Do plants grow better with fertilizer? | DFRobot Science Lab EP06

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EP 06 Do plants grow better with fertilizer?



This chapter will guide you to set up controlled experiments to explore how different soil pH and fertilizers impact on the growth of plants. A pH sensor is used to detect the pH of different soils here.



From Molecules to Organisms: Structures and Processes - MS-LS1-5

Ecosystems: Interactions, Energy and Dynamics - MS-LS2-5

Earth and Human Activity - MS-ESS3-3

Engineering Design - MS-ETS1-1, MS-ETS1-3




Imagine you are sent to outer space as a farmer someday and you need to grow plants on that new planet. There are three different types of soils (A, B, C), and you have measured their pH using BOSON sensors. The problem here is that how to choose the suitable soil for different kinds of plants, and do you have any plan to make these plants grow faster and stronger?


●Explore this question by taking a poll of students in your class.

●Copy the chart below into your notebook.

●When completed, discuss the poll results with students sitting near you.

●Why do you choose this area as the place where you grow the most plants?

●List a few reasons from your discussion which support the results of the poll.



In this activity, your group will use a pH sensor to detect the pH of different soils and choose one to carry out controlled experiments so as to explore the effects of fertilizer on plant growth.

Activity Procedure:

Experiment 1:Measure Soil pH

1.Prepare soil: get soil from different places, like nutrient soil from market, or normal soil from parks, flower pad, etc.


2.Put soil in water and stir: put the soil in a container, add water in it and stir for a while.


3.Stand and settle: let it stand still until the soil settled at the bottom of the container.


4.Connect all parts: connect the pH Sensor, controller module, and display module as the figure shown below.


5.Remove the sensor cap: remove the front sensor cap (There is a standard solution in the cap).


Tips: Please do NOT let the standard solution pour out.

6.Wash the pH electrode: wash the pH electrode for about 5 seconds (recommend washing with pour water).


7.Measure the pH of the solution: put the pH sensor into the solution for 30 seconds to detect the pH. Check the results and see if the soils from different places have the same pH values, and is there a difference between soils with different colors in pH.


Data Record 1

Copy the Data Table below into your notebook.


Experiment 2:Apply Fertilizer

1.Prepare materials: plastic bottle, toilet paper, rubber band, gauze filter (Cut the plastic bottle in half).


2.Put toilet paper into bottle mouth: put the scrunched up piece of toilet paper into the mouth of the bottle.


3.Fix the gauze filter: cut the gauze filter in a suitable size, wrap the bottle mouth with the gauze and fix it with a rubber band.


4.Put soil into the bottle: fill the bottle to the half with soil and then place it onto another half of the bottle as shown in figure below.


5.Sow the seeds: put some seeds on the soil, (the number of seeds depends on the soil range, about 5~10 here), pour some soils to cover the seeds.


6.Wash the pH electrode: prepare another plastic bottle, repeat steps 1 to 5 and mark the bottle (Apply fertilizer after the seeds sprout). Clean up the pH sensor.


7.Measure the pH value: water the plants every day, and detect the pH of the solution in the bottle below (The watering time and water quantity for the plants in the two bottles should be the same). Record the detected pH and the growth situation, fill the form.


Data Record 2

Copy the Data Table below into your notebook.



Observe and think:

1.Will the growth situation be different for the seeds planted in different soils?

2.Will the growth speed be the same for plants with and without fertilizer?



●Soil pH


●Plant Growth

Science Background:

Soil pH(acidity and alkalinity), the basic characteristic of soil, is one of the most important factors affecting soil fertility and plant growth. Too much acidity or alkalinity will reduce the availability of plant nutrients in varying degrees, specifically in the following five aspects:

1.Reduce the availability of plant nutrients. P(phosphorus )in the soil is directly affected by soil pH. When the pH is over 7.5 or lower than 6, phosphoric acid and calcium or iron, aluminum form a delayed effect state, which greatly impacted on the availability. Ca(calcium), Mg(Magnesium) and K(potassium) can easily be lost or be substituted in acid soil. At alkaline pH values, greater than pH 7.5 for example, phosphate ions tend to react quickly with calcium (Ca) and magnesium (Mg) to form less soluble compounds. The availability of boron, manganese, copper and other microelements is more likely to be reduced in alkaline soil, while molybdenum will combine with free iron and aluminum into precipitate in strong acid soil.

2.Harmful to the development of soil and damage the soil structure. There are too much H(hydrogen) and Na(sodium) in strong acid or alkaline soil, meanwhile, the lack of Ca(calcium) in these kinds of soil makes it difficult to form a good soil structure, bad for the plant growth.

3.Have a bad effect on the activities of microorganisms in soil. The ideal soil pH for the microorganisms is considered to be around 6.5~7.5. Soil pH exceeding this range could severely inhibit the activities of microorganisms, thus affecting the transformation and supply of nitrogen and other nutrients.

4.Go against plants development. The most suitable soil pH for plant growth is neutral or close to neutral. In slightly (over) acidic or alkaline soil, it will be difficult or even unable for plants to grow up.

5.May produce a variety of toxic substances. Free Al3+ and organic acids can be easily produced in over acid soil. Besides, when the soluble salt in alkaline soil reaches a certain amount, the germination and growth of crops will be directly influenced. What’s more, alkalized soil with more sodium carbonate even has a toxic effect on plants.


NPK are the most needed nutrient elements for plants among the basic necessary elements (hydrocarbon, oxygen, nitrogen, phosphorus, potassium, calcium and magnesium). Most of them will be taken away when the plants are harvested, and the amount they are returned to soil in the form of stubble and root is relatively less. Effects of P, K and N on plants:

All plants need nitrogen, phosphorus and potassium to grow. Without enough of any one of these nutrients, a plant will fail to grow.

Nitrogen (N) – nitrogen is largely responsible for the growth of leaves on the plant.

Phosphorus (P) – Phosphorus is largely responsible for root growth and flower and fruit development.

Potassium (K) – Potassium is a nutrient that helps the overall functions of the plant perform correctly.

Knowing the NPK values of a kind of fertilizer can help you select one that is appropriate for the type of plant you are growing. For example, if you are growing leafy vegetables, you may want to apply a fertilizer that has a higher nitrogen number to encourage leafy growth. If you are growing flowers, you may want to apply a fertilizer that has a higher phosphorus number to encourage more blooms.


Consider the following questions:

1.After reading the above material, please explain why different plants are needed to be planted in different types of soils.

2.Does applying fertilizer help plants grow better?

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