1. Importance & Formation of Soil

2. Importance of Soil Much of the United States ’ success is due to the productive capacity of the soil – U. S. produces enough food and fiber for its own use and exports these commodities to other countries

3. Importance of Soil Habitat for soil organisms Engineering medium System for water supply and purification Original source of most nutrients for plant and animal life – Provides nutrients for plant growth – Animals get nutrients from plants or from animals that eat plants

4. Soil Acts as a Recycling System

5. Soil Permanence Soils appear permanent and unchanging Actually very dynamic, constantly changing Changes must balance to maintain productivity

6. Soil Formation Based on weathering of rocks and minerals Physical and chemical decomposition break down rocks and minerals into the mineral matter component of soil On average, it takes about 100 years to develop one inch of topsoil

7. Factors Affecting Soil Formation Climate Living organisms Parent soil material Topography Time Different combinations of these factors lead to the formation of different soils

8. Climate Refers to the average course of weather at a particular place as exhibited by temperature, wind velocity, and precipitation Temperature and precipitation greatly affect the rate of weathering Increased temperature causes an increased rate of chemical reaction and increased growth of fungi, soil bacteria and plants

9. Climate Adequate moisture causes an increased rate of chemical reaction and increased growth of fungi, soil bacteria and plants Excess moisture retards microbe growth Water carries minerals and organic matter downward, forming horizons High rainfall areas generally have leached, acidic soils

10. Average Annual Precipitation United States

11. Climate Low humidity and high winds tend to dry out soils, reducing chemical reaction and microbe growth Photo courtesy of USDA NRCS High winds can cause cause significant erosion on some unprotected soils

12. Living Organisms Bacteria and fungi – break down organic materials Insects, “ insect-like ” creatures, and animals – break down and mix soil materials Plants – roots break up mineral matter Humans – land clearing and cultivation remove vegetation and disturb soil structure

13. Parent Material Influences texture, structure,color, and fertility Clay soils generally form from easily weathered materials Sandy soils form from more resistant materials

14. Topography On sloping land, loose material is moved downward by runoff and gravity – breaks up soil materials and deposits them at lower levels – exposes subsoil materials on upper slopes Influences percolation and drainage – sloping land has more runoff and less percolation – low-lying soil may tend to be saturated, leading to less biologic and chemical activity

15. Time Soils form by chemical and physical weathering of parent material over time – chemical weathering results from chemical reactions upon soil materials – physical weathering results from mechanical forces such as freezing and thawing, erosion, and gravitational movements Soils age and mature over time

16. Soil Maturity Initially, nutrients are released quickly, plant growth increases, and organic matter accumulates Eventually, soluble nutrients are lost through leaching, plant growth decreases, and organic matter is lost Fine clay particles move downward from surface Mature soils gradually decline to lower levels of production

17. Variety in Soils Climate, living organisms, parent material, topography, and time impact soil formation and changes in soil composition. Variations in these factors have resulted in the wide variety of soils that are present today.

18. ALL RIGHTS RESERVED Reproduction or redistribution of all, or part, of this presentation without written permission is prohibited. Instructional Materials Service Texas A&M University 2588 TAMUS College Station, Texas 77843-2588 http://www-ims.tamu.edu 2006