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Best Fertilizer: The Effects of Fertilizer on Plant Growth

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Author: Tricia Edgar
See in slideshow:
10 Plant Experiments for Kids

What’s cooking in the plant kitchen? Give your plants some food to see which type they like best and observe the effects of fertilizer on plant growth.

Problem: Do plants grow best with liquid, solid, or powdered fertilizer?

Materials

  • 12 bean seeds
  • 4 small pots
  • Potting soil
  • 3 organic fertilizer sticks  
  • Face mask
  • Hammer
  • Old pan
  • Old tea towel
  • 1 tablespoon water
  • Permanent marker
  • Cup
  • Ruler
  • Spray mister

Procedure

  1. First, place potting soil in four small pots. Make sure that you have the same amount of soil in each pot.
  2. Place three bean seeds into each pot. Make sure that the soil in each pot is damp.
  3. Label the first pot “control”. This pot does not get any fertilizer.
  4. To create the fertilizer for the other three pots, put on your face mask and place a small stick of indoor plant fertilizer in an old pan.
  5. Place an old tea towel on top.
  6. Pound the stick with your hammer until it is a powder. Put the powder aside.
  7. Do the same thing with another stick of fertilizer. Put the powder into a small cup and mix this fertilizer with a tablespoon of water.
  8. Label the other three pots “liquid,” “solid,” and “powdered”. Place the liquid fertilizer in the first pot, place a solid stick of fertilizer into the second pot, and place the powdered fertilizer on top of the soil in the third pot.
  9. Now, watch your beans grow! After 4 days, carefully remove the seeds from the pots without losing track of which seeds came from which pots.
  10. Use a ruler to measure the length of each seed’s sprout. What pot produced the seeds with the longest sprouts?
  11. If you wish, replace the seeds and continue your observation for several more days.

Results

Liquid fertilizer is the best fertilizer: the plants that receive the liquid fertilizer grow the best.

Why?

Just like people, plants need nutrients to grow. In a typical fertilizer, you’ll find lots of nitrogen, phosphorus, and potassium. These primary nutrients help plants grow new cells, and many enable different growth and food production processes to happen. If you choose a good quality fertilizer, it will also contain many other nutrients, including secondary nutrients like calcium, magnesium, and sulfur. Calcium helps plants grow roots and stand up straight. Magnesium helps plants make chlorophyll, which helps plants make food through photosynthesis. Sulfur is an important part of different proteins and plants enzymes. Plants also need very tiny amounts of trace elements like boron, copper, iron, chloride, manganese, molybdenum, and zinc as well.

The liquid fertilizer has tiny pieces of fertilizer held in suspension in the water. Placing the fertilizer into a liquid base helps that fertilizer move through the soil to the bean seed. It also helps the plant move nutrients around.

Think about it this way: the water in our bodies helps us move nutrients around, and same goes for plants. Plants need water to move nutrients from the soil into the plant. Osmosis is a process in which nutrients move from areas of low concentration to areas of high concentration. This process allows nutrients to move from the soil into the center of a plant’s roots where there are more nutrients.

Once the water and nutrients are inside the xylem tissue of the plant, the xylem acts as a tube that sends the water and nutrients up into the stem. The water molecules connect to each other through a process called adhesion, and as molecules cling together, they move up through the plant. The water becomes a long, cohesive column, and as water moves out of the plant’s leaves when the plant transpires, a new batch of nutrient-carrying water moves upwards.

Water and nutrients go hand in hand. Allowing nutrients to move through the soil in suspension helps those nutrients move more easily, and it also helps the plant use those nutrients to grow.

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