Learning outcomes Success criteria

Students should understand the following

Why fertilisers are needed in agricultural systems.

How do natural and artificial fertiliser differ

How do fertiliser improve productivity

Candidates should be able to:

Analyse, InterpretEvaluate data relating to use of

fertilisers.

The need for fertilisersWhy do we need fertilisers?In natural ecosystems minerals are recycled

back into the soil.Agriculture tends to be concentrated on specific

areas of land that are used repeatedlyMineral ions that are absorbed by the crop are

removed.The level of mineral ions in the soil

will decrease.The urine, faeces and dead remains of

the consumer are rarely returned to the same area of soil.

Productivity

Why do fertilisers increase productivity?

Nitrogen is an essential element of proteins and DNA, both of which are needed for growth.

With extra nitrate available plants are likely toDevelop earlier, Grow taller,Have greater leaf area

This will increase the rate of photosynthesis and improve productivity

Fertilisers The rate of plant growth in usually limited by

the availability of mineral ions in the soil.

Adding more of these ions as fertiliser is a simple way to improve yields.

The key mineral ions that are added to the soil are nitrate, phosphate and potassium ions (NPK).

Inorganic fertilisersThe most commonly used fertilisers are the soluble inorganic fertilisers containing

nitrate, phosphate and potassium ions (NPK). Inorganic fertilisers are very effective but also have undesirable effects on the

environment:

• Since nitrate and ammonium ions are very soluble, they do not remain in the soil for long and are quickly leached out, ending up in local rivers and lakes and causing eutrophication.

• They are also expensive.

Organic fertilisersExamples - animal manure, bone meal, composted

vegetable matter, crop residues, and sewage sludge. These contain the main elements found in inorganic

fertilisers (NPK), but in organic compounds such as urea, cellulose, lipids and organic acids.

Plants cannot make use of these organic materials in the soil: their roots can only take up inorganic mineral ions such as nitrate, phosphate and potassium.

But the organic compounds can be digested by soil organisms such as animals, fungi and bacteria, who then release inorganic ions that the plants can use.

Organic fertilisers - Advantages They are less soluble than inorganic fertilisers,

the inorganic minerals are released more slowly as they are decomposed. This prevents leaching and means they last longer.

The organic material improves soil structure by binding soil particles together and provides food for soil organisms such as earthworms. This improves drainage and aeration.

The organic wastes need to be disposed of anyway, so they are cheap.

Organic fertilisers - Disadvantages They are bulky and less concentrated in

minerals than inorganic fertilisers, so more needs to be spread on a field to have a similar effect.

They may contain unwanted substances such as weed seeds, fungal spores, heavy metals.

They are also very smelly!

Research suggests that a combination of both inorganic and organic fertilizers gives the greatest long term productivity.

Minerals should be added in appropriate quantities as there is a point at which further increases in quantity of fertilizer no longer increases productivity.

Mass of nitrogenous fertiliser added /kg/hectare

Which forms of nitrogen used in the investigation are natural fertilisers?

A2 TEXTBOOK p99

Why did the investigation include a plot with no nitrogen fertiliser added?

Suggest how the addition of nitrogen fertiliser, in whatever for, increased productivity.

The mass of each fertiliser used was different in each case. Suggest why this was necessary.

It is sometimes claimed that nitrogen fertilisers in the form of ammonium salts increase productivity of crops better than other forms of nitrogen fertilisers. State, with your reasons, whether or not you think the results of this experiment support this view.

The increase in productivity when manure was applied was lower than other forms of nitrogen fertiliser. This is because the manure has to break down before its nitrogen is released and this process takes a few months. How might a farmer who spreads manure on his crops, use this information in order to improve productivity?

Exam question(a) (i)Describe one way in which mineral ions are released from rocks into soil.

(1)

(ii)Describe how detritivores are involved in the recycling of nutrients. (3)

(b)The bar chart shows the amounts of nitrate and phosphate in soil from two different areas of grassland, A and B. Both areas are used for grazing.

(i) Explain the effect of nitrate and phosphate supply on the diversity of plants. (2)

(ii) Area B is going to become part of a nature reserve. A proposed change in land management is to stop spraying with liquid manure. Explain the likely effect of this change on the diversity of plants. (1)

(Total 7 marks)

A re a AN o fe rtilise r o rm a n u re ad d ed .C o n ta in s :2 sp ec ie s o f g rass1 0 o th er sp ec ies o fflo w erin g p lan t

A re a BS p ra y ed y e arly w ithliq u id m an u re .C o n ta in s :3 sp ec ie s o f g rass1 o th er spe c ies o fflo w erin g p lan t

7

6

5

4

3

2

1

0

A m o u n t o fn itra te an dp h o sp h a te inso il/kg p erh e c ta re

A re a A A rea B

G rass lan d a rea

n itra te

p ho sp h a te

(a) (i) named factor and it action;( rain water/erosion washes ions from rocks, temperature increasessolubility, oxidation forms salts) 1

(ii) (larger detritivores/named example) break up larger pieces (by feeding); excrete nitrogenous wastes/faeces/droppings; increases surface area available to bacteria/microorganisms/fungi/ decomposers;decomposition by microorganisms releases minerals/nutrients to soil;any 3

(b) (i) grasses able to grow faster/more/better outcompete flowering plants

in higher nutrient supply;(higher nutrient) reduces diversity; 2

(ii) reduced level of minerals/nutrients enables flowering plants to competemore effectively for nitrate/phosphate/ nutrient; 1

[7]

Learning outcomes Success criteria

Students should understand the following

Why fertilisers are needed in agricultural systems.

How do natural and artificial fertiliser differ

How do fertiliser improve productivity

Candidates should be able to:

Analyse, InterpretEvaluate data relating to use of

fertilisers.