Soils as Media for Plant Growth

Soil as a Natural Body

1. The Name

The soil is often said to cover the land, and is a collection of individually different soil bodies.

A soil is an individual tree to a forest, a three-dimensional natural body.

Soils are often used, in general, to refer to all individual natural bodies as a whole.

A regolith is a layer of unconsolidated materials overlaying the hard, unweathered, bedrock.

2. Some History of Soil Science:

(1) The "willow" experiment by Jan Baptiste Van Helmont (1577-1644) in Holland. He put 5-lb willow tree in 200 lb of soil. The willow tree received only rainwater for 5 years. At the end of 5 years, the tree weighed 169 lb 3oz, the soil weighed 57 g less than 200 lb. So he reasoned that water was the “principal of vegetation.”

(2) Justus Liebig's law of the minimum (mid 1800) (Also Carl Sprengel). (See R.R. van der Ploeg et al. 1999. Soil Sci. Soc. Am. J. 63:1055-1062).

(3) The Hatch Act in the US in 1862.

3. The Composition

Soils are composed of four main components:

1. Minerals of different sizes (clay, silt, & sand);

2. Organic materials from the remains of dead plants and animals;

3. Open space that can be filled with water and air (pore space);

4. Plant roots and other living organisms.