The Fungal to Bacteria Ratio (F:B) can tell you important information about your soil and the organisms present (or missing) and the stage of succession your current soil is in. A soil assessment can determine your ratio.
Succession is a term used to indicate where you are in the soil health cycle. Different succession levels favor different plants, from weeds to evergreen forests.
There are 10 Different Stages of Succession. The following table breaks down the important information to help you understand where your soil is at and what plants that soil favors. This can help you understand where you need to get to in order to grow the plants you desire.
Stage of Succession
F:B RATIO: < .01
SOIL CONDITIONS: No vegetation. Compacts easily. Inorganic fertilizers required to grow plants.
SOIL BIOLOGY PRESENT: None. No nutrient cycling. Plants lack soluble nutrients.
F:B RATIO:≈ .05
SOIL CONDITIONS: No vegetation. Poor soil structure. Compacts easily. Nutrients lost through anaerobic conditions.
SOIL BIOLOGY PRESENT: Ciliates (bad guys) often present. Nematodes (good guys) are rare. Plants suffer from lack of available nutrients.
F:B RATIO = .1
SOIL CONDITIONS: Limited root depth. Uses strictly nitrate. Compaction common. Little soil building.
SOIL BIOLOGY PRESENT: Ciliate often present (bad guys). Bacteria feeding Nematodes (good guys) rare. Soil food web is barely functional. Soluble nutrient levels inconsistent.
F:B RATIO: ≈ .3
SOIL CONDITIONS: Brassicas (kale, mustards, etc.) thrive. Limited root depth. Poor soil structure. Strong tap rooted plants needed.
SOIL BIOLOGY PRESENT: Protozoa 10,000/g soil. Nutrient cycling functioning. Bacteria feeding nematodes (good guys) present. Nitrate is still high, but ammonium usually present.
F:B RATIO: ≈ .5
SOIL CONDITIONS: Root crops, lettuce, greens. Nitrate and ammonium used. Compaction not tolerated well.
SOIL BIOLOGY PRESENT: Protozoa 10,000-50,000/g soil. Bacteria, fungal and predatory nematodes present (good guys)
F:B RATIO: ≈ .75
SOIL CONDITIONS: Ryegrass, vegetables, annual crops and flowers. Compaction less present.
SOIL BIOLOGY PRESENT: Protozoa > 50,000/ g soil. Bacterial, fungal and predatory nematodes present (good guys).
F:B RATIO: ≈ 1.0
SOIL CONDITIONS: Lawns with no weeds, no fertilizer needed. Corn wheat, barley, etc. Equal balance of Nitrate and Ammonium.
SOIL BIOLOGY PRESENT: Protozoa > 50,000/ g soil. Bacterial, fungal and predatory nematodes present (good guys).
F:B RATIO: ≈ 2.0 – 5.0
SOIL CONDITIONS: More ammonium needed so fungal activity must be greater than bacteria.
SOIL BIOLOGY PRESENT: Protozoa > 50,000/ g soil. Bacterial, fungal and predatory nematodes present (good guys). Microarthropods.
F:B RATIO: ≈ 5.0 – 10
SOIL CONDITIONS: Ammonium needed. Nitrate can harm plants and encourage disease causing fungi.
SOIL BIOLOGY PRESENT: Good balance of protozoa and nematodes (good guys). Functioning soil web.
F:B RATIO: > 10
SOIL CONDITIONS: Require strictly ammonium. Nitrate will harm trees. Compaction less common. Soil weight in non-growing season is mostly all fungal.
SOIL BIOLOGY PRESENT: Protozoa > 10,000/ g soil. Not as important in fungal dominated soils. Bacterial, fungal and predatory nematodes present (good guys).
WHAT DO YOU DO WITH THIS INFORMATION?
Once you identify your current F:B ratio and what you want to grow, you can add biologically active compost and compost teas to move your soil along the successional timeline.
With proper compost and application, you can move your soil through the successional timeline quickly.
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