The effect of the salt concentration of water on the productivity of Lupin plants over a fortnight.

Essay by poisonous_acid August 2006

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Aim: The effect of the salt concentration of water on the productivity of Lupin plants over a fortnight.

Hypothesis: Lupin plants that are watered with more salt will be least productive because an increased salt concentration in the water increases the osmotic gradient, which makes it difficult for plants to absorb water needed for photosynthesis, therefore they will be less productive and will die faster than plants watered with water with a lower salt concentration.



- The salt concentration of 10mLs of water i.e. 0%, 1%, 2%, 3%, 4%


- The change in mass of lupin seeds over a fortnight.


- Light

- Temperature

- Soil: Following unknown, but they should have been the same for every plant.

Structure: dark, moist, smell suggests fertilised, medium-sized granules/ particles/

Minerals: Unknown, although manure smell provides evidence for presence of minerals

Water: 10mL/ every two days i.e. 5mL/ day.

The soil was damp to start with.

Chemicals: unknown.

pH: unknown.

Amount of soil: 42g of soil every pottle.

· Frequency of watering - 10mL every two days (except for over weekends)

· Depth that the plant was placed under the soil - in centre of pot with just enough soil to cover seed.

· Type of salt - NaCl - given

· Type of plant

· Volume of water

· Length of time allowed for growth


· Electronic balance

· 25 plastic pottles

· Small 'spade'

· Spoon

· 10mL pipette

· 50g NaCl

· 2500mL tap water

· 1050g of soil

· Tray

· 5 1L yoghurt containers with lids

· 25 lupin seeds

· 500mL measuring cylinder

· Masking tape

· Pen

· Aluminium foil

· Oven

· Cylindrical pot with base 5cm in diameter

· Cylindrical pot with base 15cm in diameter

· Vivid


1. Mix up five different concentrations of salty water (shown in table) inside the 1L yoghurt container and immediately put lid on to prevent evaporation and hence preventing the increase of the salt in the water.

2. Fill 25 pottles with 42g of soil each using an electronic balance and small spade.

3. Place one lupin seed inside each centre of the surface of the soil inside each pottle, making sure that the soil just covers the seed.

4. Divide pottles into five equal groups (i.e. five pottles a group). Label each group with 0%, 1%, 2%, 3%, 4% respectively.

5. Pipette 10mL of the solution indicated on the label into each pottle.

6. Arrange the 25 pottles into five equal groups, each consisting of 5 pottles altogether i.e. one of each different concentration of salt. Label each group with A, B, C, D, E.

7. Place the groups like in the following diagram to try and ensure that the plants being watered with a solution of a specific concentration of salt receives the same amount of light. Be careful to maintain the positions of these groups over the fortnight.

8. Record observations of the growth of the plants every two days, before watering the plants with 10mL of solution of salt water (concentration indicated on label).

9. After a fortnight, gently extract plants from soil to ensure that roots are not damaged by the removing process.

10. Depending on the growth of the plants after the fortnight, make small trays out of aluminium foil by moulding around the base of cylindrical pots - small plants/ seeds are placed in trays that have been made by moulding aluminium foil around the cylindrical pot with base 5cm in diameter. Larger plants are placed in labelled trays that have been made by moulding aluminium foil around the cylindrical pot with base 15cm in diameter.

11. Bake in the oven at 500°C over two days.

12. All moisture should have been removed after baking for two days. Weigh each plant on electronic balance and record mass and any observations.


Overall trend: from tallest to shortest (based on observations): 0% Ã 1% Ã 2% Ã 3% Ã 4%


· Should have used distilled water.

· Maybe use a beaker to grow lupin plants in as it is easier to observe growth, instead of moving the soil in order to get observations.

· Difficult to extract plants without damaging roots.

· Vivid on aluminium trays may have affected the mass of the drying lupin plants.

· Some plants had fungi growing on them while others did not, depending spread of spores and proximity of plants to infected plants. Definitely affected growth of plants, as demonstrated by 0%D (it did not grow at all, while other plants watered wit 0% NaCl solution grew tall).

· Some parts of plants and seeds were burned after the drying process. These may have affected the mass of plants e.g. make them heavier/ lighter than they would be without burns.

· Maybe fungi burned! Or maybe soil is burned.

· Some seeds/ plants retained their shells while others had not before drying. These may have also affected the mass of plants e.g. make them heavier/ lighter than they would be without seed coats. Perhaps should have removed them as inconsistent, but if removed, the results may not be fair.

· Funny results - would think that plants would be heavier , but not. Maybe because their starch stores have been used up i.e. maybe stems and leaves are heavier than start stores or contain more water than a seed.

· Seed that had fungus on it are flat an shriveled. Have more burned parts on outside.

· Seeds that did not have fungi are more rounded, less burned parts on outside.

· Plants with shoots, roots, dicotyledon-like leaves and mature leaves: dried stems and mature leaves look like hay.

· Aluminium trays were of different thicknesses. May have affected drying process.

· Continual removal from soil to make observations, so seeds eventually became buried at different depths.