5.6 - Mollisols | Soil Genesis and Development, Lesson 5 - Soil Classification and Geography

The Mollisol order takes its name from the Latin word mollis, meaning soft. These mineral soils have developed on grasslands, a vegetation that has extensive fibrous root systems. The topsoil of Mollisols is characteristically dark and rich with organic matter, giving it a lot of natural fertility. These soils are typically well saturated with basic cations (Ca²⁺, Mg²⁺, Na⁺, and K⁺) that are essential plant nutrients. These characteristics of Mollisols place them among the most fertile soils found on Earth.

Key Characteristics: Mollisols – Grassland Soils

Mineral soils developed under grassland vegetation
Thick, dark-colored ‘A’ horizon, rich in organic matter
Dominant soil order of the North American Great Plains region.
Large areas of Mollisols are also found in Eastern Europe, Russia, China, and South America.
Generally very fertile for plant growth due to clay and organic matter content.
Considered to be among the most fertile soils on Earth.
Extent of world ice-free land area: 7%

U.S. Order Distribution Map for Mollisols. *Image courtesy of USDA-NRCS*

**Further Detail by the NRCS**

Quiz

Question

One of the key factors in the development of Mollisol Order soils is the prevalence of grassland vegetation. Which of the following elements would be most limiting to the development of woody shrubs and trees in a semi-arid grassland ecosystem?‏

A. Insufficient rainfall for tree growth

Incorrect: Check again! Most of the Mollisols on the Great Plains of the U.S.A. supported grass vegetation when the country was settled. Rainfall comes mainly during a growing season, often in heavy showers, but is erratic. Drought is frequent and may be severe.

B. Low soil fertility

Incorrect: Check again! Most of the Mollisols on the Great Plains of the U.S.A. supported grass vegetation when the country was settled. Rainfall comes mainly during a growing season, often in heavy showers, but is erratic. Drought is frequent and may be severe.

C. Prairie fires during periods of low rainfall

Correct: Yes! Hot-burning prairie fires kill young woody plants and trees, but stimulate the growth of native prairie grasses.

D. Beavers and other wildlife

Incorrect: Check again! Most of the Mollisols on the Great Plains of the U.S.A. supported grass vegetation when the country was settled. Rainfall comes mainly during a growing season, often in heavy showers, but is erratic. Drought is frequent and may be severe.

E. Human cultivation and agriculture

Incorrect: Check again! Most of the Mollisols on the Great Plains of the U.S.A. supported grass vegetation when the country was settled. Rainfall comes mainly during a growing season, often in heavy showers, but is erratic. Drought is frequent and may be severe.

Looks Good! Correct: Yes! Hot-burning prairie fires kill young woody plants and trees, but stimulate the growth of native prairie grasses.