# Plant Density and Growth Rate

Medium

## Science Fair Project Description

This experiment was conducted to find out how planting more plants in the same pot will affect their rate of growth. The experiment was done using garlic chives.
 Complexity level: 6 Project cost (\$): 10 Time required: 1 hour to prepare, 10 days for observation Material availability: Easily found Safety concerns: None

## Hypothesis

As the population of plants in soil increases, the rate growth of the plants will be reduced.

## Overview

Plant density

Seeds need soil, heat, oxygen and water to germinate. Initially the food required for the seed to germinate is stored in the seed. As the seed starts to germinate, the roots will start to grow towards the soil and the sprout will grow upwards. As the first tiny leaves appear,  photosynthesis is started.

In the next stage of growth the plant starts to compete for water and nutrients in the soil and also for sunlight and carbon dioxide above. Seeds that are planted too close to one another are known to grow taller initially to compete for sunlight. However this growth will not last long because as they grow bigger, the plants will have to compete for other resources in the soil like space for roots, water and nutrients.

In most cases, a high plant density will cause the plants to experience malnutrition, have stunted growth and  eventually die. This is why in plantations the spacing between plants and plant density is always controlled to produce better yields.

## Scientific Terms

Germinate, sprout, photosynthesis, nutrients, carbon dioxide

## Materials

The materials required for this science fair project:

-    1 packet of garlic chives seeds

-    5 pots

-    enough soil to fill the 5 pots

-    Water

-    Ruler (1 meter)

## Procedure

1.    For this experiment, the independent variable is the number of plants planted in the pots. The dependent variable is the height of plants. This is determined by measuring the height of the plants in each pot and calculating the average height. The constants (control variables) are the size of the pot, the amount of soil and the type of plant used.

2.    The 5 pots are filled with the same amount of soil. The garlic chives seeds are planted in each pot as described below.

3.    The pots are labeled as pot A, pot B, pot C, pot D and pot E.

a.    Pot A is planted with 2 garlic chives seeds

b.    Pot B is planted with 5 garlic chives seeds

c.    Pot C is planted with 10 garlic chives seeds

d.    Pot D is planted with 20 garlic chives seeds

e.    Pot E is planted with 50 garlic chives seeds

4.    The pots are watered twice daily, once in the morning and once in the evening.

5.    The height of the plants is measured everyday for 10 days and the average height of the plants in each pot is calculated daily and recorded in the table given below.

## Results

It is observed that initially the plants in pots D and E grew faster than the plants in pots A, pot B and pot C. However by day 6 the plants in all the pots had grown to almost the same height. From days 7 onwards, it is observed that the plants in pots A, B and C were taller then the plants in pots D and E.

Use the  graph below to plot the results of above observations.

 No of seeds Average height of plant calculated daily (mm) Day 1 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7 Day Day 9 Day 10 A -2 0 0 4 32 58 80 96 111 127 138 B -5 0 0 5 35 60 78 94 107 124 131 C -10 0 0 4 38 65 82 98 115 130 140 D -20 0 3 12 48 70 86 96 105 117 128 E -50 0 4 16 50 68 80 89 96 105 112

## Conclusion

The hypothesis that as the population of the plants in soil increases, the growth rate of the plants will be reduced, is proven to be true. Plants that grow in crowded environements will have to compete for water and nutrients. As these resources become scarce, the plants will eventually stop growing and die.

The planning of the amount of space between the plants is important in order to produce better yields from the plantation crops. The plants need  space for their roots to grow, as well as sufficient water, nutrients and sunlight.

## Also consider

What would happen if the experiment was continued over a longer period?

The experiment can be repeated using different plants like radish or beans. Are some plants able to grow more effectively in tight quarters?

How about changing the mix of plants?

## References

Does plant density affect plant growth? - http://www.csun.edu/scied/2-longitudinal/effect_of_plant_density/index.htm

Plant - http://en.wikipedia.org/wiki/Plant

Germination - http://en.wikipedia.org/wiki/Germination