Plant density and rate of growth
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.
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?
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