentrated manure is a good way of recyling the manure produced on mixed farms
easy to handle and spread on the fields smelly!

Increasing the amount of fertiliser increases yield, up to a point.

This is known as the law of diminishing returns.

 

 

 

 

The graph below shows the results of field trials using wheat.