6.4 - Uses of natural and artificial fertilisers

1. 6.4 - Uses of natural and artificial fertilisers

2. 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, • Interpret • Evaluate data relating to use of fertilisers.

3. The need for fertilisers Why 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 repeatedly • Mineral 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.

4. 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 to • Develop earlier, • Grow taller, • Have greater leaf area • This will increase the rate of photosynthesis and improve productivity

5. 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).

6. Inorganic fertilisers The 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.

7. Organic fertilisers • Examples - 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.

8. 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.

9. 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!

10. Research suggests that a combination of both inorganic and organic fertilizers gives the greatest long term productivity. Yield of wheat/tonnes hectare-1 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

11. A2 TEXTBOOK p99 Which forms of nitrogen used in the investigation are natural fertilisers?

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

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

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

15. 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.

16. 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?

17. 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)

18. (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 plantsin 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]

19. 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, • Interpret • Evaluate data relating to use of fertilisers.