Question

In the 17th century, Jan van Helmont performed an experiment to determine how much of the mass gained by a plant came from soil. He grew a willow tree for five years, weighing the soil before and after. The soil lost 0.06 kg of mass, while the tree gained 74.53 kg. What inputs needed by plants were not accounted for in this experiment?

Answer 1

Some important elements that are required by a plant for proper growth, but were not accounted in the experimentation of Jan van Helmont are the nutrients from atmosphere such as carbon dioxide (CO2) and light.

In his famous experiment, Van Helmont planted willow shoots in a soil container and calculated the plant mass after five years. The tree gained great amount of mass but the soil didn’t lose much mass. He concluded that the extra mass of the plant had come from soil as well as water used for watering the plant.

Van Helmont clearly missed the importance of elements from atmosphere such as CO2 and light. A plant actually derives most of its energy from CO2 and light through photosynthesis, but only some of its energy from the soil.  

Although, soil is important as it provides useful mineral to the plants like Nitrogen and Potassium. But, minerals do not represent major part of the plant mass.  They are essential for constant development but they do not provide energy to plant. As we know, energy is made when CO2 and water combine to form carbohydrates and sugars. So it might sound surprising but the truth is that major part of plant mass is due to stored sugars. These sugars are eventually used by plant for general metabolic processes.