BI 105A Environmental Biology

1. BI 105AEnvironmental Biology Professor Jill Nissen Montgomery College Spring 2006

2. Soils and Their Preservation Chapter 14

3. Objectives Page 308, # 1-8 • Identify the factors involved in soil formation. • List the four components of soil. • Briefly describe soil texture and soil acidity. • Explain the impacts of soil erosion and mineral depletion on plant growth and on other resources such as water. • Describe the American Dust Bowl and explain how a combination of natural and human-induced factors caused this disaster. • Define sustainable soil use and summarize how conservation tillage, crop rotation, contour plowing, strip cropping, terracing, and shelterbelts help to minimize erosion and mineral depletion of the soil. • Discuss the basic process of soil reclamation. • Briefly describe the provisions of the Farm Bill regarding the Conservation Reserve Program and the Grasslands Reserve Program.

4. What is Soil? • Soil is the thin surface layer of Earth’s crust • Consists of mineral and organic matter modified by the natural action of weather, wind, water, and organisms • Soil is essential for terrestrial life!

5. Soil Formation • Biological, chemical, and physical weathering processes slowly break parent material (rock) into smaller and smaller particles

6. Soil Formation The five main factors controlling soil formation are: • Climate • weathering rates faster in warm, moist climate • more rainfall, more leaching and more vegetation • Organisms • plants are a source of organic matter (humus) • micro-organisms (bacteria) break down organic matter • Parent Material • type of bedrock (granite, limestone, etc.) • Relief (Topography) • soil is poorly developed on steep slope • Time • soils generally take thousands of years to develop, but can be eroded in a few decades

7. Soil Composition • Air (25%) • Oxygen, nitrogen, and carbon dioxide • Mineral Matter (45%) • Weathered rock • Organic Matter (5%) • Humus, partially decomposed organic matter • Water (25%) • The movement of water and dissolved material downward through the soil is called leaching

8. Physical and Chemical Properties of Soil • Soil texture • Determined by the relative amounts of sand, silt, and clay • Influences plant growth • too much sand is poor for plants because sand does not hold minerals or water • too much clay is poor for plants because clay has poor drainage and less air spaces • Soil acidity • The pH of most soils ranges between 4 and 8, but the optimum pH is 6-7 because most plant nutrients are available in this range

9. Soil Problems • Soil erosion • Natural process, primarily caused by water and wind • Accelerated by deforestation, agriculture, and development • What’s the issue? • Reduces the amount of soil in an area and limits plant growth • Causes a loss of soil fertility when nutrients and organic matter are washed away • Sediment runoff affects water quality and fish habitat • Reduces electricity production at hydropower plants

10. The American Dust Bowl • Lured by the promise of rich, plentiful soil, thousands of settlers came to the Southern Plains in the late 1800’s and early 1900’s • The farmers subsequently plowed millions of acres of grassland, only to have the rains stop in the summer of 1931 • The catastrophic eight-year drought that followed led observers to rename the region "The Dust Bowl." • http://www.pbs.org/wgbh/amex/dustbowl

11. Soil Problems • Mineral depletion • Occurs in all soils that are farmed because plant material is removed from the cycle • Tropical Rainforest soils are naturally poor in minerals because vegetation rapidly absorbs the nutrients, but this is not an issue unless the vegetation is removed • What’s the issue? • When mineral resources are depleted, plants will no longer grow • Causes increased use of fertilizer • Leads to further rainforest depletion as farmers abandon the land and clear a new plot

12. Sustainable Soil Use • Sustainable soil use is the wise use of soil resources, without a reduction in the quantity or quality of the soil • Techniques include • Conservation tillage – residues from previous crops are left in the soil • Crop rotation – planting a series of different crops in the same field each year • Contour plowing – fields are plowed and planted in curves that conform to the relief of the land • Strip cropping – a type of contour plowing that plants different crops in strips • Terracing – horizontal platforms used in hilly or mountainous areas • Shelterbelts – rows of trees that shelter the land from wind

13. Soil Reclamation • Involves 2 steps • Stabilizing the land to prevent further erosion • Restoring the land to its former fertility • Accomplished by seeding the ground with native plants and surrounding them with shelterbelts • Slow process, during which the land cannot be farmed or grazed

14. Soil Conservation Policies • The Natural Resources Conservation Service (NRCS) • A division of the USDA • Established in 1935 (originally called the Soil Conservation Service) • Works with private land owners to conserve natural resources • mms://151.121.2.21/content/nrcs/ann2.wmv

15. NRCS • Two of its major programs include: • The Conservation Reserve Program (CRP) • Established in 1985 • Requires farmers to develop and adopt a 5-year conservation plan (non-compliance results in loss of federal subsidies) • Very successful - annual soil loss has been cut by over 90% • http://www.nrcs.usda.gov/programs/crp/ • The Grasslands Reserve Program (GRP) • Established in 2002 • Provides assistance to help landowners restore and protect grassland, rangeland, and pastureland • http://www.nrcs.usda.gov/programs/GRP/