Soil Textureand Soil Chemistry

Soil Texture• Sandy: coarse and gritty feeling, loose enough to

allow for good air flow but does not hold moisture or nutrients well

• Clay: Sticky and smooth, holds moisture and nutrients well, but difficult to dig or till because it tends to clump together

• Silt: Silky, powdery, most fertile soil, better drainage than sand, hold moisture well, silly putty

• Loam: equal parts of sand, silt and clay-best soil for growing plants

Loam

• Combination of soil textures so provides excellent drainage, moisture retention, nutrients, and air.

• Best soil for growing plants and gardening

Soil Texture TriangleTo find texture-locate

Where all three valuesmeet

Soil Microbiology

• Staining Techniques identify soil bacteria as either Gram postive or Gram negative

• Color is due to stain used and the cell wall of the bacteria

• Crystal violet-purple blue stain (gram positive)• Safranin O-red pink stain (gram negative)

counter stain• What were most of the microbes in your

sample?

Identifying Bacteria

• Three basic Shapes-rod, spherical and spiral• Spherical (coccus)• Rod (bacillus)• Spiral (spirillum)• Are Prokaryotic• Gram positive bacteria have thick cell walls, and thick

lipid cell membrane making them more resistant to antibiotics

• Gram negative bacteria have thin cell walls, and are easier to treat with antibiotics

Bacteria Shapes

Gram positive bacteria

Gram Negative

Spirillum

What is the role of these microbes?

• Function in all parts of the nitrogen cycle:• Nitrogen fixation, denitrification, nitrification• Ex: Nitrobacter, Nitrosomonas• Function as decomposers with fungi• Help keep soil fertile• Help keep plants healthy

Wrap up:

• Complete Lab Report (Summary, Data, Conclusion) and include discussion questions by next Wednesday

• Why is it important to study the soil?• Why is it important to know the soil texture?• What are some applications of the gram

staining technique?