What Do You Smell When You Sterilize Soil?

Soil Composition

• There are many kinds of soil, but the basic components are minerals, organic matter, air and water. A soil suited for the growth of most plants has 45 percent minerals, 25 percent water, 25 percent air and 5 percent organic matter. Small-sized mineral components are clay, silt and sand. Organic matter ranges from recently incorporated dead plants and animals to aged, stable humus that doesn't readily decompose. Soil composition varies widely. Gardeners often add organic matter, such as compost or mulch, increasing the soil's organic component.

Home Soil Sterilization Techniques

• There are four methods of sterilizing soil at home. Most common is using a conventional oven. Pans containing 4 inches of moistened soil are baked at 200 degrees Fahrenheit until the center of the soil reaches 180 F. A second method is using a microwave oven, placing moist soil in vented containers or open bags and heating 2 pounds of soil for two-and-a-half minutes on high. Pressure cookers are involved with methods three and four, subjecting moist soil to steam under pressure or sterilizing soil with steam without pressure.

Soil Types and Smell

• The more organic material the soil contains, the stronger the smell. Heating soil at the temperatures and for the length of time needed for sterilization cooks the organic matter and breaks down humus, releasing the smell of the breakdown products. Some types of organic materials release stronger smells than do others. The amount of moisture the soil contains can also affect the smell released.

Sterilization Method and Smell

• The strongest smell comes when conventional oven sterilization is used. This is because dry heat is used that chars some organic material. The other methods use shorter times and wet heat. No matter what sterilization method is used, soil should not become too hot or to stay hot for beyond the time needed to sterilize it. Prolonged or too high a heat forms compounds that are toxic to plants, leading to reduced seed germination or poor plant growth. These toxins include ammonium compounds, organic compounds, and minerals and salts. Some of these contribute to the smell produced. Heavier soils or soils with high organic content are more susceptible to toxin buildup.