2.  carbon (C), hydrogen (H 2 ) and oxygen (O 2 ).  Mainly present in water, (absorbed through leaf and roots from ground and atmosphere). The other source is CO 2 and O 2 in the atmosphere.  These nutrients make up 95% of plants. They are found in the carbohydrates, lipids and proteins of plants.

3.  Macronutrients are needed in large quantities  (NPK for short)

4.  Plants cannot use nitrogen in the atmosphere, as it is unreactive in the form N 2. It is needed in the more soluble form of nitrates (NO 3– ). The atmospheric nitrogen can be changed (fixed) to make it useful for plants as follows:  Lightning causes the nitrogen and oxygen in the atmosphere to react and to form soluble nitrogen-oxides.  Some plants (legumes) have nodules on their roots that can fix nitrogen.  Nitrifying bacteria in the soil produce nitrates from decaying plant and animal matter. Guano (seabird dung) is a good source of nitrates.  Nitrates are also produced in the fertilizer industry  For protoplasm in plants - growth of strong stems and leafy plants.

5.  Plants are able to absorb the soluble phosphate ion (PO 4 3- )  Guano and fishmeal were good sources of phosphate fertilizer in the past. Now most phosphate fertilisers are produced from rock phosphate, Ca 5 (PO 4 )F. In South Africa, it is mined at Phalaborwa by Foskor, where there is a large reserve of about 2500 megatonnes (Mt).  Another natural source used in modern times is bone meal  For root growth, ripening of fruit and germination of seeds.

6.  South Africa imports most of its soluble potassium salts (KCℓ and K 2 SO 4 ), as we do not have large amounts available and it is expensive to extract these salts from sea water.  Potassium regulates the water balance in plants and controls the rate of photosynthesis and respiration. It helps with the movement of sugar in plants and boosts the resistance to drought and diseases

7.  Secondary nutrients are needed in smaller quantities

8.  Absorbed as Ca 2+  Limestone (CaCO 3 ) is the raw material that is used to make calcium compounds. Dolomite limestone is used in South Africa. It also contains magnesium carbonate (MgCO 3 ) and can also supply the magnesium that is needed by plants. The dolomitic limestone reduces the acidity of the soil, which helps plants to absorb nutrients.  Calcium is needed for root development, root cell walls, transportation of carbohydrates and water in plants.

9.  Absorbed as Mg 2+  Obtained from dolomite (as mentioned above) and magnesite. Magnesite is mined in Mpumalanga and Limpopo provinces. Fifty thousand tonnes are mined per annum, of which 20% is exported.  Needed for photosynthesis and respiration in plants.

10.  Converted to sulphuric acid then made into superphosphates and ammonium sulphate.  Absorbed as SO 4 2-  Sulfur is a by-product of other processes, such as the refining of oil and the extraction of metals from ores. South Africa also imports sulfur.  Needed for production of proteins, oils and vitamins. It promotes nitrogen fixing, the formation of chlorophyll and resistance to diseases and pests.

11.  Micronutrients are needed in very small quantities. Found in the soil as soluble mineral ions  Manganese (Mn) -Activates enzymes  Iron (Fe) -Chlorophyll synthesis  Copper (Cu)-Component of enzymes  Zinc (Zn)- Activates enzymes  Boron (B) -Cell wall component  Molybdenum(Mo)- Involved in N fixation

12.  Humans need the following four major nutrients  Carbon from food in the form of carbohydrates  Hydrogen from water and found in food  Oxygen from the atmosphere, water and food  Nitrogen from food in the form of protein

13. N:P:K fertilisers are labelled according to the content of the three elements nitrogen, phosphorus and potassium. Thus, a bag, labelled 2:3:2 (22), means that 22% pure fertiliser per bag of which two parts is nitrogen, three parts is phosphorus and two parts is potassium.  Each type of plant needs different amounts of the elements for best growth. Fruit may need 2:3:2, while grass needs 4:1:1.

14.  Example 1 A 10kg bag labeled of NPK fertilizer is labeled 2:3:2 (22) 1.Calculate the percentage of these elements. 2. Calculate the mass of each nutrient in the bag Answer 1.Nitrogen is two parts of seven parts (2 + 3 + 2) in the bag and 22% of the bag is pure fertiliser. Therefore: % nitrogen = (2) = 6,3% % phosphorous = (3) = 9,4% % potassium = (2) = 6,3%

15. 2.To calculate the actual mass of each element in the bag: Take the percentage of the element in the bag, divide it by 100 and multiply by the mass of the bag. Nitrogen mass = = 0,63 kg of nitrogen fertiliser in the bag. Phosphorous mass = = 0,94 kg is phosphorous Potassium mass = = 0,63 kg is phosphorous

16.  See Flow diagrams for Nitrate and Sulphate fertilisers  LEARN THE PROCESS AS LINKED TO CHEMICAL EQUILIBRIUM AND LE CHATELIERS PROCESS