SOIL

THE BASIS FOR THE WEALTH OF A NATION

I. Introduction

Soil is a major natural resource of the world. Raw materials for most food, shelter and clothing come from the soil.

• Increasing population
  • Each day we add about 200,000 mouths to feed to the face of the earth.
• Decreasing land
  • We are gobbling up land for use as building sites for homes, highways and industries. Last figures indicted that about 3-4 million acres of land in the U.S., each year, is removed from farm land status. Approximately, 2 million (one million of prime farm land) is converted to urban use and 1 million is covered with water. The greatest impact occurs when prime farm land, such as that around metro Chicago is converted. Illinois looses approximately 100,000 acres per year. It is estimated that in California, about 20-25% of their farm land has been diverted to other uses.
• Decreasing soil potential
  • Wind and water erosion. Affected by the amount and intensity of rainfall, the type of soil, the length and slope of the terrain and the ground cover.

II. Components of the Soil

Consists of a mineral, organic, and living fractions with water and air filling the void between the physical components.

• Mineral fraction
  • Sand - 0.05 to 2.0 mm size of basketball
  • Silt - 0.002 to 0.05 mm
  • Clay - <0.002 mm
  • size of marble to 20 times smaller than the size of a marble.
  • has a platelet like structure
  • negative charges
  • Background information - Introductory Soil Science -Laboratory Manual, Palmer and Troeh... p... 60-61.

"Throughout its existence, the soil has been washed and rewashed by percolating water, yet it still contains nutrients available for plant growth. How can that be? Some essential plant nutrients are constituents of insoluble organic or inorganic compounds. Other nutrients are cations and can therefore be held by cation exchange mechanism in soil. Cation Exchange Capacity (CEC) dominates dominates the inorganic aspects of soil chemistry," primarily interacting with organic matter and clay particles. Because of the composition of these, their net charge is negative. It can be expressed as meq, the number of milligrams of hydrogen ions (or their equivalent in other cations) that can be stored in 100 g of soil. Another way of expressing it is as cmol (+)/kg or centimoles of positive charge per kilogram of soil.

• large surface area - if you took one gram (28 grams/ounce) if clay and spread it out on a flat surface, it would cover one acre.
  • The CEC of humus, montmorillonite clay, and kaolinite clay average about 200, 80 & 8, meq/100 g, or cmol (+)/kg. A soil containing 5% humus and montmorillonite clay should have about 18 meq/100 g - 10 meq from humus and 8 from montmorillonite clay.
• Organic fraction
  • Definition - plant and animal residues in varying stages of decay.
  • % organic matter range is between 1-6% of the weight of soil. The low figure will be found in soils of warm arid climates and the higher figure represents soils of cool moist climates.
• Living fraction
  • Visible:
    • rodents, earthworms, ants, etc.
  • Microorganisms:
    • Plant life:
      • In one gram of soil there are:
        • 100 million to 1 billion bacteria
        • 100 thousand to 100 million actinomycete
        • 20,000 to one million fungi
        • 100 to 50,000 algae
    • Animal life:
      • protozoa & nematodes
    • Function of micro plant life
      • Break down organic matter into compounds which can be recycled.
      • Produce organic products which play an important role in cementing soil granules together.

III. Soil Chemistry

• Essential elements
  • Three non-mineral - C, H, & O
  • Three primary - N, P, & K
  • Three secondary - Ca, Mg, & S
  • Seven micronutrients - B, Cl, Cu, Fe, Mn, Mo, & Zn

Must be available in the correct proportions.

• pH
  • Properties
    • Amount of H ions, by mass, in the soil.
    • Normal range: 5.5 - 7.5
      • Neutral: 7
      • Acid: Less than 7
      • Alkaline: Greater than 7
  • Influences of pH
    • The type and degree of activity of soil organisms.
    • Acid soils favor fungi.
    • The availability of elements to plants.
  • Altering pH
    • May be raised by adding lime (CaCO3).
    • Can be lowered by adding a source of H ions.

IV. Altering the Odds in Favor of Plant Growth

• Fertilizer
  • Yields have advanced due to improvements in many of the "input" areas. However, an argument can be made that the most important is fertilizer.
    • 1945 - 50 bushels/acre - minimum N
    • 1958 - 70 bushels/acre - 100,000 tons of N fertilizer
    • 1965 - 90 bushels/acre - 500,000 tons of N fertilizer
    • 1992 - 149 bushels/acre
    • 1993 - 130 bushels/acre -1,500,000 tons of N fertilizer
    • 1994 - 156 bushels/acre
  • An interesting experiment showed that to produce a unit of corn, the area planted can be reduced by 60% if one uses fertilizer versus no fertilizer. In other words you can produce on 40 acres using fertilizer the same amount of corn that you can produce without using fertilizer.
  • In addition, with fertilizer we have been able to build up the fertility of land.
• pH
  • Altering pH
    • Most mid-west soils range between 5.5 and 6.5. The optimum for most crops is between 6.3 to 6.7.
    • pH is generally altered by adding lime (CaCO₃) which when it, splits, the Ca⁺⁺ replaces the H+ on humus or clay. The hydrogen ions occupy the exchange sites because rain (H2CO₃) upon splitting, releases the hydrogen ions.

V. Ideal Soil

• ½ mineral, ¼ air, & ¼ water
• correct pH
• correct fertility balance
• then: your lawn will be like a green carpet, all roses will be prize winners, and your tomatoes will be the size of softballs!!

VI. Preservation of Farm Land

Additional perspective on the problem

• Efforts
  • Development rights active in Suffolk county NY and in 1988 Pennsylvania passed the Farm Land Preservation Act. Accompanying the bill was a 100 million dollar bond issue. The owner sells the development rights, assuring agriculture use and gets to use the land for a lifetime.
  • Income tax credits, used in Wisconsin and Oregon.
  • Zoning - Maryland
  • Non profit organizations - in Marin county, California, Massachusetts, and in Washington D. C. the home of the American Farmland Trust.

VII. Importance of U. S. and Illinois Farm Land

• 0.1% of the world's population produce 25% of the-world's shipped produce - U. S. farmer and associated system.
• Illinois is a major exporter of agriculture goods in the U. S.
• Illinois contains approximately 3% of all farm land, but over 10% of the prime farm land in the U. S.
  • 15% of corn acres
  • 14% of soybean acres
  • Thus, cropland is a very scarce and declining resource and the people of Illinois decisions on land use will have an inordinate impact on the nutritional welfare of the people of the world

Class notes of Dr. Don Stucky, Department of Plant and Soil Science.

Latest revision 6/17/1997